Onduline Over-sheeting on Thatch Roofs

Onduline over-sheeting on a thatched roof
Onduline is an extremely economical, flexible roofing product made from bitumen saturated organic fibres and sold in sheets to be fitted to residential or industrial roofs large and small. Onduline is a great product to use for "over-sheeting" which is the practise of fitting a new roofing solution over the top of an old, leaking or eroded roof. Onduline is a particularly good product to use for over-sheeting a thatched roof due to its flexible nature which means that the original shape of the thatched roof can be maintained - curves and all.

Thatch Specifications for Onduline Over-Sheeting

The thatch that is going to be covered must be in a very particular condition for the over-sheeting to be effective and problem free. The thatch:

  • MUST be 100% dry when the Onduline is laid
  • MUST be in good condition and must not be showing any signs of rotting

If the thatch is in this prime condition and is over-sheeted it will last for years and years preserved under the onduline where weather will not degrade the thatch. The thatch layer will also act as a great insulator for the house.

Over-Sheeting a Thatched Roof

Cintsa Thatching recently undertook an over-sheeting job on a large thatched building in the Eastern Cape. It is very rare that a thatch roof is in such a good condition that you can over-sheet but in this case the roof had been very recently thatched but was thatched very badly and leaking already. If the thatch is new like this with no signs of rotting, damp or degradation (which needs to be thoroughly checked by an experienced contractor), over-sheeting is a great option to fix the leaking.
The leaking thatched roof
The new leak-free, onduline roof
Once it was ensured that the thatch was completely dry brandering was laid over the entire thatched roof. These wooden branderings are designed to support the onduline. Onduline was then attached to the support structure using safe top screws in a colour that matches the onduline (available from Onduline).
Wooden brandering laid on top of dry
thatch roof
Fitting of the brandering over the thatch
Onduline sheeting being laid on top of
the brandering
Onduline being fixed on to
brandering with colour matching screws

Onduline roof sheeting was perfect for this roof which was made up of both straight plains and curved rondavel sections. The onduline sheeting is flexible enough to curve around shape of the rondavel sections and fit into the contours of the roof.
A straight corner section of the roof

A curved section of the roof with onduline bending to follow
the curves and contours of the roof

Onduline valley and ridge sections which matched in colour were also fitted to the roof to cover the thatch ridge and valley sections and allow adequate drainage on the roof.
Close up of one of the valley sections in the roof

A corner ridge and valley section

Corner and top ridge sections where two roofs meet

The cappings at the top of the rondavels were a little more of a challenge as the standard Onduline ridge does not fit a circular ridge. The best practise that we have worked out so far is to use the standard galvanized metal cappings made specifically for rondavels (available for purchase is most general hardware stores).
Galvanized rondavel capping fitted to the
onduline rondavel

When NOT to use the over-sheeting method

If thatch is over-sheeted when the roof or thatch condition is poor, when there are signs of rotting and degradation, when the thatch is damp or wet, there will be huge problems later as the thatch will continue to rot, dust will fall from the ceiling and it will be difficult to access the roof to fix or strip the thatch because of the over-sheeting. In the case of an old, rotting thatched roof do not use the over-sheeting method - it will lead to lots of problems later on - the roof must be stripped of thatch entirely and either re-thatched or a new roofing solution must be fitted.

For more info about Onduline visit our website http://www.cintsathatching.co.za/onduline-roofing.html


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