Airtight, non climate controlled barn; how to manage moisture?
Hi folks. I am getting ready to clear a spot for a small barn / detached garage that I am going to build. The enclosed part of the structure will be an 18×24 stick built / sheathed structure built on a monolithic slab. For pest and insect control I see value in building a tight structure but since this building will not have climate control or electricity, I have no active way to dry it out.
i am curious if it is a good idea to build an airtight structure without AC, ventilation, or dehumidification. Perhaps passive venting with screens covering “makeup air” penetrations around the base venting to a ridge vent would be sufficient to keep out mice but still let in air and bugs?
any thought on how to build a tight structure that won’t have any utilities to help it dry?
thanks!
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Replies
If you have no power source available, then your only options will be passive systems. I would put a cupola at the ridge to provide some exhaust venting, and either screened windows or doors down low (or just some intake vents if screened windows/doors aren't an option). Put a damper in the cupola that you can control from the ground with a rope. With the vents all open, stack effect will provide ventilation for you with no need for an outside power source to run fans. That's likely to be the best you can do if you don't have power available to run a dehumidifier or at least a fan.
Bill
I think it would be a mistake to build it tight.
I like Bills idea put a vent up high and screened vents down low and the building will last a long time.
I am looking across the lake at a barn from the 1890s. They made the roof water proof but nothing else. The idea is water will get in but it can quickly dry out before it becomes a problem.
Walta
That is what I am thinking too. The only reason I was going to sheathe the walls was for shear / racking resistance. I could probably address that in a different way then just use lap siding directly on the studs which will breathe plenty. If I go that route I’ll just have to spray for bugs
If you want to keep the bugs out wrap the building with window screen and cover the screen with your siding should add about .70 per square foot of wall.
Walta
Fiberglass screen is cheap and effective here. If you want to add screening to your walls, that's what I'd use. Tack it up first with some staples, then run your sheathing right over the top of it. If you need to seal any gaps, embed the screeing in a bead of polyurethane sealant prior to sandwiching the less-than-tight-fitting thing on top. Easy.
Bill
Screen and siding won't keep critters out. The nice thing about an air tight building shell is there are no air leak paths critters can follow to get inside. Also if you have sheathing and WRB up, you can always insulate and finish the place if you ever want to down the road.
An interesting design that was posted here for a smaller storage shed is to use a diffusion vent at the ridge. The idea is as the sun hits the ridge cap, it heats up the diffusion vent. This now works almost like a desiccant to suck moisture out of the building. Not sure how well it will work with something large, but it definitely won't hurt to install it.
Also think about how to limit moisture in your building, ie sub slab poly is a must.
I am not familiar with a diffusion vent but I will check it out. I also like the idea of building in a way that I could climate control later although this building is pretty much always going to be for small scale farming support.