Another insulation/ condensation question

[89efhatch]

I know this topic has been covered quite a bit but wanted to lay out my situation and see what you all think.

I have a 30x38x12 pole barn with scissor trusses. I have insulated all the walls with R19 fiberglass batts. I have done about 1/3 of the ceiling with R19 batts and noticed that the metal roof deck sweats on occasion. The ceiling insulation is on the lower part of the trusses not touching the metal. I have a 36k btu mini split that I will be installing when the insulation is done. I plan on keeping the shop around 50 degrees and warmer on weekends.

Once the ceiling is done will the sweating above it stop?
Should the insulation be touching the metal?

Any thoughts would be appreciated
Thanks
Mike

 

[89efhatch]

I should add that I do have vented soffits and peak

 

[billconner]

How long ago was slab poured and is there a vapor barrier under it? Is there a temporary heat source? Just trying to find the source of moisture that is condensing on the roof.

I would finish ceiling insulation and put a vapor barrier under it.

 

[89efhatch]

That slab was poured over a year ago with no vapor barrier. I was using a propane heater for temporary heat source

 

[billconner]

The propane heater is a significant source of moisture, a lot more than you mini split. I stick with my vapor barrier. Get as heavy of one as you can afford - 8 mil or at least 6. Sto Cote Tu Tuff is a favorite and pricey. Overlap and tape seams. I believe with vapor barrier and venting, and no source of moisture like the propane heater, condensation will stop.

Will you install a ceiling? If not, you need to find a fire resistant vapor barrier.

 

[mike93lx]

As Bill said the propane heater is probably your issue. You get a gallon of water per 100k btuh when burning propane. That's a lot.

Running a dehumidifier would help, in the short term.

R19 is not enough in the ceiling, either

 

[89efhatch]

I'll stop using the heater and just get to work finishing the ceiling. I'm regretting not getting the insulation done over the summer

 

[billconner]

Mike is correct, R19 is very minimal. I'm way upstate - 1000 islands - and code would require R49 if I'm heating it at all.

 

[89efhatch]

I know its minimal but its what I can do at the moment. Around here I think home code is r38 in ceilings, not 100% sure though

 

[billconner]

As far as I can tell, reading NYS Residential Codes on line (up-codes) all three climate zones in NY require R49 in ceiling.

It seems to be one of the things our local inspector is diligent on, so if heating a building, you have to meet the energy efficiency parts of the code.

I see the state is about to outlaw oil, gas, and propane in new buildings. Proposed is 2025 but I'd guess it will slip at least 5 years. I'm in favor of it. Part 2 is state subsidizing replacement in older buildings. Doubt I live that long but still a good thing.

 

[89efhatch]

Would covering the fiberglass batts with 2" foil faced foam board act as a vapor barrier? as well as add r-13

 

[billconner]

I find foil faced polyiso has a perm rating of 0.1 so a good vapor barrier with seams and edges sealed. Probably foil tape seams and spray foam edges.

 

[89efhatch]

Thanks for the input