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Attachment C - SCG Soil test and Footing report
WORKING FOR YOUR PROJECTS SUCCESS SOIL TEST AND FOOTING REPORT Address : 29 Ferguson Street Sunshine Beach Client : Brian Ross Date : 23 February 2021 Report No. : 30315(S)
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1 INTRODUCTION
SCG Consulting Engineers has performed a limited site investigation and established a site classification in
accordance with AS 2870-2011 and made recommendations based upon the classification for a building to be
constructed at the above site. This report does not include an assessment of Slope Stability, Landslide Risk, or
specifications for damp proofing, termite protection or moisture barriers.
This soil test and footing report relates only to the above property and the proposed construction as described
below:
Proposed Construction Residential Dwelling
External Walls Masonry/Timber
Internal Walls Timber
Ground Floor Slab on Ground
Upper Floor Suspended Concrete
Building Platform Cut Fill Pad
Masonry Articulation Required @ 8 m centres
This report must be read and considered as a whole. All of our recommendations, foundation
plans, sections and appendices must be read, considered and followed by all people involved
in this project including the client to ensure adequate long term performance of the footing
system constructed on this site. A copy of this report must remain with the client or final
owner of the building upon completion of the proposed works. If you are unsure of any
of the requirements herein, you must seek clarification from this office.
2 SITE CLASSIFICATION
After considering the results of our field investigation performed on 15/02/2021 we have classified this site in
accordance with AS 2870-2011 as:
Class P
The classification has been calculated from test work performed on the soil profile encountered on the day of our
fieldwork and consideration of AS2870-2011. Any disturbance of the soil profile may result in a change to the
classification.
The ‘P’ classification relates to the loose sands, poor bearing capacity and seepage encountered during our
testing on site. Please refer to our definitions list appended to this report for further descriptions of these
characteristics.
With respect to potential surface movements through seasonal moisture variations, the site could be considered
equivalent to a class S site.
The site preparation details that follow have allowed for the influence of the earthworks described in section 5.0
below.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 Residential Slabs
and Footings-Construction” and relates to the estimation of Ys, “The characteristic surface movement” within
reactive soil profiles. The limits used for this classification are as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
3 SITE DESCRIPTION
The construction area has a gradient in the order of 3-5%.
SCG Consulting Engineers 1 SCG Ref: 30315(S)
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Vegetation on the construction area (and nearby surrounds) consists of grasses and scattered trees.
The trees are located in the neighbouring allotment on and adjacent the proposed construction site.
The trees are of a height and proximity that could affect the moisture conditions within the proposed construction
site. Refer to the appendices to the rear of this report for guidance on Trees and Construction.
The existing surface drainage is good and sub-surface drainage is good.
4 FINDINGS
The soil profiles encountered are shown on the attached borelog sections.
Seepage was encountered during our testing program at 3.0m below ground level on borehole No:1.
This seepage may also cause collapse of excavations. If excavations are not filled with concrete as soon as they
are completed, there may be softening or collapse in the exposed soil profile, which may result in additional clean
out and increased concrete volumes. Temporary shoring or similar maybe required.
The sandy soils encountered are susceptible to collapse when unconfined. This may effect excavations and
result in additional earthworks and increased concrete volumes. Temporary shoring or Forma-Tube may be
required to retain the sands prior to concreting.
The samples classified on-site were assessed as having negligible plasticity, therefore laboratory testing was
considered unnecessary.
We have assessed the expected differential movement of the soil profiles encountered to be the equivalent of a
site with a Ys of less than 20mm.
Excavatable rock was encountered at the following depths below our test surface level:
Test Site 2 – 1300 mm
Our field testing did not encounter any unexcavatable rock, but we do anticipate stable unexcavatable rock at
relatively shallow depths beneath the base of our test sites.
The potential for water seepage on the sand/rock interface may cause a loss of bearing capacity at this level.
Therefore footings or piers should be increased in depth to pass this interface by a minimum of 150mm should
be increased in depth to found onto the rock.
The following foundation material will provide a safe bearing capacity (100 kPa) for buildings within the scope of
AS 2870-2011 and is shown shaded on the attached logs;
FOUNDATION MATERIAL - NATURAL MEDIUM DENSE SILTY SAND
5 SITE PREPARATION DETAILS
We recommend after removing the existing dwelling scraping the site clear of all organic material and debris.
Before basement excavations commence it is anticipated that temporary shoring will be required along the side
boundaries. This could comprise of non-vibrating measures such as contiguous concrete piling. The design of
the temporary retaining walls is to be designed and certified by an RPEQ, in accordance with AS4678:2002 –
Earth Retaining Structures. At the street and rear of the allotment temporary cut batters of 1 to 2 (vertical to
horizontal) and fill batters of 1 to 3 will be stable providing all fill is well compacted and exposed banks are
protected against the potential for stormwater erosion. The earthworks must incorporate a surface spoon drain
at the base and on the high side of the cut. Both drains must have an efficient outflow downslope and clear of
the construction area. Prior to any basement excavation, dilapidation reports of all neighbouring
alottments/dwellings.
Where a retaining wall is required, a cut batter of 1 to 2 (vertical to horizontal) in the sand profile taken from the
base of the proposed wall should be excavated. Backpropping to retaining walls should be provided throughout
the backfilling and compaction process. These earthworks must incorporate shallow surface spoon drains at the
base and along the high side of the cut. Drains must have an efficient outflow down-slope and clear of the
SCG Consulting Engineers 2 SCG Ref: 30315(S)
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construction area. The exposed face should also be protected against the potential for stormwater erosion.
Should these recommendations be un-achievable the builder should seek guidance from this office on temporary
shoring, benching or other suitable techniques.
Areas where existing structures or trees are removed shall be backfilled with engineer approved fill material
compacted to achieve a minimum relative field density of 98% and be in accordance with AS2870-2011. Where
trees are removed prior to construction the moisture conditions of the soils must be allowed to normalise across
the site prior to commencing foundation preparations.
Any loose or soft material uncovered in the site preparation shall be removed and replaced with approved fill
material compacted in accordance with AS2870-2011, or alternative measures to be provided by the engineer.
We recommend using a footing system as per the attached plans and details on the prepared construction pad.
Site drainage during construction is important. Stormwater run-off should be diverted away from any foundation
excavations and not be able to pond within 5.0m of the building footprint. Temporary piping or spoon drains or
other practical methods should be used. Please refer to the Appendices to the rear of this report for drainage
management.
The final surface profile should fall away from any slab on ground for a minimum of 1.5m at a grade of no less
than 1 in 20. Refer to appendices for drainage recommendations.
Where site drainage and landscaping does not conform to the specifications of AS 2870-2011 and CSIRO
Information Service Sheet BTF-18 significant damage to the building can be expected. A single copy of this
document is issued with the original issue of this report. Please consult your builder or contact this office to obtain
a copy.
