NELSON BUILDING REPORTS

Sub-floor insulation options

A few points about under-floor insulation, that’s for timber flooring.

1. Sub-floor insulation is a legal requirement for all tenanted houses from 1 July 2019.

The legal minimum under-floor insulation in Nelson/Tasman is R 1.3. But if you are installing batts you might as well go for the R 1.6 or R 1.8 variety for a slight increase in thermal insulation.

2. Despite being more expensive, it is worth installing polyester batts rather than fibreglass as polyester is self-supporting. You can staple the batts in position and they stay there. Fibreglass tends to delaminate and fall, so is usually held in place with thick plastic packaging tape. This method often is poor at holding the batts securely in the long term. The polyester batts are made from recycled P.E.T (Polyethylene terephthalate) clear plastic beverage containers.

Rigid polystyrene is another option but it has a few issues. The rigid sheets need to fit exactly between the joists to be neither too tight nor too loose. It is difficult to cut cleanly at the end of each row, or around any intrusions. The polystyrene slowly eats away at the plastic coating on electrical cables. And the manufacturing of polystyrene is toxic and not environmentally sound.

So, polyester batts are recommended.

3. The reflective foil insulation often installed in the 1980s is now considered a significant safety hazard. It is a huge aluminium sheet that is highly conductive to electricity. Should you whack a nail through an electrical cable, or rats chew through the wiring, the entire sub-floor can become electrified.

Yikes!! A potentially shocking experience. While old ceiling insulation such as Insulfluf is generally retained in place, it is advisable to remove any reflective foil sub-floor insulation prior to installing new polyester batts.