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Old 06-10-2020, 12:44 PM   #1
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spray foam open v. closed cell


Hi,

I'm remodeling a cape with a permit. It's a big job.

One huge issue is insulation. Rafters are 2x6 and architect called out R-38 in the roof. Since it's a cape, the only way to get useable space upstairs (huge value add in project) is spray foam. Otherwise inspector wants 2x6 added to current rafters to carry 12 inches of fiberglass bat. Ends up making the bathroom a closet with a toilet and half a shower...

So, I think I'm going with spray foam. He's not holding me to R-38, which is good-- if I use foam.

I have three quotes and A LOT of conflicting information. One installer is adamant that open cell is the right product for the house. It's cheaper, has less insulation value, but meets code for a reno. Finally, they say it breatehes which is better for an older house (1954) that isn't constructed with vapor barriers and house wrap. They think closed cell adds nothing by cost.

Another installer is equally adamant that open cell is crap, wicks moisture and will be a disaster in the case of ice dams and rook leaks, destroying entire ceilings as it accumulates water.

The inspector says that I want the one that doesn't act like 'a sponge.' He checked and found that was closed cell.

The open cell company (which also installs closed cell) says that's BS and that he doesn't know what he's talking about. Inspector doesn't want to debate it, I suspect and I have no interest in pissing him off...

ANyone have experience in installation of these products? I'd really like an opinion from someone who doesn't have a horse in the race.

The house is a 2 story cape, finished upstairs. Built in the 50s. Climate is cold but not crazy (NY state). We'll reach the teens in mid winter. Plenty of snow, and some mid-winter thawing as well at times. Ice damming can be a problem in our area for sure. And of course capes are prone to issues along that line in the first place. Finally, it's a flip, not my house that I'll be living in. So, I'm aiming for doing it the right way with the least $$$$.

Thanks,

Peter
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Old 06-10-2020, 02:06 PM   #2
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Re: spray foam open v. closed cell


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Old 06-10-2020, 03:28 PM   #3
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Re: spray foam open v. closed cell


Thanks for that Neal.

Kind of explains why I'm getting conflicting info. In that video, he says that most ppl expect open cell to act as a sponge. But it reality it's fairly water resistant (but not completely so).

Also brings up an interesting point that roof leaks can be disastrous with either product if they obscure the leak and end up rotting out the roof deck or rafters... In that respect, closed cell may be worse?

So, no good certain answer one way or the other

Leaning toward closed cell (almost twice as much) to keep inspector happy.

That video was helpful though.
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Old 06-10-2020, 05:58 PM   #4
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Re: spray foam open v. closed cell


https://aamanet.org/pages/understand...r-condensation


Especially interesting is dew point can be different per where you are. There was another past post and what I remember now is something like "R20 insulation for zone 6" or such. Sorry, I'm in NJ and, to keep it simple, just try to remember air space for drying out. Never insulated rafter itself or use spray foam except little cans.


1. search the r value necessary in your area to stop dew condensation per humidity and temp differences. Spray foam and its air seal capacity adds to the overall insulation value.



2. if possible, add 2x2 to your rafters, add min 1.5" rigid baffles under the roof sheathing so sheathing can dry, then use closed cell foam for as much r value you can get. Thin foam baffles will be crushed by spray foam. Then add intake air along the eave and ridge vent. Before spraying, you must make sure there is open airway for sheathing to dry.

I've read about the pro opinions for open cell. I am sceptical that its "open" pours allows for better drying. If it's as "ventilated", what good is it as an insulation? Wood frames, wood sheathing and drywall also absorb some of the vapor. Acrylic paint has some vapor retarding capacity. I didn't bother with learning specific numbers for northeast nj.



Spraying is fairly big commitment. You must make sure your roofing and all of the flashing are done well, esp the chimney and dormers, if applicable.
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Old 06-10-2020, 06:36 PM   #5
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Re: spray foam open v. closed cell


Quote:
Originally Posted by Alsomee View Post
Thanks for that Neal.

Kind of explains why I'm getting conflicting info. In that video, he says that most ppl expect open cell to act as a sponge. But it reality it's fairly water resistant (but not completely so).

Also brings up an interesting point that roof leaks can be disastrous with either product if they obscure the leak and end up rotting out the roof deck or rafters... In that respect, closed cell may be worse?

So, no good certain answer one way or the other

Leaning toward closed cell (almost twice as much) to keep inspector happy.

That video was helpful though.
We don't see a lot of foam out here but we hear all the same arguments.
Just as a side thought, we use batt insulation and a VB, which also can absorb water and hide a leak for an extended period of time so there really is no winner.

I think i would go for more R value.
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Old 06-11-2020, 05:36 AM   #6
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Re: spray foam open v. closed cell


OC is fine if at the right depths. If you are looking to the foam to give you structure, that is a poor indicator on the framing. I would use OC SPF here.
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Old 06-11-2020, 01:25 PM   #7
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Re: spray foam open v. closed cell


The air sealing of spray foam is more important than the R-value here. Closed cell is a waste of money.
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Old 06-13-2020, 06:43 PM   #8
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Re: spray foam open v. closed cell


Suggest doing a web search on Energystar dot gov for authoritative articles on this topic. I've found many helpful insulation articles on there. And they aren't trying to sell you anything. Hope this helps.
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