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David Meiland

Protimeter in plywood siding?

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This house has T1-11 siding on it. It was apparently first finished with oil stain, and later washed/primed/painted with latex after mildew appeared and kept recurring. There are horizontal band boards at 8' OC, and vertical battens at 2' OC, nailed over the siding. There is no metal flashing.

What are the chances that this is an accurate reading? I'm not sure how well this tool meters plywood, and of course the finish adds more uncertainty.

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Hi David,

If that trim is just nailed onto the face and you have no way to confirm whether the joint where the plywood meets that window casing is sealed, I'd believe it.

ONE TEAM - ONE FIGHT!!!

Mike

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The owner had taken off one piece of horizontal band that was over a joint in the ply. No paint, no caulk, nothing behind. They sided and trimmed the house raw, then painted.

I checked the meter out on some lumber and plywood that's been in my shop for over a year. The lumber is in the 9% range, a piece of AC fir plywood read 10%, and a piece of shop maple ply read 13%. Someone on JLC commented that pin meters are not entirely accurate in engineered lumber (assume that includes plywood) and I think there's something to that.

When I was in the crawl space of this house, the joists and girders were around 12%, the bottom chords of the TJIs were 14-15%, so that also makes it seem like readings in engineered wood are higher than actual.

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Hi David,

Yeah, I see readings a little higher in engineered stuff but not that much higher. Did you check it at the middle of a panel away from a penetration on the non-weather side of the house?

ONE TEAM - ONE FIGHT!!!

Mike

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Hi,

Not sure what to suggest. I suppose that the stain might have permeated the wood enough to have something to do with it, but I'd be making wild guesses.

Try this, look for a similarly built house in the same neighborhood and ask the owner if you can take ten minutes to conduct an experiment. Explain that your trying to figure out a little bit of building science relative to your working environment and that you won't harm his house; then check the siding of that house to see what you find. Depending on results, I might repeat the process at a few more houses to see if it's consistent or an anomaly.

ONE TEAM - ONE FIGHT!!!

Mike

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Four shots in one area. The meter pins thru the Tyvek are into the back of the siding near grade on the north side of the house. This is the only place with the back of the siding exposed in the crawl, the rest of it is joists directly on mudsill.

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tn_2011220152217_02_19_11%20010%20RS.jpg

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Plywood holds moisture like the dickens once it gets in. Given the construction technique and the moisture range, I'd say you have a wet ply or two in the siding.

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