The scientists all agreed, however, that current national emissions targets are ambitious and that an average global warming of four degrees Celsius by or

before 2100 is catastrophically more than likely.

Climate change is defined as the shift of weather conditions over time. Our average temperature throughout the world has steadily increased over recent decades, resulting in more unpredictable and extreme weather as compared to one or two generations back. Some places are getting hotter, others colder. Previously drier zones are getting wetter and others are drying out.

Southern Africa is experiencing these effects of global warming and resultant climate change, including more frequent extreme weather events, heat waves, drought and heavy rainfall.

Additionally, many of the good building practices and norms employed by previous generations have been ignored and forgotten in a society where price, speed of construction, lack of skills and punitive interim interest rates dictate acceptable standards. These seemingly unrelated issues are resulting in more and more roof systems failing either partially or in their entirety.

The effect of climate change on concrete tile and metal roof coverings in the domestic environmentIn his book, ‘Four Degrees of Global Warming,’ Peter Christoff writes that the international community agreed only five years ago in December 2009 that, in order to avoid the worst impacts of human-induced climate change, global warming must be limited to not more than two degrees.

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MARCH 2014

By Lyndsay Cotton, General Manager of LCP Roofing and Chairman of the ITC-SA.

ConCreTe roof Tiling praCTiCeThe practice of mechanical fixing has been largely ignored in inland areas. With the advent of SANS10400XA in the built environment, specifiers are increasingly looking at various methods to meet energy usage requirements and generally, one of these in domestic housing in South Africa, is to increase eaves’ overhangs to the maximum.

This, unfortunately, exacerbates the issue, and the likelihood of tiles lifting or blowing off the roof increases tenfold. It is always a good idea to mechanically fix tiles with 2.8mm diameter galvanized nails of the appropriate length and at a minimum of two to three rows on all eaves and at least one row on all verges. Coastal areas will necessitate the inclusion of storm clips as well.

Use of an under tile membrane in all instances, and not only where minimum pitch dictates, should be a fundamental part of a tiled roof system. Tests have proven that the membrane plays an important part in preventing excessive pressure build-up inside the roof during high wind conditions and especially when gusting. Although modern under tile membranes serve little purpose in terms of energy efficiency, they do, however, also perform a vital function in protection against water penetration during extreme rainy conditions. Although more expensive, the use of thermally efficient membranes will serve both the purpose of prevention of pressure build-ups and serve energy efficiency requirements.

MeTal SheeTingWhilst concrete or clay roof tiles have always enjoyed a timeless acceptance, the acceptance of metal sheeting as a domestic roof covering in South Africa has undergone a more seasonal popularity. Unfortunately, and especially during times of wane, good sheeting practices have fallen by the wayside and skills are lost.

SoMe iMporTanT ConSideraTionS:

Terrain CaTegorieS Should be Carefully aSSeSSed

Category one is defined as exposed smooth terrain with virtually no obstructions and in which the height of any obstruction is less than 1.5m. This category would include sea and lake shores, treeless plains with little other than short grass.

Category two is defined inter-alia as undeveloped outskirts of towns and suburbs, with few trees, hillside or other exposed areas. Newly developed estates would fall into this category.

Category three will generally include closely spaced obstructions having the size of domestic houses and also wooded areas and suburbs which are fully or substantially developed.

Category four will be terrain with numerous large, tall and closely-spaced obstructions and will include large city centres and forests.

Whilst most popular manufacturers and suppliers specify a minimum standard for their fixings or fixing spacings, the caveat is that they allow or design for a category three or even four in their minimum design standards and this is often either not known by or ignored by the system specifier.

A terrain category two roof, for example, should have a factor of 0.8 applied to all purlin spacings and a factor of 0.65 applied to terrain category one roofs.

Lack of sufficient purlins or inadequate spacings and the fixing of the purlin itself to the underlying structure is probably one of the single most common reasons for upliftment of sheeting systems.

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MARCH 2014

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roof heighTS, loCaTionS and elevaTionS

Buildings over 10m in height should have purlin spacing reduced by an additional 20% over and above the aforementioned. Furthermore, it is deemed good practice in many other countries to add an additional purlin (in between the standard spaced runs) over the last two trusses at all eave gables.

ConCealed fix profileS

Concealed fix profiles, although primarily designated for the industrial market, are very popular in residential applications, but they come with their own challenges. The 700mm wide profile is widely used in inland applications and yet it is often forgotten that this profile is ideally intended for low and medium wind conditions – not exactly the right choice in newly developed and very exposed locations.

overhangS

Overhangs are considered to be a weak point in any roof and should be kept to the minimum and, where unavoidable, overhangs greater than 500mm should be positively fixed. This will also include all lean-to roofs, canopies, walkways, gate entrances, etc. Strong wind resistant soffits should ideally be installed under all overhang areas.

fixingS

The popularity of light gauge steel structures or purlins is growing and, once again, the specifier and consumer need to be aware that traditional fixings and fasteners, such as standard tek screws, are not suitable in these applications. The chance of separation between the sheet and purlin is a very real possibility in high wind load conditions. Kare Industrial Suppliers can be contacted for expert advice in this regard.

The importance of the correct choice of fixing solely, if not for any other reason than to prevent separation, cannot be stressed enough.

holding down STrapS

Little cognizance is taken by the homebuilder of the SANS10400-K requirements for roof wire or straps. A minimum of two strands of 2.4mm galvanised wire to be built in a minimum of 340mm into brickwork for tiled roofs. For sheeted roofs this requirement extends to a minimum of 1.2mm x 30mm hoop iron strapping built in a minimum of 600mm deep into brick walls. In both instances, sufficient tail should extend above the wall plate level to completely wrap over the truss. In no instance should the positioning be further than 200mm from the centreline of the roof truss. A prudent homebuilder should request a truss layout plan well before completing his brickwork.

aCknowledgeMenTS:

Marley Roofing, Safintra

for More inforMaTion, ConTaCT:

(c) 082 441 5026 | 0861 LCPROOF(e) lyndsay@lcproofing.co.za (w) www.lcproofing.co.za

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MARCH 2014