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danomac 09-02-2010 04:22 PM

Flat roof insulating
 
I bought a manufactured house last year with an addition. I noticed water damage in the addition, so I took the drywall down.

After removing the drywall, I noticed that the roof itself isn't leaking, it looks like it is caused by condensation. This roof is a low-pitch roof (1.5:12) and had a torch-on roof installed professionally about 5 years ago.

There was absolutely no vapour barrier installed, and it appears that only half of the venting is installed (soffits have the perforated panels installed.) There doesn't seem to be any other venting, nor are there the panels between the joists to prevent the insulation (R22) from touching the sheeting.

I'd like to fix this properly before I put up the 6 mil plastic and drywall. The problem is there's no venting, and as this is an addition, it's only 1/2 a normal roof that's been bolted to the main unit. The main unit and the addition's roof lines meet perfectly and one piece of torch-on covers the entire thing.

This has me scratching my head wondering how to vent this roof properly. With the way the addition meets the unit, having any kind of ridge venting is not possible, and installing whirlybirds won't help as there is no air movement from joist cavity to joist cavity (unless I have 10 whirlybirds spaced 16" apart. :laughing:)

I suspect the major cause of the moisture damage to the drywall is the lack of vapour barrier, but I don't really want that moisture to be trapped in the cavities after I seal them up.

Are there any other types of venting or should I research a warm-roof install? I really haven't got the foggiest of where to go from here, and I don't know much about warm-roof construction at all.

Edit: There is no attic space whatsoever. There's insulation in the joists. Sort of like a shed roof, I guess.

Grumpy 09-03-2010 08:17 AM

Insulation needs to be cleared out, 1" holes can likely be placed in the rafters/joists to allow horizontal air movement, then you can install vents in the roof. You wouldn't use a ridge vent with this kind of roof even if you had a place to put one.
Please note if you place the holes too large or off center you will comprimise the bearing capacity of the beams, so you really gotta know what you are doing.

You'd want to install something similiar to this: http://www.roofingsupplyusa.com/stor...-Breather.html Since it's a fire applied roof I highly recommend calling a skilled roofing contractor to do it for you. Don't burn your house down.

danomac 09-03-2010 10:23 AM

Quote:

Originally Posted by Grumpy (Post 495345)
Insulation needs to be cleared out, 1" holes can likely be placed in the rafters/joists to allow horizontal air movement, then you can install vents in the roof. You wouldn't use a ridge vent with this kind of roof even if you had a place to put one.
Please note if you place the holes too large or off center you will comprimise the bearing capacity of the beams, so you really gotta know what you are doing.

I had thought about the holes already. I was thinking though, and if I drill them in the middle of the joists the insulation will cover the holes. Will they still do their job?

I read elsewhere in the case of skylights a few holes is enough on each side. I suppose putting them at the high point of my roof will be enough, perhaps using 3 or 4 holes in each joist.

I wouldn't attempt to torch on anything myself, I just don't have the tools. I'd get a roofing contractor to do that. Although I don't plan to finish everything all at once due to finances, I will likely fix it enough to get the vapour barrier up, then save up a bit of cash to get a roofer down here to install a vent.

Grumpy 09-03-2010 05:12 PM

There is a formula regarding the size hole you may use based on the size of th beam. I forget the formula, that's why i say to us 1" holes because they'll work for all size beams. yes the insulation may block some of the air flow if the ceiling is fastened directly to the rafters. I did not know the ceiling was vaulted.

Another option is to remove the fiberglass and insulation the roof top. You'd need a new roof to accomplish this, but then you'd need not ventilate. This may or may not meet your local code however.

danomac 09-04-2010 09:43 AM

I think I'll contact a local roofer around here and see what they have to say. They'll know what's code around here and maybe they have some magic product or something that can get me out of my suffocating position. ;) Thanks for the replies!


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