Plank Style Entry Door

      Advice on managing wood movement in a solid wood plank entry door. May 20, 2006

Question
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?

Forum Responses
(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.



From contributor C:
I have been down this road the whole year and listened to all sorts of advice on timber movement etc. Then I found the information below. Firstly, select the right timber, make sure it is all at a similar moisture level, tongue and groove or mortice and tenon the whole lot together if you care to and like me don’t trust adhesives that much.

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.



From contributor S:
The other way is to use a ledged and braced design, allowing the individual boards sufficient movement tolerance on the tongues. This way, the overall size of the door changes only very slightly between winter and summer, whereas a door made of all the boards glued together will change in width by 1% for every 3% MC change.


From contributor J:
The old doors like this in Massachusetts were made with a 7/8" thick frame and panel door clinch nailed to three 7/8" boards. Wood movement was lessened by using old heart wood, no sap wood, Eastern white pine, making the doors narrower than today's 36", and coating it real well with paint, edges and faces.

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.



From contributor G:
I would recommend looking into splines for this type of door. Almost all doors need some type of frame, either hidden or exposed. The choice of lumber would be very important however.



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