Tag Archives: metal roof condensation

My Barndominium Attic Has Moisture Issues!

My Barndominium Attic Has Moisture Issues!

Reader DAVID in CHICAGO writes:

“Greetings – I’ve got a pole barn style home that’s about 2.5 years old and I’m having moisture issues in the attic. Hoping I can talk with someone to get a consult or second opinion to resolve as quickly as possible. Let me know if it is something you can connect on. Attached is an image from the attic where you can see moisture on the underside of the metal roof. It freezes at night and then during the day when the sun is out, it melts and drips into the attic insulation. 

Attic space is dead, image below. Vented through passive soffit vents and ridge vent, with a few solar blaster ridge vents to help with active venting when the sun is out. Attic insulation is R50 blown in at 20 inches deep. Image of exterior attached. It’s sheet metal that’s then spray foamed on the inside and additional R25 batts. Image below from when we had this same issue earlier this year in February 2021 when the drywall walls and ceilings had to be torn out due to water damage. We purchase in January 2021 and the home is now 2.5-3 years old. There is a solid concrete slab that has in-floor heat. I believe it has a vapor barrier underneath from an image I saw. “

Mike the Pole Barn Guru writes:
You are victim of what is such a simple and economical solution, when planned for in advance. Why builders and building providers fail to address steel roof condensation initially drives me to consider alcoholism!

I do realize they are just ‘selling on a cheap price’, rather than providing a best solution for their client.

Easiest solve is to have two inches of closed cell spray foam applied to underside of roof purlins. Any other solutions will take removal of roof steel panels, adding a thermal break, and then reinstalling roofing.

At time of construction I would have recommended roof steel with an Integral Condensation Control (ICC) factory applied. Investment then would have been a fraction of having to solve it now.

For extended reading on ICCs https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/.

Insulation Vapor Barrier

There are some days when I feel as if I have become the “Dear Abby” for everyone else’s pole barn problems. So many of these problems could have been easily avoided, and at a relatively low cost, at time of construction.

A reader writes:

“I have a Morton pole barn that really sweats this time of year. With cool nights below freezing and days warming up above freezing it’s like raining in the barn. Roof is metal nailed to 2×4 purlins with a full ridge vent. Usually by noon it dries up but I am worried what this will do the purlins in time. Floor is stone. It is so bad that I would not put a load of seed in the barn without covering. Morton’s fix is to remove the roof and either but their insulation board down and re-install the original sheet metal or replace the roof with new metal that has the insulation fabric bonded to the metal. Either way … expensive. Any suggestions?” 

Dear Drip….

This is what is happening – warm moist air from inside of your building is rising. When it contacts the underside of the cooler roof steel, it is condensing. Over time, not only will the purlins develop unsightly water streaks, but there is also the potential for rot. It is very possible for moisture to collect around the shanks of the roof screws (and hopefully they have not used nails) and rust them, causing leaks. Many steel manufacturers will not warranty their products as roofing, unless installed over insulation vapor barrier.

Ventilation alone, is not going to solve the problem. Even a roof only building, will have the same issues.

How to solve from where you are now….

Pole Barn Condensation BarrierLeast expensive, would be to place insulation vapor barrier on the underside of the roof purlins. In order for this to work, it requires all of the seams to be tight. I’d recommend a product which has tabs with adhesive pull strips, rather than square edges which must be taped. Look at www.buyreflectiveinsulation.com for more ideas.

If you say the roof is nailed on – removal of it and trying to reuse the steel panels is not going to happen.

Spray foam is probably going to prove to be less expensive than a new roof.

Sad to say this….but for probably about two bits per square foot of roof surface adding insulation vapor barrier at time of construction, we wouldn’t be having this conversation.

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