For the purpose of installing hardwood flooring in a room above a garage, is the garage considered an unconditioned space?
The garage has been drywalled, taped and mudded. I assume that this is still considered to be an unconditioned space, right?
I ask because I’m trying to determine what kind of underlayment I’d need in the room above the garage before I self-install 3/4″ thick, 6″ wide engineered white oak hardwood. The subfloor is plywood and the home was build in 1993.
According to the National Wood Flooring Association’s guidelines recommend a class II vapor retarder when installing over an unconditioned space.
I’m also trying to avoid asphalt-containing vapor retarders like Aquabar B, so I’ve been reading about liquid-applied vapor retarders. Are there any go-to options that the wise people of GBA can recommend?
The home was built in 1993 and is in climate zone 4A.
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The terms conditioned and unconditioned aren't really used in modern building science. Today we think of a building as having a "building envelope" that stands between the interior and the exterior. Space is thought of as being either inside the envelope or outside the envelope.
The building envelope should be insulated on all sides. On the warm side of the insulation you need to have a vapor barrier or retarder to keep humid air from entering the insulation and contacting a cold surface, which would cause condensation and lead to moisture problems.
Garages can be built with the interior either inside or outside of the building envelope. If the interior of the garage is not within the building envelope, the floor/ceiling separating the room above from the garage should be insulated and should have a vapor barrier on the warm side. If the interior of the garage is within the building envelope, no insulation is necessary and no vapor barrier is necessary.
Now, in building science terms, 1993 was an eternity ago. More has been learned and put into practice with regard to building science in the past 25 years than in the previous 10,000 years. For most of the 20th century it was common to build homes with poorly defined boundaries of the building envelope, spaces like attics, basements and garages were kinda-sorta inside and kind-sorta outside.
If your house is like that, probably the garage is uninsulated and there isn't much insulation between the house and the garage either. Your long-term plan should be to tighten up the building envelope. If you're not sure where it's going to go, there's no harm in having a vapor barrier or retarder that you don't need.
Thank you for making such an effort to break this down for me. I will likely go with Bona R540 and call it a day.
And as an aside, I do plan on tightening the envelope as much as I can before we move in. I've currently got all of the baseboards off in preparation for laying the flooring, and will take advantage of the opportunity to air seal the bottom plates.
Unfortunately, the house has knee wall attics, which I feel will be a real challenge to insulate and air seal adequately. But I think that will probably need to be a question for its own post.
DC,
I think we are showing our age. Like me, you have probably always called the boundary the Building Envelope. Young bucks like Randy et al. now favour Building Enclosure.
https://www.buildingscience.com/documents/insights/bsi-024-vocabulary
Simply put, is your garage insulated and heated or cooled year-round?
If the humidity stays between 30 and 60% year-round while the temperature is generally in the range of 65 to 78, then your garage is conditioned.