[Timido]

Hi all I found a lot of good information reading on this site. My question is.

I have steel sided garage that has a open truss shingle roof. Under the steel siding and under a 1" air gap under the roof there is astro-foil type bubble wrap insulation. I want to add R-19 insulation in the walls and ceiling. Should I put the insulaiton up with the craft paper? I am afraid of having moisture trapped between the bubble wrap insulation and the craft paper.

Any Ideas? How about just putting up the insulation and cuting the craft paper so it can breath?

Thanks Tim

[robs ss]

I put 3 1/2'' of blanket insulation in the ceiling of my garage, looks like the same pitch you have. Stapled it in there with a good fit.

Then I nailed 7/16'' osb over that, then a couple months later I see black looking stuff about a foot down from the peak, pull one section of osb off, and its soaked, condensation.

So I went to the building supply and bought plastic eves trough, in ten foot pieces, my outside walls are 24' wide, so a ten foot piece went from inside the eve all the way up.

Anyway I took the eves trough and drilled about a one inch hole maybe every 6 or 8 inches, I can't remember its been so long.

Then I pulled off the outside facia board, took the shingled roof cap off, and slid the eves trough from the eves end right up under that insulation, some times I had to wiggle it just a little, but it went right in there like it was made for it.

Then i put some eve vents and roof cap vents in, and that problem went away years ago. I'm not sure if I put it between the bottom of the insulation or the top, probably the bottom, it would slide better against the paper versus the pink stuff.

I put an eve trough at each opening, I'm thinking two foot centers, can't remember for sure, anyway just another way to add some vents, but my garage is reall easy to heat, so it must of went right.

Rob

[Kevin45]

If you have 1" between the roof and the bubble wrap then get some r-32 and insulate up against the bubble wrap. I have read tons of stuff on insulating a roof from putting it against the underneath to you need all kinds of air flowing, etc., etc. Best bet is to use common sense. And if the shingles that you have are 25 year 3 tabs...figure in about 10-15 they are shot anyways. Try and collect on a warranty on a shingle. The shingle rep will find everything wrong from the installation, to the insulation and everything in between not to warrant a shingle. Even if they put them on they will still find a problem. But that is a different rant If you have airflow above the bubblewrap now you can insulate to it. Just make sure you leave an airflow space at the eve up to what you already have. Also just remember back to different home remodeling shows on the tube where they have ceilings like that in the upstairs of houses they have done. When some of them insulated they insulated right up against the ceiling itself. Moisture will not build up between the two unless you have moisture present to begin with. And as far as heat buildup, the heat would be no greater with a one inch air gap than it would with no air gap. As a matter of fact it would probably be better with none at all as that would eliminate the possibility for moist air. But in an open attic you want air flow to try and cool down the area. I know...my answer is not much help but it is something to thing about and spark up a debate on air vs. no air between.

[1ownerT]

Use insulation with the kraft paper, install so it (the paper) is exposed, do not cut, that will allow the warm moist air through. The kraft paper is the vapor barrier, if you stop the moisture there you won't have a problem.

[Henry Highrise]

1ownerT is right. The Kraft paper is the moisture Barrier....You sure do not want to cut holes in it. Put your insulation up with the Kraft paper faceing the inside of the room.

[Timido]

So if I stop the moisture there I shouldnt have a problem trapping anything between the kraft paper and the bubble wrap stuff. Maybe I was thinking too much about the 2 vapor barrier deal trapping moisture. I only plan on heating the garage while I am out there and I am thinking of a dehumidifier for the summer use. My garage has become just as much a project as the race car. Thank you all for you ideas.

[willys36@aol.com]

Or move to Bakersfield. The last moisture we saw was back in '52 . . . . . .

[home brew]

You are correct to worry about the moisture being trapped in the air space above the kraft paper. The kraft paper will act as a moisture barrier but it will always leak some moisture into the insulation above no matter how good you think you have sealed it. To be sure that the moisture that has escaped above the barrier you will have to have some way to get it to exit the cavity. The air space above the bubble wrap was used to take the moisture away before. When you put up your new insulation the moisture will be trapped between your kraft paper barrier and the foil above it. Cutting through the bubble wrap insulation will only decrease the insulation value a bit and will then allow the moisture in your fiberglas insulation to escape. I assume the air space above the bubble insulation was vented to the outside somehow to allow moisture to escape. When robs ss put in his eaves-through he was creating a way for the moisture to escape. Very ingenious. In the late 1970's and early 1980's during the energy crunch I was involved in making a 13 part television series on energy efficient homes. Builders were having problems with moisture accumulation in the insulation of the super insulated homes they were building. The Canadian National Research Council studied these problems and came up with a lot of good info.

[Timido]

Ok so on the roof I am planning on making some holes in the bubble wrap stuff so it is then vented to the air gap under the shingle roof through the ridge cap.

So on the side walls how can I vent them so they can breath? Or do I need too? If I put the insulation up with the kraft paper I would still have trapped moisture. The steel siding wouldnt breath much anyway. i quess I could drill a couple holes in the 2"x6"s every couple feet or would that not do much of anything.

[home brew]

I guess the question is how well does the steel siding seal against the outside air. If the way it is installed allows it to "breathe" then there should not be any problem. Because your 2X6's run horizontally They would tend to stop the moisture from rising. Does the steel siding seal tight to them or is there a ridge which keeps it away in places. If so the moisture could follow that path up or down. At the top of the wall you would have to drill holes in the top plate to allow the moisture to exit up into the rafters and out the ridge plate. To create a circulation up the side of the wall you would have to drill holes int the bottom of the wall. These could be filled with insect proof vents. These could also be used at the top of the wall as well. Hope this helps. You could also talk to the building manufacturer and see what they do when they erect their insulated buildings.

[robs ss]

I would contact a couple of steel building manufactures, and ask them how to do it, they might have the answers, it could save you putting in the wrong thing.

Rob

"There are questions to be answered, and answers to be questioned"

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[Timido]

I did find a product called Memebrain. It is a vapor barrier that breaths when the humidity gets high inside the cavity. I called the manufacture and they said that the product would work for what I was doing. Some kinda "Smart Barrier" They said that it is used in high humidity area so it breaths in the summer and seals up to create a vapor barrier in the winter. I am going to call a local installer and see If I can get a roll of it.

[home brew]

Interesting product. I don't know if you have seen this but if you haven't take a look:

http://www.certainteed.com/CertainTe...nProdIndex.htm

[Timido]

Yup thats the one. The guy I talked to said that the stuff is sod through installers right now. They are going to start selling the insulation at big name retailers very soon. It will have the Smart Vapor barrier on it allready.

[home brew]

Just remember that when the moisture gets to high in the insulation that product releases the moisture back into your shop. If you heat the shop and then stop heating it that moisture that was released back into your shop will condense on everything that is around. You may want to have an exhaust fan in the shop to exhaust that moist air when you shut off the heat.

What did the manufacturers of your garage have to say?