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

    The normal structural arrangement is that the inner leaf of brick-          •    Corroded guttering or downpipes can spill water to ground.
    work in the external walls and at least some of the internal walls          •    Downpipes not positively connected to a proper stormwater
    (depending on the roof type) comprise the load-bearing structure on              collection system will direct a concentration of water to soil that Is
    which any upper floors, ceilings and the roof are supported. In these            directly adjacent to footings, sometimes causing large-scale
    cases, it is internally visible cracking that should be the main focus           problems such as erosion, saturation and migration of water under
    of attention, however there are a few examples of dwellings whose                the building.
    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,     Seriousness of Cracking
                                                                                .................. _....... ............. .. .
    and it should also be remembered that the external walls must be
    capable of supporting themselves.                                           In general, most cracking found in masonry walls is a cosmetic
                                                                                nuisance only and can be kept in repair or even ignored. 'I'he table
    Effects on framed structures                                                below is a reproduction of Table C I of AS 2870.
    Timber or steel framed buildings are less likely to exhibit cracking
    due to swell/shrink than masonry buildings because of their                 AS 2870 also publishes figures relating to cracking in concrete floors,
    flexibility. Also, the doming/dishing effects tend to be lower because      however because wall cracking will usually reach the critical point

    of the lighter weight of walls. The main risks to framed buildings are      significantly earlier than cracking in slabs. this table is not
    encountered because of the isolated pier footings used under walls.         reproduced here.
    Where erosion or saturation cause a footing to fall away, this can
    double the span which a wall must bridge. This additional stress can            Prevention/Cure
    create cracking in wall linings, particularly where there is a weak                      .............
    point in the structure caused by a door or window opening. It is,           Plumbing
    however, unlikely that framed structures will be so stressed as to suffer   Where building movement is caused by water service, roof plumbing,
    serious damage without first exhibiting some or all of the above
                                                                                sewer or storinwater failure, the remedy is to repair the problem.
    symptoms for a considerable period. The same warning period should
                                                                                It is prudent, however, to consider also rerouting pipes away from
    apply in the case of upheaval. It should be roted, however, that where
                                                                                the building where possible, and relocating taps to positions where
    framed buildings are supported by strip footings there is only one leaf     any leakage will riot direct water to the building vicinity. Even where
    of brickwork and therefore the externally visible walls are the             gully traps are present, there is sometimes sufficient spill to create
    supporting structure for the building. In this case, the subfloor           erosion or saturation, particularly in modern installations using
    masonry walls can be expected to behave as full brickwork walls.
                                                                                smaller diameter PVC fixtures. Indeed, some gully traps are not
                                                                                situated directly under the taps that are installed to charge them,
    Effects on brick veneer structures
                                                                                with the result that water from the tap may enter the backfilled
    Because the load-bearing structure of a brick veneer building is the
                                                                                    trench that houses the sewer piping. If the trench has been poorly
    frame that makes up the interior leaf of the external walls plus
                                                                                    backflled, the water will either pond or flow along the bottom of
    perhaps the internal walls, depending on the type of roof, the
                                                                                    the trench. As these trenches usually run alongside the footings and
    building can be expected to behave as a framed structure, except that
                                                                                    can be at a similar depth, it is not hard to see how any water that is
    the external masonry will behave in a similar way to the external leaf
                                                                                    thus directed into a trench can easily affect the foundations ability to
    of a full masonry structure.
                                                                                    support footings or even gain entry to the subfloor area.

        Water Service and Drainage
                                                                                    Ground drainage
                                                                                    In all soils there is the capacity for water to travel on the surface and
    Where a water service pipe, a sewer or stormwater drainage pipe is in
                                                                                    below it. Surface water flows can be established by inspection during
    the vicinity of a building, a water leak can cause erosion, swelling or
                                                                                    and after heavy or prolonged rain. If necessary, a grated drain system
    saturation of susceptible soil. Even a minuscule leak can be enough
                                                                                    connected to the storrnwaler collection system Is usually an easy
    to saturate a clay foundation. A leaking tap near a building can have
                                                                                    solution.
    the same effect. In addition. trenches containing pipes can become
    watercourses even though backfllled, particularly where broken                  It is, however, sometimes necessary when attempting to prevent
    rubble is used as fill. Water that runs along these trenches can be             water migration that testing be carried out to establish watertable
    responsible for serious erosion, interstrata seepage into subfloor areas        height and subsoil water flows. This subject is referred to in BTF 19
    and saturation.                                                                 and may properly be regarded as an area for an expert consultant.

    Pipe leakage and trench water flows also encourage tree and shrub               Protection of the building perimeter
    roots to the source of water, complicating and exacerbating the                 It is essential to remember that the soil that affects footings extends
    problem.                                                                        well beyond the actual building line. Watering of garden plants,
    Poor roof plumbing can result in large volumes of rainwater being               shrubs and trees causes some of the most serious water problems.
    concentrated in a small area of soil:
                                                                                    For this reason, particularly where problems exist or are likely to
    •    Incorrect falls in roof guttering may result in overflows, as may          occur, it is recommended that an apron of paving be installed
         gutters blocked with leaves etc.                                           around as much of the building perimeter as necessary. This paving




                                        CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS

                          Description of typical damage and required repair                                   Approximate crack width             Damage
                                                                                                                   limit (see Note 3)             category

        Hairline cracks                                                                                                <0.1 mm                        0

1       Fine cracks which do not need repair

        Cracks noticeable but easily filled. Doors and windows stick slightly
                                                                                                                          <1 mm

                                                                                                                          <5 mm
                                                                                                                                                      1

                                                                                                                                                      2

        Cracks can be repaired and possibly a small amount of wall will need                             5-15 mm (or a number of cracks               3
        to be replaced. Doors and windows stick. Service pipes can fracture.                                3 mm or more in one group)
        Weathertightness often impaired

        Extensive repair work involving breaking-out and replacing sections of walls,                        15 25 mm but also depend                 4
        especially over doors and windows. Window and door frames distort. Walls lean                             on number of cracks
        or bulge noticeably, some loss of bearing in beams. Service pipes disrupted




I