ROOFING
The roof’ s orientation and shade from surrounding trees can further affect its rate of deterioration. These considerations also apply when thatch is covered with another material or roofing system.
Fitting an alternative material over thatch may improve the building’ s external appearance while retaining a rustic interior. Covering a thatched roof with concrete tiles, corrugated sheeting or another material is commonly known as over-sheeting or overcladding. However, the practice presents significant technical and safety risks.
The risk does not necessarily lie in the covering material, which may be noncombustible, but in its effect on the existing roof. The application, installation method, and other prerequisites require a thorough technical assessment.
Sisalation, fire blankets, and the spray layer
Many thatchers recommend installing sisalation directly above the thin internal spray layer as a fire precaution. In the Cape, where thatching reed is commonly used, fire blankets and drencher systems may also be installed. Drenchers wet the roof’ s exterior to protect it against radiant heat and small ignition sources.
A successfully evaluated fire-retardant product changes the fire behaviour of the thatch layer and its ease of ignition from inside and outside the building. Based on its performance during testing, the roof system may be classified as Class A, B, or C. These classifications help determine the applicable safety distances under SANS 10400-T.
When tiles or another material are installed as replacement roofing, all the thatch should first be removed. If only the internal spray layer is retained to preserve the appearance of thatch, insurers may still classify the building as having a thatched roof.
Voids between the two layers
Placing a covering over thatch creates a void between the two layers, similar to the void produced by an incorrectly constructed ridge. If a fire starts inside the building or roof space, this void can supply oxygen and trap heat, significantly fuelling the fire.
Before
The association also receives complaints about birds and, in particular, bats nesting in these spaces when they gain access.
Accelerated decay and rot
Over-sheeting can create a new dew point within the roof construction, causing condensation to become trapped in the thatch. This slows the evaporation of moisture and prevents the material from breathing. If the thatch is already damp or in poor condition before it is covered, it will continue to rot and deteriorate.
As the thatch decays, falling dust and weathered debris will persist and may increase. The underlying material is also more difficult to reach once covered, making the problem harder to address.
The appearance of the interior may change as the thatch slides downwards and sinks beneath the new covering. The weight of the covering also restricts maintenance. Over time, the tiles may lose their stable base, potentially causing the roof to sag.
Increased fire and safety risks
Any proposed covering requires the prior fire testing of the complete roof
Thatch should remain exposed to the environment so that it can weather naturally.
system. If the thatch ignites, the covering may have to be removed before the fire can be extinguished.
The external covering makes it difficult to identify the origin of a fire or reach its seat. Heat can become trapped inside the building without adequate ventilation, while the void between the two layers supplies oxygen and supports further fire growth.
Removing the covering exposes firefighters to additional hazards. Trapped toxic gases and smoke also create a life-threatening environment for occupants and firefighters.
Internal fire detectors may not activate quickly enough if a fire smoulders beneath the outer covering. Tiles can also create
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