A4 Structural safety
Structural failure in houses can be life threatening or cause severe physical injury. Care needs to be taken at the design stage to ensure structural components are suited to the environment and adequate for loads. Common areas of structural failure include:
- movement in foundations causing major cracking, due to lack of site information about soils and/or poor design
- use of untreated timber, resulting in termite attack
- damage to timber or steel framing caused by leaking wet areas
- failure of steel structures, particularly light-weight frames, through corrosion caused by salt spray.
These problems can be avoided by using a qualified inspector during construction to ensure that the structure is built according to its design and specification.
Structural repairs related to life threatening situations must be considered a higher priority requiring urgent work, for example:
- rotten floors in high set houses, especially in wet areas where there is a water leak or no floor drain, allowing water to penetrate the floor and walls and rot the framing supports
- unstable water tank stands
- rotten or rusted stairs
- walls with large cracks or leans
- piers, stumps and footings being eroded by stormwater
- buildings that are unsafe because of fire damage or severe termite attack
- loose materials such as roof sheeting or windows.
Design and specification
A qualified engineer should complete a site investigation report covering detailed information on building materials (structural), soils (geotechnical), or water (hydraulic) issues prior to commencing the structural design for new or upgraded houses.
Ensure:
- structural components of the house are engineered to suit soil and climate conditions.
- the local wind conditions have been checked, particularly in coastal cyclonic areas, and inland and desert areas subject to strong winds
- if using timber, that termite-resistant timbers and mechanical termite barriers are used throughout the construction
- if using steel, that steel framing, structural components, stairs and hand rails are rust-proofed with an approved system
- bottom plates of wall frames are detailed to avoid rot or rust, especially in wet areas
- the height of the floor above ground is sufficient for regular inspections of the sub-floor areas for termites and water leaks
- kitchens and wet areas are detailed and specified to prevent water penetrating the walls or floors
- plumbing is designed to suit the local water quality and to reduce leaks and associated structural failure.
Quality control
Before making the final payment for the project, ensure that:
- an engineer’s certificate is provided for all structural components including footings, slabs, floor framing, wall framing and roof framing with reference to the wind terrain category and soil classification
- the site investigation report is provided and corresponds to the information in the engineer’s certificate.
During construction and before making the final payment, check that:
- footings, foundations, structural tie-downs and other engineering requirements are constructed according to plans and specifications
- an engineer or an experienced inspector has inspected the site preparation and provided an inspection report
- termite barriers are installed and are undamaged
- wet areas and kitchen areas are sealed
- the builder has provided warranties for the installation of waterproofing, termite barriers, glass and other proprietary systems.
Maintenance
If attending to a house with severe structural failures, the residents should be relocated to another house and a qualified engineer should be consulted.
As part of cyclical maintenance:
- check regularly for rust, rot, termites and other signs of structural deterioration
- check for and fix water leaks including down pipes and sub-surface stormwater pipes
- check garden beds, timber floors and ramps for termites
- if garden beds have been planted against walls, talk to residents about removing them to make it easier to check for termites
- consider organising a regular program of termite inspections and treatments by a qualified pest controller
- in tropical areas or areas close to the coast, check for corrosion of steelwork and re-apply paints and other protective coatings.
During upgrades in high wind and cyclone areas:
- inspect, tighten, replace or install structural tie-downs between roof, wall and floor
- if the roof is nailed on, replace the nails with screws and cyclone washers and check that the structure of the roof is in good condition.
| Structural safety | Percentage of houses | Total houses surveyed | Change since 2003* |
|---|---|---|---|
| Type of walls—brick, concrete block, concrete, earth | 26% | 3,662 | |
| Type of walls—brick veneer | 23% | 3,662 | |
| Type of walls—steel frame and fibrous cement, timber, or steel | 30% | 3,662 | < |
| Type of walls—timber frame and fibrous cement, timber, or steel | 16% | 3,662 | < |
| Type of walls—other (insulated panel, logs, and so on) | 6% | 3,662 | |
| Termites not present | 72% | 3,660 | < |
| Walls—inside condition good = all OK | 45% | 3660 | |
| Walls—inside condition fair = water, mould | 26% | 3,660 | |
| Walls—inside condition poor = holes, cracks, water, mould | 29% | 3,660 | |
| Walls—outside condition good = all OK | 54% | 3,658 | |
| Walls—outside condition fair = minor cracking, repair needed | 25% | 3,658 | |
| Walls—outside condition poor = holes, large cracks | 21% | 3,658 | |
| Floor—finish and condition good = all floors OK | 49% | 3,658 | |
| Floor—finish and condition fair = not unsafe, but poor finish | 29% | 3,658 | |
| Floor—finish and condition poor = holes, unsafe | 22% | 3,658 |
See ‘Changes in the condition of houses’ for an explanation of the symbols used in this column.
Standards and references
AS 2870–1996, Amendment 1–1997, Amendment 2–1999, Amendment 3–2002 Residential slabs and footings—Construction.
AS 2312 – 2002, Amendment 1 – 2004 Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings.