Pole foundations – subfloor insulation damage

Causes

The insulation was incorrectly installed; there are gaps between the insulation and subfloor framing 

There was no sheet lining under the insulation, and it has been damaged or blown out by wind or has been damaged by tradespeople

Listed under: insulation, Subfloor, framing, poles, wind

Cause

The insulation was incorrectly installed; there are gaps between the insulation and subfloor framing 

Repair

  • remove and refit existing insulation, discarding any that it too damaged to be effective. Replace damaged insulation with new bulk fill or polystyrene insulation, ensuring that it is appropriate for a subfloor – not all insulation products are interchangeable

  • install ideally to the full depth of the joists. The insulation should touch the underside of the floor, should not be compressed and should fit snugly without gaps

  • insulation can be temporarily secured in place with polypropylene tape

  • install a sheet lining (fibre-cement or H3 CCA-treated plywood) to the underside of the joists to protect the insulation from moisture and wind damage. The sheet lining also prevents wind wash across the surface of the insulation, which reduces its effectiveness.

  • for more information, follow the installation guidance in NZS 4246:2016 Energy efficiency – Installing bulk thermal insulation in residential buildings. This can be downloaded at no charge from Standards New Zealand

  • since 1 July 2019, underfloor thermal insulation has been a legal requirement in all rental properties where is it reasonably practical to install it

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Cause

There was no sheet lining under the insulation, and it has been damaged or blown out by wind or has been damaged by tradespeople

Repair

  • remove and replace the insulation, installing so that it is not compressed and fits snugly without gaps
  • fix a sheet lining material such as treated plywood or fibre-cement to the underside of floor joists to provide protection to bulk insulation materials such as polyester, fiberglass or wool insulation

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