Roof for Garage-Nursery

Earthworm Jim · 04-30-2010, 09:46 PM

Hi All,

I plan on converting a spare garage into a plant nursery, and, the construction of the garage is wood. There are wooden beams which support the triangular frame of the roof running about 8 feet from the ground, I guess what you'd call the base of the triangle, and, I thought I'd make another roof which would protect these beams from the humidity which the garage will become saturated with, hopefully protecting the beams from woodrot and extending their lifespan. What would be a good way to do this? I know nothing about home improvement, I thought, maybe, take sheets of some substance... drywall? Foam sheeting? I don't know. Take sheets of some unknown substance, something that protects very well against moisture, and then nail them into the wood beams, until a new roof was formed.

I'm sure there would be a better way to do this, help is appreciated!

Thanks,

Jim

AaronB · 04-30-2010, 10:44 PM

Closed cell spray foam insulation.

Earthworm Jim · 05-01-2010, 01:22 PM

Thanks for the response. I wonder if this would be a good choice of material to create a barrier for the walls, too, which also have wooden beams exposed?

Do you think that, if I coated the inside of the bare structure with a few coats of waterproof paint, then, added the foam insulation, then, sprayed that with a couple coats of paint, it would keep the wood safe for several years? I was also then thinking, that I'd add an extra barrier, layering the foam insulation with clear 3 mil plastic sheeting... do you think that, with all these extra layers of protection, there would be a problem with condensation building up in between, cancelling out the purpose of being water/ mold proof?

Thanks,

Jim

AaronB · 05-01-2010, 03:06 PM

Once you spray 2" of foam, you will not need another moisture barrier to protect the wood from the inside.

To leave it like this, the structure must not be inhabited nor attached to an inhabited structure. If it is either if these scenarios, then you need a fire barrier.

You should, however have a way of extracting the moisture from the building when needed. like a powered exhaust fan.

**Gary in WA** · 05-01-2010, 07:03 PM

I agree with Aaron except SPF, at 2" has a permeability rating of .75. To be a vapor barrier, Class I, it would need to be 8" thick (.094). But you could use a v.b. paint to stop the moisture. http://www.henry.com/fileadmin/pdf/H...l_Brochure.pdf

Be safe, Gary

Earthworm Jim · 05-01-2010, 10:18 PM

Sorry, what's v.b. paint? What does the v.b. stand for? You think if I applied this after the 2" of foam were applied, it would be roughly as effective as 8", since I'm sure spraying 8" would be significantly more expensive? Would it be worth it to spray paint, then have foam sprayed, then spray another layer of paint on the foam?

Thanks,

Jim

AaronB · 05-01-2010, 11:37 PM

A vapor barrier is anything less than 1 perm. .75 is less than one. The smaller the number with water vapor transmission, the better.

meboatermike · 05-01-2010, 11:55 PM

v.b. paint is vapor barrier paint -- it is manufactured by a few different companies and I believe comes in different perm ratings. Perm ratings being the ability water vapor to pass through a materiel. It should have a perm rating of less than 1.0

AaronB · 05-02-2010, 12:02 AM

I feel obliged to add that GBR was correct. I do not believe that a perm rating that low would be needed unless you are running a sauna in Antarctica though, or an ice house in Ecuador.

AaronB · 05-02-2010, 12:07 AM

One more thing... you should be just fine as far as vapor transmission and temperature control with 2-3 inches of closed cell spray foam alone on the walls and ceiling/roof. No additional coatings would be needed nor additionally beneficial.