Installing Expol underfloor insulation in a villa

While the house is minus front steps, Mr Kiwi took the opportunity to install Expol insulation under the bedroom floor.

Usually this area is difficult to access and only has 2' clearance anyway. Plus it's muddy and full of cobwebs - as well as being criss-crossed with the ducting from our heating system. Not an easy - or a pleasant - job!

Above: The area underneath the bedroom floor doesn't have much clearance, plus there's heating ducting here too. Mr Kiwi has now blocked up the gaps in the weatherboards - there's no more daylight shining through!

The bedroom is south facing and therefore one of the coldest rooms in the house. It also has bare wooden floorboards: they look good, but are pretty darn chilly underfoot in winter! We may Expol more rooms later, but it's not a priority right now.

Expol is made of polystyrene sheets that fit between the floor joists. It comes in 4 different widths and has insulation value of R1.4.

Calculating how much Expol you'll need

The challenge with installing Expol in a villa is that these houses were built in a hurry, generally without plans or building regulations. Consequently, the floor joists were built by eye, rather than with a ruler, and the measurement varies from joist to joist.

In our case, the bedroom joists varied between 300mm and 500mm.

For now, we're just expoling under the bedroom - that's an area of approximately 20 square metres, which requires 4 packs of Expol.

But with the varying joist measurements, we needed to know which size to get.

Mr Kiwi went under the house and measured each joist. From there, he was able to work out how many packs of each size of Expol to get. The 4 packs he purchased were in 3 different widths, so if you're doing this job for a villa it's well worth measuring and calculating before you purchase!

What's more, not all the joists were parallel - many of them tapered. Many of the Expol panels had to be individually trimmed to ensure a snug fit. That's a slow job, and it took Mr Kiwi the whole day to install the insulation under the bedroom.

Home insulation subsidies from the NZ Government

The NZ Government is currently offering householders subsidies for insulating their homes. This is via EECA Energywise.

Alas these subsidies only apply when the insulation is installed professionally: it isn't available for DIY-ers. So no subsidies for us :(


Project cost: $$ (Materials only, for an area of approx. 20 square metres)

PS. I haven't included an "after" photo, as it's now pitch black under the house - it wouldn't be a very exciting photo!!