The builder must ensure the stability of neighbouring/existing structures is maintained through not
undermining their foundations. This is achieved via restricting any excavations to above a line radiating
downwards at an angle of 1 in 1.5 (vertical to horizontal) from the base of the foundation/structure to be
protected.
Any new vegetation including trees planted adjacent the structure should follow the recommendations appended
to this report.
6 FOOTING AND SLAB SPECIFICATIONS
Footing Details
All footings must be founded a minimum of 300mm into the NATURAL MEDIUM DENSE SILTY SAND (shown shaded
on the attached log sections). Dimensions and reinforcement requirements are detailed on the structural plans
and details.
Where the NATURAL MEDIUM DENSE SILTY SAND is deep or is covered by the introduction of or the presence of
existing fill, the footings are to be increased in depth to reach this level. Alternatively the footings can be
supported on piers founded into the foundation material or deeper as required to obtain the required strength.
Refer to the structural plans for details.
Where unexcavatable rock is encountered at depths shallower than the founding level, the strip footing (non-
retaining) depth may be reduced accordingly to a minimum of 150mm providing the footing is founded a minimum
of 100mm into un-weathered or un-disturbed rock. Additional reinforcement shall be provided in the footing at
the rock/soil interface. Please contact SCG Consulting Engineers to obtain an appropriate detail.
Drilled Piers Supporting the Footings
Where the NATURAL MEDIUM DENSE SILTY SAND is deep or to be covered by fill the footings can be supported on
drilled concrete filled piers founded at a minimum of 300mm into the NATURAL MEDIUM DENSE SILTY SAND. The
size and spacing of these piers is nominated on the structural plans.
Where drilling piers is not practical the footings could be supported on steel screw piers.
Where unexcavatable rock is encountered at depths shallower the founding level the piers shall be augered a
minimum of 100mm into un-weathered or un-disturbed rock.
SCG Consulting Engineers 3 SCG Ref: 30315(S)
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Steel Screw Piers Supporting the Footings:
Alternatively steel screw piers can be used to support the loads nominated in the structural plans. The piers are
to be designed and installed by a specialist contractor. The contractor must satisfy themselves with the soils
information contained herein to achieve the loads nominated on the structural plans. Further testing may be
required and is beyond the scope of this report.
Floor Slab Details
The thickness and reinforcement for slabs on ground are shown on the structural plans.
Ground slabs may require thickenings or stiffening beams incorporated in their construction. It may be
advantageous to excavate them at the same time as the perimeter footings. Refer to the structural plans for the
locations and extent of these.
Where the stiffening beams intersect a perimeter footing, their base must be graded down to the footing base
level, 3 x N12 bars must be cogged into the footing and lapped 500 with the beams trench mesh. Refer to the
structural plans for details.
Where the stiffening beams intersect a blockbase or retaining wall, 3-N12 bars must be dowelled 150mm into the
blockbase and lapped 500 with the beams trench mesh. Refer to the structural plans for details.
A levelling layer under the ground floor slab is to comprise of granular material such as clean sand or crusher
dust compacted in 150mm layers. Either well graded sand or crusher dust can be used.
An approved polyethylene damp proof membrane of 0.2mm (min) thickness is to be placed over the levelling
layer. Laps are to be a minimum of 200mm and be taped. All service penetrations and punctures are to be fully
taped. The membrane is to be extended down the inside face of the perimeter footings and must continue under
any thickenings or stiffening beams.
Drilled Piers Supporting the Slab
Slab piers are required where there is more than 300mm of uncontrolled fill beneath the slab. They are to be
founded at a minimum of 300mm into the NATURAL STIFF SILTY CLAY. Special attention must be paid to the extra
slab thickening required over slab piers as detailed in the structural plans.
Where unexcavatable rock is encountered at depths shallower the founding level the piers shall be augered a
minimum of 100mm into un-weathered or un-disturbed rock.
Where drilled piers supporting columns or posts are not poured with the slab they must be connected to the slab
in the following manner:
• 4-N12 bars must be anchored 500mm into the drilled pier and be bent 300mm horizontally into the footing
or slab as required.
• Where a column penetrates a beam or footing 3-N12 bars must be bent around the column to lap the
trench mesh by 500mm both sides.
Drilled Pier Reinforcement
Pier Depth mm Perimeter Piers Slab Piers
up to 1500 None required none required
1500-2500 2xN12bars none required
2500-4000 4xN12bars 2xN12bars
4000-6000 6xN12 bars 4xN12bars
Unexcavatable Rock
Where unexcavatable rock is encountered at depths shallower than the founding depth the engineer is to be
contacted for alternative footing details.
SCG Consulting Engineers 4 SCG Ref: 30315(S)
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Pad Footing Details
All pad footings must be founded to the depth nominated on the structural plans. Where this depth is not 300mm
into the NATURAL MEDIUM DENSE SILTY SAND they must be deepened down to this level.
Where unexcavatable rock is encountered at depths shallower than the recommended foundation level, this
foundation depth may be reduced providing a minimum concrete depth of 300mm is maintained and the pad is
founded entirely on un-weathered or un-disturbed rock. Starter bars for columns that are supported by the pad
footings shall be grouted 300 into the unexcavatable rock.
NOTE: The information contained herein has been compiled following our field and laboratory testing,
accepted engineering theory and discussions with and information supplied by our client, whom
is noted on the header page of this report. We offer no warranty for the use of this report by
other parties without prior written consent from this office.
The report must be read in conjunction with the attached appendices. If you do not have a copy
of these please contact our office and a copy can be issued to you.
Sean Richardson – RPEQ 5835
For and on behalf
SCG CONSULTING ENGINEERS
SCG Consulting Engineers 5 SCG Ref: 30315(S)
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APPENDICES
A. BORELOGS
B. SITE PLAN
C. DEFINITIONS
D. LIMITATIONS
E. CONSTRUCTION NOTES
E.1 General
E.2 Tiled Areas
E.3 Concrete
E.4 Reinforcement
E.5 Masonry Articulation
F. RECOMMENDATIONS
F.1 Builders
F.2 Owners
F.3 Builder/Owner - Trees
G. DETAIL SHEETS
G.1 Plumbing Requirements Class M, H1, H2 & E Sites
G.2 Site Drainage recommendations
H. CSIRO – Foundation Maintenance and Footing Performance:
A Homeowner’s Guide
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SCG CONSULTING ENGINEERS LOG SECTIONS File No.30315
Client: B. Ross
Location:.29 Ferguson Street, Sunshine Beach.
