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Question

Can you please clarify how subfloor ventilation is provided where 130x19mm Spotted Gum floorboards glued to yellow tongue particle board are installed over a concrete slab using 80mm high KDHW battens affixed to the slab. Is the ventilation provided by weep holes or are there other generally accepted methods?

Woodsolutions Answer +

The purpose of sub-floor ventilation is to ensure that moisture doesn't build up under the floor. This is important where a traditional timber floor on joists is suspended over bare earth. Where a floor is installed on battens that are fixed to a concrete slab, or where flooring is glued directly to a concrete slab, the source of moisture will be the concrete rather than the earth. With a floor on battens a polyethylene membrane is recommended on top of the slab, held in place by the battens. Alternatively, a trowelled-on moisture can be applied to the slab, as used before installing direct-stick flooring. Moisture barriers are explained in more detail in our Technical Design Guide no. 9, refer p. 31. The guide can be downloaded from our website here: https://www.woodsolutions.com.au/publications.

Sub-floor ventilation
Question

We completed a job in 2015 , installed 108 X 14 mm tassie oak boards over 19 mm particle board flooring .
subfloor, laminated lvl joists and bearers, insulation subfloor. yellow tongue particle board flooring.
construction through winter, got the roof on quiick no evidence of saturated flooring through job.
Tassie oak floor came up great, had a call june 2017 with concerns the floor had cracked/split through near center of large room 8m x 8m
note , no expansion joint installed. edge bond split , board split fairly consistent with chipboard floor join underneath.
chipboard inspection showed sheets had shrunk - the shrinkage was inside the acceptable margins/allowances.
filled the gap 1mm > 2.5 mm with selleys gap filler to monitor the movement.
seems the gap is widening through winter
closing through summer - no evoprative heating, entire house refrigerated ducted.
 

Woodsolutions Answer +

That's a little strange given that wood products usually shrink in summer and swell in winter. The floor in question is doing the opposite. With insulation under the floor it seems unlikely moisture from the ground is playing any part. We can only suggest that winter heating might be causing the floor to shrink. Even if the particleboard wasn't wet it might have had a slightly higher moisture content during the winter construction period, sufficient to cause shrinkage when exposed to prolonged heating. Also we note there is a large expanse of flooring in a room 8m x 8m. Technically there should be a control joint in any floor over 6m wide according to Australian Standard 1684, Residential timber-framed construction (clause 5.4). We suggest an inspection by a qualified person may help to determine whether any site factors are involved. The Australasian Timber Flooring Association (ATFA) provides an inspection service, more info here: https://www.atfa.com.au/request-an-inspection.

Timber floor
Question

Have recently installed a 14mm timber floor board system glued to a 12mm ply substrate that was mechanically fixed to a concrete slab. There is a plastic vapour barrier under the ply. Since install, the floor boards (glued and secret nailed) have cupped and gaps have formed at each plank joint. What needs to be done to rectify.

Woodsolutions Answer +

This is a problem that might need a building inspector to get to the bottom of it. The Australasian Timber Flooring Association (ATFA) has experienced inspectors located around the country. There are two possible causes of cupping in flooring. There may be moisture from underneath making the underside swell, or there may be drying from above making the top surface shrink. Moisture from underneath is unlikely since there is a vapour barrier. An inspector will be able to assess whether the interior of the building is unusually dry, whether the flooring was at a suitable moisture content at the time of installation, and other relevant factors. The inspector should also be able to advise on rectification, which will depend on the severity of the shrinkage and cupping. You can request an inspection here: https://www.atfa.com.au/request-an-inspection. 

Flooring, cupping
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