Add R-14 Roxul between the garage attic and the house?
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I am currently in the process of insulating my attached garage using Roxul R14 “ComfortBatts”. I live in Winnipeg and from experience — when I did this in my last house — it can improve the temperature by 10-15 degrees Celsius in the winter, without any heating. (And that was with a non-insulated garage door; my new house has insulated garage doors!)
The roof is supported by a truss system, whose bottom (horizontal 2x4s) is the garage ceiling as I squeeze the batts in. I just noticed that against the wall between the garage and the house, as part of the truss system, 2x4s extend vertically from the ‘ceiling’ level all the way to the roof.
The wall is already insulated, and has drywall facing the garage (fire code). I am wondering whether it might be worth adding insulation (same R14 roxul batts) between the vertical 2x4s, against the drywall. It seems like it might be a simple way to improve the energy efficiency of the home, since the garage attic space will be un-insulated. But I’m not sure if it’s okay to add the roxul on top of the drywall?
Also I’m not sure how much of a difference it will make, but it would be easy to do and only cost around $70 for the Roxul. The wall is my kids’ bedroom — important to keep cool in summer and warm in winter. But also important to avoid moisture/mold problems and to keep fire-safe!
To help paint the picture, the wall is currently:
Living space > drywall > vapor barrier > insulation > A* > drywall > B* > garage attic space
A* – I’m not sure if there is anything else here, like some kind of home wrap (I haven’t opened up the wall)
B* – currently nothing here but this is where I’m considering adding the R14 roxul batts
Thanks
Mike
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Replies
Mike,
There is no downside to installing Roxul there -- although it might be easier to attach it if you had a stud wall to hold the Roxul.
Thanks for the quick reply Martin!
In effect I do have a stud wall (verticle 2x4s which appear to be part of the roof truss system), located where I labelled B*. Sorry my description was not the best, I should have posted a picture.
Seems worthwhile to me. Usually to add insulation to an already-filled wall, you have to do extensive renovations either on the interior or exterior of that wall. Since this wall is enclosed in the garage attic, you can easily add the insulation to the outside of it without any of that hassle. I'm guessing it's a small part of the overall exterior surface of the home, so it won't make a dramatic difference, but it will save some amount of energy.
This is a great idea. As Nick says, most wall insulation retrofits are hard, but this is easy. I can't see any downside, other than the cost of the insulation. It should go on the standard list of low-hanging fruit for energy retrofits, for people who have that configuration.
Thanks Nick and Charlie, you've motivated me even further!
What makes this even more 'low-hanging fruit' is the fact that the adjoining room is where all 3 kids sleep (the eldest has her own room but prefers to sleep on her sisters' floor!). So the temperature of that room really matters as it can affect their sleep.
Also was watching some tests of Roxul's fire-safety on youtube today, and was very impressed with its performance compared to fiberglass.
Mike,
I'm a serious DIYer not a pro but here are my thoughts: If this wall adjoins the kids room, you might want to think about an air barrier too, if you think there is any air leakage. Whether that is simply foaming gaps on back of that wall (garage side) or a full sheet of tyvek over the roxul, you'll get better results if you control air leakage (which fibrous insulation doesn't do on its own). I didn't fully understand your description but if garage air could move through this system into the kids bedroom, I'd double down on the air sealing. Garages, cars, and gas are sources of benzene, a potent carcinogen.
Here's a consumer grade article about garages and benzene:
http://news.nationalpost.com/2013/04/09/health-canada-warns-of-latest-cancer-threat-to-canadian-homeowners-attached-garages/
Thanks Keith. I had considered the air movement concern, but because that wall is already finished with a vapor barrier on the inside, I don't want to put another vapor barrier, as that would seal the wall on both sides leading to moisture problems. Something like Tyvek would probably be great but I'm running out of time on this project so might have to do that later on.
As far as sealing against the garage itself (where the cars and gas are), I guess I am "doubling down" as you say, because a) there already is a vapor barrier on the inside of the house, and b) I'm adding a vapor barrier on the garage ceiling, under the joists & roxul. On the other hand, this project may add to the problem -- since the vapor barrier I'm adding is partially sealing the garage against the outside, reducing its ability to vent fumes. But I'm not too worried as we never idle our cars in the garage.