Date:15/01/21
Depth TEST SITE No 1 P Depth TEST SITE No 2 P
100 Silty Sand SM 1 100 Silty Sand SM 1
200 Fine to coarse grained 1 200 Fine to coarse grained 1
300 Grey brown, roots, moist 1 Grey brown, roots, moist 1
400 Loose. 1 Loose. 1
500 1 300 Silty Sand SM 2
600 Silty Sand SM 1 600 Fine to coarse grained 2
700 Fine to coarse grained 2 700 Grey, moist, loose. 2
800 Grey, moist, loose. 1 800 Silty Sand SM 3
900 1 900 Fine grained, pale grey 4
1000 1 1000 Moist, med dense. 12
1100 1 1100 Silty Sand SM 15
1200 1 1200 Fine to coarse grained, dark 20
1300 2 1300 Orange brown, moist, dense. +
1400 4 1400 UTP dense sandstone
1500 Silty Sand SM 6 1500
1600 Fine to coarse grained 6 1600
1700 Dark brown, moist, med dense. 8 1700
1800 8 1800
1900 6 1900
2000 3 2000
6 2100
3000 (Seepage) 10 2200
8 2300
10 2400
10 2500
15 2600
20 2700
+ 2800
2900
6000 End 3000
Water in hole
Depth = mm below ground level.
P = blows per 100mm penetration with an approved 9kg penetrometer.
Notation such as (SP) refers to the soil description to Table A1 AS1726 ‘Guide to the description
identification and classification of soils’.
Solid lines represent sharp interface between different soil types. Dotted lines represent
gradation form one soil type to another.
Abbreviations used
UTP - unable to penetrate, Bec. – becoming, N.S.L. – Natural Surface Level
Med. – medium, MW - Moderately weathered
EW - extremely weathered, Plast. - Plasticity
No recovery means unable to extract samples from the base of the bore hole because the soil
will not bind in the auger head.
The colour of the soil is often abbreviated, for example Gy = grey Or = orange.
(Ls=? %) Indicates sample location and Linear Shrinkage result.
The footings must be dug into or supported on piers dug into the shaded material.
Z:\0-JOB FILE\30000-30999\30315-29 Ferguson St, Sunshine Beach\GEO\30315logs.doc
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Revision 4 \ Lot 283 “ . RP48111 a \, 956 sq m Existing House SITE PLAN Site Drainage Good. (Property Boundaries are diagramatic only) Vegetati Grasses egetation ScatteredTree ™~ Unit 1/11 Project Ave, Noosa Heads BH2 . @ Ph (07) 5455 5604 Borehole location. CONSULTING [email protected] ” ENGINEERS _ web:www.scg-engineers.com ABN 40 098 481 899 DEBUILD T/A qG-7, Slope : Title: SITE PLAN measured as a percentage gradient from high ground to low ground. Project 29 Ferguson Street Sunshine Beach DO NOT DIMENSION OFF THIS DIAGRAM. | pate. Feb 2021 | pig No. 30315-S
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C. Definitions
Safe Bearing capacity: The soil nominated in this report as a suitable foundation material has an allowable bearing capacity of 100KPa and is
considered safe for the construction of a dwelling that is in accordance with AS2870-2011.
Cohesive Soils: Clays and silt soils that have inherent cohesive (binding) strength.
Granular Soils: Gravels and sand soils that have no cohesive strength. Individual particles can flow under certain conditions.
Controlled Fill: Manually placed soil which has been placed and compacted to achieve sufficient bearing capacity to support a structure
according to AS 2870-2011. Fill certified at Level 1 according to AS 3798 and 95% Relative Field Density is considered controlled fill.
Partially Controlled: Manually placed soil which appears to have been compacted under controlled conditions but, at the time of preparing this
report, no compaction certificate suitable for compliance to Level 1 of AS 3798-2007 had been presented.
Uncontrolled Fill: Manually placed soil (overlying the natural soils) which is not adequate to support a normally loaded footing or floor slab or
structural load.
Unexcavatable Rock: Strong material that does not soften in water or collapse under the combination of loading and wetting. Material that
cannot readily be excavated by a backhoe.
Excavatable Rock: A rock-like material including shaly material and strongly cemented sand or gravel which does not shrink or swell with
changes in soil moisture, but is readily excavatable with a conventional backhoe.
Load Bearing Wall: In our design work a load bearing wall is defined as any wall imposing on the footing a service load greater than 10kN/m.
A load bearing wall will normally be supported by a slab thickening or footing in our slab designs.
Natural (Strata): Refers to soil that is neither fill or imported material but one that is in its original undisturbed state and position.
Gravel: Coarse particles, larger than sand size, but less than 60mm in diameter.
Cobbles: Rocks greater than 60mm in diameter but less than 600mm in diameter.
Boulders: Rocks larger than 600mm in diameter.
SOIL STRENGTH INDICATIONS
NON-COHESIVE (GRANULAR) SOILS COHESIVE SOILS
Loose A 12mm rod/bar can be easily pushed in by hand Soft Can be moulded by light finger pressure.
Medium A 12 mm rod/bar can be pushed in 300mm with Firm Can be moulded by strong finger pressure.
Dense difficulty
Dense A 12mm rode cannot be pushed in by hand. Stiff Cannot be moulded by fingers. Can be indented by
thumb with pressure.
Very Stiff Can be indented only by thumb nail.
N.B. These indications should be used for guidance only. These indications can vary greatly under Abnormal Moisture Conditions. Please
contact SCG Consulting Engineers for on-site clarification of soil strengths.
D. LIMITATIONS
AS2870-2011: This report and associated foundation designs have been completed in accordance with AS2870-2011 the Australian
Standard for “Residential Slabs and Footings” design and construction. The standard provides performance based criteria for its design
recommendations. This criteria is not based upon crack or movement free performance. The code states “It is acknowledged that minor
foundation movements occur on nearly all sites and that it is impracticable to design a footing system that will protect the building from
movement under all circumstances”. The code provides guidance on the assessment of crack sizes in walls and floors and suggests acceptable
limits. Should the potential owner not be satisfied with this criteria we should be notified such that any recommendations can be amended to
suit their requirements. However, it should be noted this could dramatically increase the construction costs.
Field Testing: Our investigation and the results and recommendations contained herein have been compiled following careful consideration of
our clients supplied information and instructions. Such considerations include the proposed structure to be supported and its position, proposed
earthworks and land use. Any variation to this information may render this report incorrect. Furthermore this report must not be used by any
person other than our client noted at the head of the report.
Client Supplied Information: In writing this report we have considered all the information supplied to us by the client. Should the client or his
agent have omitted to supply us with relevant information our report may be irrelevant and / or inappropriate. We do not accept responsibility for
the consequences in such cases.
Borelogs: The soil profiles reported in our Borelogs Section represent the soil conditions at our test sites and have been located were we
believe best represents the soils within the proposed building envelope. However soil conditions can change dramatically over short distances,
therefore such point type exploration programs may not locate all variations. If site preparations/excavations reveal soil conditions that are
different from those shown in our Borelogs we must be notified immediately. Changes to the site classification and/or footing design may be
necessary.
