more construction ?'s roof ventilation

[MELOC]

my question concerns insulating and ventilating a cathedral type ceiling.

when we had to replace the nearly flat roof above the second floor, we put a decent pitch on it. the old roof was so low, a tall person had to duck near the edge of the rooms. my childhood bedroom was a bit small, so i thought it would be a good idea to leave the space open and have a cathedral type ceiling. this would allow for adding storage above the adjoining bathroom and in the space above the bedroom across the hall. i envisioned built in closets or shelves accessed via a library type ladder.

what i did, and never finished, was to put fiberglass insulation in the rafters with the moisture barrier facing the room. i did it this way because it would be a while until i could actually finish the ceiling and i needed a way to attach the insulation, so i just stapled it. i didn't stuff it in all the way because i felt the roof needed to vent from the eaves. i used 3 inch fiberglass which allowed several inches of vent space. i know it was not much insulation, but i couldn't see any other way to both insulate and ventilate.

so now, several years later, i still haven't finished the room and the insulation is falling down. the original plan was to use drywall, but now i am considering a much lighter material such as some sort of paneling so it can be done by one or two people. before i go to the trouble of re-installing the insulation, i was wondering how insulating and ventilating a cathedral ceiling is normally done.

[Ross]

How thick are the rafters? I'm guessing 2x4's? I've seen some cathedral ceils with no ventilation at all. Seems to work but I'd use rafter mates http://roofing.owenscorning.com/home...raftrmate.aspx To a ridge vent, then a mineral wool insulation like Roxul to get the highest R value per inch. Actually I'd seriously consider sistering on some 2x8's so you can get some decent insulation in there.

[MELOC]

awesome, russ! just what i was looking for. and no...the rafters are 2x8 and not 2x4. i have at least a little sense...and i didn't build the roof, lol. i used the 3 inch (or whatever it actually was) insulation to allow for a space where the air could flow.

if i use the raft-r-mate product, i can then use a thicker insulation. sweet!

[The Paw]

yes, those are the product, they are easy to use.

Just make sure you have a ridge vent and soffit vents as well.

[Cabin Fever]

We have cathedral ceilings in our great room. The roof support uses scissor trusses. The roof has a 6/12 pitch and the ceiling has a 3/12 pitch. The ceiling is insulated and ventilated similar to the third diagram below....

[columbia,sc]

I don't know what it is called but there is a styrofoam material that you staple between the rafters that carries air to the ridge. It goes between the sheathing and insulation. last time I saw it it was pink in color. you need the ridge vent under the ridge shingles on the roof to make it work right.

[cc-rider]

I was wondering the same thing....but decided that the temperature difference between a roof with an airgap and a fully packed roof wasn't that big enough of a difference to worry about it. I'd rather have more insulation. I DID put in the ridge vent and soffitts, and started putting that roof-mate-type stuff up, but it got expensive, so it is only on the lower 4' all the way around. I'm just going to stuff my 8 and 10" rafters with fiberglass batting, visqueen the interior and call it done until I can afford the planking to do all the ceilings. Mine are 8/12 pitch. No trusses...all handbuilt rafters.

[MELOC]

the other option i considered was to use a board insulation right up against the OSB and nix the ventilation. the other side of the roof is above an attic/storage space that is vented from the other side and the space has a ridge vent. i just wanted to eliminate condensation problems in the cathedral ceiling area as mold is a big problem in this old house.

[Wisconsin Ann]

We have a balloon framed house with the sloped ceilings on the second floor. 2x4 rafters, so not a lot of space. What I did was get some 1/2" EPS foam, and ripped it to 3/4" widths. I nailed that to the roof boards, up against the rafters. This provides 1/2" of airspace, an uses up much less of your depth than the shields linked to above. Then I glued/screwed 2x 1.75" wood pieces to the underside of the rafters on the sloped area of the ceiling. 2 layers of 2" EPS foam was tacked in place, then sealed with great stuff.

The foam can be cut either tight, so you force it in place, and it mostly seals, or leave it 1/2" narrow, so you can use the great stuff to get a better seal. It depends on how parallel the rafters are.

I went from uninsulated to vented R-20 in the sloped ceiling. The rest of the atic space was filled with blown cellulose.

Michael