Small Diameter Roundwood Trusses

Reader Contribution by Staff
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There is a glut of small diameter wood in many parts of the United States, both in national forests and tree farms. This resource is often wasted as it becomes fuel in massive forest fires. On tree farms, where it barely pays the bills, small diameter wood is sold cheaply to make paper. Instead of sending this wood to pulp mills, it could be used to create higher value building materials, including roundwood trusses.

The roundwood truss system described here enables DIYers to build their own trusses at very low cost. Virtually any truss configuration is possible, although roundwood is best suited to simpler designs such as: queen and king post, Fink, Howe, scissor, clerestory, parallel chord, sloping top chord, attic truss (for lofts and second story plans), asymmetric, gambrel and gable end trusses. You can download truss charts off the Internet and use them as guidelines.

Why are trusses so popular? Trusses are prefabricated so they’re ready to install when the walls are finished. This is important for drying in the structure as quickly as possible. Trusses are very strong, efficient and relatively lightweight. They use shorter pieces of wood joined together instead of large dimension lumber. Trusses span longer distances and eliminate the need for center walls or supports.

The downside is factory made trusses use milled wood such as 2x4s to speed construction, but this wood is usually not sustainably harvested and it’s shipped long distances. Both of these practices harm the environment.

Wood in the round is inherently stronger than milled wood and can often be obtained locally at very low cost. The only milling required is where truss members intersect at joints. Coping the end joints will create stronger trusses. You can also flatten the areas around joints on both sides where gussets are attached. You might also want to cut (rip) straight edges on the tops and bottoms of trusses for ease of attaching roofing and ceiling materials, although this isn’t required if you want a rustic look.

If you want straight edges on the tops and bottoms of trusses, crown the poles, snap chalk lines and cut edges with a power saw (Skilsaw, etc.). Use the straightest poles you can find so you don’t remove too much material. A typical 20-foot truss made with 4- to 5-inch diameter poles should have about 4 inches of wood remaining after the rip cut.

Other important points:

  • choose suitable wood: straight, uniform diameter poles of pine or fir work well
  • avoid leaning trees because they will bow and twist badly (“reaction wood”)
  • cut poles about 12 inches longer than needed so you can remove cracked ends later
  • paint the ends of poles immediately after cutting to reduce cracking
  • peel wood poles to deter insect infestation
  • keep wood under cover until ready to use
  • use a homemade jig so all trusses are uniform in size and shape
  • we used stakes in the ground as our jig to demonstrate one low-tech alternative, but working on benches or sawhorses at waist height would definitely be easier commercial shops press gusset plates on; DIYers can use the same gusset plates nailed or screwed on, nailing plates or scrap 16 gauge galvanized metal. I prefer sturdy zinc coated screws or deck screws instead of nails.
  • cope end joints with a coping saw, saber saw or sawzall. We improvised with a handsaw and cut V-notches for satisfactory results.
  • toenail joints when practical to hold pieces in place
  • protect from rain and freezing as much as possible
  • avoid twisting or dropping trusses

Is it worth the extra time and effort to build trusses instead of buying them? Factory made trusses aren’t exactly cheap. But you can gather truckloads of poles from national forests, enough for several small houses, for the cost of one firewood permit — somewhere around $25 last time I checked. Selectively thinning trees improves the health of the forests and reduces forest fires. The supply in U.S. forests is nearly inexhaustible and foresters are scrambling to find uses for this wood due to increased fire risk. Think of it this way: If people don’t use this small diameter wood, it will likely get burned up in the next forest fire. Might as well get your share and help the forests at the same time.

Note on building codes: Codes require wood that’s used in construction to be inspected by licensed inspectors. Going this route will negate any savings and you might as well buy factory made trusses. If you want to build as inexpensively as possible, move to sparsely populated rural areas with few or no building codes.

Disclaimer: Don’t attempt building your own trusses if you lack adequate carpentry experience. Even though the process is relatively simple and safe, there is always the potential for accidents.

This roundwood truss video on my Natural Building YouTube channel demonstrates the process.