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.
When you install hardwood floors they recommend a gap all aroung the
perimeter where the wood mmets the walls. That gap is covered by
baseboard or shoemold. I do not know if C & S is correct so I am not
argueing with him/her, I am just making an observation.
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
From this link:
<snippage for brevity>
Wood 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.
Wood expands and contracts in all directions, but not nearly as much
lengthwise as it does across it's width. I'd say leave around a 1/4 gap
on each end. Unless you've got a 50' deep porch, you should be ok.
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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