In wall insulation

Hi there

We are building a house in WA and just wondering is it worth paying extra for inwall insulation (between bricks)

Cheers

Yes! Have you checked how much you need to get a six star rating? Obviously if you can orientate your house for passive solar living you're away laughing to an extent. We have the foil stuff between the cavity wall bricks in most of the house, then eco glass wool blown in in the other walls. Plus we got anticon over the roof frames. We haven't had to use any heating so far this winter even on the colds nights,

Brick is not a very good insulator. The air cavity in double brick offers a small improvement, but nowhere near the levels of a well insulated house. Brick does have high thermal mass, which means it can absorb a lot of heat. So it slows the transfer of heat into the house for some time, as it absorbs heat. But once hot, it will radiate heat into the house. As it has absorbed so much heat, it will continue to radiate heat into the house long after it has cooled down outside! So really it just slows the transfer of heat, meaning the house is cooler in the mornings, but hotter in the evenings. Definitely not a good thing when your trying to sleep at night after a hot day.

So by itself, double brick is not a very thermally efficient method of construction. I'm certainly not a fan of it, but it is very popular in WA.

Insulation in the cavity definitely improves the situation, so I'd recommend it. It will thermally separate the 2 wythes (layers of brick). The outer layer will still be heated by the sun, but that heat will struggle to penetrate through your insulation, & through the inner layer of brick, into the house. Importantly, the thermal mass of the inner layer of brick is now very useful at regulating the temperature inside your house, knocking off the peaks of the highs & the troughs of the lows. Absorbing heat when the brick is cooler than the surrounding air (in the hotter part of the day), & releasing heat when the brick is warmer than the surrounding air (in the cooler part of the day). So internal brick evens out the temperature throughout the day, making it slightly cooler in the day, & slightly warmer in the night.

Foil (with an air gap) is a great idea as it reflects the sun's radiation. So it's a good idea anywhere that receives a lot of summer sunlight. Particularly on the western wall. This side of the house gets blasted by summer sun in the hottest part of the day, so is the most important aspect to look at. Hopefully you have decent length eaves, which will shade the northern side of the house from summer sun.

Beazley77's absolutely right. Along with improving the thermal performance of the construction method you use, you should also consider the orientation of your house. It makes a huge difference! "Passive solar" is the term. In simple terms, what it means is ORIENTATE YOUR LIVING AREAS TO THE NORTH. This side of the house will receive sunlight into the house in winter, warming it, but will be shaded in summer (when the sun's higher in the sky). Limit windows to the west as it's blasted by the summer sun (& locate rarely used rooms here, like garages, laundries, bathrooms). More can be found here,

http://yourhome.gov.au/passive-design/

I'm in Sydney, in a very well designed apartment. It's currently 12C outside, but sunny. Inside, in the living areas (which face north) it's beautiful, warm & sunny. Heating is never required in this place! The bedrooms (which face south) are very cool, but shut off from the rest of the house. They receive no direct sun in summer, so remain cool.

Passive solar FTW!

ddarroch, great answer. I'm about to pick a builder and most of them offer ceiling insulation batts only and they say wall insulation batts are not going to help much. I'm in Brisbane so I think I will ask for wall insulation.