Parallel Chord Pallet Trusses

http://www.motherearthnews.com/green-homes/parallel-chord-pallet-trusses.aspx

 Parallel chord truss made with small diameter poles and pallets 

 Parallel chord pallet truss made with small diameter poles and pallets. 

  Web members are cut from pallets 

Web members are cut from pallets. 

If you have access to small diameter trees and wood pallets, and live in an area not restricted by building codes, then this truss design is one good low cost roof option. Small trees are rapidly renewable, and pallets are plentiful and often available for free. Pallet trusses are especially appealing where other sources of wood are unavailable. This design is exciting to me because gradual improvements in sustainable building help make housing more affordable.

The parallel chord truss described here is similar to the one designed by Alfred von Bachmayr, who developed a truss made entirely of salvaged wood pallets. The main difference is the use of small diameter poles for the top and bottom chords in place of pallet material. For von Bachmayr’s article, see The Last Straw Journal, issue #38, The Pallet Truss: A Low Cost Alternative Roof Structure.

Using full length poles for top and bottom chords (see drawing) makes building these trusses a snap – about half the time and labor of using only pallets. Using poles eliminates the awkward and time consuming process of building the chords with short pieces of pallet wood, and they’re also stronger.

You can make custom trusses to fit your project. In this example, we’ll follow the illustration.

The chords, the long parallel members on the top and bottom, are cut from poles that taper from 4" to 5". The chords are milled S3S (surfaced with three flat sides) and the fourth side left as is (rough). The top chord is milled on the top to create a flat surface for purlins, and on two sides. The bottom chord is milled on the bottom to create a flat surface for ceiling materials, and on two sides. After milling, the dimensions of the chords are 2” thick with widths tapering from approximately from 3-1/2" to 4-1/2". For optimum strength, crown the poles before milling them. Assemble the trusses using a jig so every truss comes out the same size.

Web members made of pallet wood join the top and bottom chords together. These are approximately 5/8" thick by 3-1/2" in width. Cut the web members from pallets using a pattern to ensure uniformity. (See grayed areas in drawing.) Select pallet wood that’s not cracked. Place web members 90 degrees to each other and alternated from side to side: half are fastened to one side of the chords, the other half are fastened to the opposite side of the chords. Each connection between web members and chords is pre-drilled and fastened with four 2-1/4” deck screws and PL400. This eliminates the problem of nails splitting the pallet wood.

The truss shown above is 16” wide. This size provides sufficient space for roof insulation for extremely cold and extremely hot climates: 15” of insulation with 1” air space above. Low cost, sustainable insulation options include cellulose, rice hulls and perlite.

- 15” cellulose @ R-3.8 = R-57
- 15” rice hulls @ R-3 = R-45
- 15” perlite @ R-2.7 = R-40

Some key highlights of this truss design:
- If you do all the work yourself, these trusses are virtually free.
- Very few tools are required – handsaw, chainsaw, chainsaw guide, drill, tape measure, caulk gun.
- U.S. forests are overcrowded with small trees. Thinning these trees reduces the risk of forest fires, improves the health of the forest and saves shipping costs.
- Use noncombustible materials around stovepipes.
- These trusses could be built as part of a cottage industry to create local jobs. A trained workforce will help ensure more consistent, higher quality trusses.

Do-it-yourselfers can mill their own wood instead of buying it from a lumberyard.  The Beam Machine is one example of a low-cost chainsaw attachment that mills straight edges on poles. This $40 guide attaches to most chainsaws and is very easy to use. It guides the saw by sliding along a 2" x 4" tacked to the pole. More information on this attachment is available on the Beam Machine website.

In addition to providing material for trusses, small diameter wood can be used for studs, joists, plates, purlins, window and door frames, and other building components.  An article with more information on the use of small diameter wood can be found on the GRISB.org website.