Site Information: The site information shown on the attached plans such as surface grades and levels are estimations taken during our field
testing and are provided for a rough guide. They must not be used for any design purposes. Site plan dimensions are as measured from the
noted visible site feature during our field testing.
Previous/Future Excavations: The recommendations contained in this report have not considered the effects of any previous, current or
future excavations, mines or slope instability problems that are not highlighted in the clients supplied information or, that was not clearly visible
during our field testing. If such features exist we must be advised so that our design can be adjusted to accommodate them.
SCG Consulting Engineers Appendices C to G: Page 1 of 6
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Trees: Trees can have a considerable influence over the over the performance of a structures foundation, in particular those founded on
reactive soils (Class S, M, H & E). The trees demand for moisture will change the moisture characteristics of the surrounding soils leading to
localised shrinking and swelling which can exceed the expected soil movement. This can include trees that have been removed prior to
construction. During our Field-testing we have considered trees that existed on or adjacent the site and allowed for them in our
recommendations. We are unable to assess for the potential effects of trees planted after our testing, reference should be made to
“Recommendations for Builders/Owners-Trees” in Appendix D that follows.
Moisture Conditions: The moisture conditions noted within this report are as recorded at the time of our field testing and have been included
in our assessment of the site. Changes to site drainage, the planting of trees or a rising water table can lead to increased levels of moisture
within the soils leading to either an increased classification or design requirements. We must be notified of any increase in moisture conditions.
Also refer to “Recommendations for Builders/Owners – Site Drainage in Appendix D that follows.
Aggressive/Contaminated Soils: This report does not consider the presence of contaminants or sulphates within the tested soils as this is
beyond the scope of this report and our expertise. Engagement of a specialist consultant is advised if this form of assessment is required.
Landslip: This report does not address slope stability issues. A specialist report must be obtained to assess such hazards.
Shrinkage Cracking: Shrinkage cracking of concrete occurs as the initial moisture in the concrete evaporates from mix causing
shrinkage to occur. The cracking as a result of this shrinkage is not a sign of structural failure and is to be expected in most concrete elements
poured on-site. AS2870-2011 states “Shrinkage cracking can be expected in concrete floors”. Unless requested by our client we do not design
concrete floor slabs to be shrinkage crack free.
E. CONSTRUCTION NOTES
E.1 General
We strongly recommend footing excavations be inspected by a qualified person with appropriate experience to
confirm the FOUNDATION MATERIAL and proposed foundation depths are as nominated herein.
Similarly all preparations should be inspected prior to the pouring of concrete by a qualified person with appropriate
experience to confirm that the workmanship and construction conforms with the details and recommendations
contained herein and on associated documentation.
All building dimensions are to be obtained from the approved architectural plans.
All excavations must be totally free of all loose material and debris before pouring. They must be cleaned out so that the concrete is poured
onto undisturbed ground. Tamping and/or watering loose material is not acceptable.
Light watering of prepared surfaces is permitted prior to placing concrete.
All works must be approved by the regulatory authority prior to commencing.
E.2 Tiled Areas
In areas where ceramic floor tiles or brittle coverings alike are specified for ground floor slabs we recommend increasing the size of the slab
mesh by one grade. Use flexible adhesives when affixing tiles and delay the laying for as long as possible (at least 3 months, preferably 6
months) after the slab is poured.
E.3 Concrete
Concrete for footings shall not be less than N20 (20MPa) with 20mm Aggregate and maximum slump of 80mm. Footing concrete must be
vibrated. Concrete for floor slabs shall not be less than N25 (25MPa) with 20mm Aggregate and maximum 80mm slump. Concrete slabs
greater than 100mm thick must be vibrated. In no instance shall concrete be ‘wetted up’ on site during placement.
E.4 Reinforcement
Reinforcement is to comply with the following:
a) Concrete cover to the reinforcement must be 50mm from unprotected ground, 40mm to external exposure, 30mm to the
membrane in contact with the ground, and 30mm to the internal surface.
b) Slab fabric must be lapped by one full panel of fabric plus 25mm so that the two outermost transverse wires of one sheet
overlap two outermost transverse wires of the sheet being lapped. Slab fabric is to be supported on bar chairs placed at
800mm centres.
b) Trench mesh must have all cross wires cut flush with the outer main wires. Trench mesh in slab and edge beams must be
overlapped by the width of the fabric at “T” & “L” intersections. Trench mesh must be spliced, where necessary, by a lap of
500mm.
d) Pre-Fabricated footing cages or reinforcing bars at “T” & “L” intersections are to have a N12 corner tie bars as per the attached
details.
e) The minimum lap length of reinforcing bar is to be 500mm or 40 bar diameters, whichever greater.
E.5 Masonry Articulation
The specifications in this report have been specifically formulated for articulated masonry construction. This usually results lower construction
costs. All masonry walls must have full height articulation at a spacing noted on the first page of this report The articulation joint must separate
the masonry from footing to eaves level at this spacing. Masonry must be supported on each side of the joint in an approved manner to retain
its structural integrity.
Where used, internal masonry walls should be articulated in accordance with the masonry manufacturers requirements for the width and type of
unit used. In no instance should the spacing exceed 4.0m and articulation should always be provided at an abutment with an external wall.
If articulation of masonry is found to be unacceptable, the footing system will require re-designing.
In addition to joints in masonry, articulation is achieved wherever a 10mm (min) separation in masonry from footings to eaves is achieved. For
example, where timber panels are used above and/or below doors and windows.
SCG Consulting Engineers Appendices C to G: Page 2 of 6
Page 12
Where it is necessary to construct construction joints to meet the articulation requirements, they can be placed in places of limited visibility. For
example behind downpipes. Internal masonry walls should be articulated where they abut the perimeter walls.
The designer of the building must also ensure that articulation is established:
1. Adjacent to a change in floor level which exceeds 400 mm.
2. If any proposed extension abuts any existing structure, full height articulation must be established where the new masonry joins
the old.
3. Where a masonry wall transgresses from one footing type to another - eg from a perimeter footing to a continuous footing.
If the building has any masonry arches we must be contacted for further advice.
Methods of articulation are well documented in “Technical Note 61” by the Cement & Concrete Association.
F RECOMMENDATIONS
F.1 Recommendations for Builders
Codes of Practice: All construction work associated with this report must be undertaken in accordance with the BCA “part 3.1 – Site
Preparation” and “part 3.2 – Footings & Slabs” and AS2870-2011 “Residential Slabs and Footings”.
Underground Services/Plumbing: Where structures are built over filled, soft or loose soils, services will need to be supported so that potential
movement within the soils does not cause them damage or cause incorrect alignment which could cause leakage. Such measures can include
but are not limited to the provision of expansion joints, sleeved or foam lagged pipe penetrations throughout the structure or treatment of the
soils prior to construction. The attached illustrations detail minimum requirements.
