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How High to keep Sheathing off of slab when attaching to Sill for shed.

How High to keep Sheathing off of slab when attaching to Sill for shed.

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Old 08-20-13, 02:37 PM
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How High to keep Sheathing off of slab when attaching to Sill for shed.

I am getting ready to start sheathing a shed. the sill is anchored to the slab and I have the feeling the OSB is not supposed to rest directly on the slab when installed. I know I should keep 1/8 inch between panels, but how high sill plate should the bottom of the sheating be?
 
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Old 08-20-13, 03:26 PM
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I'm a painter not a carpenter but I've never liked seeing wood siding come all the way down to the slab - it invites moisture damage. Where is the dirt/ground in relationship to the wall? It might be wise to install some sort of flashing to allow you to keep the OSB a little higher. The carpenters should be along shortly with more advice for you.
 
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Old 08-20-13, 03:36 PM
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When I built my shed in VA I put the sheathing at the top of the sill plate, 1 1/2" away from the concrete. I was going to use vinyl siding so the starter strip covered the gap. Might have been more than needed, but what did I (do I?) know.
 
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Old 08-20-13, 04:54 PM
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First, a building generally has a foundation and slab that are several inches above grade. 6" is about perfect. Carpenters will often stick a pair of framing nails under the sill plate, and use that to support the first sheet of sheathing, which, on an 8' wall (with precut studs) is at the proper height to get nailed to both the sill plate and the top plate.

The housewrap and siding will then generally start 3/4-1" below the sheathing. As mentioned before, this is dependent on the slab and grade being at the optimum height in relation to one another. Can't see your shed and you didn't describe the grade or the foundation or sidewalks/driveways around it at all.

Judging by your comment about sitting the sheathing on the cement, it makes me wonder if your slab extends beyond the edges of the sill plate, and is at the same level as the pad inside. If so, that's just asking for water to get inside the shed.
 
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Old 08-20-13, 06:47 PM
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This is an 8x8 shed siting on a slab that is about 8 inches thick (possibly overkill, but hasn't cracked in 13 years use by the original shed), about 4-5 inches of which are above ground level.

The sill edge is exactly even with the edge of the concrete, so my statement about it sitting on the slab earlier was incorrect, I was going from an old guys memory (mine).

So, to revise the original question, I guess I'm concerned as to whether or not the sheathing should cover any of the slab (vertically), but I'm guessing the nail trick means it should just about be even with the slab. Does that sound about right, or should it be somewhat higher?

The shed will be sided after sheathing / housewrap.
 
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Old 08-20-13, 09:10 PM
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The nail trick makes it even with the slab, which is fine. It also makes the sheets easier to align. You "can" drop the sheathing down below the sill plate if you have plenty of clearance, it just makes it harder to align. You can imagine one guy working alone, trying to get the sheets at the right height when he can't see how far down the bottom of the sheet is. Since the siding and housewrap will drop down below the sheathing, holding the sheathing down too is kind of redundant. You want the water to drip off the bottom of the siding, and not be able to wick up into the sheathing. That's the primary reason why the sheathing usually does not go lower. If you drop your sheathing down 1", now your siding should be dropped down an additional inch below the sheathing. That's 2" below the plate. Now your siding is too close to grade. Get the picture?

If you want to raise it up for some reason, you can raise it up a little, but you can't compromise the perimeter nailing pattern, since that's inspected for shear nailing. If, say, you held the sheets up 3/4" from the bottom of the top plate, your sheathing nails would no longer be going directly into the center of the sill plate, and an inspector would probably flag that.
 
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Old 08-20-13, 10:21 PM
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It is recommended to keep the sheathing, siding, trim boards, what ever, 6" off the ground. Sometime you just can't. In those case you should try to use a product that will not rot when exposed to water or cover the propuct with some sort of protection from the water. Rain will splash up that high and get to the edge of exposed sheathing even when covered by siding. You could if needed install flashing along the lower edge of the sheathing before installing the siding.
 
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Old 08-21-13, 05:45 AM
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The flashing he's referring to would be a 7/16" z-flashing, installed backwards so as to cap the bottom edge of the sheathing.
 
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Old 08-21-13, 08:41 AM
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Consider using a 6" starter board of 1/2" pvc. Home Depot sells trim boards under the Veranda name in various lengths, widths and thicknesses that are pretty cheap and great for rot & vermin resistance around the bottom of a shed (or house). Lap your sheathing over the top inch of the pvc board. I don't think flashing would be required since water won't harm the plastic.
 
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Old 08-21-13, 11:49 AM
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I think I will go with the flashing and keep the bottom otherwise even with the bottom of the Sill. Thanks for the tips.

This is the first time I've really given it much thought about protecting a shed to this level.

To make a confession, the old kit shed was 13 years old, and don't gasp....I only painted it once.

It wasn't out of laziness, it's just that I hate painting because contrary to how it seems by waiting that long, I agonize over every little mistake, and eventually to procrastination just turned to a shed that needed to be replaced. I think it's some sort of disorder
 
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Old 08-22-13, 10:41 AM
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Eh, ignore "conventional wisdom" about life expectancy of anything. I haven't painted my garage in the 20 years I've lived here. Furnace, water heater also that age. Well & septic are original--40 years. All are fine with no sign of impending failure. By "conventional wisdom" these are all starting their 3rd lifespan.
I find it's the new stuff that fails prematurely--just more reason NOT to replace anything that can be fixed or maintained.
 
 

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