Timber iQ Dec 2017 - Jan 2018 // Issue:35 | Page 60

CONTRIBUTORS - TALKING TIMBER
Continued from page 56
One should 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.
COMMON ERRORS IN NEW RESIDENTIAL
ROOF CONSTRUCTION
CHOOSING PRICE OVER QUALITY
What you pay for is what you get is certainly true when it
comes to roof construction. Many people try to save on the
construction and often spend more remedying the
problems that arise from using sub-standard materials
and workmanship.
Bear in mind that to create a professional and sound
result, it is imperative to employ professional,
knowledgeable and experienced individuals, whose
expertise may cost more initially than non-qualified
individuals off the street, but will save you a great deal of
money and stress down the line.
CHOOSING THE WRONG ENGINEER
It is important to use a qualified structural engineer to
design and sign off the roof and ensure that the chosen
engineer has good working knowledge of timber and
roof construction.
USING SITE-MADE TRUSSES
Prefabricated roof trusses are cut by advanced, specially
designed machinery and are therefore far more accurate
than handmade trusses. Handmade trusses assembled on
site are a recipe for disaster. Prefabricated trusses also use
less timber and are more likely to comply with NBR
requirements if they are designed by a qualified engineer.
USING AN UNKNOWN FABRICATOR WITHOUT A
TRACK RECORD
Using reputable fabricators, such as those registered with
the ITC-SA , offers peace of mind that these companies or
individuals are regularly audited and monitored and – if
something goes wrong with the workmanship – there is
some recourse for the client. One of the membership
requirements for engineers accredited by the ITC-SA is that
they have a personal indemnity insurance policy which
covers any negligence on their part regarding the specific
structures they sign off on and take responsibility for.
58 DECEMBER 2017 / JANUARY 2018 //
Using reputable fabricators offers peace of mind (timber
trusses at Boschendal Wine Estates' Olive Press venue).
IMPORTANT LEGISLATION
Roof truss designs are assessed in accordance with
Part L of the National Building Regulations (SANS
10400) and a national standard that must be 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, Structures 11, (2), an owner of a structure must
ensure that:
a. Inspections of the structure are carried out
periodically by competent people to render the
structure safe for continued use;
b. The inspections contemplated in paragraph (a) are
carried out at least once every six months for the
first two years and afterwards annually;
c. The structure is maintained in such a manner that
it remains safe for continued use; and
d. The records of inspections and maintenance
are kept and made available to an inspector
upon request.