Mike Guertin’s article in the latest issue shows full-width rafter chutes made of foil-faced polyiso. It said the spaces would then be filled with cellulose. Since the foil face is basically impermeable, where does any vapor go? I’m guessing they expect it to go out at the top and bottom, not sure.
Would this be an appropriate method with high-density fiberglass glass insulation in New England (already recognizing that some folks on this forum don’t think highly of glass)?
Pete
Edited 12/17/2007 7:32 pm ET by PeteBradley
Replies
Didn't read the article but my guess is the polyiso should be warm enough to prevent condensation from forming. Any moisture that gets past it should be able to dry out in the vent space.
Rich
Rafter chutes rarely cover more than every other rafter bay. Unless you've got out-and-out holes in the ceiling, the space in-between is plenty to allow moisture to escape.
The pic shows chutes in every bay. I agree that one inch of foam is going to keep the "cold" side pretty warm.Pete
"Rafter chute"? I've never heard of them. What is it? What's it supposed to do?Ever wonder why "holistic" doesn't start with "w"?
They do seem to travel in herds, at least at home centers. Here's a picture of the ownens corningius species in the wild:
View Image
Pete
Edited 12/18/2007 8:36 am ET by PeteBradley
Thanks. I know those as "baffles".
We use them to keep the insulation from pressing against the bottom of the roof sheathing, so as to allow air to move freely from the vents at the plate line to the ridge vents.
They have to extend far enough up the roof to exceed the depth of the insulation.
The reason you see them every other bay in many cases is on buildings with open soffits (by far the most common here in the Great Northwet) we use vented "bird's" blocks between every other set of rafters or trusses. If you have continuous venting across your plateline, you'd need a baffle in every hole.
Chute. What was the original question?Ever wonder why "holistic" doesn't start with "w"?
Note that virtually all designs are some sort of impervious plastic. But there's never been (that I've heard) any complaints that they cause condensation against them.
If your view never changes you're following the wrong leader
I thought styrofoam was considered somewhat permeable. You're right though, I've seen them made of black plastic too.Pete
Most of the materials I see are relatively impermeable. The foam is generally the type that is closed pore and won't allow much air through.
If your view never changes you're following the wrong leader
Not to highjack your post. I'm interested in something to help with ice dams. I have a low slope roof (for a snow area) with hips and hip valleys that are building up pretty big dams. Today it got warmer so I bought some salt and put it in those areas. It's not leaking inside that I can see but the soffits look like they get damp.
So I guess I need rafter chutes to block out insulation with more soffit vents feeding into the chutes. A cold roof is a good roof.
Does that make sense?
Edited 12/18/2007 12:04 am ET by popawheelie
Now I remember reading somewhere you're supposed to shoot the ones in the back first. Don't spook the herd that way.Ever wonder why "holistic" doesn't start with "w"?
Yes. Or fill several tube socks with salt and lay them on the roof in a vertical orientation, just crossing the line where ice dams tend to occur.
If your view never changes you're following the wrong leader
I like the tube sock idea. Very home made idea.
Pete,
Sorry I didn't pick up on this a while back. Condensation isn't an issue provided you keep the air inside the house from leaking through the drywall. The inside face of the iso board should be warm enough to avoid condensation - but if you have a lot of air leaks or some other heavy moisture load in the attic - don't try it.
I used this same detail on my entire roof 12 years ago and in a few spots where I've checked, it's dry.
The air flow through the continuous 1 in channel is by far superior to what you get from the insulation chutes / baffels they sell. I've investigated several vaulted ceiling problems where moisture condensed on the underside of the sheathing where the chute and insulation came in contact with the sheathing. The full width site made channels appear to preform better and you get improved insulation in the cavities.
MG
Hey Mike,
Thanks for the timely article. Used the 'chutes' on my current remodel job--a 6 pitch that peaks up to a ridge then goes flat for 10 feet with no vents anywhere above.
Used the chutes to create an air passage over to new vents in the soffit over on the flat roof side.
I should end up a little better for R value than just FG and I'll have ventilation!
Cheers,
Pat
I like the idea, bu thow to you keep the foam, one inch off teh shealthing?
When you look at the photos in the article, you'll note the upfolded pieces of foam. Initially I rip cut 8 ft strips 16 in wide (for 16 oc spacing rafters). I measured in 7/8 in in along each edge and cut through one face of the iso and most of the way through the foam itself leaving the other foil face intact to act as a hinge. I flipped the foam strips over to the 'top' of the panel and stuck it with 2 or 3 pieces of tape.
I had this idea to make chuts out of foam and thought that I would cut 1 inche strips and glue them in the bay along side the rafter. I never thought to use the face of the foam to just flip them up. Thanks.
Thanks Mike. This looks perfect for what I'm doing.Pete
Why did OwensCorning want to put a cookie on my computer when I opened this thread?
bump
Peaceful,easy feelin'.
Because the picture in Pete Bradley's post is a direct link to Owens Corning's site.
Yeah, it may be cold, but at least it's a wet cold !
Thanks, Luka.So this leads me to wonder about the wider implication of viewing pictures anywhere on the web and what this might do for one's computer.Any insight?
cookies? Just get over them. Sad but true. And then delete your cookie file once in a while, but then be prepared to have to wait as you visit your normal sites and be prepared to have to sign in to your web sites and to use those long long forgotten passwords.
Man, I don't know if I can ever get over cookies. I did not get this fat by accident, it took a lot of work . . . oh . . . never mind.I still miss her. SNL was never the same.
Like I said, get over it. And enjoy.