The company has recently introduced new methods of protecting thatched roofed structures in South Africa, and it is no longer necessary to have a 30 metre long mast installed. Should lightning strike, then current flows through the wire mesh and thermal effects (generated heat) may occur, and set the roof alight.ĭehn Africa can assist in the avoidance of lightning related disasters, and ultimately extend the lifespan of these structures, through the provision of lightning protection system components for use specifically on thatched roofs. When a thatch roof is constructed, wire mesh is used to reinforce and secure the bundles of thatch. However, prior to providing these protective measures, it is important to analyse the risk effects described in standards guide, such as SABS 0313: 1999, SABS IEC 61662-1: 1995 and IEC 62305-2. If recommended protective measures are not considered, the effects of lightning can cause serious damage. Thatch is particularly prone to ignition because it becomes ‘fluffy’ at the surface and, if moist, methane and other flammable gases can be formed. Constructed of material such as straw, reed, grass or coconut leaves, a thatched roof is more susceptible to catching alight as a result of a lightning strike than any other roof type, according to the South African National Standard (SANS). Is there a fireplace in the building, fuelled by solid fuels (e.g.Thatched roofs are extremely popular in South Africa.Does the building have a chimney? – If yes, does it extend above the roofline?.Does the kitchen have a concrete ceiling?.What is the structure of the walls (brick & mortar, timber)?.What is the present condition of the roof?.Is there a Certificate of Compliance from a competent person?.Is the thatching contractor registered with the Thatchers Association of South Africa (TASA)?.What is the experience and competence of the thatching contractor? “Lightning flash density” is defined as the average number of lightning strikes per km² per year.īecause thatch roofs pose a higher risk of fire than, say a sheeted or tiled roof, insurance companies asked to underwrite the risk of a thatch roof will typically seek answers to some or all of the following questions.

The vulnerability of a thatched roof to a lightning strike is determined by the “lightning flash density” of the area. Thatched roofs in areas of South Africa where lightning is prevalent must be protected by suitable lightning conductor systems. If a thatched lapa has been erected within the safety distance of 4.5 m, then – in common with smaller lapas – further steps must be taken to ensure adequate fire safety. This is to prevent a fire from spreading to neighbouring structures.

South African building regulations stipulate that any thatch roof covering a roof-plan area greater than 20 m² must be constructed at least 4.5 m from any boundary. This means that the twine could eventually become exposed after 20 years or so.įire safety distances for thatched roofed structures For a 175 mm-thick thatch layer, the thatching twine will generally be located in the middle of the layer (about 80-100 mm below the top surface). In general, the rate of loss in thickness may be assumed to be in the order of 20 mm to 25 mm in cover over seven to nine years. Inspections of the roof, in particular of areas such as valleys, the areas under trees, and areas with slopes of less than 45°, should be carried out regularly to determine the condition of the thatch layer. The walls and foundations carrying a thatch roof must be designed to be able to carry the additional weight of thatch when the roof is redressed. Re-dressing of the thatch cover (adding of a new thatch layer) becomes necessary when decay has reached the stage when the fixings (twine stitching) become exposed on the surface. If maintenance is not done and decay is allowed to reach the stage where the twine fixing of the thatch is exposed, then the lifespan of the roof is considerably shortened. Re-dressing of the thatch roof (removal of rotten thatch and the addition of a new layer) is usually necessary on a 15-20 year cycle. Thatch roofs require regular inspections every 5-7 years. With proper maintenance and re-thatching at required intervals, a well-constructed thatch roof should have a long lifespan of more than 50 to 100 years, or even more.

South african thatched roofs