Beware of Roofers in Homes with Spray Foam Insulation
You have two choices when change happens: You can embrace it, or you can fight it. Some parts of the home building and home improvement industries are in the first camp. These are the home performance contractors, green builders, and spray foam insulation contractors. Some are in the latter camp. They could be in any trade really — insulation, HVAC, drywall. But today I’m focusing on roofers because of something I saw recently.
Attic ventilation and spray foam don’t mix
That photo above is from an existing home that had spray foam insulation installed in the attic over the master bedroom. What you’re looking at there is the place where a power attic ventilator had been. You might be thinking, well, what’s wrong with that? Clearly the fan is gone now, as it should be in a sealed attic. Right?
Yes indeed. One of the biggest benefits of using spray foam is to get greater airtightness. That means you get rid of attic ventilation, whether it’s passive (ridge, gable, soffit vents) or active (fans). Actually, you should get rid of power attic ventilators whether or not you’re sealing the attic, but that’s another article. The point I’m making here is that a sealed attic should be, well, all sealed up.
What the photo above shows, however, is that the power attic ventilator that was removed from that hole came out after the spray foam went in. In this case, it also was installed after the spray foam went in. Oops!
This particular attic already had enough air leakage from poorly installed spray foam. The fan made it much worse. The house is here in Atlanta and had serious moisture problems because of all the humid air the fan (and leaks) introduced into the supposed-to-be-sealed attic.
Educate your roofer
Some roofers understand the new things we do with homes these days in the name of building science. Most don’t. They know roofing materials, underlayments, flashing, and attic ventilation. Some know more than others, of course, but you should probably assume the worst any time a roofer comes to your spray foam insulated home.
Tell them the attic is to have no ventilation of any type. The photo above shows the scar from a power attic ventilator installed in a spray foam attic, but I’ve heard of several cases where roofers installed—or tried to—ridge vents.
Sealed attics should not have any type of attic ventilation connecting it to the outside.
Update, 23 Oct. 2022: Attics encapsulated with spray foam insulation on the underside of the roof deck should be treated as conditioned attics. In humid climates with open-cell spray foam, the attic humidity can be very high in the summer and can damage the roof if you don’t do something about it. One method is to use a small exhaust fan, which is what I do in my house. But this ventilation is at a lower rate and is more controlled than what the article above is focused on.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has written a book on building science. You can follow him on Twitter at @EnergyVanguard.
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Another timely post Allison.
Another timely post Allison. Quality thinking.
In this ‘get er dun’ world, slowing down and thinking about comprehensive design is the antithesis of the process contractors want to implement.
Getting thought and graphite OUT of process seem the goal everywhere.
Good timing Allison. I spent
Good timing Allison. I spent quite some time last week convincing a local church that the job their roofer/spray foam contractor (There’s a combo you’ll like) was proposing wouldn’t work. The new roof is sorely needed, that part seemed OK.
The proposal to insulate the underside of the roof with several inches of open cell foam had a serious flaw. It didn’t include the gable end walls AND the contractor proposed enlarging the gable end vents and adding a ridge vent. Hey, a well vented attic is a good thing, right?
The contractor is PO’ed because I cost him a 40K job (BIG roof) and he knows it’ll work because he’s done it “Many, many times” before (I want his customer list!).
The church is talking to a reputable air sealing/insulation contractor and with the tens of thousands of dollars they save may spring for an upgrade on the roofing shingle they choose.
Isn’t the wood that is
Isn’t the wood that is penetrating the foam a problem? Here in greater Cincinnati moisture already in the attic from the house (showers, laundry) can find its dew point inside the wood member. Dry rot ensues.
Although a little difficult
Although a little difficult to tell from the quality of the photo it appears that the A and B ratio was off … Which, if this is the case, the homeowner may have even more to be concerned with in the near future.
I also believe that I’ve never seen an example on this blog of an actual consistent aesthetically-attractive 5″ average (R-20) open cell with rafters being fully encapsulated in foam. It’s something that must be involved when discussing “proper application” of spray foam.
Hello all,
Hello all,
Just watched the BBC movie (recommended) on the Shuttle Challenger disaster and decided to further refresh my memory of the event by reading the Wiki.
While this line from the article may be a bit of a stretch in regard to the situation Allison shared, I believe it does address one of the shortcomings of human reasoning, and worth repeating. I believe Ms. Vaughan (below) was referring to our propensity for saying “…nothing bad has happened yet because of (fill in the blank), so don’t be concerned.”
The quote:
“This phenomenon was termed “normalization of deviance” by sociologist Diane Vaughan in her book on the Challenger launch decision process.[6]”
Apologies for dredging any bad memories of the Shuttle program…
Best wishes.
Open cell spray foams have R
Open cell spray foams have R values of around 3.6 per inch, not 4 as noted in above comment. 5″ of open cell is therefore about R18, not R20.
