Vapor Barrier for Closed Cell Spray Foam Insulation
We’re just about ready to have closed cell spray foam installed (our choice for basement wall insulation). We’ve lined up a great contractor in the Baltimore area who’s going to let us follow him around the basement with our video gear so we can share the whole experience with you. Stay tuned for that in the next 2-3 weeks, we’re sure you’ll enjoy the series.
If you’re familiar with most basement insulation methods, you’ll recognize the complete lack of a vapor barrier between the stud walls and the concrete block wall (waterproofed in the white area with Super Thoroseal, and in the grey area with SunnyDry). In most installations, you’d see polystyrene foam board (a.k.a blue board) or a polyethylene plastic, but not here. The reason?
Here’s two pictures of the basement’s concrete block walls today:
Closed Cell Foam Is Its Own Vapor Barrier
Closed cell foam hardens and becomes it’s own vapor barrier. Each small bubble in closed cell foam is jammed up very close to the bubble next to it, and each bubble is completely closed (creating an incredibly high R value of 6-7 per inch).
1-3 inches of closed cell spray foam is appropriate to create a vapor barrier between .1 perms and 1 perm (the ideal for most areas in the continental U.S.) This provides for inward drying when the sun hits the basement walls in the Summer (and the vapor pressure force is inward), but keeps moist interior air from touching the walls in the Winter (when the vapor pressure force is outward).
Better Than Fiberglass
While closed cell foam costs more than traditional fiberglass insulation, it provides an 80-100% increase in R-value, serves as its own vapor barrier, doesn’t have performance issues even when wet, and is highly resistant to mold growth – all traits that make the cost worth considering, and led us to our decision.
A Note on Open Cell Foam
One quick note to folks considering open cell foam: this product is completely different than its closed cell counterpart. Open cell foam does not act as a vapor barrier, and does experience performance degradation when wet. Given installation cost considerations, we believe open cell foam simply doesn’t make sense for most installations.
What do you think? Will you install closed cell foam on your next insulation project?
Comments & Conversation on this Article...
14 Responses to Vapor Barrier for Closed Cell Spray Foam Insulation
November 5th, 2009 10:37 am
I’d definitely consider the closed cell foam! The basement of my 1890s townhouse needs a lot of work, including repairing cracks in the walls, a drainage system, and possibly relaying a concrete floor$. It’s going to be a lot of work and money, but given your reviews on the closed cell foam it is something I will try to work into my budget.
I unfortunately know first hand that fiberglass is not resistant to mildew and mold. The question is whether I take the all waterlogged fiberglass off myself to save money and prevent additional growth or wait until I’m ready to do the whole project (which may be as late as 12 months from now), keeping any possible mold spores from spreading. What’s OPC’s opinion?
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November 5th, 2009 10:40 am
Can’t wait to hear how it works out for you
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November 5th, 2009 7:51 pm
Vanessa, good question. We removed the fiberglass two years ago in our house and have ‘paid the price’ in much higher energy bills… I guess I would have to evaluate the situation – is it a little bit of mold/mildew that might be killed with bleach / replacing the insulation or is it a systematic problem? Could you replace the bad part of the fiberglass immediately?
I think your energy losses will also be dependent on whether or not the basement is out of the ground. For a completely underground basement, there’s going to be significantly less disadvantage to not having insulation. For above-grade basements, that’ll cost you big time.
The lack of a drainage system is the biggest problem. Are you getting a lot of water in the house? Is the grading around the house poor?
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Terry Pierson Reply:
December 27th, 2011 at 10:33 pm
Bleach will not kill mold. A better choice would be white vinegar.
I’m on a project now where a completely underground basement/crawlspace area walls were insulated with a closed cell spray foam with a thermal barrier over it. There is considerable moisture in the basement and the 1st level floors have started to buckle. Wicking is occurring as the spray foam has created a straw like affect and there is no air flow except up in the direction of least resistance. The thermal barrier has started to crack in places and there is a potential off gassing issue. Can not be in the basement/crawlspace without mask the odor is so bad. What is your experience with improper application of the closed cell spray foam and off gassing issues.
