Moisture in the shop?

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Forum topic by Sailor posted 01-21-2011 05:08 AM 1588 views 0 times favorited 6 replies Add to Favorites Watch
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543 posts in 3534 days

01-21-2011 05:08 AM

After searching for answers in the forums I could not come up with anything, so I believe I will ask the proffesionals.

I have just moved my shop into a single bay of our barn, 13.5’x25’. It is built on a slab and I have the walls insulated and I will have the roof insulated in the near future. I used R13 bat fiberglass insulation without a vapor barrier other than 1/2” plywood on the walls.

I have a few questions:

I plan on using the attic space for storage, so I am going to insulate between the rafters right up against the roof decking. The soffit is closed off with vinyl vent soffit so at the moment it is breathing freely. How should I insulate down around this area? Should I seal it off comepletely not letting any airflow in or out?

I hope to have the entire space insulated. It does have a metal garage door that I plan on putting some 3/4” foam board in as much as I can to give it some insulation although I doubt it will be very efficient. What should I do about moisture in the shop throughout the seasons? It may not be relevant however because I probably will do alot of work with the garage door open.

How should I prepare myself to deal with moving projects from my shop to inside the climate controlled house?

I live in southeast Alabama so we have hot and humid summers…... very hot, very humid…..
Thank you all.

-- Dothan, Alabama Check out my woodworking blog! Also my Youtube Channel's Facebook page

6 replies so far

View Gregn's profile


1642 posts in 3253 days

#1 posted 01-21-2011 06:37 AM

You should have some kind of vapor barrier over the insulation before the 1/2” plywood Plastic sheeting is what I’ve use for batts without a paper vapor barrier. From the soffit end there is a Styrofoam vent that should be stapled in place to help circulate air between the roof decking and the insulation. These are generally placed about every 3rd cavity. They are about 4’ long and about 1” in depth. Then batts and the vapor barrier.

Depending on how you plan to heat the shop you may want to add a humidifier, an air conditioner will help to regulate the humidity in the summer. A humidity gauge will help in regulating the humidity in the shop. This will help in keeping the humidity levels equivalent that of the house. If you don’t plan to air condition the shop you will want to at least use a dehumidifier to aid in controlling the humidity.

-- I don't make mistakes, I have great learning lessons, Greg

View childress's profile


841 posts in 3811 days

#2 posted 01-21-2011 07:41 AM

When I would frame roofs most of the attic was vented between every 2 or 3 rafters. When the insulation was installed, they would start those bays about a foot back to let the air flow. If I’m understanding you correctly…

-- Childress Woodworks

View bill merritt's profile

bill merritt

203 posts in 3558 days

#3 posted 01-21-2011 08:07 AM

I live in South also, I would make sure the walls are not letting any moisture in (the plastic test) before I did anything to the walls. Just a thought.

-- Bill Merritt -Augusta Ga. woodworker

View Eric_S's profile


1565 posts in 3465 days

#4 posted 01-21-2011 02:25 PM

Get a dehumidifier. Growing up we had one running all the time in our basement. You’ll have to check it maybe once every couple of weeks to empy the water if their isn’t an auto drain.

-- - Eric Noblesville, IN

View botanist's profile


167 posts in 3808 days

#5 posted 01-21-2011 04:28 PM

I don’t think plywood is a good enough vapor barrier because it would start to mold and decay the minute any moisture condensed on it. It’s better to use plastic sheeting and then plywood. Dust from woodworking is hard enough to deal with; you don’t need to deal with mold spores as well. Use a dehumidifier in the summer to control moisture.

View 8iowa's profile


1591 posts in 4031 days

#6 posted 01-21-2011 04:47 PM

Here in Gainesville, when I enclosed our carport, I installed a thru the wall 12,000 BTU A/C unit, insulated the walls and ceiling, cut 1” foam panels and glued them to the garage door, and outside, I put vinly seal stop around the garage door.

Most of the Summer I’m in the U.P., so I set the thermostat on 80 degrees and this does a great job of keeping rust away. When I’m in the shop in hot humid weather I turn the A/C down to around 75.

Today, we’re having light rain/drizzle and the outside temperature is 56. I’m running a small 1500 watt ceramic electric heater on low, and the inside temperature is 67, with a relative humidity of 64% – just about ideal.

-- "Heaven is North of the Bridge"

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