I'm planning a small (~8"x12") "bumpout" off my garage. It will be built on an existing concrete slab. I don't want any of the wood to be in ground contact because the drainage isn't great in that area. I'm looking for ways to get the framing up off the concrete to prevent "wicking" of moisture. For example, I guess I could lay one course of block but it would be overkill. Any suggestions?
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Shed Base Question
- Thread starter cjer
- Start date
mmhouse
Well-known member
If it's just wicking of moisture from the slab you're worried about lay a row of asphalt shingles down on the slab (mineral side down) and put the bottom sill plate on them. When done, trim the shingles away from the edges of the sill plate. This should prevent any wicking. If you don't have shingles lying around you could also use 50# rolled roofing with no mineral surfacing (or something similar).
Last edited:
84scrambler
Well-known member
Depending on how high you can go you can either use those pre-manufactured concrete blocks that have slots on top for wood or simply build your shed on pressure treated 4x4's or something equivalent (skid type design) and place them on the 12"x6"x1" concrete block.
bazzateer
Well-known member
8" x 12" ?? Is it worth it for that small a space?
Or did you mean 8' x 12' ?
Or did you mean 8' x 12' ?
nate379
Banned
PT wood for your bottom plate and there is a foam strip that gets used, made just for framing in concrete, sorry I don't know what it's called.
What some guys will do is put PT down and then build a reg wall with a bottom plate. Then when you put your drywall up inside, you can keep it off the floor 1" or so and still have something to screw the bottom to.
What some guys will do is put PT down and then build a reg wall with a bottom plate. Then when you put your drywall up inside, you can keep it off the floor 1" or so and still have something to screw the bottom to.
Nate is talking about sill seal.
I'd take a look at how close the wall will be to the ground before making a decision. Remember when it rains, what might splash up. Not sure what you are using for an exterior.
I'd take a look at how close the wall will be to the ground before making a decision. Remember when it rains, what might splash up. Not sure what you are using for an exterior.
Recommendations:
Anywhere the wood contacts concrete use PT (pressure treated) wood. This would include either on the slab / CMU block course or against the garage block wall.
Ideally, wood should have a minimum 6" separation from grade . . that is, any horizontal exterior surface. So that means either dirt, gravel, or concrete. This is to keep water from splashing up on the wood wall when it rains.
Were it my project, I'd run a course of 8" tall CMU blocks around the perimeter of the slab. Holes would be drilled into the concrete slab with some pins (rebar cut to short lengths, threaded rod, bolts, etc) epoxied in place. Actually, bolts with the hex head point up would be good. Then set down the course of CMU blocks and pack the hollow cores with grout, setting anchor bolts into the wet grout to hold on your PT sill plate on top of the block course. The grout will cure around the head of the bolt "pins" and lock the block course in place. Put the sill sealer between the PT sill plate and the grout-packed CMU course.
This would give you a solid anchoring method into the concrete slab and get your wood up off the ground sufficiently for a good long life.
For anchoring the PT wall studs to the existing garage block wall, I'd use the sill sealer there, too. And some kind of concrete anchor / fastener to attached the studs to the block wall.
Anywhere the wood contacts concrete use PT (pressure treated) wood. This would include either on the slab / CMU block course or against the garage block wall.
Ideally, wood should have a minimum 6" separation from grade . . that is, any horizontal exterior surface. So that means either dirt, gravel, or concrete. This is to keep water from splashing up on the wood wall when it rains.
Were it my project, I'd run a course of 8" tall CMU blocks around the perimeter of the slab. Holes would be drilled into the concrete slab with some pins (rebar cut to short lengths, threaded rod, bolts, etc) epoxied in place. Actually, bolts with the hex head point up would be good. Then set down the course of CMU blocks and pack the hollow cores with grout, setting anchor bolts into the wet grout to hold on your PT sill plate on top of the block course. The grout will cure around the head of the bolt "pins" and lock the block course in place. Put the sill sealer between the PT sill plate and the grout-packed CMU course.
This would give you a solid anchoring method into the concrete slab and get your wood up off the ground sufficiently for a good long life.
For anchoring the PT wall studs to the existing garage block wall, I'd use the sill sealer there, too. And some kind of concrete anchor / fastener to attached the studs to the block wall.