Insulation choices
After sorting out the cladding options for our homes, we started to think about insulation. What material should we choose to do the hard yakka of reducing heat flow through the walls, ceiling and floor?
Having good insulation, along with double glazed windows, makes sense year round.
In winter, it stops warmth leaching from the Timbercrete walls through the thin cladding to the air outside. The more heat we lose, the more electricity we’ll need to use to keep the rooms at a comfortable temperature. Of course, the reverse is true in summer. If the heat from the furnace-like northerly winds gets to our internal walls, the inside temperature could get uncomfortable. By not having air conditioning, we’ll be relying on ceiling fans and air circulation to drop the temperature overnight. Keeping inside the house at a reasonable temperature means a combination of insulation not allowing too much heat to enter during daylight and using breezes to cool the rooms overnight.
Lots of insulation options available.
Browsing the Your Home website showed there is plenty to choose from.
First decision is between reflective and bulk. Reflective insulation is usually shiny aluminium foil laminated onto paper or plastic. Because it’s double sided, this insulation reflects radiant heat back into the home (winter) or back outside (summer). Bulk insulation relies on pockets of air trapped within the material to resist heat transfer. Choices include glass wool, polyester, sheep’s wool and polystyrene.
The concrete slab will sit on a layer of polystyrene board to insulate it from the ground. The edges are also insulated from the surrounding air. We’l stick with the standard arrangements for the slab.
What insulation features are important to us?
Trying to decide which insulation was optimum for our design meant starting with a list of features that were important to us.
First thing to think about is the traditional cost/benefit analysis to make sure we get good value from the purchase price.
Next, what are the sustainability credentials for each product? Is it made from a renewable source (eg wool) or a recycled material (eg recycled plastic)? Is it such a high performing material that the overall energy saving benefit trumps the competitors’ green manufacturing credentials?
Finally, how is this material going to impact on our health and that of the builders? Does it contain chemicals which we’d prefer not to have in our home? Will the builders have to go to great lengths not to be exposed to the material when slicing and dicing it during construction?
Two candidates chosen for walls and ceiling.
We’ve selected two candidates for further investigation.
The first option is polyester batts made from recycled plastic. Scanning the website of one supplier (Insulation Australia) highlighted the advantages of this material. Sustainability credentials are good as it contains up to 85% recycled materials (eg PET bottles) and the batts can be recycled at their end of their life. Health looks good as well because the builders won’t require any protective equipment for installation. The batts are described as non-irritant, non-toxic and non-allergenic – lots of “nons” there.
Our second option is more like the Rolls Royce of insulation. We are thinking of a combination of bulk and reflective insulation as supplied by Kingspan.
Kooltherm K12 is a rigid, foam-like insulation that is coated with a reflective surface. From the sustainability perspective, no CFCs are used during the manufacturing. The supplier claims it has zero Ozone Depletion Potential and low Global Warming Potential. For the builders, the materials are chemically inert. Funnily enough, the main issue during construction is the amount of UV radiation reflected off the surface. Sunglasses and sunscreen are the order of the day when working with the panels in sunny weather.
The Kooltherm would be used in combination with Aircell Permishield which is a reflective insulation. Patented materials are used to manufacture Permishield so it’s hard to determine the sustainability credentials. Like the Kooltherm, the main health concern with installation is getting sunburned. The material itself is non-toxic and non-hazardous.
Plan to finalise insulation choices.
Having decided on a couple of options, we need to investigate cost/benefit.
It’s relatively easy to get a feel for the different costs because suppliers can provide budget quotes from the plans. However, there is more work to get an idea of the insulation merits. We’ve decided to use the NatHERS rating program to help answer that question. Our consultant will run the model twice, once for a material similar to the polyester batts and then again for the Kingspan insulation. That should give us the missing half of the cost/benefit balance.
Apart from providing information about insulation, running the NatHERS model will tell us what energy star rating we have achieved with the designs. Can’t wait for that one!
