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Bonus room over garage

Other than the additional square footage, there is nothing "bonus" about this room. It is unusable in summer and winter. It is of typical design...small flat attic above 8' flat ceiling in center of room that contains R-30 batts; sloped ceilings following roof rafters that are only R-19 and do not have continuous air chutes (therefore the side attics are not connected to the upper attic for ventilation purposes); side attic areas with the knee walls being non-backed and insulated with R-13 batts. Knee walls are only 3' high, so the side attics are largely inaccessible due to ducts etc.
I plan on accessing the side kneewalls from the garage ceiling below, removing the batts, installing top plates, apply an air sealant, reinsulating them and then backing them with duct board. While there, I will also block the open ends of the floor joists from the side attics. I do not want to remove the drywall from the sloped ceilings if at all possible, but would like to increase the R value in that area. Seems to me that dense packing this area would be the way to go. Home is located in Indiana and is about 8 years old. No real solar gain as room only contains one small window facing northeast. No evidence of any moisture presence or shingle degradation at all.
Roof is gable with soffit and ridge vents, although an ineffective design since the two attics are not connected properly.
Am I on the right track? Any other suggestions would be appreciated.

Asked by Chris Brown
Posted Oct 27, 2010 1:38 PM ET


5 Answers

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"room only contains one small window"

It doesn't sound like it meets the code-minimum fenestration, ventilation or egress requirements, which would substantially limit it's legal use.

Answered by Riversong
Posted Oct 27, 2010 5:43 PM ET


The window is a 3-0 x 5-0 and is proper height from the floor to constitute proper egress. If this is a code violation, then every other bonus room in this market suffers from the same faults. There are at least 2 dozen in my neighborhood constructed in exactly the same manner with one window in the end wall and stair access at other end of the room.

Answered by Chris Brown
Posted Oct 28, 2010 12:38 PM ET


I'm not a fan of using dense-packed cellulose in a cathedral ceiling unless there is a ventilation channel between the top of the insulation and the roof sheathing.

Obviously, improvements require attention to the room's air barrier; the air barrier needs to be in contact with the insulation. You also need to improve the R-value of the installed insulation.

My own advice: don't cut corners. Do it right, even if you have to remove some drywall for access. But how far you go depends on your budget and your goal.

Answered by Martin Holladay
Posted Oct 28, 2010 12:42 PM ET


Code requires any habitable room (other than bathrooms) to have a minimum of 8% of floor area in glazing with at least half of that (4%) operable for ventilation. Of course, without cross-ventilation, there is no effective passive air exchange.

Answered by Riversong
Posted Oct 28, 2010 5:30 PM ET


A 3 x 5 double-hung does meet egress code - it's about the smallest DH which does. But I wouldn't call it a 'small' window.

Answered by James Morgan
Posted Oct 28, 2010 7:08 PM ET

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