To achieve satisfactory long-term performance from a suspended timber floor, it is essential that correct sub-floor drainage and ventilation be in place.
- Provision of adequate sub-floor ventilation will help to avoid serious problems with floors such as swelling or shrinkage, decay and risk of termite attack;
- Recommended minimum area of openings for sub-floor ventilation is 6300 mm2/m length of external wall. The vents should be spaced not more than 600mm from each corner, evenly distributed and located to ensure cross-ventilation. For example, a pressed metal vent of 230mm x 75mm gives 11,000 mm2 of clear ventilation and such vents should therefore be spaced at no more than 1700mm centres. Figure 1 shows how to locate vents. Figure 2 provides a comparison of commercially available vents;
- The under-floor ground surface should be graded and drained to prevent the ponding of water. Where the ground is excessively damp, an impervious membrane should be placed over the ground surface. Minimum ground clearance should be 400 mm to the underside of the timber framing and
- The area around the building should be graded and drained to minimise water accumulating or moving under the building. Downpipes, outside taps and drains should also be detailed and maintained to reduce ground water.
References: Toby Technical Bulletin TB011. Timber Research and Development Advisory Council of Queensland (TRADAC) Report, September 1994
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