I've taken a job making and installing solid wood v-groove paneling in cherry for a large room (approx 20' x 40'). The client prefers wider boards (avg. 7 in. width in random widths from 5" and up). I've purchased 5/4 stock, and re-sawn the boards to make 7/16" thick paneling. Tongue length is 3/16". I'm trying to get a handle on what I need to do to accommodate wood movement and to figure on what would be the widest board possible. The house is on the ocean front in RI, so high humidity is a factor.
Current moisture content of the boards is 7.5%. I ran an oven dry test on some samples to determine this. (Curiously, the 10" sample pieces shrank approx 3/32", which is about half what the Forest Products tables said they should). What I determine is that in an average July, the moisture content should get to be about 15% (with a possible high of 17%), which means that a 9" board will expand to about 9 5/32". There appears to be minimal potential shrinkage as the boards drop to a probable low MC of about 7%.
It would make sense that I should space the panels as I install them, perhaps as much as 1/8" (which may look bad in winter). I also should have expansion joints every so often to break up the overall runs (total expansion for the 40' wall should be about 9" or more). Any thoughts or suggestions will be appreciated. I don't have direct experience on a project this large.
(Cabinet and Millwork Installation Forum)
From contributor Y:
If you pre-stain and seal your boards before you install them that should minimize the movement somewhat and also make the spaces that open up in the winter less noticeable. Is there a way you can float each board in the field so that they can all move on their own and settle in naturally? Or are they getting nailed to the wall individually?
I made up a spreadsheet to track the movement. The overall increase from its current 8% MC to that of an average July (using RH and temp records for Newport, RI ) would take the MC to 14 3/4%, with a worst case of 17 3/8%. There's no AC in the house - windows are open in the summer. Given this, a 10" board will expand at least 3/16" and as much as 1/4". The 36' wall has a total movement of 8 to 11". Shrinkage is minimal -- 3/4" all told going down to 6% in the winter. The house is not used a lot in winter, and the temp is kept relatively low when they aren't there.
Some of this expansion will be taken up by putting a little space between the boards as I install them. All the boards will be pre-finished, front and back. I will also have several larger expansion joints every so often. I had suggested at one time of doing a variation of a "board-and-batten" look, with narrow battens between wider boards that would have a deeper groove in them so there would be no gaps at all.
The clients didn't really like the mockup I made of it, so I will have slightly thicker corner board with a 1/2" deep groove that will allow that much movement at the corners. A similar board will be at the midpoint of the wall, flanking an existing 6x6 post. Faux "keystones" will be installed above the doors and windows also with 1/2" grooves, so a 40' wall will have 5" of expansion with them. A spacing of 3/32" between boards should accommodate all the movement of an average summer, with the expansion joints taking up the extremes.
Also, whenever I use a board wider than 7", I will nail it with brads through the center face instead of the tongue and have a narrower board next to it, so there isn't more than 6" between fasteners. This should ensure that the movement will be more than the tongue and groove (3/16" ). Again, thanks for your help and interest. I'm hopeful that I've anticipated the worst problems.
Another thing, have you considered looking at some of the older houses in your area? Maybe some old Victorians that would have lots of woodwork such as you are going to be installing and looking at the way it acclimated to its home? I will say that I have put plenty of tongue and groove up where I live on Cape Cod and never had a problem with it expanding to the point where it pushed itself off the wall or buckled from the humidity in the summer.