Allowing for Shrinkage and Swelling

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Forum topic by HorizontalMike posted 06-28-2013 09:58 PM 696 views 0 times favorited 2 replies Add to Favorites Watch
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7770 posts in 3111 days

06-28-2013 09:58 PM

Topic tags/keywords: shrinkage swelling species allowing for

OK, we all know this happens and that we should always allow for this to happen in our projects.

BUT how much:
  • per inch of width?
  • per Species of wood?
  • in the deep South?... of far North?

All of the literature says to allow for this, but I am lost as to finding any reference source that tells me that a 9in(or 4in, etc) wide pine board will need xxx fraction of an inch of space for expansion/contraction.

Help me out folks, is there a source I am missing, you know… that one source that eludes me?

-- HorizontalMike -- "Woodpeckers understand..."

2 replies so far

View GrandpaLen's profile


1651 posts in 2470 days

#1 posted 06-29-2013 07:11 PM


I don’t have a chart with an easy answer to your question but, I down loaded this from Oklahoma Cooperative Extension Service, a while back when I was trying to find the answer to the same question you have.

Dimensional Changes in Wood

It is based on the average relative humidity in the environment that houses the wooden item.
This is an explanation of the formula to closely figure the shrinkage and swelling of the wood Species as the % of humidity increases and decreases.

Like you, I never found a ‘quick reference Chart’ that gave the +/- movement to allow for when milling.

...not quick calculations but it’s all I have to offer.

Best Regards. – Grandpa Len.

-- Mother Nature should be proud of what you've done with her tree. - Len ...just north of a stone's throw from the oHIo, river that is, in So. Indiana.

View HorizontalMike's profile


7770 posts in 3111 days

#2 posted 06-29-2013 10:16 PM

Saved, Thanks.

-- HorizontalMike -- "Woodpeckers understand..."

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