ROOF TRUSS TYPES

conventional roof truss types

Conventional Trusses

These trusses are most commonly known among roof truss types and is  manufactured in a Truss Plant by a Roof Truss Fabricator. The truss itself is design by an estimator/designer using engineered software. This program design the truss using the criteria put in by the user. The program calculate the timber size, grade and length as well as the nail plate size and position.

A job-card is then issued to the truss plant, who will pick the timber, cut the angles as per the engineered design and then assemble the trusses. The nail plates are temporarily fixed in position on the table before the truss is pushed through a roller press at which point the nail plates are fully pressed into the timber.

Raised-Tie Trusses

This truss type, also known as a Rafter-Bearing Truss is supported on its rafters. The tie-beam or bottom chord is raised higher than the wall plate level to give a higher ceiling finish level. This truss type can also be left exposed with the ceiling installed on top of the rafters. This is only recommended if the trusses were manufactured using special selected timber or par ( planned all round ) timber.

These trusses are also assembled in a Truss Plant. Also, the exposed bolted truss is similar to this one, except for the timber members are bolted together with 2-Ply top chords or bottom chords offering a nice bulky exposed truss.

raised-tie_truss
raised-tie_truss

Raised-Tie Truss

This truss type, also known as a Rafter-Bearing Truss is supported on its rafters. The tie-beam or bottom chord is raised higher than the wall plate level to give a higher ceiling finish level. This truss type can also be left exposed with the ceiling installed on top of the rafters. This is only recommended if the trusses were manufactured using special selected timber or par ( planned all round ) timber.

These trusses are also assembled in a Truss Plant. Also, the exposed bolted truss is similar to this one, except for the timber members are bolted together with 2-Ply top chords or bottom chords offering a nice bulky exposed truss.

scissor_truss

Scissor Truss

This truss type also offer the opportunity to have a sloped, raised ceiling giving more volume and head space if required. The scissor truss can also be used to as a future in a room. If manufactured properly with par timber it can be left open as well.

You are restricted by certain criteria’s such as the roof pitch, the span and the roof covering. This design works better with a lightweight roof cover such as metal roof sheeting, but will struggle to design with cement roof tiles as roof cover.

Attic Truss

The attic truss is so versatile and has many possibilities. Its main function is to create space in a roof to be used as either residential space, office space or storage space. This truss is also manufactured in a Truss Plant. However, when an existing roof is converted to an Attic Roof it is all done on site. Certain parts of the roof can be manufactured, but the majority of the work is done on site.

The design depends a lot on the usage of the truss. The following roof loads is applied:

  • Residential – 1.5kN/m2
  • Office Space – 2.5kN/m2
  • Storage – 5kN/m2

To make it easier to understand, 1.5kN = 150kg, which means if the truss is designed for residential usage, like a bedroom or living room, the load applied to the bottom chord is 150kg/m2. Now you will understand the impact storage load has on the design at 500kg/m2.

attic_truss
attic_truss

Attic Truss

The attic truss is so versatile and has many possibilities. Its main function is to create space in a roof to be used as either residential space, office space or storage space. This truss is also manufactured in a Truss Plant. However, when an existing roof is converted to an Attic Roof it is all done on site. Certain parts of the roof can be manufactured, but the majority of the work is done on site.

The design depends a lot on the usage of the truss. The following roof loads is applied:

  • Residential – 1.5kN/m2
  • Office Space – 2.5kN/m2
  • Storage – 5kN/m2

 

To make it easier to understand, 1.5kN = 150kg, which means if the truss is designed for residential usage, like a bedroom or living room, the load applied to the bottom chord is 150kg/m2. Now you will understand the impact storage load has on the design at 500kg/m2.