I'm installing tongue & groove v board on the ceiling of a screened porch. I was planning on allowing 1/2" expansion between the first and last row of decking next to the wall. As I cut the boards to length, do I need to allow for expansion next to the walls? I guess the root of the question is, do boards expand and contract length wise.
Installing 1X6 tongue & groove v board...
Dec 11, 2004
6 Replies
Good question.
No, they do not.
Minimally, though I'd not butt them tight. Probably allow 1/4" gap at each end. Just cover the gaps with a molding.
Here's the first source I could find support my assertion that wood does not change in length... at least not appreciably. Over an 8 foot span, .01% is about the thickness of a playing card. And 0 to 28% MC is a monsterous change.
From this link:
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movement along the grain is almost negligible. From 0 to 28 percent moisture content, a typical board will move only 0.01 percent of its length. However it will move about 8 percent across flat grain and 4 percent across quarter grain. This is why woodworkers consider quartersawn lumber more stable. It's also why boards with mixed grain (and mixed expansion rates) tend to cup.
Cheers, Steve
I know what everyone says about expansion and all, but nailed wood does not expand like wood sitting on a pile. Once you nail that ceiling up it is not going to move any appreciable amount. Ask me how I know - that's all I have are tongue and groove ceilings in my house and it's over twenty years old. Forget about any suggestions to leave a gap at the ends - it's just not necessary. Your wood will not expand enough longitudinally to amount to spit. You're going to find that you have to back cut the groove on the last ceiling board in order to fit it up in and you'll need to cut it a couple of hairs narrow to allow for tilting it in place and that's all the space you need to provide. Think about it - every piece of wood is nailed to a rafter and locked into place with the boards on each side of it. It isn't going to be moving much at all.
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