It’s hard to complain about the performance of modern, pre-hung, insulated, metal exterior doors. They keep out weather like a submarine hatch but there’s a problem. Two problems, actually. First, they cost a lot. It’s not unusual to pay $1000 or more for a good prehung exterior door. And second, ready-made metal doors can be boring. This kind of dissatisfaction is why I began making high-performance exterior wooden doors back in 1990. The oldest are now in their 27th year of service as I write this, and they continue to work as well as the day I hung them. That’s one of my doors to the left. Building your own involves just moderate skills and difficulties. It’s not for a newbie woodworker, but you don’t have to be a master woodworker, either.
Four-Step Warm Door Recipe
Here’s the basic approach I use to build insulated, exterior doors:
- The outside is made of a weather-sealed exterior skin of 3/4-inch thick vertically-laid tongue and groove lumber.
- The centre part of the door is hidden, made of a 1-inch thick structural frame that surrounds an insulating foam core.
- The interior layer of the door is another 3/4-inch thick layer of tongue and groove lumber similar to the exterior face.
- The top, bottom and sides are capped with a 1-inch thick border of wood that goes around the perimeter, both for good looks and to keep rainwater out from between internal laminations.
Whether you decide to build a wooden door yourself or have a professional do the job, real wood exterior doors are practical, effective and beautiful. Here are more key details:
Step#1: Build the Inner Frame
- I recommend an inner frame made of wood that measures a full 1-inch thick. You could build the inner frame thinner, but that reduces insulation.
- Standard 5/4 decking stock, available at every building supply outlet, is ideal for the inner frame because it measures a full 1″ thick. This matches the standard thickness of rigid foam insulation you’ll install later for warmth.
- The main thing to remember about the door’s inner frame is that it must be strong. The tongue and groove indoor and outdoor layers won’t add much resistance to sagging, so rigidity depends largely on the frame.
- The easiest, super-strong way of connecting the top, bottom and sides of the inner frame is with lap joints, screwed and glued together with a weatherproof adhesive. Moisture shouldn’t ever get this far, but if it does, at least you don’t have to worry about the glue letting go. Regular carpenters glues go soft after extended contact with moisture, so you’ll need to use something else. Either type II or type III wood glue or polyurethane glue works best. Look for names like Titebond III, Weathertite or any brand of liquid polyurethane glue.
Step#2: Building the Exterior Skin
- The outdoor skin keeps driving rains out of the inner core, yet it must also be free to expand and contract seasonally with changes in humidity
- The 3/4-inch by 3-inch wide tongue and groove boards I use for this purpose does a good job, but only if the joints between neighbouring pieces are sealed with caulking during assembly. The best product for this job is polyurethane caulking. This wasn’t available when I made my first doors, but I certainly do recommend it now. It’s strong, sticks like crazy, remains flexible and takes paint. No other high performance caulking boasts all these claims.
- Choose the best tongue and groove boards for the exterior face of your door, with the knottier pieces reserved for the inside, where it’s always dry.
- While you’re building the outer door face, lay a bead of caulking down the groove of each board before nestling it with its neighbour.
- Each board should also be glued and nailed to that part of the underlying frame that it crosses, using stainless steel finishing nails driven through the tongue of each board, diagonally.
Step#3: Insulating the Foam Core
- With the outer skin complete and installed (but the interior skin still not in place), cut pieces of 1-inch thick rigid foam board to fit within the spaces of the inner frame, leaving a 1/2-inch gap all around.
- Secure the sections of foam to the back of the outer skin with glue, to keep it still in preparation for air-sealing the rigid sheets to the door frame with expanding polyurethane foam.
- Inject foam into the gaps around pieces of foam, let it harden, then use a hacksaw blade to remove the hardened squeeze out.
Step#4: Building the Exterior Skin and Perimeter Frame
- This step is just like applying the exterior skin, but easier. Use polyurethane caulking between each piece of tongue and groove wood, but the odd cracked knot is okay on the inside.
- Complete the door by adding a cap of wood around the entire perimeter of the door. You can see this cap in the photo above. It hides the edges of the frame, interior and exterior layers.
If you count your time (or pay for someone else’s), building a wooden warm door probably comes out more expensive than a ready-hung metal one. That’s why there’s a place for easy-install, ready-hung doors of all kinds. And though I’m glad they’re there, I’m also glad there’s an opportunity to exercise the craftsmanship that adds a little variety and creativity to the world. And talking about creativity, consider adding carvings to your door. This is a topic in itself, but here’s a glimpse of what carved door details look like up close.