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Community and Q&A

What is your opinion on covering open framing prior to rain?

GBA Editor | Posted in General Questions on

Year after year I find myself in the situation of being mid-framing and having multiple rain storms come through. I tend to cover up PSLs, LVLs, and other engineered lumber. I also try to cover as much of the frame as possible. I often see other builders in the same boat not do anything about the rain and let it dump on their open frame, which makes me question why I throw away profit margins on labor and a huge waste of plastic. How would you handle a rain storm on an open framing project as it applies to moisture content of the wood, dry time, mold issues, and engineered lumber?


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  1. Robert Riversong | | #1

    Most engineered lumber uses glues that are designed to allow short-term wetting, such as with CDX plywood (OSB is more vulnerable and will not return to its original thickness after swelling).

    KD lumber comes damp from the lumberyard (19% MC at the time of milling, possibly higher from yard exposure), and occassional wetting is not going to change its equilibrium moisture content. A new house generally requires a full year to fully dry to equilibrium conditions.

    I build mostly with green lumber, dripping wet off the saw mill, and leave it exposed to rain, sun and wind until the frame is closed in. It tends to dry to less than KD levels after a couple months of exposure. It certainly doesn't get wetter and I've never had a mold problem (I insulate, however, with cellulose which has borate mold inhibitors).

    You may be putting more effort into weather protection than is warranted.

  2. GBA Editor
    Martin Holladay | | #2

    I agree with Robert. As long as people have been building houses, framing lumber has been getting wet until the house is "dried in." That's normal. Of course, you still have to follow common sense guidelines and code, including obvious points like no electrical wiring work until the house is dried in.

    The one exception has always been OSB subfloors. Once they swell, the only solution is to get out a belt sander and knock down the edges. Advantech OSB has solved that problem. (Some builders, of course, never experienced the problem, because they stuck with board subfloors or plywood and never switched to OSB.)

  3. Derek Vander Hoop | | #3

    Of greater concern than edge-swelling is whole sheet swelling. That is something you cannot sand out. Here is the midwest, all builders of large homes have experienced weeks during framing where it seems to rain every day-and-a-half. With walls erected but no roof on, rain has no where to go and thus, lays on the deck for days on end. Back when we used to use OSB as a subfloor, builders had issues with OSB swelling to such an extent that the nail holding ability of the OSB was compromised. Wood floors laid on top of the OSB squeaked, something not easily remedied. Our approach back in the day was to use OSB under carpeted areas, and plywood under wood floors. But then we had issues with the plywood delaminating! Martin mentioned Advantech, which in my opinion, is the best product out there. Unfortunately, it is very expensive. Structurewood performs almost as well at almost half the cost. Unless you live in an area of the country where it doesn't rain, it doesn't make sense to use OSB as a subfloor.

    We don't cover our erected walls and floors, as they will dry off quickly in the open air. We do, however, cover our delivered piles of lumber. Stacked tightly, rain water quickly penetrates the stack, and doesn't dry out quickly. Our lumber companies here in the Milwaukee area are glad to provide the plastic sheets that wrap their lumber as it comes from the mill, if a builder asks for it. That's the easy part. The hard part is getting the carpenter to cover the stack at the end of the workday, day after day!

  4. Robert Riversong | | #4

    "The hard part is getting the carpenter to cover the stack at the end of the workday, day after day!"

    Ain't hard if the "builder" is the carpenter. I still have trouble with anyone calling themselves a "builder" if they don't build the house.

  5. Derek Vander Hoop | | #5

    "Ain't hard if the "builder" is the carpenter. I still have trouble with anyone calling themselves a "builder" if they don't build the house."

    Yes, I know what you mean. Carpenter/Builders were much more common years ago, and the ones that are still around today that "get it" bring a lot of value to the homeowner and to the home. That you cover your lumber and are concerned with excessive moisture indicates to me that you "get it."

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