Development Application Part 2 of 2 Planning report Geotechnical report and plans MCU11/0168 & OPW11/0257

                                                                                   •    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
                                                         Clump of trees,
                                                         heaht se ccted                 walls, an increase in the dust mite count can ensue within the
                                                         -or distance                   living areas. Dust mites, as well as dampness in general, can be a
                                                         ?ream ;Noose                    health hazard to inhabitants, particularly those who are
                                                L7t                                      abnormally susceptible to respiratory ailments.
                                  Lawn
                                                                                   'fhe garden
                                                                                   The Ideal vegetation layout is to have lawn or plants that require
                         1` rnn                                                    only light watering immediately adjacent to the drainage or paving
                           Patio                                                   edge, then more demanding plants, shrubs and trees spread out in
                                                                                   that order.

                                                                                   Overwatering due to misuse of automatic watering systems is a
                                                           Di airit u              common cause of saturation and water migration under footings. If
     Carport                                               ?alhsvay                 it is necessary to use these systems, it is important to remove 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
                                                           vsrden bed
                                                                                   the building. If it is not possible to remove the relevant roots
    Drivewayl                                                    d yr lh
                                                           mulch                   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
                           Medurn                                                  offenders before they become a problem.
                           height tree
                                                                                   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.

should extend outwards a minimum of 900 mm (more in highly                         Excavation
reactive soil) and should have a minimum fall away from the                        Excavation around footings must be properly engineered. Soil
building of 1:60. The finished paving should be no less than 100                   supporting footings can only be safely excavated at an angle that
mm below brick vent bases.

It is prudent to relocate drainage pipes away from this paving, if
possible, to avoid complications from future leakage. If this is not
                                                                                   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.
                                                                                                                                                              1
practical, earthenware pipes should he replaced by PVC and
backfilling should be of the sarrte soil type as the surrounding soil
and compacted to the same density.                                                     Remediation
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                   Where erosion has occurred that has washed away soil adjacent to
the building    preferably riot 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. If subsoil drainage is
                                                                                    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
                                                                                                                                                              L   I
needed this can be installed under the surface drain.
                                                                                    specialist consultant.

Condensation                                                                        Where isolated footings rise and fall because of swell/shrink effect,
In buildings with a subfloor void such as where bearers and joists                  the homeowner may be tempted to alleviate floor bounce by filling
support flooring, insufficient ventilation creates ideal conditions for             the gap that has appeared between the bearer and the pier with
condensation, particularly where there is little clearance between the              blocking. The danger here is that when the next swell segment of the
floor and the ground. Condensation adds to the moisture already                     cycle occurs, the extra blocking will push the floor up into an
present in the subfloor and significantly slows the process of drying               accentuated dome and may also cause local shear failure in the soil.
out. Installation of an adequate subfloor ventilation system, either                   If it is necessary to use blocking, it should be by a pair of fine
natural or mechanical, is desirable.                                                wedges and monitoring should be carried out fortnightly.

Warning: Although this Building'Iechnology File deals with                             This BTF was prepared by John Lewer FAIR, MIAMA, Partner,
cracking in buildings, it should be said that subfloor moisture can                    Construction Diagnosis.
result in the development of other problems, notably:




           The information In this and other issues in the series was derived from various sources and was believed to be correct when published.

                The information Is advisory. It is provided in good faith and not claimed to be an exhaustive treatment of the relevant subject.

                        Further professional advice needs to be obtained before taking any action based on the information provided.

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