Attic Ventilation/Mold
After consulting with several roofers/mold remediation/insulation contractors, I’m at a loss on what to do with my attic. I live in Zone 5A. When I bought the house five years ago, there was mold throughout the attic. I had it remediated, replaced the baffles, added a lot of cellulose insulation, moved the bathroom vents so they vented out the roof instead of the soffit, and installed LED retrofits in all the can lights. The roof was replaced four years ago and new ice/water was installed.
The mold has returned in several places, primarily in the areas of the baffles. All of the nails from the new roof are rusted. There was water on the top plate where the mold is worst. I’ve been up there since when it’s been raining and there’s no apparent leak. One roofer said there might have been an ice dam in that area, but I don’t know. I also found condensation on the underside of the plastic baffles where they contact the insulation in numerous areas.
I have trusses. I believe the ridge vent is cut too wide, approximately 3″ on each side, resulting in more exhaust than intake. Three roofers have told me that is not the issue.
I had an inspection done with a thermal camera, which did not show any areas of heat entering the attic.
At this point, I intend to change to fully vented soffit to replace the current one-every-three and remediate the mold. Remediating the mold will require the installation of new baffles and the remediation company wants to use plastic baffles. I don’t know if I should instead have permeable baffles.
I would really appreciate any suggestions to make it less likely this problem doesn’t return and advice on whether I should use plastic baffles or some other material.
Thanks,
Matt
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Replies
Did you seal your top plate penetrations? I would consider using a blower door to help diagnose air leakage. I’m sure you’re aware that condensation is usually the result of warm moist interior air condensing on cold condensing surface. I imagine that you have interior air leakage into the attic at your top plate. I would use rigid foam as my baffle and air seal to truss with spray foam.
I would try my hardest to air seal your attic using a blower door and smoke and or ir.
The other possibility is night sky radiation, but because it’s mostly at you baffles I think you top plate is more likely the issue.
I would also go through building science corp insight papers an read a few about attic ventilation to get a grip on the factors at play.
Thank you for the response. The top plates are not sealed. I was just reading an article about that. I will look into using a blower door. Neither sealing the top plate or using the blower door had been recommended previously, but make a lot of sense.
If the ceiling is not well air-sealed, having significantly more ventilation at the ridge than at the eaves is known to pull air from the living space, introducing moisture into the attic. (I have found that many roofers consider themselves to be building science experts, erroneously.)
Do you live in a high-wind area? I've seen many coastal homes that suck water or snow in through the soffit vents.
Thank you for the response. One of the recommendations was to remove all of the insulation and air seal with closed cell foam around the openings. I didn't think that would make a big difference because there doesn't appear to be much heat loss to the attic. However, I'm thinking I should do it anyway. It makes sense that the ridge might be pulling air from the living space.
It is not a high-wind area.
You don't have to use foam; tapes and sealants also work, but I would definitely seal the attic from the living space before trying other potential solutions.
Be very careful with closed cell foam. I made that mistake and am installing an attic dehumidifier in the house in a couple of weeks to bring the RH below 40%.
How did you use closed cell foam and what happened?
Thanks
The roof has 2x4 trusses, we created a vent then placed 2 inch es of ccSPF over the vent. In hindsight we should have followed BSC advice and creating a permeable surface at the ridge vent to allow for moisture to escape. In the garage I placed 1 inch of rigid 4x8 insulation on the rafters, then covered it with a permeable reflected surface. That allows the humidity to escape but keeps the temperature moderate. The humidity stays below 40%.
For the house, I am going follow Akos advice, and install a dehumidifier to remove the moisture from the attic. It should pull 18 CFM from the conditioned space and vent moisture to the outside. If my calculations are correct, the moisture should drop to 30%. If not, then I will have not take remedial class back at the University.
It’s a dirty job but renting an attic vacuum makes quick work of removing the existing insulation, even batts if you tear them up a little. Once your attic has been completely cleaned out, sealing wall plates, wire penetrations, recessed lights etc is pretty easy. Pressurizing with blower door and using a fog machine will help identify the less obvious leaky spots.
Thanks. The company quoted me $3,000 just to remove the existing insulation. Seems pretty high.
The last one that we vacuumed out was 1000 sq/ft and cost approx 2k for labour/disposal/equipment rental.
If you're DIYing it you might be able to air seal without fully removing the insulation. It'll take longer, be dirtier, but it's possible if the budget is tight and you have decent attic access.
Thanks. I think I'm just going to bite the bullet and hire someone to do it.