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.
Thatch roofs require regular inspections every 5-7 years. 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. 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 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. 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.
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.
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. 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). This means that the twine could eventually become exposed after 20 years or so.
Fire safety distances for thatched roofed 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 is to prevent a fire from spreading to neighbouring structures. 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.
Thatch and lightning
Thatched roofs in areas of South Africa where lightning is prevalent must be protected by suitable lightning conductor systems.
The vulnerability of a thatched roof to a lightning strike is determined by the “lightning flash density” of the area. “Lightning flash density” is defined as the average number of lightning strikes per km² per year.
Thatch roofs and insurance risk
Because 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.
What is the experience and competence of the thatching contractor?
- Is the thatching contractor registered with the Thatchers Association of South Africa (TASA)?
- Is there a Certificate of Compliance from a competent person?
- What is the present condition of the roof?
- Has the building been rewired?
- What is the structure of the walls (brick & mortar, timber)?
- Does the kitchen have a concrete ceiling?
- Does the building have a chimney? – If yes, does it extend above the roofline?
- Is there a fireplace in the building, fuelled by solid fuels (e.g. wood)?
- Are the chimneys fitted with spark arrestors?
- Does the building have an approved lightning conductor system?
- Has the thatch been provided with a fire retardant system?
- Is the building protected by a drencher system?
- Are any fire fighting hose reels installed at the premises?
- What is the distance to the nearest Fire Station?