Arrange plumbing fixtures so that the slab and beam penetrations are kept to a minimum and where necessary sleeved to allow for movement
with 40mm thick closed cell polythene or similar material. Where the penetration is within 150mm of the base of a beam or footing, the depth of
this footing element should be deepened by approximately twice the diameter of the penetration. All plumbing and drainage must comply with
the requirements of the National Plumbing and Drainage Code AS3500.
For Class H & E sites, AS2870 - 2011 requires that plumbing pipes servicing dwellings in class H & E sites be fitted with sleeved expansion
joints, rotational swivel joints and foam lagged penetrations.
Refer to the attached detail sheet “Plumbing Requirements Class M, H and E sites.
Site Drainage - Class A Sites: The ground surrounding the dwelling and the building site must be graded and drained so that stormwater is
shed away from the house area in all directions during and after construction. Particular attention should be given to all drainage so stormwater
is not introduced to the foundation soils leading to potential scour. Roof water must be diverted away from the building prior to and after the roof
is installed. Correct drainage is an essential part of our recommendations. If the site is not prepared correctly, excessive foundation
movements may occur leading to damage within the supported structure.
Site Drainage - Class S, M, H & E Sites: The ground surrounding the dwelling and the building site must be graded and drained so that
stormwater is shed away from the house area in all directions, during and after construction. A minimum grade of 1 : 20 (vertical : horizontal) for
1.5m must be provided. Hard landscaping such as terrace slabs adjacent the dwelling can assist in this. Roof water must be diverted away
from the building site prior to and after the roof is installed. Where building delays occur, temporary downpipes may be necessary. Constant
maintenance of roof drainage is essential. If a rainwater tank (or similar) is to be sited within 6 meters of a structural footing, we should be
consulted for further advice. External water taps, air conditioner overflows, tank and hot water cylinder overflows should be over grated pits
connected to the drainage system. The ground surrounding the building must be graded and drained so water is shed away from the house in
all directions.
Particular care should be taken with drainage, plumbing and electrical trenches so that they do not introduce moisture into the soils supporting
the foundations or destabilise the footings by undermining them. The base of any trenches under the floor or within 1.5 meters of the building
should be sloped away from the house and should be backfilled with compacted clay plug.
Correct drainage is an essential part of our recommendations and is documented in the CSIRO handout BTF-18 attached to the clients copy of
this report. (Additional copies available upon request.) If the site is not prepared correctly, excessive soil moisture may occur in some areas,
which can lead to excessive foundation movements possibly damaging the supported structure.
Bracing for Wind Forces: Unless noted, we do not detail slab thickenings or pad footings to conform to wind bracing. Where a bracing wall is
to be bolted to a slab, 40mm bottom concrete cover attained for a radius of 150mm is required around the bolts unless noted by other
consultants.
Inspections: We require 24 hours notice if you require engineers site inspections. Inspections can be booked between 8.30am and 4.30pm
Monday to Friday by telephoning 07 5455 5604.
Silt Retention: The builder is responsible for ensuring appropriate silt retention measures are in placed and maintained throughout
construction.
Site Classification: The site classification is calculated in accordance with the “AS2870-2011 - Residential Slabs and Footings-Construction”
and relates to the estimation of Ys, “The characteristic surface movement” within reactive soil profiles. The limits used for this classification are
as follows:
Predicted Surface Movement Classification
Ys = <=20mm S Slight
Ys = >20 – 40mm M Moderate
Ys = >40 – 60mm H1 High-1
Ys = 60 – 75mm H2 High-2
Ys = > 75mm E Extreme
Problem sites P Problem
SCG Consulting Engineers Appendices C to G: Page 3 of 6
Page 13
F.2 Recommendations for Owners
Foundation Maintenance and Owners Responsibilities: The soils surrounding and under the foundations must be protected from scour or
washout from stormwater by ensuring adequate drainage as noted above.
Localised concentrations of moisture such as overflows from hot water cylinders or air conditioners can lead to excessive localised foundation
movements and must also be adequately drained away from the foundations as noted above.
In all types of soil conditions, if an automatic watering system irrigates within 2.5 meters of a foundations, instability problems and excessive
foundation movements are likely to occur. Also site drainage as discussed above must be maintained.
Ongoing foundation maintenance is documented in the CSIRO handout BTF-18, attached to the client’s copy of this report. (Additional copies
available upon request.)
Refer to the attached detail sheet “General Requirements for Site Drainage”
Additional Requirements - Class A & S Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer to the
following section “Recommendations – Builders/Owners – Trees”. In all types of soil conditions, if an automatic watering system irrigates within
2.5 meters of a footing, instability problems may occur. Water should not be allowed to pond on the ground near the building. Finished surface
grades around the building should also ensure scour of soils cannot occur. Additional field gullies and drainage might be required. In all
instances the ground should be sloped away from the foundations at a grade of no less than 1 in 20 (vertical to horizontal) for at least 1.5m.
Additional Requirements - Class M, H & E Sites: Trees and dense shrubs must be kept well away from the building foundations. Refer to
the following section “Recommendations – Builders/Owners – Trees”.
The soil near the building should be protected against the increased moisture that occurs in gardens or permeable landscaping built adjacent
the foundations. Automatic irrigation systems must not be used adjacent structural foundations. If required, these forms of landscaping must be
constructed over impermeable membranes that drain the excessive moisture away from the foundations into correctly installed field gullies and
drains.
We strongly recommend the construction of hard landscaped paths or terrace slabs adjacent building foundations for at least a distance of 1.5m
to protect the foundations from excessive moisture.
F.3 Recommendations – Builders/Owners - Trees
Trees and landscaped gardens can have a dramatic influence over the moisture content of the soils they are grown in. This can lead to
increased soil movement through shrinking and swelling. Where these trees or gardens are within close proximity of structural foundations the
soil movements can affect the structural integrity of the foundations.
For Class M, H and E sites the following recommendations for the minimum distance between trees and footings should be followed:-
Site Class Offset to Tree
Class M : 0.75 x h
Class H : 1.0 x h
Class E : 1.5 x h
Where ‘h’ is the mature height of the tree, further refinement of this recommendation can be pursued where tree species can be considered.
Where a row or group of trees exists the above recommendation should be doubled.
In some instances the installation of root barriers can lessen the effect of trees on foundation performance. Please contact SCG Consulting
Engineers for options.
The following table provides some guidance on mature tree heights:-
APPROXIMATE TREE HEIGHTS
10 to 20m Height – Acacias, Ash, Athel Tree, Candlebark, Manna Gum, Pepper Tree, Willows, Yate, Yellow Gum
20 to 30m Height – But-But, Cedars, English Oak, Lemon Gum, Palms, Planes, Sheoaks, Silky Oak, Spotted Gum, Casuarina
30 to 60m Height – Blue Gum, Cypress, English Elm, Figs, Karri, Pines, River Gum, Sugar Gum
The removal of trees from the proposed construction can also greatly affect the moisture conditions of the soil. We recommend allowing the soil
time to reach moisture equilibrium prior to construction commencing. Please contact our office for further guidance on this matter.
