In order to stabilize the entrance to the dome, it is necessary to create massive columns that will help hold the shape that you want and support the arch over the doorway. I came up with a double-bag arrangement as shown at right. In order to do this, I needed to completely fill the bags to the top and then sew or staple a secure hem that would contain the contents of the bag, even when tamped. The length of these very full bags would then match the width of two bags laid side-by-side. You can also see how the column bags are locked into the dome wall bags.
This is one method of anchoring the door frame to the bag column, by placing a piece of threaded rod between the bags, with chunk of wood fastened with a washer and nut at one end of it. Then the door frame can be attached to the other end and tightened against the column. Other approaches to this are to simply drive a longer piece of threaded rod all the way through the column and fastening it in a similar way...or to put a piece of plywood with lots of nails poking through it and a heftier chunk of wood attached so that this offers something to anchor the frame to later.
As the column and the wall grow taller, and the wall slants inward with its natural curve, the two elements will eventually blend into a simple shape. If you look at the picture above and then at this one, you can see that the column gets shallower as it rises.( The picture above is of the one side of a doorway and this picture is of the other side.) The height pictured here is about where the arch form will be placed to begin the arch over the door.
This detail shows how the wooden door frame is bolted to the bag column by recessing the nuts so that they will not interfere with installing the door. Once the frame is cinched up tightly, the excess threaded rod can be sawed off.
We used standard culvert couplers as window supports in Riceland. These are inexpensive and come in a variety of sizes, as shown. It is easy to set the couplers wherever you want, and just stack the bags around them. It may be necessary to brace them into place until they get locked in with the bags, but once this happens they become quite firm. They should be slanted to match the curve of the wall. Notice the blue tarp at the base of the bag wall; it is used to protect the bags from ultraviolet exposure of the sun when not working on the project. It's important to keep the bags covered because the sun does degrade them. So do be sure to put a finish stucco on when you are done.
This simple 2X6 inch (4X15 cm) door frame will accommodate a wooden door, or a steel door could be attached to it. The header across the top is a bit skimpy...a 4X6 inch (10X15 cm) piece would be better. A heftier header made of logs could support the bags above it without creating an arch form, if this is desired.
The form for the arch pictured here was made with two pieces of plywood cut to the right shape, and then 2X4's (4X10 cm's) (about the length of completely filled bags) were nailed at intervals between the plywood. This form was then set on top of the door frame. If some shims fit between the form and what it rests on, then these can be easily removed when the time comes to release the form. The form can be used over and over for any arch of this size. Note that the bag wall is covered with tarps to keep the sun off of them.
Completely full bags that have been securely hemmed at the top are used to make the arch. The bags are placed in such a way that they radiate outward, and should be tamped into place. Proceed by placing the bags symmetrically on either side of the form. When you get to the top, it is a bit tricky to get the last few bags into place; it may require some persuasion with a piece of plywood or something to get them to slip into place. Do not remove the form until the wall of the dome has completely covered it, or else you run the risk of the arch splaying out and collapsing.
Once you arrive at the level where you want the loft to be, the joists for this can be placed right on the bag wall and shimmed to be perfectly level. You can see that these are also kept evenly spaced and vertical with blocking nailed between them. I used 2X8 inch (4X20 cm) joists for this loft, but small logs could also have been used. With logs, they can be pre-drilled and pinned to the bag wall with pieces of 1/2 inch (1.3 cm) steel.