Open cell or closed cell foam???????
Hi fellas, Friend of mine runs an isulating co. One of his suppliers wants to demonstrate a new open cell foam product. They will foam my garage shop addition for free.(nice huh) My questions are:
1. Whats the difference between the two? (open or closed cell)
2. Can I use tar paper instead of tyvec under siding?
3. Scissor truss roof-Top cord a 6 bottom a 5 Do I need a ridge vent?
Thanks Fellas, Lou
Replies
Didn't you ask this last week, Lou?
type of insulation has nothin to do with the trpaper vs tyvek decision.
closed cell is far better than open cell. For one thing, it has a greater R-value. For another it is a VB in and of itself. There are some situations where the open cell can hold water like a sponge. It has to be applied thicker to be certin to eliminate dew point condensation than open cell does.
If installed right, the open cell should not require a roof vent. But you can do that if you want. using a vent and under sheathing channel will help the shingles slightly. And with free installation, you can certainly afford to do that!
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piffin, I'm losing my mind! Why would this company consider using open cell then? So tyvec would be better to use? Right? wrong? or does not matter?
-Lou
I looked around. I can't find your mind here at my place. Maybe you lost it in the Tavern...;)Whether tyvek of TP depends more on type of siding, especially with foam because thefoam prevents infiltration better than tyvek does, making TP just fine.I don't know why open cell is chosen. I have never used it. I assume that cost and availability has something to do with it.
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the open cell can hold water like a sponge.
Just finished tearing off a modified roof where open cell sheets had been used for recovery over roll roofing. The open cell sheets were saturated. No signs of leaks inside ( the old roll roofing was definately comprimised ), the moisture must have been coming from inside.
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I think last months JLC had a peice on this.................I know the one I got today had a rebuttal so I am thinking last month or 2 mos. maybe ago.[email protected]
I'm doing a reno job for an engineer right now, finishing off the upstairs of a large garage. He did his own research and decided to go with closed cell in the walls and roof (hot roof) but closed cell in the floor.
I asked him why. His reason is that the floor is open web wood trusses and the open cell expands a lot more than closed cell, so it will seal better around the webs.
Because of it's location there is very little chance of it getting wet, so holding moisture isn't an issue. I still would have gone with closed cell but it's his house.
Open cell is still a vapor retarder, so whether or not you need a vent or additional vaper retarders depends on your climate and heating/cooling equipment. Free foam is a good deal though!
Mike,
You wrote, "Open cell is still a vapor retarder." Not true, although the error is common. Closed-cell foam is a vapor retarder; open-cell foam is NOT a vapor retarder. Some cold-climate builders who have omitted the vapor retarder with open-cell foam under the mistaken impression that the foam created a vapor retarder learned, to their chagrin, that vapor can pass through the foam and condense on the wall and roof sheathing, leading to rot.
Open cell foam has perm ratings of 5-15, a class 3 vapor retarder is 1-10 perms. I didn't say it was a good vapor retarder. Definitely not a vapor barrier.
Mike Maines,
A vapor retarder is defined by the 2000 IRC as a material having a permeance rating of 1.0 or less when tested in accordance with ASTM E 96. Therefore, materials with a permeance rating in the range of 5 to 15 perms are not vapor retarders. In fact, most manufacturers and installers of open-cell spray foam tout the advantages of the fact that their foams can "breathe." As far as I know, however, they don't mention the disadvantages associated with the fact that these foams are vapor permeable.