Attic moisture in Houston winter
Hello everyone. I’m trying to learn and remedy my attic moisture problem. I just moved into a newly built home in Dec 2017 and during the winter months (20 degrees) my unvented, unconditioned attic developed a lot of water droplets between the batting and silver heat radiant barrier, which apparently also happened in the summer too to me and my neighbors (all the same builder in this gated community). My single dehumidifier ran almost 24/7 during that period to no help. Some of my neighbors got the builder to switch out the batting for open cell foam and condition the attic, which during the summer of 2018 had no issues, whereas my batted attic had developed moisture in the ducts. I’ve been debating to ask them to install the foam, but they will void my attic warranty and won’t guarantee it’ll work. They don’t have a solution to the winter moisture buildup with batting. Was wondering if anyone have a better solution, or if it is a solution to the moisture issue? Thank you very much.
Concerned new home owner.
Alex
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Replies
I would be surprised if an unvented and unconditioned attic is code approved construction, but every county has different rules. You may want to have the county building inspector have a look. But understand even if they should decide it is not built to code they take no responsibility what so ever and likely just get a lot of tail covering.
It sounds like you are unlucky enough to also have an attic full of HVAC equipment and ductwork. If so venting the attic is not a great idea.
If the builder has a local name and reputation to protect you have some leverage if not they often take their cooperation thru bankruptcy after every big project and come back with a new but similar name.
The local TV stations love this kind of story during ratting week.
What R value of foam did they install in your neighbors homes?
Is this the same builder that built the home saying there work will void your attic warranty and won’t guarantee it’ll work?
Please search “conditioned attic” on this site and spend a few hours reading.
Walta
Hi Walta. Thanks for help. They foamed it 5.5inch thick. Not sure of the R-value. It is the same builder. We live in a gated community that's newly built. I'll read up "conditioned attic" on this site. Maybe it was "conditioned, since they did cut out big holes in the plenum so will cool the attic whenever the AC turns on. They've since covered the plenum. They are one of the biggest builder in Houston. It's just a bit frustrating since they don't have an answer for this rare cold spell phenomenon in Houston. One suggested adding a fan that would force outside air into the attic, which does have all the ducts, and hvac equipments. Anyhow, thanks for the input.
Alex
Alex,
You've told us that your attic is unvented and unconditioned, but you didn't tell us where the fiberglass batts are.
Do the fiberglass batts follow the roof slope? Or are the fiberglass batts on the attic floor?
For information on code-approved ways to construct an unvented attic, see this article: "Creating a Conditioned Attic."
It certainly sounds as if your attic doesn't meet code requirements. If your house (a) wasn't built to minimum code requirements, and (b) has moisture problems due to the code violations, then you have a legal case against the builder. Whether or not you want to sue the builder is up to you.
Hi Martin. The fiberglass is under the roof deck, following the roof slope. There's no fiberglass batts on the attic floor. They had like an 6in hole in the plenum, blowing cold air whenever the AC is on, so not sure if that qualifies as "condition". It feels like a mess none the less without a solution. Now I'm trying to slowly learn to remedy it. Much thanks for the help.
Alex
Regarding summer condensation:
When you have excessive humidity in conditioned space and a dehumidifier can't keep up, look at where the moisture is coming from. Probably from air infiltration - which is improved with blower door directed air sealing.
Verify that your dehumidifier is working correctly (discharging significant water, not just running).
The dehumidifier was running 24/7, I complained about it since it kept me up at night. I'll have them try the blower door directed air sealing. Much Thanks for the advice.
Best,
Alex
Typical TX construction... not to code! You can not install impermeable insulation against the roof decking; see 2015 IRC2015 R806.5. See attached.
FYI, 5.5" R20 open cell foam against the roof decking is NOT code either! This is dishonesty at all levels.
It's unfortunate that building officials AND code verifiers allow this to happen, but its very common here in TX. Time to join your neighbors and have some talks with the builder. Fixing the problem would be a lot cheaper than a class-action lawsuit.
As much as I hate Lawyers for any reason, I really hope crappy Builders start getting what they deserve.
P.S. There is another option for Vapor Diffusion Port, though I'm not a fan of it. See https://www.greenbuildingadvisor.com/article/vapor-diffusion-ports
Thanks Armando for the input. Just want to clarify. I went to the link and saw in 5.1.1. the air-impermeable insulation (eg open foam) that " it shall be applied in direct contact with the underside of the structural roof sheathing (decking?). That's what the neighbors did. The builder only put in batting under the roof sheath. No sure if they installed rigid board or sheet insulation "directly above the structural roof sheathing. So do you think putting open foam under the roof deck is bad in houston weather? Thanks for the help.
Alex
Here is a good paper from Building Science Corp. about some tests done in Friendswood, TX in 2015. This will give you all the basics you need to know... https://buildingscience.com/documents/building-america-reports/ba-1409-field-testing-unvented-roofs-asphalt-shingles-cold-and
You can download the document on a link at the bottom.
Thanks so much Armando. Gonna get the attic right eventually.
Best,
Alex
Alex,
It sounds like your builder installed radiant-barrier roof sheathing. That type of sheathing only works if the radiant barrier faces an air space. If the builder installed fiberglass batts against the radiant barrier, then the radiant barrier is worthless.
It sounds like the roof assembly is unvented -- with no ventilation channel between the top of the fiberglass batts and the underside of the roof sheathing. That approach is a code violation. You can't install fiberglass batts between rafters unless one of the following three approaches is also implemented: (a) a ventilation gap between the top of the insulation and the underside of the roof sheathing, with connections to soffit vents at the bottom and a ridge vent on top, or (b) an adequately thick layer of rigid insulation above the roof sheathing, or (c) an adequately thick layer of closed-cell spray foam installed against the underside of the roof sheathing (i.e., the flash-and-batt approach).
The reason for these rules is that you can get wintertime moisture accumulation on the underside of the roof sheathing if you ignore the rules. That's what's happening in your attic.
Your builder appears to have ignored code requirements, so your builder needs to fix this mess at the builder's expense.
Thanks so much Martin. I'm gonna see what they have to say. I'm giving them the benefit of the doubt since I don't know the exact specs. At this time I'm leaning toward having them do open foam under the roof deck and conditioning it. Do you think there's a better solution? Appreciate everyones help.
Best,
Alex
Alex,
Open-cell spray foam doesn't perform as well in this location as closed-cell spray foam, but it can work if certain features are included. For the full story, see "High Humidity in Unvented Conditioned Attics."
Thanks Martin. Definitely informative. The builders should use this website for sure. Much thanks.
Alex
Hi Martin, Bill here. Correct me if I am wrong, if one can spray about 2 feet of closed cell insulation either side of the ridge rafter and then spray open cell over it and rest of roof sheathing, you would "seal" the rafter and protect from moisture and rotting, while also reducing upfront costs (open cell foam is less-expensive in Houston). Then, add dehumidification to attic space (keep humidity to around 50%?). Is this a good design?
Alex,
The summer condensation problem is very likely caused by outside humid air getting in, as discussed above. The spray foam insulation provides a good air barrier under the roof deck., but you will still have to check the gable walls, soffits and the rest of the attic for any outside air leaks. Blower door directed air sealing will help with this. It is an important component of fixing your problem, and worth the cost in energy savings, even if you have to pay for it yourself.
Thanks Peter. Will ask the builder to test the blower door test. I'm trying to mitigate the problem, before it becomes a bigger problem with mold. Much thanks.
Alex