Thread: Warped custom hardwood door - Advice Request

Structural ply is not a stable platform.

You would be better off making the door as a simple ledge and brace type door.

Unfortunately, you've got three major issues.
To start with, plywood doesn't stay straight or flat.
Next, is only cladding one side. Timber will move with changes in temperature and humidity, so, if there's nothing to balance the movement on the opposite face, it will bend.
This is made worse by using brushbox, which tends to move and carry on more than it's fair share.

Having the steel on a diagonal might allow it to twist with the movement of the door, so you can try moving it so that it's vertical to get the most out of it. The amount of force that timber moves with is pretty incredible, so you might need two or three pieces. And there's no guarantee that it will work.

There's no quick and easy fix, physics is against you on this one.

I pretty much aggree with the other posts. Timber continually expands and contracts, the most of which is across it's width. What you are witnessing is the combined widths expanding at a ratio many times greater than that of your ply substrate. Because ply is an engineered board, it will never keep up with how solid timber wants to behave. If you are genuinely after a once and for all fix, you are better off starting again from scratch.

Also, if it's an attic door, I imagine you have two largely differing environmental conditions occurring on either side. This just complicates things further. For T&G boards used in this manner, you really need 1 to 2mm gap between abutting edges to allow for movement and use glues with a good amount of flexibility. All solid timber floors move too. You'll be hard pressed to find one that doesn't have visible gaps between boards. And if not, you can expect to find cupped boards from them pushing against each other in humid conditions.

Allowing for timber to do what it wants/needs to is essential to your design. Trying to restrain it will always lead to disappointment. Good luck.

Originally Posted by CMB

If you are genuinely after a once and for all fix, you are better off starting again from scratch.

Didn't want to be the one who said it, but that's the short answer.

Pao; Welcome to the forum. Just chalk this down to experience and make another door.

Yes, it happened to me with a cupboard door.
Start again.
What you do to one side do to the other, but as has being mentioned, if you are using it for an "attic" door the environment on both sides may be different and it may still warp.

Nice idea but I think it's the wrong kind of door for the application. Houses change shape with the seasons, our structural plywood has to follow. Even then, on the coldest of winter days, I have to lock my front door to keep the dang thing shut! Perfect fit in summer.

The seasonal temperature swings in my attic go from outdoor ambient in winter (-30C)
to +55 / 60C when summer outdoor is 35C. Plan on 5cm hard foam insulation sheet on the attic side (who will see it anyway?)
The nice/house side of the door has to float loose in a frame. What is that called? Rails & stiles?
Your flooring is/was probably thinner than a solid core door would be so it will react faster to changes with less mass for internal resistance.

It's too bad but you got some hard, straight advice above.