Insulation
So…I did search the site before bothering anyone.
Is there any good reference guide on getting r-49 in the roof? I see you can buy the pink stuff with r-49 printed on the label. But I thought I wanted to use mineral wool. I don’t see a mineral wool product in r-49.
Also, when the county requires r-49…does the sheeting, roof felt, drywall on the ceiling give you any “r”? Just curious.
My new house is a single level, about 2,000 sq ft, trusses throughout with raised heel. I have read on this site about raised heel and they sound smart. Just don’t know how deep the heel should be for r-49. Most people around here do blown in. We are DIY so batts are going to have to suffice.
Thanks anyone who can help.
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A 16" heel should get you there. To hit R49 you need about 14" for mid grade fiberglass, add 2" air space above that for baffles -- ensures airflow from soffit to ridge. Can't say I've seen batts installed that thick before. Loose blown cellulose is cheaper and DIY easy if you can find a blower for rent at a hardware store.
You can rent blowers and DIY blown insulation. The box stores often include rental of a blower for free with a minimum amount of blown insulation material. Blown insulation is a lot better than batts in an attic like you’re describing, so I’d try to find a way to use blown insulation before deciding you’re stuck with batts. All blown insulation manufacturers state how deep a layer you need to get to a specific R value, so just find out how deep a layer you need from that table for R49, then blow in that much material.
It helps to put some yard sticks in a few places in the attic to see how much you’ve put in as you’re blowing. I’d put some contrasting colored electrical tape in a big band around the target depth on the yardsticks too so that you can easily see from a distance when you get to the right level.
If you’re using batts, you can layer them and add the R values together. A layer of R21 and a layer of R15 would give you R37 total, for example. If you do this, you want to lay the batts perpendicular to each other (one layer in line with the joists, the next layer across them, for example) so that you don’t have gaps that line up all the way through the layers of batts.
For the purposes of code, “R49” means R49 worth of INSULATION, the other stuff doesn’t count (for the prescriptive codes). In reality, you do get some small contribution to total insulating value from things like plywood sheathing, but it isn’t much. Roofing felt is probably so small as to be basically immeasurable in terms of R value. If you’re insulating the floor of a vented attic, anything on the roof itself doesn’t count at all since the air space in the attic is outside of the building envelope.
Bill
Before you put any insulation up there be sure to do the best you can to seal any places where air can leak up from the living space. That usually means a foam gun.
Thank you. You folks are amazing. This tied together all the bits I read in articles.