This document discusses the requirements and responsibilities for estimators and designers of timber roof trusses in South Africa. It states that a rational design must be used according to industry standards and codes of practice. Estimators and designers must have thorough knowledge of relevant technical standards and pass certification courses. Fabricators must also meet certification and competency requirements to ensure trusses are designed and manufactured correctly according to the design intent. Inspections of erected roof structures should be carried out by a competent person to confirm compliance.

1. ESTIMATORS & DESIGNERS
THE RATIONAL DESIGN
According to SANS1900 (Manufacture of monoplaner
prefabricated timber roof trusses [nail-plated]), the design
used to manufacture each roof truss in a batch or order shall
be a rational design.
The definition of a rational design means that a design is done
by a process of calculations and reasoning, and will include, or
use, as a basis, a code of practice or accepted published
technical documentation. In the case of nail-plated roof trusses
this will be attained by applying design software supplied by an
accredited (software) system in South Africa.
The design shall include the grade of timber, dimensions of
timber, the geometric configuration of all the members and
the dimensions and positioning of the nail plates, connectors
and cleats to be used.
It therefore stands to reason that estimators and designers of
monoplaner roof trusses in South Africa not only need to
know how to use the software provided by their system, but
must also have an intimate knowledge, and be able to
demonstrate their understanding, of the following:
• SANS 10160 and SANS 10163 – General Loading Code, and
the basis of structural design and actions for buildings and
industrial structures and code of practice for The Structural
Use of Timber in the design of timber structures
• SANS 10243 – The Manufacture and Erection of Timber
Roof Trusses
• The Application of the National Building Regulations (SANS
10400)
• The ITC-SA Roof Erectors Handbook for the Installation and
Bracing of Pre-fabricated Timber Roof Trusses (Volume 2)
It is highly recommended that both the specifier and consumer
insist that the estimator and designer are able to demonstrate
and prove their knowledge and ability in this regard.
COVERSTORY
The application of SANS1900
and the minimum requirements
of the ITC-SA in the design,
manufacture and inspection of
erected roof trusses
"Productivity and efficiency can be achieved only step by step with
sustained hard work, relentless attention to details and insistence on
the highest standards of quality and performance.” – J.R.D. Tata
JUNE 2014
Incorrect truss loading.

