Building Insulated-Core Carriage Doors

Detailed instruction on how to construct a custom architectural wood door with an insulating foam core. April 4, 2011

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.

Forum Responses
(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.

From contributor K:
It's my understanding that lauan is a trade term covering 40 or more species imported from the Phillipines region. Some are more rot resistant than others. I think Meranti is supposed to be one of the better ones.

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.

From the original questioner:
"Real lauan" was the seller's term not mine, but I understood him to be referring to the decline in quality of the product. Twenty years ago, lauan plywood was a usable product made from lauan aka "phillipine mahogany." I believe the species is actually closer to pine than mahogany, but it had similar coloration to mahogany and I suppose "phillipine pine" isn't quite as catchy. Nowadays, lauan or "Luan," as sold at home centers, is produced in China from just about anything and will disintegrate if you stare at it really hard.

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?

From contributor K:
For a top level of quality I would not recommend a lauan ply face. I did it originally as a cheap expedient, and 20 plus years of service bears that out. I hope to get more than 20 years of service out of a marine ply face, and I am willing to go with a lauan interior because I am still a day late and a dollar short. I believe a well maintained marine ply grade of panel should last indefinitely, and by well maintained I mean a continuous coat of finish and detailing of construction and installation to keep moisture out of the core. I know I won't keep the finish up, but I will work on the other aspects.

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.

From the original questioner:
20 years of service is nothing to sneeze at! I may relent and go solid wood construction, but as of now I'm intrigued enough by the insulated panels to try it out.

From contributor K:
I build Carriagehouse doors for a living. If you want insulation with a carriage look, build a frame for each slab with 1" true stock, I like 5/4" soft maple for frames, Sapele for facing. Join it together with cope and stick joinery, good glue and a few fasteners. Skin one side with 1/4" Luan, then place tightly cut 1" insulation blue board or whatever you can like. Then face the sections first with the center stiles rabbeted together (lapped) have a 1/2" deep x panel thickness rabbet on each side, also install the, top, window and bottom rails (don't rabbet the bottom rail, ripp at 12.5 degrees, bottom cut all panel material at the same angle to stop water infiltration). Take this opportunity to plug the screw holes and sand them down fairly well. Now you're ready for your panels or tongue and groove. Install them, leave 1/8" for movement, and be sure to put "nailers" in there to keep it strong. Use glue but don't get it on the insulation board. Place the two side stiles, screw, plug, sand, size, and ease edges. Be sure to rough build the door 1/2" over your finished size. If you want, email me and I'll get a couple of drawings to you. 6'/0" x 8'/0" is the widest I've ever built. Also, this door set should take you two days to build plus finish (I'm lousy at finishing, I sub it out). Below is a picture of a door I built about five years ago. It is a layered door built exactly like I posted, except I mixed panel types. It's an overhead door, 8/0 x 8/0.

From the original questioner:
That's a beautiful door - just what I'm looking to do. A few questions:
1. You lost me on the "nailers" reference. Are you talking about shooting some finish nails at the edges of the panel to better secure it to the rails and stiles? Or adding some backing behind the face to have something to nail the tongue and groove to?

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.

From contributor K:
I'm a dummy when it comes to making a PDF of a drawing, I just don't know how, I think I need a scanner. So I'll try to explain instead. A nailer is an additional horizontal member that goes across the panel area inside the frame, it provides a place to fasten the panels or tongue and groove and it gives great rigidity to the slab. If your panel area is 52" high, then put two pieces in equidistant (2 at 3" spaced at 21") also, for a door that's 72" wide I'd be sure to put an diagonal piece from corner to corner, lap joined to everything else. 72" is pushing the envelope for layered doors, 5' would be safer and easier for hinging. However, if you need 6', then be sure to use a good hinge setup. Full mortise hinge are what I use for the majority of the large doors I do. They run about $100.00 each and are worth every penny. You'll find them at a commercial or architectural hardware supply house. I think that it's an Assa Abloy product (Emtek). These hinges are rated for 600 lbs (no sagging). Also, I build the doors 1/2" larger so that I have control of finished size. Clamps leave compression marks, edges get dinged, stuff happens. Never build a large door at the finished size - you'll kick yourself.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

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.