Help – My Barndominium Vaulted Ceiling Drips

Reader HOMER in PIEDMONT writes:

“I called in today and was referenced to send an email – 

I have come across your website and have gained a vast amount of knowledge – I was hoping to get some more information on my situation – I also understand that you actual don’t sell insulation and that any advice you give me might not benefit your business – I am willing pay a consulting fee if you like or if i can purchase any products through your company that will help me get out of this pickle i will be more than happy to – 

So my situation (the pickle) 

I built a 30×60 barndominium with vaulted ceiling (the purlins on top are 8″) i used about 1/2″ to 1″ of closed cell spray foam all over it then laid the typical pink batting insulation in it – the issue I am having is I am in Oklahoma – on a morning of a cold night – when the sun comes out it heats the metal roof up and creates condensation – hence a ceiling that rains throughout the day – it seems to happen closer to the peek more than the bottom portion of the ceiling 

I have tried pulling some of the batting insulation out of the middle section to help create more air space – it did seem to help a bit but still saw condensation on the spray foam insulation – when i removed my test panel (also i used 3/8 bead board for my interior sheeting) 

On the peak of the roof I didn’t use the foam vent ridge cap but filled it in with spray foam (I was going for air tight) which might be more of the issue 

I truly am sorry to bother you with this issue and any help or direction would be greatly appreciated – please reach out via email or phone and I am sorry if I didn’t give enough detail to paint the picture that I am facing.”

Mike the Pole Barn Guru says;

Thank you for reaching out to us. Our goal is to assist our clients from making crucial (and often costly) errors they will regret forever. While your circumstance is crucial, it can be rectified.

According to Johns Manville, a minimum of 1-1/2″ of closed cell spray foam is required in order to provide an adequate air and vapor barrier (we have always recommended two inches, as we feel it is better to be safe than sorry). Right now, the underside of your closed cell spray foam is cool enough on those cold mornings so warm moist air rising inside meets it and condenses. This is more pronounced as you approach interior peak due to warm air rising.

If it was my own roof – I would remove all fiberglass roof plane insulation, increase thickness of closed cell spray foam to at least two inches, then fill balance of 2×8 cavity with either open cell spray foam or rock wool batts (rock wool is not affected by moisture and does not lose R value during cold temperatures).

Only other possible solution (have not tried, so is only hypothetical) would be to mechanically dehumidify the interior of your barndominium to a degree low enough to eliminate your challenge. This would probably need to be under 20% relative humidity – so low as to become uncomfortable to live in (Dry, itchy skin & eyes) and causing shrinkage of wood in floors, cabinets, doors and furniture.