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I'm doing a built-in for a closet. The closet is over the stairs so its front is sloped. I created an L shaped front and shelf from solid maple. The bottom foot or so is up against the wall that I can screw into. The top surface is hovering, supported by the miter (in the photo there is another shelf sitting on it).

I originally envisioned that the lower shelf would rest on the sloped wall. It currently is but that may change in the summer.

All the fronts are 1.5" thick. The shelves are 3/4" thick.

The front is mitered along its top edge and joins the shelf. I used two small pins on the very edges and just glue in between for the miter.

On the underside, I reinforced the miter (with two square 3"x3"x3/4" pieces at 90 degrees near the sides, plus a long narrower 3'x1"x3/4" piece of pine in between along most of the length of the miter, glued to the top and the front faces).

The problem I'm not sure how wood movement will affect this structure.

The main front will surely expand by at least 1/2", more than the shelf will expand inwards. This will cause the shelf to hover. With all the other stuff on top of it, I'm afraid the miter will fail.

I thought about attaching the shelf to the front face on the underside with a larger brace, corner, or even metal strip (going 45 between them). But I'm afraid due to the difference in contraction/expansion, the brace itself will force the faces into each other, breaking the miter.

I'm concerned about attached the shelf to the walls for that reason.

So my question is, is my best bet to go with the flow and just reinforce that miter say with smaller metal brackets (so there is less force from the front's expansion). That way the entire structure will rise as one.

Or should I fight the expansion? For example, I can create 45 degree blocking along the outer edges on the underside of the front. I could then screw those into the wall and screw the front panel into the blocking. That way the front panel will be attached in all four corners

I could also attach the sides that the upper shelf will rest on. If the sides are screwed into the wall, the front face will butt up against them. Would that prevent the front face from moving up? Would the wood bow or warp because the sides are being blocked but the center of the front panel if free to move up?

Additional idea I had was to actually create a 1/2 gap between the bottom part and the top part. The top part can be attached to the walls. Not sure I love this visually. Maybe there's a way to conceal the gap?

Wondering if anyone's done anything similar or has any advice.

Font view

Back view. I glued a piece of ply to the back to constrain the movement and then attached 2 more braces between the top and the ply

  • Excellently worded Question, +1. Maybe it's what you had available but this cries out to have been made from board material and not solid wood! The expected movement in solid wood (pine especially is quite a big mover) could be a problem. But as @Ashlar says in his Answer if you have aircon swings in temp and humidity will be much lower than they might be otherwise which will help a lot. Finish can help reduce the maximum expansion and contraction of wood too, what finish were you thinking of using? – Graphus supports Monica Mar 7 '18 at 13:44
  • I finished it already with water-based poly. 3-4 coats on the outer faces, 2 coats on the interior and sides. Agree about plywood. Didn't think of it until later. I didn't plan to do the lower shelf at all at first. But wife and I talked and decided it was a good idea after all. Originally I wanted this nice wooden wall with a chunky top edge with just one big basket/shelf behind it. But as it is now, there was no point to make it 1.5" thick at all since the bottom part is enclosed... – Vlad Mar 7 '18 at 14:59
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First, if the space is air conditioned, I would not worry about the expansion. The temperature/humidity change will be minimal.

The 1x3 you glued on the back side will help strengthen the miter joint. If you will have heavy loads (on a shallow shelf?) you could add another layer of 1x3 glued to the back to resist the rotation force between the shelf and front panel at the miter. It is not clear how long the shelf is but if you secure the sides to the shelf, they will be of great help in keeping the miter square. Do not secure the back of the shelf to the sloped surface, let it float.

Unless the shelf length is very long or your storing steel weights on the shelf, I would not be too concerned.

  • Thanks. The thing is we don't worry much about conditioning. We keep doors and windows open in the summer a lot and we live near a lake. One of my solid 16" cabinet doors expanded almost 1/2", while another 12" door expanded 1/8". I expect this new shelf therefore to move easily 1/2". I'll see what I can do to reinforce the miter in any case. The miter is 3' long. – Vlad Mar 7 '18 at 14:48
  • I don't have a moisture meter, but with some average values and worst case scenarios plugged into online calculators, I get expansion of up to 1". Didn't think about it before. Would've used plywood instead. Those sides on top of the shelf are ply. I ran out of wood so I stretched what I had by laminating sheets of it onto ply. Wish I'd thought of that earlier for the whole thing. – Vlad Mar 7 '18 at 14:57

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