1. INDUSTRY INSIGHT
T
he South African Weather Service reported that the
Gauteng Province had received the heaviest rainfall
in 14 years and, furthermore, that it was deemed to
be very unusual. Elsewhere over the corresponding
period, various news agencies reported heavy rainfall in
other parts of the country with the resultant damage to
property and loss of life. This causal effect of global
warming cannot be ignored.
Many truss fabricators and timber framers, during
prolonged periods of inclement weather are continually
posed with the question of whether structures under
construction are being potentially compromised when
exposed to rainy and flooding conditions.
Firstly, we need to look at the basic moisture properties of
air or kiln dried timber and the South African climate in
which these structures are erected.
After drying and grading, the moisture content of
structural timber will be less than 15%. Timber is naturally
hygroscopic, which means that it will tend to try to reach a
state of equilibrium and balance with the moisture content
of the environment in which it exists.
Research by Prof. Tim Rypstra (now retired), of the
Department of Forest and Wood Science of Stellenbosch
University, concludes that over 90% of South Africa's
climate is made up of a timber equilibrium moisture
content of 8%. Furthermore, research also indicated that
most modern heating and cooling systems will maintain an
average timber moisture content of 8% in buildings. From
this, it can be accepted that a timber structure, be it a
completely timber framed building, or only the roof
trusses, once ‘settled’ into its environment, will migrate to
an average moisture content in the region of
approximately 8%.
The degradation of timber
(structures) caused by
prolonged exposure to rain
"Heavy rains cause countrywide havoc - news24 - 11 March 2014"
By Lyndsay Cotton, General Manager of LCP Roofing and Chairman of the ITC-SA.
Even after prolonged exposure to inclement weather, and despite the fact that teeth of this nail plate have broken off after
being forcibly removed, the joint itself is still in excellent condition.
72 JUNE / JULY 2014 //

2. INDUSTRY INSIGHT
The degradation of timber is caused by repeated wetting
and drying, which causes the timber to swell and shrink,
and can be broadly defined within two categories:
• Weathering: Repeated and irregular movement of
moisture into and out of timber, which will cause
various deformations, such as swelling, raised grain,
warping, cupping and splintering.
• Biological attack: This occurs both on the surface and/
or inside the timber element. The excess of moisture is
the primary cause of attack by mould, algae and fungi.
Attack by wood borers and termites would also fall
within this definition.
A well-designed and constructed building will not be
conducive to conditions which support mould growth or
fungal attack, as it will stay dry enough to prevent mould
spores from becoming active.
Mould, which comes from a variety of sources, feeds off
the starches and sugars on the surface of timber, and is a
result of prolonged high moisture, but does not cause
rotting. Mould growth is a superficial occurrence and will
not influence the structural durability of timber.
It is rather the effect of bad design and poor construction
techniques, such as high levels of condensation due to
inadequate ventilation and poor circulation, leaking pipes,
gaps in flashings, leaking roofs and porous concrete
elements which will lead to the growth and long-term
establishment of mould.
For mould growth to occur on timber, the moisture content
will have to be above 19% for a period of a week or more
and will survive when, by weight, the moisture content of
the structural timber is between 20% to 28%.
The fibre saturation point of timber is at approximately
28% (but can vary depending on the species).
This is the point at which wood decaying fungi will develop
and this condition will have to exist for more than a week
for it to develop and survive.
THE FOLLOWING FOUR CONDITIONS MUST BE
SATISFIED IN ORDER TO PROMOTE FUNGAL
GROWTH:
• Oxygen: This condition will not occur when timber is
below the water table.
• The optimum temperature for fungal activity is
between 24 and 30 degrees Celsius. Fungal activity is
dormant at 0 degrees Celsius and diminishes beyond
30 degrees Celsius.
• Fungi require a food supply in order to survive, which is
derived from the wood cells. The application of a
fungicide will cut off this source of the food supply.
• The moisture content must exceed 20%
Active mould growth would be indicative of a continuing
moisture problem and must be investigated.
The fibre saturation point of timber is at approximately 28% (but can vary depending on the species), the point at which wood
decaying fungi will develop. This condition will have to exist for more than a week for it to develop and survive.
// JUNE / JULY 2014 73

3. Should the need exist, and really only for aesthetic
reasons, the visual effects of mould growth can be
removed by applying a weak solution of standard
household bleach. The purpose is not to ‘kill’ the mould,
but to remove as much as possible in order to restore the
visual effect of the timber.
Timber ages, and with aging and weathering, it releases its
colour which is contained in the tannins, resins and waxes
which are close to the surface of the timber. Although the
sealing and preservation of timber is always preferable,
the release of these tannins, resins and waxes, especially
in timber where these levels are high, could cause a
sealant coat to delaminate. The high temperature levels
generally prevalent in roof voids could have the same
effect, although this effect would be greatly reduced with
the majority of the types of structural timber used in South
Africa.
The sealing of timbers in roof voids and framed structures
is therefore generally unnecessary unless the incidence of
wood borer and termite infestation cannot be excluded,
whereupon the preservation of the timbers would be
mandatory.
TECHNICALITIES ASIDE, WHAT DOES THE
AFOREMENTIONED MEAN TO THE
FABRICATOR, FRAMER, BUILDER AND
HOMEOWNER?
• Structural timber in South Africa is under strict third
party surveillance through certification by an
accredited certification body such as the South African
Technical Auditing Services (Pty) Ltd (SATAS).
• Roof truss and framing design and quality are
controlled by internal or independent third party audits
initiated by the Institute for Timber Construction.
• Trusses or frames delivered to the building site should
preferably be covered by the contractor, but it should
be specifically noted that the timber should be stacked
off the ground and adequate ventilation must be
provided. Completely enclosing with heavy tarpaulin is
to be avoided.
• Surface fungi and discolouration will not have any
negative effect on the strength of structural timber,
provided the timber is allowed to dry to below 15% as
soon as possible.
• The prolonged exposure of timber trusses to a rainy
period not exceeding four or five weeks will not have
any negative structural effect, especially if the
structure is erected and braced according to the design
intent.
• The structure should be covered as soon as possible,
weather permitting.
• Free airflow should be allowed for as long as possible
or until the moisture content is below 15%, whereupon
ceilings or internal cladding can be installed.
• Untreated timber structures should not be exposed to
repeated wetting and drying over a period of many
months or even years.
• The homeowner is to ensure that all flashings and
waterproofing systems are annually maintained, as
most manufacturer and applicator guarantees will only
be valid should an annual maintenance plan be in place
and executed.
• Fabricators and framers must ensure that all
documentation and quality control procedures are in
place and are available for inspection should it be
required.
FOR MORE INFORMATION, CONTACT:
(c) 082 441 5026 | 0861 LCPROOF
(e) admin@lcproofing.co.za
(w) www.lcproofing.co.za
INDUSTRY INSIGHT
Evidence that once the timber is allowed to dry out, there is still perfect adhesion of the plate to the timber, even after forcibly
removing the nail plate.
74 JUNE / JULY 2014 //