Lowering costs is a major goal of earthbag building. One way to reduce costs is by using wood poles for lofts, roofs and other parts of the house. The poles are practically free if you obtain a firewood permit from the US Forest Service. There may be similar programs in other countries. This is a good way to obtain dirt cheap building materials, plus you’re helping improve the health of the forest and reducing risk of forest fires by thinning out smaller trees. (In recent years, wildfires have burned up to 9 million acres (3.6 million hectares) of land in the US.)
Okay, so you’ve obtained good, straight poles that are a little longer than needed, painted the log ends to reduce cracking, removed the bark and dried them under cover for about one year. You might even be fortunate to find standing dead trees that are ready to build with. Now you’re ready to start building your loft when the earthbag walls are at loft height (usually around 8’ high). First, set the beam in place with the crown upwards. Mark the beam and cut to final length. It’s a good idea to apply a tar product on the log ends so it will not absorb moisture. On domes, the beam will usually sit directly on the earthbags and extend almost to the outer edge of the earthbags. Drill a hole in each end of the beam for ½” rebar with holes aligned so the rebar goes into the center of the earthbags. Cut and pound in 24”-30” rebar pins to secure the beam in place. If the beam sits on a bond beam, then you’ll probably have to remove some wood on the bottom so it sits flat and level on the concrete. And, you’ll have to plan ahead and embed anchors in the bond beam for the beam and loft poles.
With the beam in place, now you’re ready to set the loft poles. Probably the easiest way to cope the ends of the logs to fit the beam (see drawing) is with an electric chainsaw. Gas powered chainsaws are preferred for cutting lots of wood. Electric chainsaws are good for smaller jobs on a construction site such as notching or coping wood. (Hand tools work too, of course, but it will take much longer.) In comparison to gas powered chainsaws, electric chainsaws are less expensive, much quieter, don’t create clouds of noxious smoke, don’t require fueling and, if there’s a cord handy, they’re ready to use almost instantly. You could probably buy a used electric chainsaw and resell it at the end of your project for about the same as you paid.
Here’s how I would cope the log ends to fit the beam. First, I would make a partial notch so you can get the pole in close contact to the beam. Use a compass to trace the beam curvature onto the pole, being careful to keep the compass horizontal the whole time. Mark both sides in the same way. Darken the line with a felt tip marker so it’s easier to see. Now move the pole aside so you can make numerous parallel kerf cuts about ¼”- 3/8” apart into the end grain with the electric chainsaw. Be careful not to cut past the line. Use a hammer to knock out the kerfed wood then use the lower edge of the tip of the chainsaw blade to ‘sweep’ (move side to side) the joint smooth. Make the interior of the joint slightly concave so you get a tighter fit. Test the fit by sliding the pole into position. Trim some more if necessary. You could use a wood chisel at this point for a more precise fit. Next, cut the pole to length, coat the end and insert the rebar pin in the joint for extra bearing strength. Toenail a few nails or screws to secure the joint. Then add a rebar pin to secure the other end to the earthbag wall (or use an anchor in the bond beam).
Repeat the process for the other poles, always checking for level and keeping the crown up. Trim the top of the poles if necessary so the tongue and groove decking sits flat. Install the decking with small head deck screws. Start at the leading edge above the beam and work toward the walls. You may need to shim some low places.
Photo source: Kelly Hart of GreenHomeBuilding.com fame