Roof Trusses
Although roof trusses only started being used in Australia in the 1960’s they now have around 80% of the total ‘Pitched Roof’ market.
They are all designed using well proven computer programs and manufactured in factory conditions. (the whole process is high tech and relies on specialised equipment…….site work is limited to erection of the completed trusses).
Trusses can span large areas without needing intermediate supports. Because the individual components are engineered to share the stresses acting on the roof the total amount of timber is usually much less than an equivalent ‘Conventional Roof’.
Components
The following diagram is of a standard timber roof truss.
For more complex roof shapes there are a range of special trusses that can be made.
Steel roof trusses would look generally similar although they would use a different jointing method rather than nail plates.
The timber components are normally pine and will be either ‘F’ or ‘MGP’ graded. The size is determined from the manufacturers computer program.
Nail Plate (or Gang Nail)
The chords and webs are joined by nail plates. The plates are galvanised steel sheets that have spikes protruding on one side.
The plates are hydraulically pressed into the timber at the manufacturing plant, with one plate on each side of the join. They form a solid fixing that is very strong.
As well as joining chords and webs they are quite often used to splice timbers together particularly when a long bottom chord is needed.
For more about house construction see: Basic Timber Frame