ROOF TRUSS DESIGNS
Is the legislation over your head or under your control?
– Alicea van der Ryst
A house without a roof is like a forest without trees, the known attributes or functions of the one only becomes complete with the presence of the other.
A roof is arguably one of the most important parts of any home construction as it protects the home’s contents, finishes and most important of all the residents residing therein from the elements. The roof is further one of the largest, heaviest and most costly structures in any home design. Due to the makeup and importance of the roof the Institute for Timber Construction South Africa (ITC-SA) offers insight into legislation governing this aspect of a building as well as guidelines for a correctly built, sound timber roof structure.
Important legislation:
Roof truss designs are assessed in accordance with Part L of the National Building Regulations (SANS 10400) and a national standard that is applied by all local authorities when assessing a building plan application. The legal mandate for the National Building Regulations is the National Building Regulations and Building Standards Act (Act 103 of 1977) (NBR).
In line with the Construction Regulation 2014, Government Gazette No 37305, dated 7 February 2014, an owner of a structure must ensure that:
1. Inspections of the structure are carried out periodically by competent persons in order to render the structure safe for continued use;
2. The inspections contemplated in paragraph (a) are carried out at least once every six months for the first two years and thereafter yearly;
3. The structure is maintained in such a manner that it remains safe for continued use;
4. The records of inspections and maintenance are kept and made available on request to an inspector.
Essential elements:
These four elements are vital in roof truss construction to ensure a sound end result:
1. 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. Beware of unmarked timber as this is not structurally graded timber.
2. 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.
3. ITC-SA accredited System Suppliers must be used:
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.
4. All connections and bracing details must be in accordance with the design intent:
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.
Clearly the old saying reigns true that you get what you pay for. Rather side step a possible disaster in your home by ensuring that the engineer pocketing your money has a reputable background and that the structure of your roof complies with the relevant legislation.
Should you require any help in ensuring that your building plans are NRB approved contact our offices and we will be glad to assist.
This article is a general information sheet and should not be used or relied on as legal or other professional advice. No liability can be accepted for any errors or omissions nor for any loss or damage arising from reliance upon any information herein. Always contact your legal adviser for specific and detailed advice.