I am thinking of a plank style door for a Cape Cod house. I have made other exterior doors but they have been frame and panel. I am at a loss as to how to do one and to compensate for movement. The site is NE Ohio. I had the idea of a torsion box substrate but not sure. Does anyone have any thoughts?
(Architectural Woodworking Forum)
From contributor W:
Here's the solution to the exterior slab door challenge:
1. Mill the planks with thick tongue and groove edges.
2. Through-mortise all the interior planks; five mortises would be sufficient for a standard 80 door height.
3. Mortise the interior edges of the outside planks at the same heights as the interior plank mortises.
4. Mill through-tenons for a good fit.
5. Assemble the door by gluing the tenons to the outside planks only, thus allowing the interior planks to float with changes in relative humidity, while the door maintains a constant width.
6. Consider finishing the planks prior to assembly, at least in the joints, so if the interior planks shrink in width they don't expose unfinished joints.
Seal it properly with a good 2 part urethane (to keep as much moisture out), and make sure when you install the door there is sufficient space to allow for the calculated movement. You will see I did that. For example, if you use New Guinea rosewood for the doors which has a radially shrink rate % of 1.1% and a tangential shrink rate of 2%, with a door of 820mm wide, with a relative humidity of 40% rising to 80% (which is does not happen) the movement in the door dimension is from 820 to 822.69mm. For sure you can leave a gap around the door to accommodate this small movement (2.69mm). Incidentally if realistic figures are chosen: 45% to 65% humidity, the movement changes to 1.14mm.
Finally, the doors were way loose, looser than people are generally willing to accept these days. There will be a fair bit of warping and shrinking, summer to winter. I deal with this by telling the customer ahead of time, so they know what to expect. Another solution is to make a board and batten storm door, and a frame and panel entry door. The storm door can meet the customer's need for a plank type door, but the frame and panel door can close tightly, and stay flat.