FEATURE
Bear in mind that roof structurers constructed out of materials other than timber will have their own set of specifications and guidelines .
FASTENERS
There are numerous types of fasteners , but in South Africa , essentially there are three types used : metal nail plates , bolts and nuts , and nails .
Metal nail plates are the more commonly used and the preferred way of constructing a truss . Bolts and nuts are generally used for customised exposed trusses , and in general , nails are used for the smaller connections with smaller load transfers .
The main standards for Fasteners are SANS 1273 and SANS 1700 1 & 2 with approx . 40 plus products covering the spectrum of individual fasteners .
The Standard for Connectors is SANS 54545 and EN equivalent 14545 . The favoured material for fasteners is metal . Looking at the critical considerations around trusses and fasteners , with respect to metal nail plate fasteners , one needs to ensure the fasteners used to build the trusses are the same as what the trusses were designed to use . Each plate manufacturer has computer software that the various truss fabricators use to design the premanufactured metal nail plated timber trusses .
As these differ from one manufacturer to another , so do the strength values of the metal nail plates . The software assumes in the design of the trusses that the correct metal nail plate is being used . If inferior or incorrect nail plates are used , this could cause severe problems with respect to the truss design , resulting in truss failure that could causing injury or death of the occupants and resulting in excessive repair and replacement costs to the building owner .
Bolted and nail trusses are acceptable if they have been correctly designed by a competent person . Such a person being a structural engineer or technologist . The danger of incorrectly ‘ designed ’ roofs is when the fasteners on the joints are inadequate to transfer the load from one member in the truss to another member in the truss at the joint or where the timber used to build the truss is not graded or is sub-standard and is incapable of supporting the loads or where the roof has not been correctly braced . Such ‘ guesswork design ’ is unacceptable and downright dangerous .
Building Inspectors must play a far more active part in ensuring such construction is not allowed .
“ Affordable Housing does not mean cutting corners but delivering the best quality at an affordable price for safe and secure living .”
Do you have any new products to share with the industry ? We want to hear all about it !
Send a short write up with a photo to rory @ interactmedia . co . za www . saaffordablehousing . co . za
For the latest industry and association news , events / exhibitions information , articles , etc .
Read it all online
Visit our website www . saaffordablehousing . co . za
26 JANUARY - FEBRUARY 2021 SAAffordHousing saaffordablehousingmag SA Affordable Housing www . saaffordablehousing . co . za