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Fred Reply:
December 28th, 2011 at 3:01 pm
Bleach will kill mold on non-porous surfaces, and I have seen it effective on small areas. There are concerns with it though – as it does not necessarily solve the problem on porous surfaces.
All that said, I’ve never heard of closed cell foam wicking moisture. Open cell foam, definitely. When you say there’s a thermal barrier over the foam, what do you mean? No such thermal or vapor barrier is required with closed cell, however, a vapor barrier is required with open cell. Open cell, in my opinion, should never be used in a basement.
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February 15th, 2011 4:36 pm
do you need poly around electrical boxes before you spray foam the basement walls
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February 16th, 2011 12:22 am
Randy, our spray foam installer taped off all the electrical boxes in the front, but did not shield them from foam on the back. From our examination, little if any foam tried to enter via the gaps where the romex enters the box.
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February 27th, 2011 4:00 pm
I live in New Hampshire, a cold climate. I have a full walk out basement with three walls below grade. We have chosen to have closed cell foam insulation installed. Our contractor has advised us to leave 1/2 to 3/4 of an inch gap from the cement to the 2×4 wood studs and he will install 2 to 21/2 inches of spray foam. Do I fill the remainning wall cavity with something else like fiberglass insulation ? and do I also install a plastic vapor barrier on the conditioned side of the 2×4 walls ? The answer has been difficult to attain. Thank You
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March 1st, 2011 11:21 pm
Russ,
You should leave a gap of 1/2-3/4 of an inch between the studs and the wall. If he is spraying in closed cell foam, no additional vapor barrier is required. With 2.5 inches of foam below grade, we see no reason to add additional insulation of any kind on top of the foam.
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April 7th, 2011 11:26 pm
“We removed the fiberglass two years ago in our house and have ‘paid the price’ in much higher energy bills” – Can’t tell if I’m misreading this. If you had spray foam blown in, your electric bill should have been cut almost as much as half.
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April 10th, 2011 1:19 pm
Drew – before we had the spray foam, we had removed the fiberglass to deal with mold and leaky walls. The foam has indeed made a huge improvement in our bills.
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April 11th, 2011 1:20 am
Thanks for the clarification, Fred. I’m from Louisiana, I don’t have to tell you what a nightmare mold abatement can be, especially the cost. Plus most older fiberglass uses a resin that can outgas formaldehyde. Granted it may not be a lot, but in addition to mold, that’s another thing that can cause asthma problems for some people.
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December 5th, 2011 5:55 pm
propertyperfections.com
This company sells a mold killer and a mold sealer. Both liquids. The sealer is put on secondary to seal and protect from future mold growth.
Bleach does not penetrate to kill the mold spores. You can treat with bleach and still have mold redevelope when the temp and humidity conditions are appropriate.
Bleach kills surface mold only, not penetrated spores.
I have no personal stake in this company, just use the product and buy it at the listed price, no kick backs etc. I have been hit by mold and take it very seriously.
If the moisture problems are not fixed, and all surfaces treated, it can be an expensive and dangerous merry-go-round. We walked away from an old house rather than endure the cost of trying to fix it, and left 90% of personal contents to avoid carrying the spores to a new place.
Horror stories exist of people near death from mold, left the house, but took the contents without decontaminating them, … the end result .the new house was contaminated by spores from the furniture. The problem followed them. I met the family at an environmental doctor in Dallas. They had endured 100,000′s of thousands of dollars in house decontaminations, and health costs. Nothing to play with.
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December 5th, 2011 6:07 pm
Couple of other things…
I have heard that mold can be killed by microwaves?? (books, papers, but don’t know)
Ionizing the air is used and proclaimed, by testing, to kill mold spores, black lights are used…. again have no proof but worth searching. I have an ionizing air machine that we use, occasionally by the central air return intake, but use it sparingly and when not at home, to kill any circulating spores. They are said to kill germs bacteria and viruses as well. It is said one should not breathe the air from the machine, in concentrated quantities??
As a side note, the Bible actually goes into some detail on how to handle mold…
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