TABLE 2. CLASSIFICATION OF DAMAGE WITH REFERENCE TO WALLS.
Description of typical damage and required repair
Approximate crack width limit
Damage category
<0.1 mm <1mm <5mm
Hairline cracks Fine cracks which do not need repair Cracks noticeable but easily filled. Doors and windows stick slightly.
0 -Negligible 1 -Very Slight 2-Slight
3 -Moderate
5-15mm (or a number of cracks 3 mm or more in one group) 15-25mm but also depends on number of cracks
Cracks can be repaired and possibly a small amount of wall will need to be replaced. Doors and windows stick. Service pipes can fracture. Weathertightness often impaired. Extensive repair work involving breaking-out and replacing sections of walls, especially over doors and windows. Window and door frames distort. Walls lean or bulge noticeably, some loss of bearing in beams. Service pipes disrupted.
4-Severe
Source: Reproduced with the permission of Standards Australia Limited© 2011. Copyright in AS 2870-2011Residential slabs and footings vests in Standards Australia Limited.
Warning: Although this Building Technology Resource 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, and mould. ► 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 remove garden beds to a completely safe distance from buildings. EXISTING TREES Existing trees may cause problems with the upheaval of footings by their roots, or shrinkage from soil drying. 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. Soil drying is a more complex issue and professional advice may be required before considering the removal or relocation of the 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.
Tree height selected for distance from house
Garden bed covered with mulch
Carport
Path
Driveway
FIGURE 2 Gardens for a reactive site.
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 home owner 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.
Foundation Maintenance and Footing Performance© Commonwealth Scientific and Industrial Research Organisation (CSIRO) 2024 CC BY-NC-ND 4.0. (Replaces Building Technology Resource 2021, Building Technology File 18, 18-2011 and Information Sheet 10/91)
IMPORTANT DISCLAIMER: This information is prepared for Australia and general in nature. It may be incomplete or inapplicable in some cases. Laws and regulations may vary in different places. Seek specialist advice for your particular circumstances. To the extent permitted by law, CSIRO excludes all liability to any person for any loss, damage, cost or other consequence that may result from using this information.
© CSIRO 2024
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