SA Affordable Housing May - June 2020 // ISSUE: 82 | Page 17

FEATURE
THE REGULATIONS
The South African National Building Regulations (NBR) were
updated by the Department of Trade and Industry in May 2008,
with the General Requirement relating to Roofs changed to
incorporate certain safety elements. For example, instead of
simply having to “resist any forces” to which the roof might be
subjected to, the regulations now state that “The roof of any
building shall be so designed and constructed that it safely
sustains any actions which can reasonably be expected to
occur and in such a manner that any local damage (including
cracking) or deformation do not compromise its functioning”.
Simply put, if there is a major wind or some other bad weather
conditions, the roofs of our homes are expected to be able to
stay on the house and protect us from the elements without
themselves being damaged.
Instead of simply being “durable and waterproof”,
roofs are expected to be “durable” and should not allow
“the penetration of rainwater or any other surface water
to its interior”. As previously, roofs must “not allow the
accumulation of any water” (but not simply rainwater,
which was the limit of the old building regulations) “upon
its surface”. In addition, the roof should be “adequately
anchored against wind uplift” which was not covered in the
previous edition of the regs.
Lastly, the General Requirements specify (as they did
previously), that the roof should be designed “as part of a roof
and ceiling assembly” and should provide “adequate height
in any room immediately below such assembly”. This last
point is subject to interpretation as not all roofs incorporate
ceilings as such.
"There is the problem of third-party interference
after these structures were erected, which
mainly involve adding additional services like
air conditioning systems, water system and
electrical systems to the structures, which they
were not designed for."
THE SOUTH AFRICAN NATIONAL STANDARD FOR ROOFS
It was only in 2011 that Part L: Roofs was published by the
SABS, and the guidelines are now much more comprehensive
and useful. As with most of the NBR, those that apply to roofs
relate to South African National Standards (SANS) other than
the one specific to that particular element. For instance,
where any roof is to be supported on the wall of a building
as described in the relevant section of Part K: Walls, the roof
must be constructed in accordance with the rules laid out by
the relevant SANS (in this case 10400). In addition, the new
SANS remind designers and builders that other sections are
also vitally important when it comes to roof design, including
Part A: General principles and requirements; Part B: Structural
design; Part C: Dimensions; Part R: Stormwater disposal; Part
T: Fire protection; and Part V: Space heating.
Anybody building a house must either be a “competent
person” in terms of the regulations, or must employ a
“competent person” to put in plans and oversee the building
operation. Circumstances vary from site to site.
There are several SANS that relate to roof timbers, all of
which must be complied with when roof trusses and other
THATCH OF THE DAY
A thatch roof.
roofing elements are constructed. In addition there are
standards that relate to roof coverings and other elements.
The full list is contained in Part L of SANS 10400, but they
include:
• SANS 542, Concrete roofing tiles
• SANS 1288, Preservative-treated timber
• SANS 1460, Laminated timber (gluglam)
• SANS 1701-1, Sawn eucalyptus timber – Part 1:
Proof-graded structural timber
• SANS 1701-2, Sawn eucalyptus timber – Part 2:
Brandering and battens
• SANS 1783-2, Sawn softwood timber – Part 2:
Stress-graded structural timber and timber for frame
wall construction
• SANS 1783-4, Sawn softwood timber – Part 4:
Brandering and battens
• SANS 2001-CT2, Construction works Part CT2:
Structural timberwork (roofing)
• SANS 10407, Thatched roof construction
Roof design depends on a number of factors including the
type of covering you are going to use, and the span over
which the roof structure is to be supported. More often than
not, the roof structure is assembled from a series of roof
trusses. These rest on wooden wall plates, and are designed
to span the walls of the house. They will be either nailed or
bolted together on site, or delivered to site on order by a
specialist truss manufacturer.
IMPORTANT FACTORS REGARDING CONNECTIONS
It is vital that roof trusses and other roof framing elements
have joints that are accurately cut, securely made and fitted
so that the component parts are drawn tightly together. All
trussed roofs must be provided with approved bracing that
prevents any possible buckling of the rafters, tie-beams
and long web members. The bracing also needs to keep the
trusses in an upright position. Whoever is doing the maths
need to be certain that no section of the truss has a length
that is greater than 60 times its least (or smallest) dimension.
If rafter construction is used instead of roof trusses,
and the roof covering is regular sheeting or tiles (as
already mentioned), it is important to accurately assess the
parameters for rafter spans and the size and grade of rafters.
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