Garage conversion – Insulating slab on grade & single head heat pump
Hello – we’re converting an existing garage (~500sf) to an accessory dwelling unit and I have two questions I’m looking for input on:
– we’re considering the option of using a single head heat pump vs. ducted w/integrated air handler to heat/cool the space and wonder if anyone has experience with heat distribution/airflow using a single head with multiple rooms? There will also be an HRV in the space that I think could help with airflow.
– We will be using closed cell spray foam on the walls (5″) & ceiling (6″), but because the garage is existing and close to a fence on one side I’m thinking of insulating the floor from the inside using foam board and then T&G OSB on top for sub-floor. I’ve been reading that polyiso can absorb water, but like the increase in R-value over EPS (don’t want XPS for GWP). Would a moisture barrier below the polyiso be sufficient to keep it from absorbing moisture? Or should I let go of the idea of using polyiso and plan for EPS? We live in SW Ontario, zone 6 – is there a minimum R value I should aim for on the floor?
Open to any and all thoughts… Thanks in advance!
Allan
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Replies
Most polyiso is foil faced in my area and i would think only the edges would be a concern.
I am sure others may disagree, but I would use poly with the high perm rating of EPS.
With all that closed cell your using what difference does it make to have a little bit more global warming with XPS on the floor?
In zone 5 garage/shop I used 6" high density EPS under concrete slab which made the floor so warm that i never hooked up the radient heat floor tubing i planned to use as primary heat.
In zone 6 NH remodel i used 1" XPS (ceiling height restricted thicker foam) on concrete floor with subfloor on top similar to your proposed plan. While it is warmer than before......it is still very cold. Be sure to use more than 1".
Thanks very much for your comments Dirk.
Re: GWP of spray foam - we have a contractor that uses insulthane extreme, with a GWP of 1.
And if I'm using poly as a vapour barrier under the EPS anyway, why wouldn't I use polyiso instead (for higher R-value)?