Issue 29 – July 2011
Where a suspended floor is constructed with particleboard flooring, product suppliers specify a minimum clearance between the underside of the particleboard and the ground. Generally, this is given as 550 mm minimum, but it may be specified as a minimum dimension of 450 mm between the ground and the bottom of the joist (which will give at least 550 mm clearance with commonly used joist sizes).
Where damp soil conditions exist, it is recommended that the ground be covered with polythene, even where the minimum subfloor ventilation requirements of NZS 3604:2011 and E2/AS1 paragraph 10.7.2 are being met (net open area of 3500 mm2 per m2 floor area). Where minimum ventilation requirements are not being met, the polythene ground cover is required. (In this case, ventilation net open area of not less than 700 mm2 per m2 of floor area must still be provided – see E2/AS1 10.2.7.1.)
Note that MDF sheet is not able to be used for flooring under NZS 3604 paragraph 184.108.40.206 as it is not permitted to be exposed to ground atmosphere. There is no specific minimum clearance specified for H3 CCA-treated plywood.
- NZS 3604:2011 Timber-framed buildings