Girder trusses are designed to carry additional loads other than standard roof loads. These loads can be other trusses that attach by sitting on top of the girder, or they may attach to the side of the girder using truss hangers. Girders may also be designed to accommodate special applications or designs.
Most roof trusses are designed to bear on the exterior walls only. Trusses touching interior walls can transfer roof loads to walls not designed to carry a structural load. Trusses touching interior walls can also create point loads on trusses at points not designed to support point loads.
The trusses get attached to the walls during construction. They sit ON TOP of the walls. There are multiple ways to attach them and how you do it really doesn't matter. You just screw or bolt them down so they don't flop around before the roof gets installed.
In most situations, the trusses/joists bear on the double 2x top plates of the wall assembly below. The most direct load path would be to always align a stud (or studs if necessary) directly below each truss/joist. However, this may be undesirable from a design standpoint—e.g., when wall studs are at 16-in.
Roof trusses can be stored vertically or horizontally at ground level, or, alternatively, on a secure storage platform above ground level. In either case, the roof trusses must not make direct contact with the ground or any vegetation. They must be arranged to avoid distortion and restrained securely to avoid collapse.
A standard gable roof is the simplest arrangement, with gable end trusses at both ends and common trusses spaced in between. Gable end trusses sit on the end walls and carry roof loads directly into the wall below. Common trusses are designed to act as bending members spanning between the exterior walls.
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.
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.
The vast majority of trusses utilize 2x4 dimensional lumber but webs can vary from 2x3 up to 2x12 lumber depending on the design. The grade and species of lumber used for webs is typically different from the chords of the truss to drive economic efficiency.
One method is to use toenails. The other method is to use readily available connectors that are made specifically for this purpose. If toenails are to be used, the resistance to withdrawal for the number and size of toenails to be used must exceed the uplift on the truss design drawings.
Bracing ensures that trussed rafters maintain a rigid, secure and stable roof structure.
A 30-foot-span truss typically costs $3.25–$4.25 per foot, while a 26-foot-span truss costs $3–$4 per foot. Type: Roof trusses are pre-engineered at a factory and then shipped to your site, so they only come in predetermined types. These include an attic truss, a scissor truss, and a queen and king post truss.
Unlike rafters, trusses transfer all their load to the outer bearing points, so they don't need support from interior room partition walls. This design efficiency offers more flexibility in interior layout and potentially reduced costs.
Typically, the two main trusses are installed at either end of the roof, then a ridge beam is installed above to connect them. Any additional trusses are attached next. Because trusses require that bottom chord to create compression and tension, there usually must be a flat ceiling underneath.
Trusses are generally designed to be supported on the outer wall with inner walls being non load bearing.
at intervals along the roof to ensure each truss is braced. to be fixed to the underside of the rafters (where diagonal bracing passes through the room space, ceiling boards can be fixed over the diagonal bracing onto battens fixed to the rafters on each side of the bracing).
Roof rafters are used in traditional stick-framed architecture. Trusses offer a new way of building a roof, and are less expensive than rafters. Rafters are built on-site, while trusses are pre-fabricated. Trusses are considered stronger, but offer less flexibility for remodeling.
The distance a 2×6 can span is determined by the species, grade, location, use, load, and spacing. Based on building codes, a 2×6 can span anywhere from 2'-1” to 20'-8” depending on the affecting factors. Ceiling joists don't normally have the same load restrictions, and so can span greater distances.”
The pitch of a roof truss (Rise/Span) should be 1/4 to 1/6 to its slope for proper drainage and slope = 2 times pitch . The spacing of roof trusses is kept 1/3 to 1/5 of the span. Roof trusses usually require very light members.
Trusses are usually made in a factory and shipped to the construction site. Comprised of prefabricated lightweight wood, trusses are made most commonly made from 2x4 or 2x6 beams but can sometimes be as large as 2x8.
The joists should be placed on and fixed to a timber wall plate which is bedded in mortar on top of the inner skin and strapped down using galvanised holding-down straps.
The Golden Rule of Attic Safety
Here's the golden rule for attic adventures – always step on the studs or trusses. These are the bones of your attic, offering the firm support needed to bear your weight.
Where the distance from the top of the braced wall panel to the top of the rafters or roof trusses above is between 91/4 inches (235 mm) and 151/4 inches (387 mm), blocking between rafters or roof trusses shall be provided above the braced wall panel in accordance with Figure R602.
How long do trusses last? When properly installed and maintained, trusses can last for the life of the building. They are designed to meet the building's needs throughout its intended lifespan, which can be several decades, depending on the construction type and materials used.