And why would ANYONE install open cell spray foam in a vaulted space without a vapor barrier? There is another name for open celled spray foam – it’s called “sponge”. It works great as long as there is no moisture (which will significantly decrease R value), but when you vault a space and spray in open cell foam, rising humidity can really soak that foam over time, and holding moisture next to wood is not exactly best practice, especially in southern humid environments. Closed cell with a thermal or ignition barrier would be a much better way to go – either sprayed in or structural insulated panels (sips).
There’s only a couple name
There’s only a couple name brand foams that have r values as low as 3.6… The most obvious being a Canadian product. Our name brand R is 3.83. Technically, if we are spraying exactly 5″ (code allows for a +/- 1/2″) we have R-19.15. So, in the world of astrophysics, being off by .85 I’m sure will make a astronomical difference over the course of light years of celestial bodies and beyond. However, we tend to be liberal and on the + side of application thickness so it’s quite easy to go over an R-20 … Not to mention that an additional .22″ (R .85) of foam only adds 3 cents material cost and no additional labor costs so we feel clients earned that 3 cents when paying for a good SPF job.
Depending on what climate zone the home is located there must not be a vapor barrier on the open cell foam. In zones 1 and 2 installing a vapor barrier on the bottom side of foam in the roof-line goes against the basic prerequisites of building science, especially in the south zones 1 and 2. BSC has a wonderful picturesque illustration – also supported by FSEC, EEBA and SouthFace – of exactly how the attic, which is now treated as conditioned space (key words, conditioned space), must be arranged/set-up/organized for best installation practices.
General rule of thumb:
North – vapor barrier on inside of conditioned envelope.
South – vapor barrier on outside of conditioned envelop.
These basic A,B,C’s of remedial building science hold true regardless of what insulation is applied.
Ted:
Ted: Thanks!
Bill S.: Great job! It’s too bad that there are so many companies like that out there, but it’s nice when you catch something like that and nip it in the bud.
Bill H.: Yep. I wish we could blame it all on them, but that wasn’t the case in the home I wrote about here.
Rick W.: Yes, ideally you want all the rafters/top chords covered with foam. Atlanta’s not as harsh on that kind of thermal bridging as Cincy, but it’s still a problem.
Jeff: Now
Jeff: Now you’ve got me wondering if I’ve shown any nice foam job photos. I think I have, but I can’t quickly think of which articles they’re in. I do have some nice foam photos, though, so let me try to rectify that in an upcoming article.
Steve W.: I thought normalization of deviance was just how we all live our lives. ;~)
Gary N.: Don’t know if the line is still hot or not, but hey, the wires are safetied off with wire nuts. You’re absolutely right, though. That’s poor workmanship.
Charles: In a cold climate, open cell spray foam on a roofline definitely needs a vapor retarder. Here in Atlanta, vapor diffusion isn’t going to rot the roof unless the humidity in the attic is too high.
Allison: Missing from your
Allison: Missing from your article is a clear understanding of why the attic fan was installed. I can assume that the homeowner had their shingles replaced and the roofer insisted there should be ventilation? Also, there’s foam on one of the wires, so are you sure the fan wan’t there when the foam was installed? Then, who convinced them to remove the fan and now, was anything fixed? I need more background.
Steve: I also watched that movie and it was excellent. A great example of science winning over politics and being true to your self.
Jason H.:
Jason H.: Good question. I’m not sure I remember that part of the story clearly, but I think the roofer was there for something, maybe new shingles, and saw that the fan had been removed so they reinstalled it (or put a new one in the old one’s place). Also, the spray foam contractor did a poor job, and I think they came out more than once to try to make their work right, so maybe that’s how foam ended up on the wire.
Having worked in my field for
Having worked in my field for 15 years I’ve seen a lot of foam installs. Open cell for the most part, but a few metal buildings built for residentail that required closed cell.
(hot humid south)
I have some pictres of excellent open cell foam installs. full rafter depth with no voids or bellys in the foam. fully covered faces of 2×6 rafters.
these companies…and they are far and few between…consistantly do good jobs.
testing the attics for leakage with a blower door, the owners/installers (I should say owners are the installers) do consistant R-25 installs, air tight
at eaves to ambient.
code allows us to drop from R-30 required to R-25 as cathedralized ceiling requirement.
in my years in the energy rating business of inspecting, verifying & testing installs…3 companies consistantly met requirements.
out of the 20+ companies that are
currently in business, have gone out of business etc.
I can’t think of any occasion ever that foam was installed on a tile or slate roof. IMO to do so would just be a waste of the homeowner’s money.
good job Alison, keep it up!
I have 2 gable vents, one at
I have 2 gable vents, one at each end of my roof. I was looking to install soffit vents. Is it possible to have too many soffit vents?
Also, does spray cellulose insulation need a vapor barrier since cellulose is made out of paper?
Also we are in Austin.
Also we are in Austin.