2. The submission of a quotation on an official company letterhead
is not necessarily sufficient proof of this.
An estimator and/or designer should be appointed by his
employer (the fabricator) on a basis of proven competence,
and the acceptance of an appointment letter where he accepts
his responsibilities according to the aforementioned standards
and regulations.
Furthermore, as a minimum standard, the estimator should
have passed the basic designer course, and the designer the
intermediate designer course, as laid down by the Institute for
Timber Construction (ITC-SA).
In terms of the recent South African Qualifications Authority
(SAQA) registration of the ITC-SA as a professional body, a
roof designer will be issued with a certificate of competence
by the ITC-SA which together with his fabricator appointment,
will ratify his ability to undertake design work in terms of the
fabricator's manufacturing category.
THE LETTER OF APPOINTMENT OF AN
ESTIMATOR IN RESPECT OF THE
PREPARATION OF QUOTATIONS WILL
ENSURE:
• That all quotations are in writing with both the fabricator
and client details.
• To ensure a traceable job number to at least the year of
quotation.
• That the inclusion of both roof area and the roof plan are
mandatory on the quotation and that the roof plan is to
include, as a minimum, the fabricator details and COC
number, client details, job number, design codes of relevance
and loads applied.
• That number(s) and/or titles of the architect’s drawings that
are used in the preparation of the quotations.
• Must state loadings, maximum truss centres, maximum
batten/purlin centres, span, pitch, overhangs and any
additional information required to define any unusual truss
profiles. (In the event of there being a range of spans and/or
pitches, the minimum and maximum spans and pitches shall
be stated).
• State quantities of all bracing and runners required to
provide stability to the trusses. Bracing shall be in
accordance with either the ITC-SA requirements or any
special requirements specified by the design engineers, or
as laid down in SANS 10163 & SANS 10243.
• Details and quantities of all cleats, hurricane clips and
hangers necessary to ensure compliance with the design
requirements must be provided. Where specially fabricated
cleats are required and their design or cost is not known,
these may be excluded, but this exclusion must be clearly
stated on the quotation.
• Where sundry timbers are quoted, the total quantities,
sizes and purpose must be clearly stated.
• The estimator must check that any member sizes and
grades specified by the client or his architect for any trusses,
beams or joists are adequate. If any sizes are found to be
inadequate, this must be clearly noted on the quotation.
• A statement must be provided to confirm whether or not
delivery is included.
• VAT must be clearly included on the quotation
• The estimator (or any member of the company) must not
knowingly mislead the customer with respect to quotations
or any item shown on the quotations.
THE LETTER OF APPOINTMENT OF A
DESIGNER WHO WILL APPLY THE
SYSTEM SOFTWARE FOR DESIGN OF A
ROOF STRUCTURE WILL ENSURE:
• That all requirements pertaining to the estimator function
are complied with.
• The design will include all structural elements to be supplied
by the fabricator and will include not only trusses, but any
beams, all necessary bracing, rafters or joists and their
connections. The fabricator must ensure that the following
items are complied with:
• Design must be carried out in accordance with the
National Building Regulations, SANS 10160, SANS
10163, SANS 10243 and the ITC-SA recommendations
for Truss Analysis and Design.
• Designs which are not of a conventional domestic
nature shall be checked by the Systems Registered
Professional Engineer before manufacture. Such designs
may include roof or floor systems in the following
categories of A (high Risk), B (Medium Risk), C (Low
Risk) and D.
• The designer must check that any member sizes and
grades specified by the client or his architect are
adequate.
• The client or his engineer must be informed of any
unusual loads or forces (vertical or horizontal) which
may affect the supporting structure. Examples of loads
in the category may include point loads applied to walls
which may not have been designed as load bearing in
addition to girder bearings which may affect lintels and
foundations.
• The designs of trusses which contain elements of 38 x
50mm must be checked by the Systems Registered
Professional Engineer. In addition, the use of such sizes
must be clearly stated on the quotation. Where 38 x
50mm material is specified in the design, the material
must be mechanically stress-graded or proof-graded and
assigned working stresses in bending, tension and
compression, to the satisfaction of the SABS or CSIR
and the supplying mill must provide proof of its SANS
permit to structurally grade such a sized timber element.
• The designer must make every reasonable effort to
ensure that the design is in accordance with the most
recent version of the architect’s drawings. Any
significant variation or discrepancy between the latest
drawings and those used to prepare the quotation must
be reported to the client as soon as possible after it is
noticed. The client should be made aware in writing
that cost variations may arise.
THE MANUFACTURE OF MONOPLANER
PREFABRICATED TIMBER ROOF
TRUSSES
SANS 1900 furthermore determines the minimum standard
for the manufacture of monoplaner prefabricated timber roof
trusses in terms of the following:
• The roof truss material and final product
• Inspection of the manufactured product before leaving the
fabricator’s yard
• Methods of testing
• Packing or loading and marking
JUNE 2014
COVERSTORY

3. COVERSTORY
JUNE 2014
IN TERMS OF THE ABOVE, NOTABLE
MENTION CAN BE MADE OF:
TIMBER:
Each member of timber shall be structurally graded and the
maximum difference in thickness of members in a joint area
shall be 1.0mm. There shall be no wane, dead knots or resin
infiltration within the connector plate area unless a larger
plate is used to compensate for the ineffective area.
NAIL PLATES:
Nail plates must have a firm and even contact between the
faces of the timber and the nail plate. The teeth must not be
flattened and ALL the teeth must be fully embedded in the
members of a joint with a maximum clearance on 1mm in a
member where the member is subject to the maximum
tolerance in terms of thickness.
JOINT CLEARANCE:
In open joints, and due to inaccuracies in cutting and assembly,
the joint clearance shall not exceed 2mm, except in joint
lengths exceeding 300mm, a tolerance of 5mm at one end and
0mm at the other end of the joint will be allowed.
PERMISSIBLE DEVIATIONS:
Span = 10mm, height of individual trusses = 20mm
MARKINGS:
Each truss shall bear the manufacturer’s name or trade mark,
the last two digits of the year of manufacture and the batch or
job number.
THE INSTITUTE FOR TIMBER
CONSTRUCTION (ITC-SA) CATEGORIES:
The ITC-SA has determined the following categories of
competence for fabricators:
Category A: Very complex roofs including scissor trusses
greater than 5m span, site splicing, attics and dormers, other
spans greater than 10m, piggy back trusses, cantilevers greater
than 2m, complex industrial and commercial structures,
laminated timber structures and, most importantly, public
buildings and schools.
Category B: Complex domestic and simple industrial and
commercial roofs, hips and valleys up to 10m span, non-
standard loads and scissor trusses up to 5m span.
Category C: Simple roofs up to 9m span, valleys, girders and
support cleats, stub ends, cantilevers up to 2m, simple hips to
9m span and minimum pitch of 15 degrees.
Category D: Gable to gable roofs with no hips and valleys up
to 6.5m span.
A category B fabricator may not manufacture a category A
roof, and similarly a category C fabricator may not produce a
category B structure unless the design has been checked and
confirmed in writing by the fabricator’s relevant software
system and resident Professional Engineer.
In the case of Public Buildings (as defined by SANS 10400) all
roof structure designs must be checked and confirmed by the
software system even if the fabricator is classed by the ITC-SA
as a category A graded fabricator.
Nail plate pulling out.

