Attic bedroom conversion: Insulate the floor or not?
Greetings. Im Rick . Im converting my storage area over my garage to a bedroom and bath. The original builder framed (trussed) out the attic space for storage or legal livable conversion.
The trusses have a knee wall built in. I’m not going to condition the attic. Im going to condition the knee walls and cathedral ceiling (the room inside the attic). The space is vented with soffit vents ridge vents.
The garage was insulated originaly so the garage ceiling was included. Hence, the area under the floor in the storage area is insulated with batts faced to the ceiling drywall.
My question, after looking at everything I can find on GBA and other sites is……Should I remove the insulation under the floor. All illustrations I have seen show that space not insulated. What’s the downside of keeping the existing insulation?
Thanks in advance for replies.
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Replies
Rick,
If this is a bedroom over a garage, you definitely want to insulate the floor. For more information, see "How to Insulate a Cold Floor."
Thank you Martin. The article you pointed me too was spot on. It raises one more question about insulating the floor.
There are faced R-13 fiberglass batts in the floor bays now. I would like to raise that R value to R 38 or thereabouts. The house is in Climate Zone 4 (Long Neck, Delaware (Rehoboth Bay), summers are warm and muggy; the winters are very cold, wet, and windy ; and it is partly cloudy year round. Annually, the temperature typically varies from 29°F to 84°F and is rarely below 16°F or above 91°F. The muggier period of the year lasts for 4.3 months, from May 27 to October 3. The muggiest day of the year is August 2, with muggy conditions 76% of the time.)
One solution offered from one insulation contractor has suggested, once the two ends of the joist bay are air sealed, blow dense pack fiberglass into the bays over the existing batts through holes cut in the OSB subflooring. The combination of R-13 batt and dense pack Spider) added on top should get me near R-38 The truss chord is 10 inches wide. Thoughts on this approach? If I were in a very very cold climate for any length of time Id take the batts out and do rockwul ( which is going in the ceiling and walls)
Thanks in advance for any and all responses.
Rick,
Q. "One solution offered from one insulation contractor is this suggestion: once the two ends of the joist bay are air sealed, blow dense-pack fiberglass into the bays over the existing batts through holes cut in the OSB subflooring. The combination of R-13 batt and dense pack Spider added on top should get me near R-38. The truss chord is 10 inches wide. Thoughts on this approach?"
A. That will work.
Dense packing over batts will improve air tightness and overall thermal performance. It's a standard approach for removing the potential thermal bypass when there is an air gap above the floor insulation.
Temperature striping of the floor at the joists is more pronounced when there is no air gap above the insulation, but in temperate climate zone 4A that's not a problem the way it can be in climate zone zone 7.
Thanks Martin and Dana. Very helpful. After of month of insulation education, I'm ready to roll.