The pain and suffering emanating from Knysna’s devastating fires need no elaboration. Lives lost and hundreds of homes destroyed at a cost of billions of rands. But in true South African spirit the people of Knysna and the surrounding areas are doing their best to move on. Infrastructure is being rebuilt and many new, modern houses are rising from the ashes.
Since SASFA (Southern African Light Steel Frame Building Association) presented a seminar in Knysna on light steel frame building there has been great interest in light steel frame building and the first house built in this manner - the Wilcox Jones house in Campbell Street – is nearing completion.
“There is no doubt that there are many advantages to LSFB,” says the project’s architectural draftsman Nelis Genade. “Firstly, it is a cost-effective building method, with financial savings coming mainly from significant time savings to complete the building project, less rework, reduced logistical costs –which are of growing importance due to the escalation of fuel prices and general construction inflation - and a drastic reduction of rubble on building sites, when compared with the brick-and-mortar alternative.”
He adds that the finishes in LSFB structures are typically better than in conventional houses and that the thermal insulation is excellent. “This ensures a really energy efficient building making it easier to keep cool in summer and warm in winter,” he says.
It is a well-known fact that a LSF building is significantly more energy efficient than heavy masonry dwellings – both with regard to ‘embodied energy’ of the materials and components, as well as ‘operational energy’ relating to heating and cooling of the building over its design life.
According to John Barnard, Director of SASFA, minimum insulation requirements of LSF houses are specified in SANS 517 for each of the six different climate zones in South Africa.
“Knysna falls in the ‘Temperate Coastal’ zone and external walls must have a minimum total R-value (the measure of thermal insulation) of 2.2. By using Isover’s Cavity Bat (102mm thickness) glass wool insulation, the walls have a better insulation with a R-value of 3.23 – almost 50% higher than the minimum requirement, and five times higher than the insulation offered by a double leaf brick wall. In addition, double-glazed PVC windows have been used for their excellent thermal and acoustic insulation properties,” he says.
Charl van Zyl, who represents Rancor Meyer Bros the contractor building the Wilcox Jones house, explains that the project comprised the demolition of the remains of the burnt-out house, the digging of the foundations, the laying of the slab and then the erection of the new 200m² double-storey LSFB house. Work began on the 19th September 2017 and will be completed by the 10th December 2017.
“That is 82 days or 12 weeks, which is remarkable for a house of this size and detail,” says Van Zyl. “In fact, this is one of the main reasons why the owners chose LSFB as they are renting accommodation while waiting for the house to be completed. This speed of construction will translate into significant bottom line savings for them. They were also attracted by the energy efficiency and the saving of electricity for heating and cooling over the long-term.”
Van Zyl adds that a particular advantage of LSFB on this steeply sloping site, was that the light steel frames and trusses, as well as the cladding and lining materials, were relatively easily brought up to the site. “The delivery and handling of heavy masonry materials would have been a huge problem and the significant increase in loads required with these materials compared to LSFB materials would have exacerbated the situation”, he says.
One of the unique solutions that Rancor Meyer Bros introduced on this project was the pre-painting of the external cladding material while it was still on the ground. Van Zyl says this was quicker than if they had painted after erection and added that both sides of the FC planks could be primed enabling a better-quality job overall.
Meanwhile Rancor Meyer Bros have signed up a further three residential projects in Knysna Heights since they started building in Campbell Street. “By observing the rapid progress of the building process, architects, developers and owners are clearly impressed by light steel frame building,” van Zyl concluded.
The external cladding - which consists of OSB board fixed to the light steel frame covered by the vapour permeable membrane (Tyvek) and cladding on the outside with fibre cement planks fixed in shiplap fashion – was supplied by Marley Building Systems.
The steel frames for this project were profiled using ArcelorMittal’s high strength galvanised steel sheet by Cape Town-based light steel frame manufacturer, Pholaco.