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Moisture where Deck connects to home


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I am planning on installing ?? hardwood floors in my single level home with basement. The hardwoods will be installed above the basement level. As part of my preparations I have been taking moisture readings. The moisture content of the 1/2" plywood subfloor is mostly 8%. However along a certain exterior wall I have had readings much higher 13-18%. The partcleboard I removed along these exterior walls was not wet. Just outside this specific wall a deck ties into the house. Please see the attached sketch.

Note the floor joist run continuously from inside the basement to outside underneath the deck. The exterior edge of the subfloor is exposed to the outside.

What would you do reduce the moisture seen inside the house?

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I am planning on installing ?? hardwood floors in my single level home with basement. The hardwoods will be installed above the basement level. As part of my preparations I have been taking moisture readings. The moisture content of the 1/2" plywood subfloor is mostly 8%. However along a certain exterior wall I have had readings much higher 13-18%. The partcleboard I removed along these exterior walls was not wet. Just outside this specific wall a deck ties into the house. Please see the attached sketch.

Note the floor joist run continuously from inside the basement to outside underneath the deck. The exterior edge of the subfloor is exposed to the outside.

What would you do reduce the moisture seen inside the house?

Well the sketch didn't make it?. How about a few pictures of the area.

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From what I'm seeing, there's no flashing or water management details anywhere....not on the deck, the window, the sills, the rim joist/subfloor....nothing.

My WAG is the lack of flashing anywhere is allowing incidental amounts of water, in multiple locations, to enter the walls. The water dissipates out into adjacent materials creating the readings you're getting, which aren't all that bad, not bad enough to make stuff look or feel wet, but they're enough to give you elevated moisture levels and enough to mess up a wood floor.

The readings don't provide a smoking gun to a single source; they're like what I find in simple boxes lacking flashing anywhere.

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The deck members should be flashed where they connect to the house to keep moisture out. If the floor joists are the same members as the deck joist then there is no way you can do that properly. In your case the joists are conduits that bring outdoor moisture into the house.

I'm not saying you can't install your hardwood floor, just that there isn't much you can do to lower the moisture levels in that area, short of rebuilding the junction between house and deck.

What Kurt said.

Marc

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I've repaired lots of situations like that where the floor joists are cantilevered out of the house to become deck joists. There's almost never any flashing over the joists, and when there is, it's a piece of 1-1/2" x 1-1/2" 26-gage angle nailed to the wall above the joists, with one leg sitting on top of them. Woefully inadequate, and in any case, you probably don't even have that. When I've had to build cantilevers like that, I've had a sheet metal shop make individual flashings for each joist, with flanges on the wall and hoods protecting the top and sides of the joist.

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I would treat the area as if there is a moisture problem (there is) and use an appropriate vapor barrier under the flooring. There may not be enough moisture to cause a problem with the framing lumber, etc. but a real hardwood floor is much more moisture sensitive. Take precautions.

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Same here. We call them horse collars. Is that name used in other areas?

Saddles here. We make them oversized and do a backer rod/sealant joint between the flashing and the joist.

Why are so many building accessories named after horse stuff?

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Same here. We call them horse collars. Is that name used in other areas?

Saddles here. We make them oversized and do a backer rod/sealant joint between the flashing and the joist.

Why are so many building accessories named after horse stuff?

Cowboys with hammers? [:)]
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Horse stuff was everywhere about 100 years ago when we just about all got our construction stuff together :-) My Daddy was born in 1908. The first vehicles he remembered seeing were horse drawn wagons. Thus it had been for almost forever. Trucks were the first engine powered vehicles he remembered. They had obvious commercial value. Horse drawn vehicles were still around (for produce sales and junk collecting) into the early 1960s in my own experiences. We forget how central everything 'horse' once was to our society.

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