Insulating the roof

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One of the obvious ways of improving the energy efficiency of a house is to improve the insulation. In our case, there were tatters of 40-year-old insulation left in the rooft, but they weren’t going to do much for us.

We were lucky to get in quickly enough to receive the $1600 grant from the Australian Government for insulation. This applied even though we had some (useless) insulation in place:

The program targets homes that are currently uninsulated, or have very little ceiling insulation and were built before the mandatory thermal performance requirements under the Building Code of Australia were introduced commencing in 2003.

For us, the required insulation cost $1650, leaving us only $50 out of pocket. The standard insulation used by our chosen insulation installer was also excellent: Autex GreenStuf. It is:

  • made of recycled plastic
  • fire resistant
  • free of any loose particles
  • unappetising for bugs or rodents

It will basically last forever, and is even made in New Zealand, much closer than the European products on offer.

(The Government program has now dropped to $1200, but that should still be enough to do a moderate-sized terrace.)

That was just the beginning of the process. Doing some research, the insulation provides useful “bulk insulation”, slowing down the transfer of heat across the ceiling. But the roof space still gets extremely hot, as the corrugated iron roof heats up, and then re-radiates the heat into the house. After a while, this heat works its way down through the insulation, and into the living area.

Working with Wilhelm to install reflective foil insulation

The solution (or at least part of one) is to install reflective foil, also called sarking. We are using Aircell Retroshield, which is like giant bubblewrap covered in reflective foil on both sides. The shiny surface reflects the heat, and the air bubbles provide additional insulation (upwards of R3.2 in summer, R1.5 in winter).

For a new house, this is simply laid down at the same time the roof is put on. It’s a much slower job retrofitting it.

Thankfully I’ve got Wilhelm, our handy fix-everything-guy, to help me. So we’ve spent a number of afternoons up in the roof, nailing up the foil to the underside of the joists.

I think all of this is making a difference. Even with the back of the house completely uninsulated (old extension; flat roof), the house stays upwards of 10 degrees cooler than outside. Which is a good thing with the 35+ degree weather we’ve been having recently!

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2 thoughts on “Insulating the roof

    Understanding the house « Lewisham House said:
    January 17, 2010 at 2:19 pm

    […] very hot up in the roof. We’re putting in place reflective foil to reduce the amount of heat getting into the roof space, but once it’s in there it’s […]

    […] time back we installed a R3.5 batts in the roof of the original half of the house, along with reflective foil. Despite this, the roof space still gets very hot in summer, and after a run of really hot days, we […]

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