As part of thinking about building a house, I’ve given consideration to building a super insulated house. In different parts of the world this is called different things, often a passivhaus, named after the German standards.
Once you get reasonable insulation in your house, the main source of heat leakage is through air leakage – cold draughts in your house are a major source of energy loss. Air leakage is controlled through making the house air tight, which in turn relies on an air barrier. In most houses, this barrier is the dry wall / gyprock / gib board (depending on whether you’re American, Australian or kiwi). The trouble with this is that it’s really difficult to keep airtight – think of the opportunities for leakage:
- Power points, light switches
- Skirtings at the bottom of the walls, particularly with timber floors
- Door cavities, particularly sliding doors
- Light fittings, particularly down lights
- Window surrounds, doors
- Any vents
- Fittings like baths or showers that aren’t entirely sealed to the wall cavity
The Remote building style offers a different position for the air barrier and insulation. Basically the idea is that you build your framing in timber as is common in many countries (less common in Australia). You then sheath the whole house in plywood or OSB, and put your air barrier on the outside of that (typically a stick-on membrane). There are relatively few penetrations through the outside skin of the house, and you generally need to seal this well for water tightness anyway. You then put your insulation on the outside of the board – typically polystyrene, and your cladding over the outside of that.
A big advantage here is that it leaves your wall cavities empty of insulation, making running services a lot easier, and making retrofitting services also easier.
I’m thinking I’d extend this to the roof as well – instead of having insulation in the ceiling you’d push the insulation to the outside of the roof joists, and then put the roofing outside that. This would include your entire roof cavity into the conditioned portion of the house – it would be insulated and heated/cooled with the rest of the house. Since it’s fully insulated you’d have a number of advantages, including: no bloody fibreglass batts in the roof (I hate going in our current roof cavity), little to no dust, so much more useful for storage, easy to run wiring and lighting, no compromise in insulation if you decide to install downlights.
The main concerns I have identified so far are:
- Not sure on the durability of polystyrene and similar insulation – what’s the real life expectancy? What about pests such as insects and vermin?
- You need to fix the roofing and the wall cladding. Will this create thermal bridges, assuming you use metal fasteners? It seems that a decent number of screws through your insulation can ruin both your air barrier and your insulating properties.
- OSB and plywood are known for having formaldahyde and other chemicals. A very airtight house with these building materials on the inside isn’t ideal, although can be somewhat alleviated by active air ventilation (HRV or similar)
Still working on this as a concept, but I think it has a lot to offer. But it might be cheaper/easier to just go with a building style that is more familiar in this part of the world.