I am going to build a pair of carriage doors for my personal shop, primarily for my own use but also as a test run for possible future work. Both of the doors will be 6' wide and 8' tall.
My default plan is to build with solid wood (likely mahogany), with beefy mortise and tenon joinery and epoxying any exposed end grain (in much the same way I would build a solid wood entry door). There will be a window. I may include a diagonal member in the design, although for style reasons I'm trying to avoid it.
That said, I'm perusing a second option, on which I'm seeking advice. The shop is heated/cooled, meaning there would be significant energy loss through the big doors if they are just solid wood. I'm looking at using honeycomb foam panels. I have no affiliation with the company - if they're crap, please let me know. Once I receive the panels, I would insert windows, attach trim to mimic a typical carriage door design, then stain/varnish or (more likely) paint.
My concerns are: (1) will expansion/contraction of 1" or less trim, affixed to a stable surface, be a problem, and (2) will the door bear up to outside exposure. The seller assures me that all will be fine, but of course he would. Any thoughts? The panels are made with lauan skins.
(Architectural Woodworking Forum)
From contributor M:
If you have a vacuum press, then you can lay up your own insulated panels. Use pink board and 1/4" ply. I make stiff shelves this way, but you could actually benefit from the insulation value.
When I built my shop over 20 years ago I made a pair of hinged 2 1/4"x4'x8' doors by gluing and nailing 1/4" lumberyard lauan to a light pine core frame infilled with blue expanded polystyrene. They are still in service, though overdue for replacement. The outer layer of veneer is missing in places, started failing five years ago over the voids in the core, and has basically weathered away in places. A few years ago I had to re-nail the skins to the frame, but these cheap, crude panels are still keeping out the weather. When the weather improves I plan to salvage the blue board and more or less copy them, using 6mm ocoume marine ply for the exterior and lauan for the interior skin, laying the sandwich up with epoxy in a vacuum press. I know it's not a perfectly balanced panel but I'm willing to experiment on my own project to save a few bucks; considering I got 20 plus years out of the last set these ones should outlast me.
I'm not sure about the Sing panels you referred to. It may be overkill for what you want to do, depends on pricing. We have built a number of doors recently with a plastic honeycomb core from Plasticore. I don't know the insulation value or cost, but that is another possibility.
I don't think you have to worry about an inch or two of edgebanding moving enough to be a problem, For joinery, we plow a groove in the edge of the panel and let in a t-shaped edgeband to get plenty of glue surface between band and skins. Usually we use this technique for doors that are getting a face veneer, thus hiding the band/core joint.
Even if this seller's lauan is closer to the original in quality, I'm still concerned about it as an exterior covering. The experiment for me is to build these doors to a top level of quality, both in appearance and longevity. I want them to be the same (or at least similar) quality as if I built from solid wood -- but with an insulating component.
I hadn't considered building my own insulated panels, but I suppose it wouldn't be too difficult. I'll need to get a bigger bag for my vacuum press! I still worry about downward sag on the side opposite the hinge. If I build the insulated panel as a torsion box, but filled with foam, would that insure that the door is completely stiff? Would it be better to incorporate some internal diagonal members into the panel?
A torsion box panel with plywood skins and a foam core, well glued with a waterproof adhesive, will be plenty stiff enough for a shop door without interior bracing. The key is that the core transmits the shear stresses to the skin adequately, and the skin is sized appropriately for the overall load. Cold molded boats are built all the time this way, and the foam doesn't have to be super strong as the stress is distributed throughout its large surface area.
I guess the construction depends on what you want the door to look like. If a simple flush panel is desired, a sound plywood face could serve economically. For a plank look, you could apply thin veneers to a torsion box core, or build a solid mortise and tenon ladder frame faced with tongue and groove planks and infilled with insulating foam. For a frame and panel look, you can do a solid frame and doubled panels with a foam core, or fake it with thin trim applied to a torsion box. There are many ways to skin this cat.
2. Why do you overshoot the finished size by 1/2" and what do you use to trim to size? Again, that's a great looking door.
Comment from contributor A:
Twenty seven years ago I built a prototype entry door for my own home in upstate NY where the winters are rough and average snowfall around 100 plus inches. It was basically a light pine frame torsion box with 1/4" oak ply in and out and infilled with high "R". I applied a 1/2" solid oak stile and rail design with various other gingerbread on the outside and a small (approx. 10" x10") 1" thick Low E Glass panel at eye level. It withstood two children, dogs, cats, and NY winters famously and is still in excellent condition and in no need of anything except perhaps refinishing, although I think it looks great as it is.