Step 7. Insulation

Insulation are those materials used in buildings to reduce heat loss in the winter and heat gain in the summer. Most people are fairly familiar with the concept of insulation. For those who are not there is lots of information on the internet including Wikipedia. In a passive solar designed building the insulation is very important because, in winter it helps to keep the heat from the sun in the building, and in summer it helps to keep heat out.

In the walls of the Greeny Flat we used two layers of insulation. The first is a reflective foil and foam product called “E-therm” which has reflective faces on both sides of 8mm of foam. The foil helps to reflect heat back the way it came (i.e. back out in summer and back in in winter) while the foam provides a “Thermal Break” at the framing members. Without it we would lose much more heat through the wall framing because wood doesn’t insulate as well as the batts in the cavities. This can be the biggest problem with steel framing as heat will readily pass in and out of the building through the frame unless an effective thermal break is installed.

Exterior reflective insulation wraps the outside of the Greeny Flat

Exterior reflective insulation wraps the outside of the Greeny Flat

Polyester batt insulation in the Greeny Flat walls

Polyester batt insulation in the Greeny Flat walls

We placed the studs 600mm apart and used advanced framing techniques (i.e. less wood) to allow for more insulation in the walls. In the cavities we used R2.0 polyester batts made from recycled PET plastic bottles. It’s nice to work with and doesn’t make you itchy (like fibreglass) but watch out if you accidently drive a screw into it… it will spin into a ball on the end of the screw and pull the insulation out of a sizeable area around the screw hole.

Note that the plumbing lines are on the interior side of the insulation.

And don’t forget that the windows and exterior doors are also an important part of the insulation and air-sealing layer.

SIPS panels were used for the roof of the Greeny Flat.

SIPS panels were used for the roof of the Greeny Flat.

For the roof we used a structural insulated panel system (SIPS). The panels are made of 150mm of polystyrene foam with corrugated colourbond steel glued to the top side and flat white colourbond sheet glued to the underside forming the ceiling.

The panels are structural which means that there is no framing in the roof. They span from the ridge to the eaves with no rafters or other supports. They are quite expensive to buy but very quick to install and once the roof is on, a lot of jobs are done including the roof structure, insulation, finished roof and finished ceiling so there are dramatically reduced labour costs.

 

Insulation under and around the edge of floor slabs in other projects.

Insulation under and around the edge of floor slabs in other projects.

Neither of the above photos are from the Greeny Flat. In America and Europe it is very common to insulate underneath concrete slabs as well as around the edge of the slab. Our climate is much milder so underslab insulation is probably not necessary unless you are using heat pipes in the slab. Slab edge insulation will help prevent a lot of heat loss but has to be very carefully detailed so as not to provide easy access for termites into the building.

Of course if your building is up off the ground it is essential to insulate and air-seal under the floor in our climate (Southern Highlands of NSW, Cliimate Zone 6).

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