Comments on: Humidity in a Spray Foam Attic

By: Annie

Annie — Fri, 19 Jul 2019 12:35:20 +0000

We spray foamed an
We spray foamed an unconditioned/ unfinished attic space that sits above the garage. This large attic can be accessed by going through the laundry room of the house . Its a new construction home and we were told by the foam company it would get too hot in there so to go ahead and foam that room until we were ready to finish it. It was very clear we would not be finishing any time soon and already a few months in and it is a sauna in there. Humidity high. We live in Atlanta. What can we do now? We had plans to finish, but not for some time. There is no ductwork accessibility into the area and the soffit vents were covered up by the foam. There is no ways for this area to escape it appears. We do have windows in there. Any guidance as to next steps would be very appreciated. Thank you

By: Jeremy

Jeremy — Wed, 19 Jun 2019 19:48:21 +0000

Very interesting info and
Very interesting info and comments! I’m dealing with a similar challenge: open-cell SPF under the roof deck with a bad odor in hot, humid weather (CZ4a). I’ve had a data logger for RH&T in the attic since about a year before it was encapsulated, though having one at the floor and ceiling is better. Mine is about 18″ from the ridge. Might have to add a sensor.

I have a slate roof and requested that baffles be installed under the roof deck. There are other defects with the installation, including SPF pulling away from the rafters pretty significantly (>1/4″), and some skippers at the ridge. Hot, humid air POURS out from those gaps at the ridge. I just touched them up with canned foam, but I doubt it’ll make much difference.

I tried covering the SPF with plastic sheeting in desperation a few weeks ago as it started to get warm because I realized that I would have to a) reinsulate all of my ductwork (long story) and b) jettison the ERV if I were to revert to a vented attic. I wanted to see if that would lessen the odor, knowing that it couldn’t be kept due to being a vapor barrier in the wrong place. It did lessen the odor, but not enough. So I stuck in an exhaust fan to depressurize the attic as a band-aid measure. And sure enough, the plastic did have condensation all over the side facing the SPF on a hot, humid day. And, interestingly, some condensation on a small portion of the interior side near the ridge. I immediately removed it and the odor and RH both increased.

So, I think Steve McKenna is right about the fundamentals: Hot air can hold more moisture. I’m clearly getting stratification in the attic, partly due to an air handler on the attic floor and uninsulated ductwork. But it happens on sunny days when the A/C is not being used, just to a lesser extent.

The AccuVent baffles are channeling air heated by the roof to the ridge, which is no surprise. I’m still puzzled about the source of the moisture. If the roof heated the air in the baffles from 85º outdoor ambient to 115º in a closed system, the RH would fall. That doesn’t seem to be happening. On an 85º day (DP 71º), I’m seeing 81º (DP 80º, really) at the ridge. Does the SPF, rafter and roof deck really hold that much moisture?

By: Carlos

Carlos — Sat, 08 Sep 2018 13:51:17 +0000

In reply to Brian Besold. Hi group I need help one of
Hi group I need help one of my clients did close cell insulation at the roof raptors and he still have the floor fiber glass and it's very humid and he wants do flooring it's very humid and hi doesn't have any kind of ventilation or any like that what option I can do to do this place nice and comfortable

By: Joe Glickman

Joe Glickman — Sun, 01 Jul 2018 02:13:28 +0000

If I may add to this
If I may add to this discussion, I had open cell foam sprayed under the roof decking. There's about 7 and 1/2 in a phone between all of the rafters and at the Gable end. Prior to this there was Rockwall in the Attic floor. It's been quite humid here in Upstate New York the past few days and most of the house stays at around 60 to 65% relative humidity. I have a whole house dehumidifier down in the basement that keeps the humidity below 59% and average is 55%. I have my central air system on the 1st and 2nd floor running at 59 degrees Fahrenheit. It feels nice and cold in most of the house. When I went up to the Attic a couple of days ago I noticed that the wood was wet, particularly along the edges of the rafters where it met the spray foam. I took my moisture meter and it was reading 54%. I have never had this problem in the Attic until the open cell foam was sprayed there. It seems to be trapping the humidity in the Attic. My humidistat was reading almost 80% humidity around the attic floor level so I assume it was even higher towards the ridge. I peeled back some of the open cell foam and the rafter was dry underneath it. So it seems to be happening where the rafter is exposed to air in the Attic. I'm trying to figure out a way to solve this before I start growing mold or having other structural issues because of this. I do have a supply vent going up to the Attic but it is very weak so not a lot of cold air is going up there. I don't know if keeping the house so cold is contributing to the problem but I am contemplating putting an air conditioner up in the attic if that will help solve the problem. Any advice or thoughts would be appreciated.

By: Larry Rosser

Larry Rosser — Wed, 15 Nov 2017 00:17:35 +0000

Dan Geist, I would be most
Dan Geist, I would be most interested in your data with closed cell foam for a home in Atlanta, Ga.

By: Scott Partlo

Scott Partlo — Wed, 09 Nov 2016 01:35:31 +0000

Eldon,
Eldon,

I still think a foamed attic is often a good idea. However if you still have reservations then I suggest:

Seal the ceiling plain (wire penetrations, electrical boxes ect)
Add insulation to R60
Get rid of the power vents

By: Thomas Peterson

Thomas Peterson — Tue, 08 Nov 2016 18:39:26 +0000

Steve, I agree with
Steve, I agree with everything that you said. I tried to say what you said earlier, but with less clarity.

By: Eldon Nifong

Eldon Nifong — Tue, 08 Nov 2016 16:44:22 +0000

I have air handlier abd
I have air handlier abd furnaace in attic.
And have thought about have underside of roof spray foam insulated since attic is hot in summer and cold in winter. Home is rambling ranch built in the 50s.
Also condered power roof vents.
After reading articles here, have done neither.
I do have 16 inches of insulation on attic joist.

By: Erich Riesenberg

Erich Riesenberg — Fri, 21 Oct 2016 22:35:43 +0000

I have one story home, with
I have one story home, with an attic converted to living space and a basement.

I insulated the cathedral ceiling by:

1) cutting and cobbling expanded polystyrene into the rafters, for six inches of eps between the rafters,
2)another 4-6 inches of eps under the rafters, and
3)5+ inches of mineral wool under that eps.

I was able to remove the central air and furnace, and install a 5,000 window air conditioner. I like this because it frees up floor space and is simple.

During summer I have found placing the air conditioner in the attic keeps the house cool and comfortable, while placing it in the first floor leaves the attic uncomfortably warmer and humid.

I have assumed it is because the humid air rises, so having the air conditioner on the second floor is better at removing humidity.

On another note, the attic is unventilated. There have been suggestions to install venting above the roof deck. I understand the need to monitor indoor dew point, but it seems that if the eps is tightly fit, and it is, along with overlapping layers below that, there should not be interior moisture reaching the roof. I cut the eps for a tight fit, and used a great deal of caulk and Great Stuff Pro spray foam to seal it.

By: Kris

Kris — Thu, 20 Oct 2016 15:55:53 +0000

BSC is one of my 3 sites that
BSC is one of my 3 sites that I visit regularly and as the article states he has spoken about this "ping pong" effect before. Hopefully he'll get the code changed to allow conditioning in these sealed attic spaces.