When explaining the concept of an earth sheltered house I often resort to, “Well, it’s like a hobbit house.” The arched door is a nod to the round door described in the book that provides a little whimsy without requiring any special framing or hinges. Bottle windows are often incorporated into earthen structures and I wanted to see if I could incorporate one into a door. Here’s how I did it.
First I drew the door in Sketchup and Draftsight. It’s 36 by 80 inches, the size of a standard front door. The basic structure consists of 2x4s connected via lap joints. The structure is sheathed with ¼ inch plywood and the edges trimmed with 3/4” common boards.
The window, built independently of the rest of the door, is a hexagonal frame. The bottles are the cutoff ends of wine bottles and the infill is cob.
Framing the Door
I used 2×4 stud lumber for the door framing members. Since studs have rounded edges I ripped off one side with a table saw to make a good connection with the trim. I also like to have a nice clean corner to measure off of when checking that the door framework is square.
I used a miter saw to cut the framing components to size. The critical angles for building the hexagonal archway are 15° and 30°.
To create the lap joints I used a radial arm saw to remove the excess material. As radial arm saws are fairly uncommon you can also use a handheld circular saw to make kerf cuts and then a chisel and mallet to remove the rest of the material. An orbital sander will clean up any ridges left over.
I laid out the frame excluding the arched portion on furniture clamps. Once, I was satisfied that the frame was square I applied wood glue all the surfaces of the lap joints and screwed them together.
For the diagonal brace I marked it in place and cut it to fit. Its attached to the rest of the frame with glue and pocket screws.
The lap joints and diagonal bracing are key structural components to keep the door from sagging. Note, I didn’t cut lap joints for the arched pieces as this would add complexity and they’re not structurally significant. I fastened the arch pieces together with pocket screws.
As an afterthought I added a second diagonal brace which is probably not necessary. It’s most important to have a diagonal brace running from lowest point of the hinged side to the highest point of the non-hinged side to transfer the majority of the weight of the door to the hinge.
I used ¼ inch plywood for the door sheathing. I put the frame on the sheet of plywood traced it out and then cut. It’s better to leave a little excess plywood and sand it off later. I fastened the sheathing to the frame with wood glue and finishing screws. Once I had one side sheathed I put insulation in the open cavities. I used some leftover Rockwool comfort board but you could use polyiso or some other insulation panel.
The last step to the framing was attaching trim boards around the perimeter of the door to hide the edge of the plywood. I ripped 1x common boards down to the width of the door and used a router to create a hinge mortises. I also used 1x common boards for the door jamb and routered a hinge mortise on the jamb at the same time. To make sure the trim board was tied to the door frame I put a couple of flat head structural screws under each hinge.
After staining the door I hung the door in the cottage. The bottle window is extremely heavy so its best to put it in after you have the door installed.
The Bottle Window
This part of the build largely follows the CottageOnWheels bottle window video.
I used a tile saw to cut off the bottom 1 and a half inch of each wine bottle. The door is 2 and a half inches thick and I want the bottle to have a ¼ inch reveal to catch more light. I taped the cut bottoms together using a reflective insulation board tape.
For the window frame I ripped 1x common boards down to 2 and a half inches, mitered the ends and fastened the sides together with screws and metal brackets. The frame is about half an inch smaller than the window opening in the door.
I used the hexagon piece of plywood I cut out of the door sheathing to create the form for the bottle window. I put two half inch wooden dowels through the frame to give the window more support.
For the infill I made a batch of cob using bagged clay, perlite, sand, straw and water. The perlite was to reduce some of the weight of the window. I worked the cob in between the bottles using a small trowel.
After a little over a week I felt the window was dry enough to install. I fastened trim to one side of the window frame and got some helpers together.
I was really afraid that the window would fall apart when I picked it up but it held together and felt pretty sturdy. It was fairly easily to put in the door. The back side of the window had some voids so I touched it up with some left over cob mixture.