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I'm preparing to put up rhombus shaped wood siding on a shed. It's 148mm x 20mm. I'm concerned about expansion across the grain as the siding gets humid, wet, etc. What is the proper way to install this siding? If I don't leave any gap, how will it react upon expansion? Any recommendation on nails vs. screws?

rhombus shaped wood sizing

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  • Where in the world are you? In Oregon I might not leave any gap but in a desert or really hot area it might be needed. are you installing it horizontally and have a vapor barrier? (May sound silly but I have seen vertical installs I never understood. – Ed Beal Apr 4 at 16:08
  • I am in the Czech Republic, temperate. Something like the Northeastern US. I'm installing it horizontally with no vapor barrier; I plan to fasten directly to the frame. – rcampbell Apr 4 at 16:21
  • Even if it's just a shed.....I'd put a vapor barrier up. Helps keep the moisture out! – Limo DRIVER Apr 4 at 17:21
  • Do the siding boards go up flat against the studs/sheathing with only the beveled edge to direct the water out, or does the "top" board overlap the "bottom" board? – FreeMan Apr 5 at 13:20
  • The siding boards go up flat against the studs, but the rhombus shape allows the top board to overlap the board below it so what any water is directed down due to the sloping edges – rcampbell Apr 5 at 13:32
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As pointed out by the others, I think it is wise to provide vapor barrier and insulation for your region's concern. THe supplier shall have recommended the method of installation, concerning gap between boards, and naling vs screwing.

The recommendation below is directly copied from the linked article FYI use, https://www.workshopcompanion.com/KnowHow/Design/Nature_of_Wood/2_Wood_Movement/2_Wood_Movement.

"ESTIMATING WOOD MOVEMENT It’s also useful to know how much a board is likely to move. You must anticipate the movement when fitting drawers and doors, inserting panels in frames, and dozens of other operations.

The rule of thumb is that if the board shows mostly flat grain on its face, allow for 1⁄4 inch total wood movement for every 12 inches across the grain. If it shows mostly quarter grain, allow for 1⁄8 inch movement. This will accommodate an annual change of 8 percent moisture content — much more than is common in most areas.

Also consider the time of year. Wood shrinks to its smallest dimension in the winter and swells to its maximum in the summer. The wood in winter projects will expand; the wood in summer projects will contract. In the spring and fall, remember that the wood will expand half your total movement allowance and contract the other half."

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