Questions and answers with industry professionals about these little but crucial fixings that keep the roof overhead.
Easily overlooked and often undervalued, the screws and fixings that keep metal roof sheets in place are just as important as the roof itself.
“You can have the best roof sheeting, but once your fasteners fail and the sheeting is lying in a car park somewhere, what good is it?” asks Reitze Hylkema, managing director of Kare Industrial Suppliers. “The whole roofing structure is one system – the steel, insulation, roof sheeting, gutters, flashings and every small fastener – it all forms one unit. Therefore all the components should have the same lifespan and need to be compatible,” he points out.
Walls & Roofs asked professionals in the industry a couple of questions and the following people weighed in: Reitze Hylkema of Kare Industrial Suppliers, Tammy Grove of Safal Steel, Llewellyn Africa from Corroshield South Africa, Sally Stromnes from Safintra and Wayne Miller from BlueScope Steel Southern Africa. The Southern African Metal Cladding and Roofing Association (SAMCRA) director, Dennis White, also commented on behalf of the association. This is what they have said:
What is law?
Hylkema: The standard that prescribes fasteners for roofing is SANS 1273. It was revised in 2009, when more emphasis was placed on corrosion resistance of the fastener. However, we still see failures because while it is one thing to have a standard, it is another story for the industry to apply it or for building inspectors to correctly police it.
White: With very few standards being obligatory, it is dependent on specifiers to specify compliance with the code. However, all buildings constructed within the jurisdiction of local authorities of South Africa are regulated by the mandatory National Building Regulations and Building Standards Act (103: 1977). These regulations set the minimum requirements to ensure that buildings are designed and built so as to provide their occupants with a healthy and safe environment.
Regulation AZ4 of the National Building Regulations (NBR) states that all functional regulations will be satisfied by adopting the building solutions that comply with the relevant parts of SANS 10400, which in the case of roofs is Part-L, while Parts A and B also have relevance.
Unfortunately the current version of Part-L does not specifically address fasteners. After pull-out strength, the most important factor influencing the performance of a fastener is durability, in other words, its ability to resist the corrosivity of the environment in which it is placed.
Clause 126.96.36.199.c of Part-L requires that any roof covering, or part thereof, “shall resist, with an appropriate degree of reliability over its design working life when being maintained, … the effects of UV radiation without the deterioration of its essential properties, … chemical attack from common atmospheric gases and saline atmospheres in marine environments and puncturing and penetration when the roof is in use”. Clause 188.8.131.52 requires that “products used in roof coverings… shall preserve their properties satisfactorily with normal maintenance, specified by the manufacturer for at least… 10 years”.
Clause 3.12 of Part-B defines the design working life as “Assumed period for which a structural component is to be used for its intended purpose, without… severe abuse or poor maintenance and without major repair being necessary”. Clause 184.108.40.206 requires a design working life for cladding and roofing materials of 15 years.
What amendments can be expected?
White: Currently most parts of SANS 10400 are either under review or being rewritten. Clause 220.127.116.11 has been amended to 15 years in the draft for Part-L. The draft also contains clauses pertaining to fasteners and their compliance with SANS 1273, which is a hybrid of Australian codes AS 3566 parts 1 and 2 “Fasteners for roof and wall coverings in the form of sheeting”. SANS 1273 Clause 18.104.22.168 “fasteners coating” requires “… the corrosion resistance of the roofing fastener equals or exceeds that of the roof sheeting.”
The forthcoming code for metal roof and side cladding to be known as SANS 10237 also addresses the subject in greater depth together with other aspects pertaining to fasteners.
What are some of the biggest failures attributed to?
Stromnes: Fastener failure is primarily due to inadequate or non-compliant coating of the fastener. The coating is the sole protection provided to the fastener substrate, and as it weathers off, the shank and head become exposed to water and contaminants, which rapidly eat away at the core steel, causing fasteners to fail.
Grove: Fasteners are a major contribution factor to corrosion on the sheeting. As they are fundamental in holding the sheet down, there should be no compromise on quality to try to save costs.
Africa: Structural failure of fasteners occurs as a result of corrosion. There are too many false claims coming from suppliers and no single governing body policing the market to verify which fasteners conform to the standard and which don’t. In addition, application failures are the result of incorrect installation due to a lack of knowledge.
What other factors influence the performance of fasteners?
1. Thermal expansion: with pierce-fixed profiles, thermal movement, particularly of long sheets, can result in failure from fatigue. Long fasteners fixed through insulation are also prone to this form of failure. Metal cladding fixed over insulation boards or blankets can expand 50% more than without insulation. Aluminium has a coefficient of expansion twice that for steel. Aluminium cladding requires the fasteners to be fitted into oversize holes to avoid the development of slots or in extreme cases cracks. Buckling of flashings is induced by thermal expansion as is the shearing of blind (pop) rivets.
2. Incorrect placement of fasteners: misaligned and/or over tightened fasteners break the weatherproof seal of the washers, create pockets susceptible to crevice corrosion and in extreme cases, induce cracking in the ribs of the cladding. The pull out/pull through values are negatively affected.
3. Wind loading: flashings are commonly fitted on the extremities of the cladding envelope where the wind loading is at its most severe. It is imperative that they are fixed with an appropriate fastener. Blind rivets rarely meet the requirements.
What are some of the biggest challenges in the industry?
Africa: We find that users who are skilled in traditional designs are very reluctant to consider innovation and embrace new techniques.
