Closed Cell Spray Foam
bigapplerunner
| Posted in General Questions on
Is closed cell considered unhealthy given petrochemical? Contractor is proposing “Huntsman Heatlok HFO High Lift” in case helpful. Worried about the health of my family as we plan to live in the house a long time.
Plan is to spray 2″ of closed cell in the stud bays now that the walls are open (I realize it’s not the most efficient with thermal bridging, etc. but very old leaky house and getting it air tight is the first objective) and then add rockwool.
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Replies
bigapplerunner,
You may find Scott's article useful: https://www.greenbuildingadvisor.com/article/spray-foam-gone-wrong
Thanks, Malcolm. Thankfully, we have a very good spray foam contractor who did our attic last year without any issues.
Hello Thomas:
I see you mention a house in Northern New Jersey. I am in NJ as well. Would you mind sharing the info re: the spray foam contractor you've had a good experience with? (Is that allowed here? Is there a personal messaging system? While I find website super-interesting and helpful, I am not that well versed on the various functionalities or, for that matter, policies.) Thanks!
Just because it's a "petrochemical" doesn't necassarily mean it's unhealthy. Just don't be tempted to eat it, and you don't want to breathe the vapors during the installation. As long as the spray foam is properly cured (that's the important part), it's a very long-term stable material that doesn't really pose any health risk. The issues all come up when the material isn't applied correctly and doesn't cure properly, which is a risk, but a small one. HFO blown foams are the more green version, so your contractor is proposing one of the newer/better variants, so that's a plus.
All that said, spray foam is probably least useful in walls. You're correct that it can do a very good job of air sealing, but it's not really the only way to do that. My preference is to run a bead of canned foam (great stuff, etc.) around the perimeter, then install mineral wool batts, then install the interior drywall and detail it air tight. It's pretty easy to install drywall airtight, you just need a bead of sealant around the perimeter prior to hanging the sheets of drywall.
2" of closed cell spray foam is going to be around R12 or so, and that assumes they get a very even layer, which may or may not be the case since it's tricky to do. Mineral wool in 2x4 walls will get you R15, and will probably be cheaper to install than the spray foam, even with the extra air sealing steps. Open cell spray foam would normally be installed overfilled and trimmed, and may actually end up slightly higher R value as a result, but it still, at best, will only get to close to where mineral wool would be.
Are there any other peculiarities to your walls that are making spray foam the option your contractor is recommending?
Bill
Thanks, Bill. That all makes sense and I appreciate the detailed response.
The home is 150+ years old and the original sheathing is horizontal cedar boards. There are cracks and holes in places from old lighting and previous attempts to blow in fiberglass, there are additions on top of additions meaning a lot of nooks and crannies. When I stand there now with everything down to studs, it is very very leaky. I think great stuff works well with newer sheathing, but I suspect with the size and complexity and age of walls, spray foam would do a better job?
Would add that we are also redoing the siding and windows early next year. Contractors propose adding 1/2" rigid foam on the exterior. They are generally uncomfortable adding more than 1/2". However, in climate zone 5, 1/2" rigid foam is not sufficient to add fluffy inside per the tables on this website.
So I figured 2" of spray foam would solve the extreme leakiness of the old home + ensure enough foam to add mineral wool without creating condensation issues. We would then pack out the walls with 1.5" 2x2 or 2x3 sideways to deepen the cavities and add 3.5" R15 mineral wool.
As long as the 1/2" exterior rigid foam is EPS with high perm, moisture should not be an issue.
Very much open to more / better ideas! We have been going in circles for months on this point.
Thank you,
Thomas
Having trouble responding to this post for some reason.
Thanks, Bill. That all makes sense and I appreciate the detailed response.
The home is 150+ years old and the original sheathing is horizontal cedar boards. There are cracks and holes in places from old lighting and previous attempts to blow in fiberglass, there are additions on top of additions meaning a lot of nooks and crannies. When I stand there now with everything down to studs, it is very very leaky. I think great stuff works well with newer sheathing, but I suspect with the size and complexity and age of walls, spray foam would do a better job?
Would add that we are also redoing the siding and windows early next year. Contractors propose adding 1/2" rigid foam on the exterior. They are generally uncomfortable adding more than 1/2". However, in climate zone 5, 1/2" rigid foam is not sufficient to add fluffy inside per the tables on this website.
So I figured 2" of spray foam would solve the extreme leakiness of the old home + ensure enough foam to add mineral wool without creating condensation issues. We would then pack out the walls with 1.5" 2x2 or 2x3 sideways to deepen the cavities and add 3.5" R15 mineral wool.
As long as the 1/2" exterior rigid foam is EPS with high perm, moisture should not be an issue.
Very much open to more / better ideas! We have been going in circles for months on this point.
Thank you,
Thomas
I would find out what they want for a full cavity fill with open cell foam. Open cell spray foam is more environmentally friendly and it uses 1/4 of the polymer of equivalent thickness of closed cell foam.
In what way is open cell more environmentally friendly?
It's greener because it uses a lot less material per unit R value compared to closed cell spray foam. Using less "stuff" to get to your R value target is better, from a green perspective. Unless you need either higher R per inch of closed cell spray foam (which is usually only an issue when space is limited), or you need the vapor barrier you get with thicker layers of closed cell spray foam, open cell is usually a better option since it's both cheaper and greener, and usually also gets a full cavity fill where closed cell is usually under filled.
Bill
The plank siding is probably the biggest issue then, since that's not really practical to air seal with canned foam. You could use the exterior rigid foam as the air barrier (and interior drywall too, to have some redundancy), and then use batts in the stud bays. That would be one option. I would certainly try for more than 1/2" exterior rigid foam. Under 2" of rigid foam is usually not terribly difficult to work with.
If you have other issues too, such as rough sawn studs that aren't standard sizes, making it difficult to get a good fit with batts, then spray foam would be an option here as a way to save on labor. I would try for a full fill of open cell spray foam in this case, which will give you a good air seal, and a full-depth fill since open cell is normally installed OVER filled and then trimmed flush with the face of the studs. Open cell should be cheaper than closed cell, but you're doing a deeper fill too, so it might be a wash and cost about the same. This would be a lot easier, and also likely cheaper, than furring out the interior of the wall and adding batts over a layer of closed cell spray foam. I would go with open cell spray foam if you go with spray foam, then push for thicker exterior foam to at least get up to the recommended ratios from the tables.
Bill
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What you’re proposing is exactly what I did in my own personal home - it worked great. I have 2-3” closed cell foam sprayed over the interior side of the horizontal cedar boards that make up the sheathing and then ~4” of rockwool on top of it. My house had “true” 2x6 framing. It was a job as the studs are all different spacing, but I cut the rockwool batts horizontally to fit and stacked them in the cavities.