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Acceptable moisture content levels in wood tongue-and-groove boards?

cabinflyer | Posted in General Questions on

To all,

Searching this site and the web. Surprisingly, I could find very little on what is an acceptable level of moisture in wood V groove T&G 1×6″ paneling. FYI the wood species is Red Pine (Norway Pine)

The ceiling areas the wood will be placed has a 1 1/2″ space behind it and the air barrier.

I have found some wood at 1/3 the price of kiln dried, and in the lengths I need. However, the wood was air dried, and currently is showing 10-12% moisture content. I think kiln dried is about half that.

The wood I found is of high quality. I have purchased wood from this supplier for a log home in the past, and have been very pleased. The current project unlike the log home is very airtight and energy efficient.



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  1. GBA Editor
    Martin Holladay | | #1

    The table below comes from this resource: National Wood Flooring Association Installation Guidelines.

    A lot of sources tell installers to aim for 7% to 8% moisture content, but the answer depends to some extent on geographical location and climate. Indoor RH levels in winter are lower in very cold climates than in more mild climates.

    I've never seen softwood tongue-and-groove boards buckle after installation; in general, installing dry is better than installing damp. (When installed during hot, humid weather, softwood boards are likely to shrink the following winter.)

    The traditional advice is to stack the boards carefully indoors, with stickers between each layer of boards and gaps between the boards for air circulation, and leave the central heating at 70 degrees F. If the boards spend a couple of weeks this way, you should be good.

    Using a moisture meter can be tricky. You might want to read this article: Avoid These Mistakes When Moisture Testing Wood Floors.


  2. Expert Member
    Michael Maines | | #2

    I've installed pine floors that were drier than they should have been, and crushed the edges when they expanded. I've also installed a cherry floor that was too dry and buckled when the relative humidity rose. Many T+G installations show gaps when they shrink. So I think there is reason to be concerned. As Martin says, it depends to some degree on your situation. V-match helps hide some movement.

    In my location, Maine, we have possibly the highest humidity swings in the country, so equilibrium wood moisture content (MC) in winter is about 6% and in summer it's 14%. On the coast it's a bit more humid. Ideal MC depends on the time of year, the installation location, species of wood, size of wood members, expansion coefficient of the wood (how much does it move with changes in moisture, depending on species and grain orientation), what stage the building is at (new and still releasing construction moisture, or old?), etc..

    If you're interested in "going deep," this book covers the subject:

  3. Expert Member


    Following the table in Martin's response is the way to go. Acclimatizing wood to the conditions present during installation is a hit or miss approach.

  4. Rob Myers | | #4

    All of the above is good advice but the amount of movement for air dried wood may be acceptable for a ceiling. Assuming worst case (tangential shrinkage, flatsawn wood, no acclimatization) the change in dimension for a 1x6 Red Pine board going from 12% to 6% moisture would be about 3/32 inch (and according to the chart provided by Martin the equilibrium MC is probably higher than 6%). In my house I used acclimatized air dried white pine in my ceiling with no issues (in fact I think there would probably be more issues with kiln dried).
    I always prefinish the boards (if there is shrinkage the newly exposed surface on the tongue shows less) and I leave a small gap at the edge of the ceiling to allow for any movement.

  5. cabinflyer | | #5

    Thanks for the responses so far. Just to clarify the 1x6 T&G will not be for flooring, but for walls and ceiling.


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