Housing in Southern Africa September 2015

Roofing, Ceilings, Insulation & Cladding

Raising roofing requirements With the ever increasing pressure to reduce the costs of building materials, the durability of products is regularly sacrificed. The main function of the cladding system is to weatherproof the building for either its ‘design working life’ or a period specified by the owner.

W ith coated metal cladding, the steel core of thematerial and geometry of the clad- ding system provide the structural strength whereas the coating pro- vides the durability in a given environ- ment. “A cladding system comprises the profiled cladding together with the fastening method used to attach it to the supporting structure,” says Dennis White, Southern AfricanMetal Cladding and Roofing Association (SAMCRA) director. All buildings constructed within the jurisdiction of the local authori- ties of South Africa have to comply with the National Building Regula- tions and Building Materials Act, Act 103 of 1977. SANS 10400 sets out the deemed-to-satisfy rules, compli- ancewith the National Building Regu- lations. SANS 10400 Part-L requires a ‘design working life’ for cladding of not less than ten years (this has been increased to fifteen years in the shortly to be published update). In addition, any roof covering and waterproofing system will resist: • The effects of UV radiationwithout the deterioration of its essential properties • The effects of condensation at the under-surface • Attack fromcommon atmospheric gases and saline atmospheres in marine environments. Minimum thickness of protective

coatings to steel based cladding is also specified but is limited to within 5 km of coastal areas and ar- eas with ‘aggressive environments’. Unfortunately this is a classic case of one size not fitting all. There are many coastal areas where salt laden air is carried further than 5km inland such as across the Cape Flats and up the West coast. ‘Aggressive environ- ments’ is a rather nebulous descrip- tion as such environments are not always apparent. For example a rural townwith a high incidence of sulphur dioxide or wind borne fallout from tall chimneys can carry contaminants long distances from industrial plants. There are other invisible contami- nants like humidity and the period of wetness of the coating, which can have a major impact on the perfor- mance of coatings, bothmetallic and painted. Corrosion during the dry months on the Highveld is greater than the wet months. Pollutants accumulate on the surfaces during the day and are converted into a corrosive poultice when mixed with dew. It must be remembered that not all coatings react in the same way

to a corrosive agent. As an example aluminum is more resilient than zinc to chlorides but less so to highly alkaline substances. It is imperative that the protective coating to clad- ding is matched to the particular environment in which it is located. It is therefore of paramount importance that the fasteners, together with the washers are not only strong enough to resist these forces but also that the durability of their protective coating is at least equal to and preferably bet- ter than that of the cladding. The same criteria apply equally to the weatherproof seal between the washer and cladding. Premature failure of the durability of any of these components will at the very least cause leaks, the rapid deterioration and perforation of the cladding and, finally, the cladding being blown off the structure. Fasteners and washers with inferior protective coatings and weatherproof seals may initially save a few cents but will ultimately cost a tidy sum when it comes to mainte- nance. All fastenersmust comply fully with SANS 1273. For further informa- tion call SAMRA on 011 726 6111. ■

September 2015