Greenhouses, Sheds and Outbuildings: What to Consider Before Building

LESLIE: Tom in Washington is on the line and needs some help building a shed. Tell us what you’re working on.

TOM IN WASHINGTON: We want to add on a good-looking 8×20 unheated storage building. We plan to use cedar shingles, exterior plywood, 26-gauge metal roofing. And I had a couple of questions for you. Should I use – it’s an unheated, uninsulated shed. Should I use house wrap, like Tyvek or TYPAR or one of those?

TOM: Yeah. I think it’s not a bad idea.  House wrap will help keep the moisture out of the building.

TOM IN WASHINGTON: We also have an 8×6 greenhouse that’s going to be built on the end of it. And I wanted to ask you if it needed some air-circulation vents or any special device knowing that the greenhouse is “attached” to the unheated storage building.

TOM: Yeah, I think when you build a greenhouse you definitely need some air vents in it, if nothing else just to make it possible for you to work in that in the summer. So I would definitely plan some cross-ventilation into the greenhouse.

TOM IN WASHINGTON: And I was planning on doing ¾-inch plywood on the floor, ½-inch on the roof and wall.

TOM: Is this going to be a wood-framed floor or is it going to be a concrete slab?

TOM IN WASHINGTON: Wood framed on 2×10 joists.

TOM: I mean what kind of foundation are you going to use?

TOM IN WASHINGTON: Just a pure block concrete.

TOM: It sounds like you’re building this on a crawlspace. You’re going to put a footing down, then build up block and then put the floor structure on top of that. Is that correct?

TOM IN WASHINGTON: That’s correct.

TOM: Well, then, yeah. You can use three-quarters on the floor and ½-inch on the roof.

TOM IN WASHINGTON: And then would I do any caulking or sealing in the seams or cracks or would the house wrap just be sufficient for the moisture prevention?

TOM: Well, you just follow good building practice. You put – you’ll use the house wrap, you’ll apply the siding material and you’ll caulk around the windows and doors. Make sure you have the right kind of flashing in place to keep the water out and you’ll be good to go.

TOM IN WASHINGTON: Hey, I love your show.

TOM: Thanks, Tom. We appreciate the call. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.