Be roof cover clever
at roof tiles and roof sheets and what to select for commercial,
industrial and residential sectors.
When it comes to choosing a roofing material, generally the homeowner or client needs to answer several questions before making a final selection: what is the function of the roof? Will the selected covering complement the style of the building? What are the cost implications? However, the choice of roofing material is mostly dependant on the homeowner or client’s personal preference. In some housing estates, the choice of roofing material is dictated by the estate itself to maintain the aesthetic of the estate. The function of the roof also determines the materials – for instance, a warehouse or factory must use sheets due to the long span and low pitch usually associated with these types of buildings. In terms of application, when it comes to market sectors such as commercial, industrial or residential, sheets may work well in all three applications although they really come into their own in the industrial market. Tiles are well suited for commercial and residential markets.
Tiles or sheets?
Why would you choose a roof tile over a roof sheet? The life span of tiles is longer than that of sheets. Roof tiles are very diverse, boasting a plethora of different profiles, colours and colour blends. The design range is wider than that of sheeting, giving architects and homeowners more of a creative choice with regards to the look and feel of the roof and building in general. When it comes to pricing, tiles are more cost effective than sheets, however, it costs less to keep a sheeted roof maintained. Tiles are more resistant to corrosion than sheets, especially in coastal areas. Aluminium sheets are more resistant than zinc alum sheets – in fact, zinc alum sheets should not be used within 5km of the coast. Tiled roofs with a pitch below 17.5⁰ will leak due to the low pitch. Sheets are a better choice on low pitch roofs and profiles such as IBR or saflock are well suited for low pitch roofs. From a security point of view, sheets offer better security than roof tiles, which can be removed to gain access to the ceiling void of a house, whereas sheets are physically screwed to the purlins. High wind areas could be better suited for sheets which have been positively fixed to the purlins. Metal roofs are considered green as they can be recycled and produced from recycled materials. Sheeted roofs also use less timber in the roof structure than tiled roofs. For a sheeted roof the maximum centres of the roof trusses are 1.2m as are the 50×76 purlin distances. The trusses for a tiled roof are spaced at a maximum distance of 760mm and 38×38 battens are spaced between 320 and 340mm. Tiles are suited for residential and commercial projects where the roofs don’t cover too wide a span due to the required pitch of 17.5⁰. In addition, tiles are better
suited for developments where cost is a consideration – for the cost-conscious developer or contractor, there could be substantial savings. Some themed housing estates specify various tile profiles and colours to achieve a certain look, for example the flat slate concrete tile for an English feel or double Roman Tuscan blend for the Mediterranean look.
Andrew Gove, director at GWR Roofing, shares installation challenges and best practice advice with us. “Be sure that you are buying from a reputable supplier – all the main suppliers in South Africa are SABS approved and their mark should be on the product. Don’t buy cheap imports! Product and supplier information is freely available online and it would be a wise decision to read up on the product you will be installing on the roof.” Installing roof tiles or sheets has its challenges. In terms of tiles, fitting the trusses from their stacks to the roof can take time and is hard work. Tiles that have not been cured properly can result in high breakages on site – normally a reputable supplier will replace breakages, but time and money is wasted in the process. Gove further mentions that tiles that have not been laid correctly will break or chip when walked on. Poor batten installation will affect the performance and aesthetics of the roof. If the trusses are not straight and the battens not lined, the roof tiles will show obvious ripples and waves. Battens that have been incorrectly spaced will also cause a problem; if the battens are spaced too close extra tiles will be used and shortages will result. If the tiles are spaced too far apart, the tiles could leak. Generally, some roofing installers do not lay ridges very well. They might neglect to lay down a line of DPC before laying the ridges, get the cement mixture incorrect or not cut and clean the mortar after laying the ridge. “Proper checking and reporting of breakages of tiles by staff on site is crucial, proper training of erector staff is essential,” says Gove. Tiles are robust and easy to work with if staff are trained and know what they are doing. Sheets can easily be scratched through poor handling and are costly to replace. Trimming sheets in the valleys and on the hips can sometimes be untidy due to incorrect training or a lack of proper tools. The same goes for the installation of screws – drills without a clutch are often used to install tek screws (used to secure IBR or corrugated sheeting to roofs); these drills often overtighten the screw and cause dents.
Lack of skill when it comes to installing flashings, such as ridges and barges, often results in poor finishing. It is not possible to install sheets when the wind picks up enough and a sheeted roof has to be totally dry before people can safely walk on it to continue installation.
WHAT TO CONSIDER WHEN CHOOSING ROOFING MATERIAL
- What is the function of the roof? Is it commercial, residential or industrial?
- Will the look complement the style of the building?
- What are the cost implications?
- How long is the roof expected to last?
- What is the prevalent weather in the area?
- In the case of a re-roof, what covering is most suited for existing roof trusses?
- What is the specified pitch of the roof?