SCG Consulting Engineers Appendices C to G: Page 4 of 6
Page 14
G DETAIL SHEETS G.1 Plumbing Requirements Class M, H1, H2 & E Sites SCG Consulting Engineers Appendices C to G: Page 5 of 6
Page 15
G.2 Site Drainage recommendations
SCG Consulting Engineers Appendices C to G: Page 6 of 6
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G.2 Site Drainage recommendations
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TYPICAL DRAINAGE « RETAINING WALLS.
TYPICAL DRAINAGE ~ CUT FILL SITE
Guidelines for Site Drainage
1. The site must be prepared prior to construction works that enables the site to drain
throughout construction and not allow flooding of foundation works, temporary pumping
systems could be required existing drainage paths are trapged. Temporary down pipes must
be installed following roof construction and drained away from the construction area.
Drainage tranches should be clay capped to stop moisture entering foundations
2, Upon completion the ground surrounding the dwelling should be graded away from the
dwelling as indicated. Paving and terrace slabs adjacent the dwelling improve this crainage.
Perimeter drainage should be provided arounc the dwelling as indicated and must be
drained to anproved drainage facilities dovnsloge from the dwelling.
3, Rear of wall drainage beyond constructed retaining walls must be drained to approved
drainage facilities downslope from the dialling. These drains should he provided with flush
‘ut facilities at the upstream end of the drainage line and regularly maintained
SITE DRAINAGE RECOMENDATIONS ALL SITES
SCG Consulting Engineers Appendices C to G: Page 6 of 6
Page 16
H.
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4 Foundation Maintenance
and Footing Performance:
A Homeowner's Guide
2
BIF 18
replaces
Information
Sheet 10/91
Buildings can and often do move. This movement can be up, down, lateral or rotational. The fundamental cause
of movement in buildings can usually be related to one or more problems in the foundation soil. It is important for
the homeowner to identify the soil type in order to ascertain the measures that should be put in place in order to
ensure that problems in the foundation soil can be prevented, thus protecting against building movement.
This Building Technology File is designed to identify causes of soil-related building movement, and to suggest
methods of prevention of resultant cracking in buildings.
‘oil Types
The types of soils usually present under the topsoil in land zoned for
residential buildings can be split into two approximate groups ~
granular and clay. Quite often, foundation soil is a mixture of both
types. The general problems associated with soils having granular
content are usually caused by erosion. Clay soils are subject to
saturation and swell/shrink problems.
Classifications for a given area can generally be obtained by
application to the local authority, but these are sometimes unreliable
and if there is doubt, a geotechnical report should be commissioned.
As most buildings suffering movement problems are founded on clay
soils, there is an emphasis on classification of soils according to the
amount of swell and shrinkage they experience with variations of
water content. The table below is Table 2.1 from AS 2870, the
Residential Slab and Footing Code.
auses of Movement
Settlement due to construction
There are two types of settlement that occur as a result of
construction:
¢ Immediate settlement occurs when a building is first placed on its
foundation soil, as a result of compaction of the soil under the
weight of the structure. The cohesive quality of clay soil mitigates
against this, but granular (particularly sandy) soil is susceptible.
* Consolidation settlement is a feature of clay soil and may take
place because of the expulsion of moisture from the soil or because
of the soil’s lack of resistance to local compressive or shear stresses.
This will usually take place during the first few months after
construction, but has been known to take many years in
exceptional cases.
These problems are the province of the builder and should be taken
into consideration as part of the preparation of the site for construc-
tion. Building Technology File 19 (BTF 19) deals with these
problems.
Erosion
All soils are prone to erosion, but sandy soil is particularly susceptible
to being washed away. Even clay with a sand component of say 10%
or more can suffer from erosion.
Saturation
This is particularly a problem in clay soils. Saturation creates a bog-
like suspension of the soil that causes it to lose virtually all of its
_ bearing capacity. To a lesser degree, sand is affected by saturation
because saturated sand may undergo a reduction in volume —
particularly imported sand fill for bedding and blinding layers.
However, this usually occurs as immediate settlement and should
normally be the province of the builder.
Seasonal swelling and shrinkage of soil
All clays react to the presence of water by slowly absorbing it, making
the soil increase in volume {see table below). The degree of increase
varies considerably between different clays, as does the degree of
decrease during the subsequent drying out caused by fair weather
periods. Because of the low absorption and expulsion rate, this
phenomenon will not usually be noticeable unless there are
prolonged rainy or dry periods, usually of weeks or months,
depending on the land and soil characteristics.
The swelling of soil creates an upward force on the footings of the
building, and shrinkage creates subsidence that takes away the
support needed by the footing to retain equilibrium.
Shear failure
This phenomenon occurs when the foundation soil does not have
sufficient strength to support the weight of the footing. There are
two major post-construction causes:
° Significant load increase.
¢ Reduction of lateral support of the soil under the footing due to
erosion or excavation.
¢ In clay soil, shear failure can be caused by saturation of the soil
adjacent to or under the footing.
GENERAL DEFINITIONS OF SITE CLASSES
©) Foundation.
cM ist sand, and rock sites with little or'no ground movement from moisture che
: : ‘Slightly reactive clay sites with only slight ground movernent from moistiit ‘changes :
” Moderately teactive clay or silt sites, which can experience moderate ground movernent from moisture changes
Highly reactive clay sites, which can experience high ground movement from moisture changes
"Filled sites Be .
Pe “Sites
E | ' |) Extremely reactive sites, which can experience extreme ground movement from moisture changes...
