Q&A OF THE WEEK: "How Should I Insulate the Floor of an Apartment Above an Unheated Garage?"

Posted on April 21st, 2023

Q: How should I deal with the floor of the apartment I’m building over the unheated three-bay garage at my daughter’s place? I’m getting conflicting advice from contractors. Some say infloor heating is not needed if insulation is installed within the floor. Others say electricity is too expensive for heating, while other say we’ll need infloor heating of some kind for sure to warm the floor. What do you suggest? I live in Canada so cold weather is the issue.

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Spray foam applied within the floor frame cavity of a heated space over an unheated one is enormously more effective than the same R value of non-foam insulation. The difference mostly comes down to the ability of spray foam to seal out drafts and prevent air circulation within the insulation layer.

A: I’ve seen this situation often, and both insulation and electric infloor heating are what you should install. My recommendation comes from the experience of many people I’ve worked with. Every winter I hear from homeowners with bedrooms over unheated garages and all these people all complain about very cold feet, even if the floor is insulated. You can keep the room as hot as you want, but feet will still remain freezing if the floor is cold because the space below (the garage) itself is unheated and cold. The best way you can seal out drafts and boost insulation is with spray foam applied between the joists, underneath the floor. That said, the new space will still have cold floors without some kind of infloor heating.

What size of apartment are you looking at creating? It’s probably not too large if it’s over a garage, and that’s important. Electricity is expensive for heating, yes, but you need to balance that with the complexity of other systems you could use to heat the floor instead and the small space you’re dealing with. The infloor heating should not be the only source of warmth in the space, just the option you turn on when the floor is super cold. One way or the other, you’ll want to heat the floor. Even with floor insulation, you’ll need floor heat to be comfortable during the coldest weather. Many difficult examples have proven this to me over the years. The beauty of electric infloor heating is that it’s the easiest to install of all the infloor options. Schluter’s DITRA-HEAT system is the best I’ve seen by far and I keep my eyes open for these things. I’ve seen this in action for a number of years and it works very well.

Click below for a video tour I made of this system back in 2015.

Video Feature

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