Open Cell vs Closed Cell

[NateMoss]

I appreciate all the info on spray insulation and have been reading old threads and posts on this issue. I would like some more feed back on where contractors prefer to use closed cell vs open cell and the reasons why you use it in certain situations versus others. Thanks, Nate

[Bluewoodrock]

Some considerations when choosing open or closed cell foam



R Value: open cell is 3 to 3.5 per inch, closed is 6 to 7 per inch. obviously CC is about 2x better per inch than OC. Closed cell makes a good choice when insulation depth is limited.


Perm rating: OC is very vapor permeable, CC is an effective vapor retarder. this might dictate the choice based on where the foam is applied.


Cost: CC costs more than OC. OC is often a good choice when budgetary concerns are considered.


Structure: CC foam adds strength to structures ( it essentially glues everything together). OC does not. Check out this video

http://www.ccfoam.com/video/winduplift.php

Personally I'm more of a CC kinda guy, but open cell has it's uses also.

[caddis]

Open cell is also better for reducing sound transmission.

Due to the cost issue, we don't try to sell closed cell uness we need the higher R-value (for instance needing to get R-30 in a 2x6 cavity), or areas where moisture may be an issue. We always spray closed cell on foundation walls.

[Bluewoodrock]

Dave makes a good point about foundation walls. CC foam also makes an excellent insulation under concrete slabs.

I also like CC when the foam is to be left exposed (such as in unfinished attics), as all foams should have some sort thermal or ignition barrier over them. CC foam provides a much more durable substrate for application of thermal barrier protection in situations where a spray on thermal/ignition barrier is used.

[NateMoss]

When CC is aplied to the foundation walls, is it sprayed directly onto the block/poured walls? Also when spraying CC in a wall cavity, are there any special considerations with house wrap and moisture barriers. Here in the south, most people use some type of house wrap. We often use felt paper or house wrap. Do the lack of vapor transmitting qualities throw up a moisture issue of any kind. We never put another vapor barrier on the inside of the walls befor sheetrock.

[NateMoss]

I have also recieve some info from Icynene about their foam being the only oc foam on the market that has the ability to be left unexposed. However, I am in discussion with a building inspector that says due to a gas fired appliance (furnace) in the crawlspace this is not ok. The crawl space ventilated with foundation vents. Any thoughts? If worst comes to worst then I will need an ignition barrier sprayed, but Icynene seems to think I dont.

[NateMoss]

Also, anyone familiar with a Graco E-10 system? there is a manufacturer right down the road that has suggested it for a remodler like myself, a 12k price tag comes with it.

[Bluewoodrock]

Icynene is full of it. Icynene is virtually the same as any other OC foam, and it needs to be covered as a general rule. In some situations it may be permissable, but I think it's always a good idea to cover exposed foam with some sort of fire protection.

An e-10 is a light duty machine, we use e-30s. I think the principal of "you can do a little work with a lot of machine, but it's hard to do a lot of work with a little machine" applies here. An e-10 is probably okay for OC but I would suggest an e-30 if you planned on every day use.

[Riversong]

CC foam also makes an excellent insulation under concrete slabs.

As long as it's in the form of boards of uniform thickness and uniform (and tested) compressive strength, which means XPS not spray urethane.

[Riversong]

Also when spraying CC in a wall cavity, are there any special considerations with house wrap and moisture barriers. Here in the south, most people use some type of house wrap. We often use felt paper or house wrap. Do the lack of vapor transmitting qualities throw up a moisture issue of any kind. We never put another vapor barrier on the inside of the walls befor sheetrock.

Since CC foam is vapor impermeable, it's imperative that the wall assembly can dry to the outside. You might want to consider a ventilated rainscreen if you're sealing the wall cavity.

[Martin Holladay]

Riversong,
I'm not sure why you wrote, "Since CC foam is vapor impermeable, it's imperative that the wall assembly can dry to the outside." That's not really true. You can use a vapor-impermeable wall sheathing (for example, foil-faced polyiso) with closed-cell spray foam and the wall will perform fine. In such a case, the wall assembly is definitely not drying to the outside, but what's the problem?

[Riversong]

You can use a vapor-impermeable wall sheathing (for example, foil-faced polyiso) with closed-cell spray foam and the wall will perform fine. In such a case, the wall assembly is definitely not drying to the outside, but what's the problem?

I agree with Joe Lstiburek on this one. All thermal assemblies should be able to dry in at least one direction and preferably in both.

MEWS studies have shown that once moisture enters a wall (and it always does at some point in its life), impermeable exterior insulating sheathing prevented drying to the outside and maintained cavity temperatures at the mold and decay danger zones for the entire 2 years of the evaluation.

It's utter foolishness to build a hermetically-sealed thermal envelope (except for a walk-in cooler) because it requires the lifetime perfect integrity of the skins. Thats a hubris which we can't afford.

[Martin Holladay]

So why do you insist that this type of wall must dry to the outside? Why can't it dry to the inside? You really didn't answer the question.
Wall: Siding, foil-faced polyiso, 2x4 studs with 3 inches of closed-cell foam, gypsum drywall. No interior poly. It dries to the inside. What's the problem?

[Bluewoodrock]

As long as it's in the form of boards of uniform thickness and uniform (and tested) compressive strength, which means XPS not spray urethane.

I'll have to disagree with you here, we often use SPF for insulation under slabs. Obviously care needs to be taken so all point loads are distributed onto footings before the SPF is installed, but the compressive strength of 2lb closed cell foam is more than suffiecient to support a standard slab in most residential applications.

The SPF is far more resistant to breakage than board stock in my expierience, and provides an excellent monolithic thermal barrier under slabs. No worries about untaped seams or concrete guys busting up the board stock.

The end result is a warm,dry concrete slab, and we can all agree that's a good thing.

[Riversong]

So why do you insist that this type of wall must dry to the outside? Why can't it dry to the inside? You really didn't answer the question.

The question was: "What's the problem?" Now you're asking a different question. I was assuming CDX or OSB sheathing.

Wall: Siding, foil-faced polyiso, 2x4 studs with 3 inches of closed-cell foam, gypsum drywall. No interior poly. It dries to the inside. What's the problem?

Now you've got siding, perhaps wood, tight up against a non-breathable foil WRB with no drying potential inward, which is the dominant exterior drive.

If water gets behind the foam sheathing and saturates the outer face of the studs, drying through the studs to the interior can be slow enough to create problems, particularly if there is a water vapor drive from inside to out.

The only thing that can dry to the inside is whatever air space is between the drywall and the spray foam. I would not consider that a moisture-tolerant envelope.

Your mileage may vary.