Attic insulation – no win situation?
Ok, I posted here recently about having new windows and new HVAC system but not seeing any gains in efficiency. I pointed out that I wanted to add to the attic insulation but needed to have some K&T wiring removed first. I’ve now had the electrical work completed and am looking at options for the attic. Here is my issue: the attic is unfinished, but we use it a lot. It’s a walk-in attic that we use for storage of seasonal items, camping gear, etc. We have some old plank flooring and several sheets of plywood that I’ve added. I don’t want to just go up there and blow in 2 feet of cellulose because it will render the space useless. I don’t want to add risers to get my flooring higher because we’ll lose headroom. I might add that we have a fantasy of finishing the attic into a master suite at some point, so I always have my eye on that potential. I’m considering the option of spray foam on the underside of the roof deck. Thoughts? Can it easily be trimmed flush if I wanted to add drywall? Any idea how much it would cost? (attic is 24x40ish, with I THINK a 10/12 roof pitch) I’ve been looking at the DIY spray kits, but they seem to get iffy reviews.
Current attic space is unvented with a couple inches of old rock wool. I haven’t introduced attic venting for a couple of reasons.
One: I used to read a lot of stuff on this forum from a guy who’s name I can’t think of right now that wrote articles for FHB. He was all about eliminating air penetration and moisture and was very against attic venting. He convinced me.
Two: I don’t have soffits, so it would be difficult to get return air for any kind of roof vent. Also I don’t want to give up the 2×4 rafter space to chutes if/when we ever finish the attic.
Thanks in advance for any replies!
Replies
I am certainly no expert so you can consider this a bump if you like.
With the limitations of maintaining the storage space I think you are on the right track to use foam. It can be cut flush, that is what they do on foamed walls.
No idea as to cost.
Thanks to all the responses. Would be best to give the bath exhuast vents their own vent stack.
More questions but its late so hopefully tomorrow.....
Live by the sword, die by the sword....choose your sword wisely.
One: I used to read a lot of stuff on this forum from a guy who's name I can't think of right now that wrote articles for FHB. He was all about eliminating air penetration and moisture and was very against attic venting. He convinced me.
That would be Freddy Lu, AKA Fred Lugano.
If you can afford the foam go for it.
If you're serious about the foam come back and you'll get some more "how to do it" advice.
Joe H
That's him! Thanks Joe.From what I've read, you can get R21-24 in a 2x4 space, which would be a huge improvement over the 2 or 3 inches of rock wool I have up there now.I guess if I think I'll ever want to run power to fixtures, I should attach a couple of wire chases just in case, before it was sprayed.I've watched the videos on the DIY kits you can buy. It looks like I might be able to do it for around $1500, give or take. I'm just concerned that it could be a disaster, as sticky as that stuff is. It's like having pressurized epoxy coming out of a fan spray nozzle. What could go wrong?The attic space is 8'2" at the peak. I have 2x4 rafters and 2x6 joists. If I do much of anything with either the floor level or rafter depth the space will get small quickly, I'm afraid.
You might contacr a local insulator and see what they charge.
Add a layer of foam to the bottom of the rafters & then drywall, you'll only lose 2" and get a hell of a benefit.
Joe H
I'm not sure I understand what you mean by that. Are you saying fill the bays with spray, then add rigid to the surface, then drywall over that? Do you just screw through the rigid when hanging the drywall?
Yup.
Just don't over tighten the DW screws or you'll have a wavy surface.
Joe H
I guess I need to figure out whether I want closed cell or open cell foam, too. As I understand it, closed cell has better R values per inch. Anyone have any comments on the benefits of one over the other?
Those 2x6 joists sound interesting to me.
How so?
I contacted a local insulator as you suggested and they ballparked $2200 - $2500 for 3 1/2 inches of Icynene SprayFoam, scarffed. That actually doesn't sound so bad.
remember that these are ceiling joists, not floor joists. Same thing in my house. 2x4 rafters, and 2x6 ceiling joist below. Not at all un-common.
So that initial ballpark figure is for open cell foam. I'm still waiting on their estimate for closed cell. I like the prospect of R7 per inch and better air blockage.
Yes, and I'm hoping to be able to put a bedroom on them. There is obvious concern, but the truth is that there are many many old homes in my area that were build this way that have finished spaces upstairs sitting on 2x6's. In fact, my house has an original finished upstairs bedroom sitting on the same joists.I did consider sistering on 1x6's to strengthen them, but I think that exercise by itself could be problematic with the plaster and lathe underneath.
They may be fine. It all depends on how far they span.
12 feet.
Yeah, I'd say thats stretching it. Thats clear span? No walls below? If you are worried about cracking plaster by sistering joists, be prepared for some cracking once that space is lived in. They span 14' in my attic, but i have no intention of ever living up there. It's a walk up just like yours, but I need it for the storage.
Yeah. The house is 24' wide. The rooms are all basically 12' across. The front living room runs the width of the house, 12x24, with the joists all sitting on a load bearing wall. At that point the joists all turn 90 degrees and run off of a center load bearing wall for the other smaller rooms.
Spray the bottom of the roof deck. Done quite a few. Check out http://www.tigerfoam.com they should have all of the answers for you. When I need to trim it I use a large thin blade carving knife.
Also consider increasing the depth w/ e.g. 2x2 nailed to the existing rafters. You lose only a little headroom, but gain some insulation power. If you screw it, you gain some structural strength; 2x4 rafters ain't much.
Ok, so everything I'm finding on this forum and around the internet seems to point to closed cell being the way to go, but much more expensive.
What do I need to know about the moisture issues? Sounds like open cell can act like a sponge and hold water, but closed cell is a vapor barrier and could cause mold if there was a gap anywhere?