Shop Moisture Question

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Forum topic by SteveKorz posted 06-10-2010 06:36 PM 1316 views 0 times favorited 8 replies Add to Favorites Watch
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2134 posts in 3137 days

06-10-2010 06:36 PM

Topic tags/keywords: workshop moisture rust vapor barrier insulation question

Hey All!!

About a week ago, I had a tree crash into my shop. It messed up the roof and crushed some pearlings. The overall structure was OK, but now the entire thing leaks like a screen. I’m doing a mass Exodus of tools and wood at the moment.

I’m ordering new metal and I’m going to redo the entire shop. I’m also going to insulate it with R9 1” foamboard, so I can work in the winter. Foamboard seems like my best option, since it is a post and frame structure.

My question is this: When I insulate this shop, I thought about wrapping it in heavy bisqueen plastic (6 mil) as a vapor barrier. I’m putting in a new entry door, 3 windows, and a new overhead door that will also be insulated, so the shop will be tight. If the temperature isn’t kept controlled all year inside, will this lead to a moisture problem in the summer? I’m trying to avoid all the moisture issues and cut down on the tool/tablesaw/bandsaw rust, etc. If it did lead to an internal moisture issue, would I be able to run a dehumidifyer in it during the “above freezing” temps for 9 months out of the year without it affecting my wood (warpage, cupping, etc)??

I’m really looking forward to your imput here, I’m sure that most of you have battled this issue over time. Since construction will most likely begin within 10 days, I’m trying to get my ducks in a row and plan a little.

As always, Thanks in Advance!


-- As iron sharpens iron, so one man sharpens another. (Proverbs 27:17) †

8 replies so far

View woodsmithshop's profile


1250 posts in 2969 days

#1 posted 06-10-2010 07:10 PM

hi Steve, sorry to hear about the tree falling on your shop, I just cut one down to get it away from my shop.I don’t know about the vis-queen vapor barrier, I have heard arguments both ways, I have not tried it myself. a dehumidifier in the summer will help, I keep my shop heated during the winter so I have no problems with humidity then. I don’t use a dehumidifier in the summer anymore, I do keep my shop closed up, I don’t open windows, or doors unless it is close to equal humidity inside and out, also it remains cooler in summer by not opening windows, I use fans, and if it gets too hot I will turn on my a/c, I have a 12000 btu window unit and it does a fair job while I am working, I don’t leave it on all the time, ( the wife won’t let me). I am fairly heavily insulated so my shop is not hard to heat or cool. the more insulation the better, it pays off in the long run.

-- Smitty!!!

View Dick, & Barb Cain's profile

Dick, & Barb Cain

8693 posts in 3723 days

#2 posted 06-10-2010 07:29 PM

The plastic vapor barrier is good, but only on the inside walls.

Don’t use it on the outside, because it will trap the vapors inside the walls.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN.

View dbhost's profile


5590 posts in 2655 days

#3 posted 06-10-2010 07:37 PM

Have you considered expanding foam insulation? R9 isn’t much, better than nothing for sure, but still kind of lacking…

-- My workshop blog can be found at

View a1Jim's profile


115177 posts in 3000 days

#4 posted 06-10-2010 08:17 PM

Your better off with a house wrap under your siding it’s designed to let moisture out but not let any wind or moisture penetrate into the structure.

-- Custom furniture

View Leslie's profile


44 posts in 2476 days

#5 posted 06-10-2010 09:28 PM

I would not use poly with the foam borad, the condensation between the poly and the foam will be alot. You could use kraft papper or house wrap, but it’s not going to do much from the inside. You could combine the two. Put up your 1” foam and seal around it with the spray foam (the can stuff) this will help seal up the draft your going to get with the 1” foam. But as dbhost said spray foam is best, I have a 3100 sf house that is like a big beer cooler I used soy froam insl. My house stays around 70 all summer here in Tx and my bill is around 225.00 a mth. Not bad for a 2 stroy open floor plan.

-- Leslie, TX

View Grumpy's profile


21459 posts in 3274 days

#6 posted 06-11-2010 11:49 PM

Sorry to hear your bad luck story Steve. Good luck with the repairs.

-- Grumpy - "Always look on the bright side of life"- Monty Python

View SteveKorz's profile


2134 posts in 3137 days

#7 posted 06-12-2010 02:50 PM

I’ve changed gears a little… I discovered that the foamboard was only going to give me an R 7.2 (Ouch). I figured out that it was only going to cost me about 500 dollars more to insulate the whole thing with fiberglass batting, and that includes studding out the walls (as this is a pole barn) and putting interior plywood on the studs to finish out the inside.

I couldn’t find anyone in our area that sprays the expanding foam, and no one even rents the equipment.

The fiberglass batting is going to give me an R13, with finished inside walls I might pull R14. I am scrapping the heavy plastic Bisqueen idea, and going with Jims idea on housewrap. It is still comparable to the plasitc sheeting in price, but has the benefit of letting out the moisture (which I didn’t know it did until Jim brought it up and I did a little research).

Grumpy- What started to be a bad thing is now turning into a really, really good thing. I’m finally going to take the plunge and get a shop that I can work in year round.

It’s been a while since I’ve talked to some of you all, I hope you’re all doing great. Thank you guys for your help! I greatly appreciate it.


-- As iron sharpens iron, so one man sharpens another. (Proverbs 27:17) †

View Dick, & Barb Cain's profile

Dick, & Barb Cain

8693 posts in 3723 days

#8 posted 06-14-2010 06:40 PM

That spray foam is really expensive, I think bats is the way to go.

House wrap tip, video.

-- -** You are never to old to set another goal or to dream a new dream ****************** Dick, & Barb Cain, Hibbing, MN.

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