i ich.include soft soils, such as soft clay. ‘or silt or loose sands: landslip; mine subsidence, collapsing soils} soils subject
fo erosion’ reactive sites subject to abnormal moisture conditions or sites which cannot: be classified otherwise \o 8
Page 17
Tree root growth Trees and shrubs that are allowed to grow in the vicinity of footings can cause foundation soil movement in two ways: ¢ Roots that grow under footings may increase in cross-sectional size, exerting upward pressure on footings. ¢ Roots in the vicinity of footings will absorb much of the moisture in the foundation soil, causing shrinkage or subsidence. :Unevenness of Movement The types of ground movement described above usually occur unevenly throughout the building's foundation soil. Settlement due to construction tends to be uneven because of: ¢ Differing compaction of foundation soil prior to construction. Differing moisture content of foundation soil prior to construction. Movement due to non-construction causes is usually more uneven still. Erosion can undermine a footing that traverses the flow or can create the conditions for shear failure by eroding soil adjacent to a footing that runs in the same direction as the flow. Saturation of clay foundation soil may occur where subfloor walls create a dam that makes water pond. It can also occur wherever there is a source of water near footings in clay soil. This leads to a severe reduction in the strength of the soil which may create local shear failure. Seasonal swelling and shrinkage of clay soil affects the perimeter of the building first, then gradually spreads to the interior. The swelling process will usually begin at the uphill extreme of the building, or on the weather side where the land is flat. Swelling gradually reaches the interior soil as absorption continues. Shrinkage usually begins where the sun's heat is greatest. Erosion and saturation Erosion removes the support from under footings, tending to create subsidence of the part of the structure under which it occurs. Brickwork walls will resist the stress created by this removal of support by bridging the gap or cantilevering until the bricks or the mortar bedding fail. Older masonry has little resistance. Evidence of failure varies according to circumstances and symptoms may include: * Step cracking in the mortar beds in the body of the wall or above/below openings such as doors or windows. * Vertical cracking in the bricks (usually but not necessarily in line with the vertical beds or perpends). Isolated piers affected by erosion or saturation of foundations will eventually lose contact with the bearers they support and may tilt or fall over. The floors that have lost this support will become bouncy, sometimes rattling ornaments etc. Seasonal swelling/shrinkage in clay Swelling foundation soil due to rainy periods first lifts the most exposed extremities of the footing system, then the remainder of the perimeter footings while gradually permeating inside the building footprint to lift internal footings. This swelling first tends to create a dish effect, because the external footings are pushed higher than the internal ones. The first noticeable symptom may be that the floor appears slightly dished. This is often accompanied by some doors binding on the floor or the door head, together with some cracking of cornice mitres. In buildings with timber flooring supported by bearers and joists, the floor can be bouncy. Externally there may be visible dishing of the hip or ridge lines. As the moisture absorption process completes its journey to the innermost areas of the building, the internal footings will rise. If the spread of moisture is roughly even, it may be that the symptoms will temporarily disappear, but it is more likely that swelling will be uneven, creating a difference rather than a disappearance in symptoms. In buildings with timber flooring supported by bearers and joists, the isolated piers will rise more easily than the strip footings or piers under walls, creating noticeable doming of flooring. Wail cracking po due to MNeVven. iio i i As the weather pattern changes and the soil begins to dry out, the external footings will be first affected, beginning with the locations where the sun's effect is strongest. This has the effect of lowering the external footings. The doming is accentuated and cracking reduces or disappears where it occurred because of dishing, but other cracks open up. The roof lines may become convex. Doming and dishing are also affected by weather in other ways. In areas where warm, wet summers and cooler dry winters prevail, water migration tends to be toward the interior and doming will be accentuated, whereas where summers are dry and winters are cold and wet, migration tends to be toward the exterior and the underlying propensity is toward dishing. Movement caused by tree roots In general, growing roots will exert an upward pressure on footings, whereas soil subject to drying because of tree or shrub roots will tend to remove support from under footings by inducing shrinkage. Complications caused by the structure itself Most forces that the soil causes to be exerted on structures are vertical — i.e. either up or down. However, because these forces are seldom spread evenly around the footings, and because the building resists uneven movement because of its rigidity, forces are exerted from one part of the building to another. The net result of all these forces is usually rotational. This resultant force often complicates the diagnosis because the visible symptoms do not simply reflect the original cause. A common symptom is binding of doors on the vertical member of the frame. Effects on full masonry structures Brickwork will resist cracking where it can. It will attempt to span areas that lose support because of subsided foundations or raised points. It is therefore usual to see cracking at weak points, such as openings for windows or doors. In the event of construction settlement, cracking will usually remain unchanged after the process of settlernent has ceased. With local shear or erosion, cracking will usually continue to develop until the original cause has been remedied, or until the subsidence has completely neutralised the affected portion of footing and the structure has stabilised on other footings that remain effective. In the case of swell/shrink effects, the brickwork will in some cases return to its original position after completion of a cycle, however it is more likely that the rotational effect will not be exactly reversed, and it is also usual that brickwork will settle in its new position and will resist the forces trying to return it to its original position. This means that in a case where swelling takes place after construction and cracking occurs, the cracking is likely to at least partly remain after the shrink segment of the cycle is complete. Thus, each time the cycle is repeated, the likelihood is that the cracking will become wider until the sections of brickwork become virtually independent. With repeated cycles, once the cracking is established. if there is no other complication, it is normal for the incidence of cracking to stabilise, as the building has the articulation it needs to cope with the problem. This is by no means always the case, however, and monitoring of cracks in walls and floors should always be treated seriously. Upheaval caused by growth of tree roots under footings is not a simple vertical shear stress. There is a tendency for the root to also exert lateral forces that attempt to separate sections of brickwork after initial cracking has occurred.
Page 18
The normal structural arrangement is that the inner leaf of brick- work in the external walls and at least some of the internal walls (depending on the roof type) comprise the load-bearing structure on which any upper floors, ceilings and the roof ate supported. In these cases, it is Internally visible cracking that should be the main focus of attention, however there are a few examples of dwellings whose external leaf of masonry plays some supporting role, so this should be checked if there is any doubt. In any case, externally visible cracking is important as a guide to stresses on the structure generally, and it should also be remembered that the external walls must be capable of supporting themselves. Effects on framed structures Timber or steel framed buildings are less likely to exhibit cracking due to swell/shrink than masonry buildings because of their flexibility. Also, the doming/dishing effects tend to be lower because of the lighter weight of walls. The main risks to framed buildings are encountered because of the isolated pier footings used under walls. Where erosion or saturation cause a footing to fall away, this can double the span which a wall must bridge. This additional stress can create cracking in wall linings, particularly where there is a weak point in the structure caused by a door or window opening. It is, however, unlikely that framed structures will be so stressed as to suffer serious damage without first exhibiting some or all of the above symptoms for a considerable period. The same warning period should apply In the case of upheaval.