Posted By terrynew on 05 Mar 2010 08:41 AM
in my cold Ontario climate.
That's the key consideration.
My first question is: am I right that I don't need thermal breaks at the garage door sill and garage man door sill, since this 'room' is unheated?
There's a lot difference between "don't need" and "good idea." The garage slab will undoubtedly be somewhat warmed by the earth heat underneath. There's no sense in losing that benefit by having that heat migrate to the cold outdoors. A thermal break and both doors will help keep natural heat inside the garage. Now, if you don't care if the garage drops down to 0°C, or however cold it might get, then don't bother. But that goes contrary to using ICF for the garage walls.
More importantly, does this mean that I should be installing a thermal break all along the slab under the walls where the garage meets the rest of the house (kitchen in my case)? I'm using a passive solar design where all the house windows face south so that the exposed slab in the living area soaks up the sun's heat during the day and releases it at night. Will all this heat be sucked out the colder garage portion of the slab if there isn't a thermal break?
If so, should I be be pouring two slabs side-by-side with a few inches of blueboard in between them? Furthermore, should I similarly be isolating the concrete in the ICF exterior walls between the garage and the rest of the house, or is that overkill and does it risk weakening the walls?
How do the costs pencil out if you use ICF for the wall between the kitchen and garage? That would give you the thermal break at the floor, provide a good fire barrier wall between house and garage, and keep the solar heat gain inside the house envelope. If not that, then I think you really should put a thermal barrier in the slab. Put the barrier entirely on the garage side of the wall line. If you use a wedge shape you can keep the slab strong at the break.