Hylkema: Revisions to the energy-efficiency standards have resulted in insulation being specified in thicknesses never seen before, which requires extremely long fasteners. This brought with it concerns about the stability of the insulation and the entire installation. Also, there is no independent body to test the coating on fasteners, so there is no proof that the products conform to the standards as they claim to do.
Stromnes: Independent and credible verification of coating properties claimed by fastener vendors is not stringently applied. Many fasteners sold in South Africa are not compliant with our legislation, and are not manufactured to the standards required for the Class of fastener they claim to be.
Traceability of fasteners is another issue – if fasteners cannot be identified by the manufacturer, and tracked back to the actual batch of manufacture with complete certainty, the responsibility for fastener failure falls on others in the supply chain, and not on the fastener manufacturer, which is where the responsibility truly lies. This has massive cost and credibility implications for installers, suppliers and professionals on the project.
White: It is to be noted that warrantees issued by the major suppliers of coil used for the manufacture of cladding are conditional to the cladding being fixed with fasteners, the protective coating of which, is specified in the body of the warranty for the different environments in which the cladding may be installed.
Most cladding manufacturers specify the size and type of fasteners to be used but only a few specify the protective coating.
Another problem is that builders’ merchants sell a variety of mostly unsuitable fasteners, ranging from nails with plastic tops to drive screws, often with nominal electroplated coatings coupled with inadequate washers and non-UV resistant weather seals. Most are unaware or simply choose to ignore the need to match the durability of the coatings on the fasteners with that of the cladding material. This situation is acerbated by the flood of inferior imported fasteners with coatings, claimed to comply with international standards, but which rust within a year of being installed. The builders’ merchants and importers are flagrantly disregarding the Consumer Protection Act.
How has the industry changed over the last few years?
Hylkema: Up until about five years ago, virtually none of the roll-formers specified the type of fastener or the coating. This has changed and over the last two to three years, the bigger roll-formers have started specifying that roofing contractors must use the fasteners with the correct coating on it. Although it has taken time to filter through the industry, we are seeing improvements.
When specifying roofing accessories, what are the key points to consider?
White: Until such time as SANS 10237 plus the revised parts of SANS 10400 are published and hopefully, sometime in the not too distant future, the Department of Trade and Industry will require imported products to comply with internationally accepted codes, it is up to the professionals responsible for specifications and reputable cladding contractors to ensure that the fasteners used in the metal cladding industry are both structurally sound and durable.
1. Match fasteners to the quality of sheets. Even better, understand the site location and do a simple analysis of the environment before determining the grade of fasteners to use.
2. Only buy products from known manufacturers with global experience in tackling various site situations in order to reduce the risk of failure.
3. Ask for specifications and test reports to verify the product details.
4. Enquire about quality control processes to understand the difference between a mere trader and one who is representing the manufacturer directly.
1. Use Class 3 or 4 fasteners with a similar coating alloy as the sheeting, as the fasteners are the primary source of corrosion on the sheeting.
2. All screws should have rubber sealing washings which should be free of carbon fillers.
3. Fasteners should be as durable as the roof sheeting. The minimum class as suggested for the type of sheeting should be used.
4. If an inferior class fastener is used, the replacement of the sheet will be at an earlier interval.
1. The lifespan of the roofing fastener should match or exceed that of the roof sheeting.
2. The material of the roofing fastener must be compatible with the material that the sheeting is made of so that you don’t get galvanic corrosion between the fastener and the roof sheeting material. Compatibility of the roof fastener with the roofing material is crucial.
3. Ensure that the coating on the screws will last in the environment that they will be used in.
4. Make sure that the supplier of the fasteners can back up what they claim about their fasteners. Stromnes added that “this ties back to traceability and therefore accountability by the fastener manufacturer, who should be prepared to stand behind his product for the duration of its service life”.
1. At BlueScope we recommend the use of fasteners according to Australian Standard 3566.2-2002.
2. All sealing washers supplied on self-drilling fasteners must be non-conductive (i.e. having a conductivity ≤ 0.5 x 10ˉ6 amps).
3. Stainless steel fasteners are not recommended for use with any metallic coated or prepainted steel.
4. Accessory fasteners such as pop rivets should be made from aluminium when fastening metallic coated or prepainted steel.
Do you have any advice to enhance durability?
Grove: Regular maintenance of the material will extend the longevity of both the fastener and roof sheeting. Washing with fresh, clean water should be done at least every six months and more frequently at the coast. However, never use abrasive or solvent type cleaners and don’t use rough cleaning cloths, wire brushes or steel wool to clean the roof. Also, touch-up paint is not recommended.
Miller: When a long lasting product is used for roofing, walling or accessories, it is vital that the performance of the fasteners used to fix the cladding and accessory materials, gives the same or superior life as the cladding or material with which they are used.
Have there been any new developments?
Africa: A new drill point, S17, has replaced the Type 17 or TY17/T17 drill point for timber application. The S17 allows drilling as close as 10mm from the edge of a timber purlin without splitting it, compared to the T17, which in the same scenario tends to cause the timber to split.
“Remember, the cladding, insulation, fasteners and ancillary items form a system,” stresses White. “The cladding and flashings provide the weatherproof envelope, insulation the thermal value and the fasteners anchor the system to the supporting structure. Any system is only as good as its weakest link.”
The Southern African Metal cladding and Roofing Association, which came into being in October 2013, was formed by concerned players from all sectors of the industry, with the aim of restoring the credibility of the metal cladding industry. For further details of their objectives please visit their website www.samcra.co.za.
Thanks to SAMCRA, Kare Industrial Suppliers, Corroshield, Safal Steel, Safintra and BlueScope Steel Southern Africa for the information given to write this article.