-It should be noted, however, that where framed buildings are supported by strip footings there is only one leaf of brickwork and therefore the externally visible walls are the supporting structure for the building. In this case, the subfloor masonry walls can be expected to behave as full brickwork walls. Effects on brick veneer structures . Because the load-bearing structure of a brick veneer building is the frame that makes up the interior leaf of the external walls plus perhaps the internal walls, depending on the type of roof, the building can be expected to behave as a framed structure, except that the external masonry will behave in a similar way to the external leaf of a full masonry structure. Water Service and Drainage Where a water service pipe, a sewer or stormwater drainage pipe is in the vicinity of a building, a water leak can cause erosion, swelling or saturation of susceptible soil. Even a minuscule leak can be enough to saturate a clay foundation. A leaking tap near a building can have the same effect. In addition, trenches containing pipes can become watercourses even though backfilled, particularly where broken rubble is used as fill. Water that runs along these trenches can be responsible for serious erosion, interstrata seepage into subfloor areas and saturation. Pipe leakage and trench water flows also encourage tree and shrub roots to the source of water, complicating and exacerbating the problem. Poor roof plumbing can result in large volumes of rainwater being concentrated in a small area of soil: * Incorrect falls in roof guttering may result in overflows, as may gutters blocked with leaves etc. * Corroded guttering or downpipes can spill water to ground. © Downpipes not positively connected to a proper stormwater collection system will direct a concentration of water to soil that is directly adjacent to footings, sometimes causing large-scale problems such as erosion, saturation and migration of water under the building. ‘seriousness of Cracki 9 . In general, most cracking found in masonry walls is a cosmetic . nuisance only and can be kept in repair or even ignored. The table below is a reproduction of Table C1 of AS 2870. . AS 2870 also publishes figures relating to cracking in concrete floors, however because wall cracking will usually reach the critical point © significantly earlier than cracking in slabs, this table is not reproduced here. :Prevention/Cure Plumbing Where building movement is caused by water service, roof plumbing, sewer or stormwater failure, the remedy is to repair the problem. It Is prudent, however, to consider also rerouting pipes away from the building where possible, and relocating taps to positions where any leakage will not direct water to the building vicinity. Even where gully traps are present, there is sometimes sufficient spill to create _ erosion or saturation, particularly in modern installations using sinaller diameter PVC fixtures. Indeed, some gully traps are not situated directly under the taps that are installed to charge them, with the result that water from the tap may enter the backfilled trench that houses the sewer piping. If the trench has been poorly backfilled, the water will either pond or flow along the bottom of the trench. As these trenches usually run alongside the footings and can be at a similar depth, it is not hard to see how any water that is thus directed into a trench can easily affect the foundation's ability to support footings or even gain entry to the subfloor area. Ground drainage Jn all soils there is the capacity for water to travel on the surface and below it. Surface water flows can be established by inspection during and after heavy or prolonged rain. If necessary, a grated drain system connected to the stormwater collection system js usually an easy solution. Tt is, however, sometimes necessary when attempting to prevent water migration that testing be carried out to establish watertable height and subsoil water flows. This subject is referred to in BTF 19 and may properly be regarded as an area for an expert consultant. Protection of the building perimeter i It is essential to remember that the soil that affects footings extends well beyond the actual building line. Watering of garden plants, shrubs and trees causes some of the most serious water problems. For this reason, particularly where problems exist or are likely to occur, it is recommended that an apron of paving be installed around as much of the building perimeter as necessary. This paving
Page 19
height selected ¢ for distance from house 2. Drained Carport pathway. Path--— Garden bed 5 “covered wilh Driveway! mulch iG ' should extend outwards a minimum of 900 mm (more in highly reactive soil) and should have a minimum fall away from the building of 1:60. The finished paving should be no less than 100 mm below brick vent bases. It is prudent to relocate drainage pipes away from this paving, if possible, to avoid complications from future leakage. Tf this is not practical, earthenware pipes should be replaced by PVC and backfilling should be of the same soil type as the surrounding soil and compacted to the same density. Except in areas where freezing of water is an issue, it is wise to remove taps in the building area and relocate them well away from the building — preferably not uphill from it (see BTF 19). It may be desirable to install a grated drain at the outside edge of the paving on the uphill side of the building. Tf subsoil drainage is needed this can be installed under the surface drain. Condensation In buildings with a subfloor void such as where bearers and joists support flooring, insufficient ventilation creates ideal conditions for condensation, particularly where there is little clearance between the floor and the ground. Condensation adds to the moisture already present in the subfloor and significantly slows the process of drying out. Installation of an adequate subfloor ventilation system, either natural or mechanical, is desirable. Warning: Aithough this Building Technology File deals with cracking in buildings, it should be said that subfloor moisture can result in the development of other problems, notably: ¢ Water that is transmitted into masonry, metal or timber building elements causes damage and/or decay to those elements. * High subfloor humidity and moisture content create an ideal environment for various pests, including termites and spiders. ¢ Where high moisture levels are transmitted to the flooring and walls, an increase in the dust mite count can ensue within the living areas. Dust mites, as well as dampness in general, can be a health hazard to inhabitants, particularly those who are abnormally susceptible to respiratory ailments. The garden The ideal vegetation layout is to have lawn or plants that require only light watering immediately adjacent to the drainage or paving edge, then more demanding plants, shrubs and trees spread out in that order. Overwatering due to misuse of automatic watering systems is a common cause of saturation and water migration under footings. If it is necessary to use these systems, it is important to rermove garden beds to a completely safe distance from buildings. Existing trees Where a tree is causing a problem of soil drying or there is the existence or threat of upheaval of footings, if the offending roots are subsidiary and their removal will not significantly damage the tree, they should be severed and a concrete or metal barrier placed vertically in the soil to prevent future root growth in the direction of the building. If it is not possible to remove the relevant roots without damage to the tree, an application to remove the tree should be made to the local authority. A prudent plan is to transplant likely offenders before they become a problem. Information on trees, plants and shrubs State departments overseeing agriculture can give information regarding root patterns, volume of water needed and safe distance from buildings of most species. Botanic gardens are also sources of information. For information on plant roots and drains, see Building Technology File 17. Excavation Excavation around footings must be properly engineered. Soil supporting footings can only be safely excavated at an angle that allows the soil under the footing to remain stable. This angle is called the angle of repose (or friction) and varies significantly between soil types and conditions. Removal of soil within the angle of repose will cause subsidence. ' Remediation Where erosion has occurred that has washed away soil adjacent to footings, soil of the same classification should be introduced and compacted to the same density. Where footings have been undermined, augmentation or other specialist work may be required. Remediation of footings and foundations is generally the realm of a specialist consultant. Where isolated footings rise and fall because of swell/shrink effect, the homeowner may be tempted to alleviate floor bounce by filling the gap that has appeared between the bearer and the pier with blocking. The danger here is that when the next swell segment of the cycle occurs, the extra blocking will push the floor up into an accentuated dome and may also cause local shear failure in the soil. If it is necessary to use blocking, it should be by a pair of fine wedges and monitoring should be carried out fortnightly. This BTF was prepared by John Lewer FAIB, MIAMA, Partner, Construction Diagnosis. The information in this and other issues in the series was derived from various. sources and was believed to be correct when published. Further professional advice needs to be obtained before taking any action based on the information provided. The information is advisory. It is provided in good faith and not claimed to be an exhaustive treatment of the relevant Subject. Distributed by CSIRO PUBLISHING PO Box.1139, Collingwood 3066, Australia Freecall 1800 645 051. Tel (03) 9662 7666 Fax (03) 9662 7555. www.publish.csiro.au Email: [email protected] © CSIRO 2003. Unauthorised copying of this Building Technology file is prohibited