In a truss, the bottom chord and the top chord are under tension and compression forces as a result of the loads on the roof. Which chord carries tension and which carries compression depends on the direction of the overall loading on the truss.
Once a truss is in place, it must be temporarily braced to prevent movement that could lead to misalignment or collapse. Temporary bracing involves installing diagonal braces that stabilize the trusses until permanent sheathing and bracing are applied.
A truss that is assumed to comprise members that are connected by means of pin joints, and which is supported at both ends by means of hinged joints and rollers, is described as being statically determinate.
Place one precut patch brace on one side of the truss to gauge whether it is straight. Install angled braces to shore up the rafters. Give more support to the walls by installing chains attached to the wall plates and linked in the middle with a turnbuckle.
A truss gives a stable form capable of supporting considerable external load over a large span with the component parts stressed primarily in axial tension or compression. The individual pieces intersect at truss joints, or panel points.
The truss will be anchored with nails, powder driven fasteners, or masonry anchors.
But by design, trusses do not need supporting anywhere else, no matter how large they are, they should only be supported at the pitch point.
A truss connector plate, or gang plate, is a kind of tie. Truss plates are light gauge metal plates used to connect prefabricated light frame wood trusses. They are produced by punching light gauge galvanized steel to create teeth on one side.
Bracing ensures that trussed rafters maintain a rigid, secure and stable roof structure.
Brace each preassembled block of trusses back to the previous block—using horizontal braces on the top and bottom chords. Once all blocks of trusses are installed with horizontal and cross bracing, diagonal bracing must be installed, every 6 metres (20 feet), on the undersides of top chords.
In many cases, builders can connect a truss using two or three nails. However, counties with good building codes, as well as contractors who take pride in making quality homes, use hurricane ties or a similar product to make the connection more secure. This is when a 6” TimberLOK screw can help.
Design engineers normally try to keep it at 45°to 60° as it is the best compromise.
Trusses can have intermediate support, especially if one side is vaulted. If so, load goes into the wall, then through the floor joists to the lower floor walls and foundations.
When a truss collapses, it is usually because of the failure of either the top chord (in compression, unless a cantilever) or the bottom chord (in tension, unless a cantilever).
When storing the trusses horizontally, blocking needs to be used on eight to ten foot centers, or as required, to minimize lateral bending and moisture gain. As far as how long trusses can be exposed to the elements, a ballpark number is about a month.
Nail fix two timber braces from the horizontal timber on the table lift to the timber length screwed to the truss face. Use two nails per brace as shown. Individually nail fix the trusses within the truss pack using a short length of bracing. This will allow the trusses to be released individually when required.
Strength: Roof trusses are stronger than traditional timber framing. They can support heavier loads and are less likely to sag over time.
After you install the truss clips, nail a board on top of each interior wall that will overhang it by at least an inch on each edge. This lip will act as a bumper if the truss attempts to lift again. You can also avoid truss lift altogether by updating your insulation.
CONNECTOR PLATE A galvanized steel plate with teeth punched out on one side, which is hydraulically pressed or rolled into both sides of a joint to fasten chord and web members together.
Bottom-chord-bearing trusses (left) sit atop a wall plate or sill like a standard floor joist. Top-chord-bearing trusses (right) hang from the top plate.
Rafters are built on-site, while trusses are pre-fabricated. Trusses are considered stronger, but offer less flexibility for remodeling.
Nail the bracing into the top chord of each truss, making sure to follow the truss manufacturer's layout while setting trusses. Install diagonal bracing, representing a “W” pattern throughout the structure (See red blocking in Diagram 1). Lateral bracing alone is not adequate to secure roof trusses before sheathing.
According to the International Residential Code (IRC), eave overhangs cannot exceed 24 inches when measured horizontally.
A truss is considered geometrically stable if it can maintain its position and configuration under the applied loads. A stable structure deforms when loaded, but returns to its undeformed shape when the load is removed.