4. A FABRICATOR SHOULD THEREFORE:
• Be a professionally registered ITC-SA fabricator member
with a current certificate of competence (COC).
• Be able to provide documentation in support of category
classifications and design confirmations before the order is
placed on the fabricator.
• Be able to prove that a clear and level surface inside his
facility is available in order to manufacture both the lengths
and heights of the largest truss in the batch or order.
• Assume responsibility for the quality of the manufactured
product and product liability insurance must be proved.
• Prove that the correct storage, transport and
erecting procedures are used, as timber trusses can easily
bend out of plane during handling, transport and erecting
and which may impact the structural integrity of the roof
structure. The use of specially designed trailers will always
be the preferred method of transport.
INSPECTIONS OF
ERECTED ROOF
STRUCTURES:
A competent person in terms of
SANS 10400 part L (ROOFS) is
defined as a person who:
1. is registered in terms of the
Engineering Profession Act, 2000
(Act no 46 of 2000) or
2. is registered in terms of the
Architectural Profession Act,
2000 (Act no 44 of 2000) and
3. is generally recognized as having
the necessary experience and
training to undertake rational
assessments or rational designs in
the field of roofs and roofing.
It is a common misconception that
the issue of the so-called ‘Engineers
certificate’ (or various permutations
thereof) for roofs in terms of
Regulation A19, Form 4, as contained
in SANS 10400 part A means that the
structure is designed correctly and by
a person deemed to be competent.
This is not necessarily the case and in
the overriding majority of cases it
merely confirms that the roof
structure has been erected according
to the design intent.
The building owner, financier and
insurer could assume the risk for a
structure that has not necessarily
been designed and erected correctly
and under supervision of a recognized
competent person.
MINIMUM
REQUIREMENTS:
By no means of negating any of the preceding issues, as a
minimum requirement, the following should be required by the
specifier and consumer in order to satisfy both the
requirements of the ITC-SA, of Regulation A19 in respect of
roofs and the risks assumed by financiers and insurers:
• The issue of a Truss Manufacturers Certificate by an
authorized designer of the fabricator and who is proved to
be competent by virtue of the issue of his certificate of
competence.
• Proof of the fabricator’s valid certificate of competence in
his applicable category.
• Proof of the fabricator’s defective product liability
insurance.
• Confirmation by a competent person who is generally
recognized as having the necessary experience and training
to undertake rational assessments or rational designs in the
field of roofs and roofing that the roof structure has been
erected according to the design intent.
• Preferably a fabricator who operates under the SANS1900
quality scheme (SABS or SATAS) and who is permitted to
apply either mark to its manufactured product.
JUNE 2014
COVERSTORY

5. FINAL THOUGHTS AND GUIDANCE:
The existence of ‘roof truss brokers’ within the South African
truss manufacturing landscape raises a number of concerns.
The following aspects are contended to be pertinent and
deserve particular regard when agreements for the
manufacturing of roof trusses are facilitated by roof truss
brokers:
• Consumers should comprehensively acquaint themselves
with the wording of agreements entered into with brokers.
• Consumers should insist that agreements with or facilitated
by brokers contain a clause detailing warranties, insurance
and liabilities.
• It remains advisable that agreements for the manufacturing
of trusses are entered into between the consumer and the
roof truss fabricator directly, to ensure maximum
protection for the consumer. However, in the event that a
broker does facilitate the related agreement, it is important
that the parties related to the agreement include the
consumer and the fabricator. Should the consumer and the
broker be the sole parties to the related agreement, the
consumer may only have right of recourse against the
broker and not against the fabricator, leaving the consumer
at risk.
“One's philosophy is not best expressed in words; it is expressed in
the choices one makes... and the choices we make are ultimately
our responsibility” – Eleanor Roosevelt.
FOR MORE INFORMATION, CONTACT:
(c) 082 441 5026 | 0861 LCPROOF
(e) lyndsay@lcproofing.co.za
(w) www.lcproofing.co.za
COVERSTORY
JUNE 2014