Knowledge Base

Heavy Timber Trusses

 

Decorative and Structural Trusses

If a building has an overlying space or attic with hidden framing or non-decorative trusses that support the roof or additional building floors, then the timber truss SWC supplies may be purely Decorative. This is a less demanding application and may permit use of materials with less strength, more decorative shapes, smaller members, less fasteners and other features. Because of their physical make-up, all timber trusses are at least slightly structural. Engineering certification of a Decorative truss can be required, but typically is not needed.

Should the timber trusses be integral to support of the roof or overlying structure, then the trusses are also Structural. The trusses may provide direct support of the roof via purlins and/or ceiling decking, or the trusses may support a ridge beam to which rafters and other roofing components are anchored. The Structural timber truss requires engineering certification by the customer or SWC. We provide this service if required. The customer only needs to provide building plans or sufficient detail regarding the roof configuration for our engineer to make roof load assumptions.

Glue-laminated Trusses

Glulam Truss beam thickness is normally 3”–7”, but can be larger. Because of the laminated construction technique, beam depth can be supplied much larger than solid timbers (which are normally limited to 16-20 inches of depth), with beams up to 60” deep having been manufactured.

Common materials used for manufacture of Glulam beams are: Southern Yellow Pine, Douglas Fir, Alaskan Yellow Cedar and other species. Like solid wood, each of these species has different appearance, structural performance properties and resistance to the elements.

Various Glulam appearance grades are also available, including Industrial, Visual, Architectural and Premium grades. Each of these is determined by characteristics such as amount of wane, number of knots, surface finish applied and number or size of defects filled.

Glulam beams and trusses may also be treated using a variety of water or petroleum-based treatments, depending on the components application and level of protection required. Click here to return to Products - Timber Trusses

Multi-ply Trusses

Multi-ply Truss are fabricated using multiple layers of thinner timbers (normally 2”, 3” or 4” thick) bolted together in some combination of overlapping members. Most of the time the top and bottom chords are comprised of two members “sandwiched” around a single king post and webs. Gusset plates are normally not used, with a series of bolts, nuts and washers holding all layers together. This configuration results in a unique appearance and is sometimes more economical because thinner material is used and no shaped plates are required.

As a general rule of thumb, these trusses are designed with the thickness of the combined layers in the top and bottom chords being equal to the thickness of an equivalent single-layer, solid timber truss.  Most Multi-ply Trusses have three sandwiched layers, but SWC has fabricated trusses with thinner components and spacers having up to five layers for a unique appearance. Click here to return to Products - Timber Trusses

Joint Configuration

External Plate & Bolting - External plating and bolting is the most economical way to join truss members.  Gusset plates and bolts are required for all Structural trusses (except Multi-ply or Embedded Tensioner Trusses) and most Decorative trusses.  Most of our trusses are constructed with externally placed, 1/4-inch, A36 gusset plates.  The plates are custom-shaped by our designer to coincide with the members of the truss using our in-house CAD system.  Plate thickness may increase for larger trusses to 3/8” or 1/2” thicknesses.  Bolt sizing may vary according to truss proportions, but we normally utilize 3/4-inch bolting.

Our designer produces a CAD file that is downloaded to our shop’s Plasma Cutter, where the plates are cut from sheets of steel. Plate is most frequently painted with a general purpose alkyd-based, black paint. Galvanized gusset plates and fabrications can be supplied for exterior applications at the customer’s request. The galvanized finish can be left as-is or painted over-coated with the standard black paint described above. Powder coating in a variety of colors and finishes is also available. If special circumstances require it, higher strength or stainless steel plate can be supplied.

Hidden Plate With Exposed or Hidden Bolting –  If partially or totally concealed connection hardware is desired and a customer’s Heavy Timber Trusses are either (a) Structural and/or (b) oversized, our most common method of construction is to use “Hidden” or “Knife” plates.

This method involves cutting concealed slots or “plunge cuts” in the center of timbers, into which a single gusset plate is inserted out of view. The plunge cuts are generally made from the top sides of the truss members so they are not visible from below. Holes are drilled through the timbers to coincide with holes in the gusset plates. Bolts are installed with washers to bear on the wood.

The bolts may be installed with the bolt head, nut and washers exposed at the surface, counter-sunk flush with the surface, or counter-sunk below the timber surface, covered with a wooden plug and sanded smooth so the all hardware is completely hidden from view.
 

The counter-sunk and plugged approach may only be used if the timbers are of sufficient thickness to permit this configuration.

There are some truss geometries that will not allow hidden plate construction for engineering reasons. SWC will advise the customer when hidden plates are not permitted.

There is significant additional labor associated with the hidden plate fabrication approach so extra lead time must be allowed.

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