Essential elements of sound roof truss construction

The roof is arguably one of the most important parts of any home construction; it protects the home’s contents, finishes and residents from the elements and it is also one of the largest, heaviest and most costly structures in any home design. There are four elements in roof truss construction that are vital for a sound end result:

The timber used must be structural timber and comply with the design intent (SATAS or SABS marked): Structural timber needs to be marked with red ink on the face of the timber at 1m intervals. If it does not bear these structural markings, it will be condemned. One should beware of unmarked timber or timber with black crosses on it, as this is not structural timber.

The designer must create an accurate cutting bill: The cutting bill will dictate the exact lengths and angles at which the timber must be cut for proper assembly.

The right engineering systems must be used: In South Arica, there are currently three main ITC-SA registered systems, namely International Truss Systems, MiTek Industries and Multinail Africa. The metal connector plates used must be supplied by the specific engineering system that is being used. In addition, these plates must be the correct size, and positioned in the right locations as per the standard methods and tolerances.

All connections and bracing details must be in accordance with the design intent: In other words, everything that holds the structure together, such as the number of nails, bolts, washers, brackets and cleats, must be in accordance with the engineering design. All necessary bracing accessories must be stipulated on the design plans.

For more information, visit www.itc-sa.org.

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