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Old 12-27-2011, 07:47 AM   #1
maxpower_454
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Default New Pole Building Roof Sweating!

I just got my garage built, 30X40X12 with 4/12 trusses and the metal roof is sweating! I have overhangs all around with a full ridge vent. I was thinking this would be enough ventilation to keep it from sweating but I guess not.

I only have stone on the floor (no concrete yet) so there's no vapor barrier on the floor yet. Is the moisture coming up from the ground? If I put plastic vapor barrier on the ground will the sweating stop?

The building is not heated yet and there is no insulation or even a ceiling in it. I plan on installing all those in the spring but don't want my building sweating all winter either.

I got the sides of the building wrapped in Tyvek but there's no vapor barrier or anything on the roof since the building company said I shouldn't need it (and it was expensive!).

I will post pics soon to help out.

What can I do to stop this? Will it stop when I put a ceiling in and put insulation and vapor barrier on top? Would tyvek under the roof have stopped this?

Last edited by maxpower_454; 12-27-2011 at 08:09 AM.
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Old 12-27-2011, 09:43 AM   #2
trbomax
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Default Re: New Pole Building Roof Sweating!

Should have put a layer of fan-fold down before the steel roof. Stops sweating permanently. Too late now.
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Old 12-27-2011, 10:30 AM   #3
green.bubbly
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Default Re: New Pole Building Roof Sweating!

The going thing with steel buildings is to use spray foam. You have to find a way to keep moisture from coming in contact with the cold steel roof.

I did not install any insulation before my panels were installed either. My building will be used as a home and I am stick framing the inside. I will simply insulate my walls and apply sheets of foam board against the metal siding.
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Old 12-27-2011, 02:56 PM   #4
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Default Re: New Pole Building Roof Sweating!

You've got a cold pop can in a relatively warm and humid environment. Water from the air will condense on all sides of that metal roof just like a cold pop can. You may not have noticed but water was condensing on the top of it too.

This is just one of the reasons I chose to roof my pole barn with composition shingles just like a house. Tyvek undeneath would have helped to limit the exposure of the bottom of the roof to moisture but other products would have been better.

When you finish the inside of the building you will limit the amount of air being exposed to the metal underside and that should limit the codensation somewhat.
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Old 12-28-2011, 05:39 AM   #5
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Default Re: New Pole Building Roof Sweating!

Same problem here with my pole building. I'm close to the stage your in except I have my slab in w/vapor barrier and yes it sweats too. I'm thinking I'll apply 3/4" closed cell foam to the bottom side of the roof tin,that should stop it...
I've been told to add a power fan vent,think I'll try foam first.
I've been told and many will till you to spray foam it... too much bucks and Morton told me it will void the warranty !(I don't have a warranty building is 30 years old) They said if a fastener leaks or somehow I get a hole in the tin water will get in between the under side of the tin and the foam and become trapped, causing rust and premature tin failure. Sorry you foam guys I know this will start something, Just trying to inform the OP with info I've been told by the largest pole builder in North America.
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Old 12-28-2011, 08:51 AM   #6
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Default Re: New Pole Building Roof Sweating!

I wouldn't get too bent out of shape about it just yet, you're talking new construction, likely built over damp earth, it will take several months for the ground under the building to dry out. Once the soil dries out your problems will be much reduced.
The same thing happens when people build a new building with a fresh concrete floor. Especially when you put plastic and insulation under the slab, it can take months for the all the water to evaporate out of the concrete.

The end solution is to keep the warm moist air away from the cool steel as much as possible, however just as Morton says, should moisture get to your steel you don't want to trap it there.
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Old 12-28-2011, 10:27 AM   #7
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Default Re: New Pole Building Roof Sweating!

Powerventing the space can be done in an effort to warm the roof, the warm pop can will not form condensation. At first it will just bring more moisture laden air in contact with the cold roof which will make the condensation worse and then the extra air will warm up the roof and stop the condensation. I wouldn't powervent to fix this.

Once the building is closed in the roof will stay warmer and air flow beneath the roof will be drier and lesser.
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Old 12-28-2011, 01:26 PM   #8
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Default Re: New Pole Building Roof Sweating!

I have been told by our new poll barn sales person they approve one type of spray foam and one type will void their warranty. Check with your foam and barn company for
the approved type.
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Old 12-29-2011, 11:40 AM   #9
35mastr
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Default Re: New Pole Building Roof Sweating!

My shop has been up for a few years and still sweats. Until there is a thermal break between that metal roof. It will never stop sweating. I have mine under control now with a Dehumidifier. Stays nice and dry now.
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Old 12-29-2011, 01:42 PM   #10
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Default Re: New Pole Building Roof Sweating!

Not a worry. Once you insulate and put the ceiling up it will end. Until then a dehumidifier and air movement are all you can do.
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Old 12-29-2011, 06:07 PM   #11
maxpower_454
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Default Re: New Pole Building Roof Sweating!

I still don't regret not getting the double bubble vapor barrier. It really doesn't sweat much and I think it might go away after I put the ceiling in like others mentioned. If it doesn't, I'll just sheet it with foam. I'm sure it won't cost me $1200 to sheet it!
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