Apart from the growth of algae and moss also rodents, birds and storms can damage a thatched roof. Below we will give you an overview over different possible damages caused by rodents, birds and storms and how they can be fixed.
Cause of Damage
Damages by Rodents
Popular myths claim that in the past rats and mice caused damages to thatched roofs. As at that time the attics were very frequently the place to store the crops it is more likely that the rodents were attracted by this food source than by the thatching reed, that might have been used primarily as a nesting hole.
Apart from the occasional marten moving into the attic Hiss Reet in recent years has not heard about any other damages caused by rodents.
Damages by birds
Not only humans enjoy and value thatched roofs. Also among our feathered friends thatched roofs are highly popular. In past times it was quite common that the ridge of a thatched house served birds, especially sparrows, as nesting site. A reason might have been the warmth escaping through the ridge as the highest part of the roof. Today a narrow-meshed net prevents birds from nesting on the ridge of thatched roofs.
However, the stalks of fine thatching reed still are a popular building material for bird´s nests of all kinds of birds. Once the first stalks are picked out entire holes are produced by the birds. Later on these holes will have to be mended or even re-thatched.
Storm Damages
During a storm the pressure on the windward side and the wind suction on the lee side of a house are considerable.
Normally the elastic and flexible soft roofing is capable of resisting this wind stress. A decisive factor for the susceptibility of soft roofings against storm damages is the shape of the roof as a whole, especially its height, the shape of the gable ends (so hipped gables present a smaller target for the wind load than full gable walls), differences in details on the roof and the positioning of the roof in relation to the landscape.
In order to help the roof covering to absorb the wind load and the thus caused vibrations of the roof framework pressure compensation (e.g. through the Owl Hole and an effective ventilation of the roof covering) under the soft roof have to be ensured.
This applies in particular to thatched houses with converted attics which are prone to suffer considerable damages caused by the direct impact of dynamic pressure and wind suction forces. Typically storm damages occur at the ridges and the verges, less commonly also at the main roof area. Especially areas affected by algae and moss growth or previously damaged by rodents or birds are susceptible to storm damages.
Different Options of Repairing a Thatched Roof
Patching the Roof Skin
First the hole in the roof has to be cleaned by hand and all damaged or mouldered stalks have to be completely removed.
The exposed binding wire is bent downwards. According to the size of the hole a conical reed stopper is crafted and should be tied up two to three times.
The stopper is inserted in the hole in the roof in such a way, that the butt ends face outwards. With the hand or the legget the stopper is dressed, so that he becomes flush with the upper edge of the roof surface. When repairing damages at the verge and at the valleys the stalks are pulled out by 10 cm, so that they protrude over the desired area of transition. Then handful by handful of fine new reed stalks are stuffed into the roof and finally dressed.
For further protection 5 mm galvanised iron wire is placed along the verge and tied to the roof battens. Valleys are repaired accordingly but no galvanised iron wire is used in this case.
Overlaying the Roof Skin
The covering-over of roofing that has grown thin is condemned by the technical literature. This new outer coat creates a heterogeneous roofing with a central joint.
This neutralises the special constructional features of a homogeneous, single-shell roof construction and leads to a reduced durability of the overlayed roof.
Furthermore, the difference between the costs of covering-over and re-thatching the roof is quite small as the biggest part is made up by wage costs anyway.
Replacing the Roofing
In contrast to the covering-over of the roof it is good professional practice to replace it instead. If the seam or the binding is visible on a thin roofing it is removed completely, working square wise. Beginning from the bottom the roof is re-thatched in layers. If the roof surface above the hole is in good order two bonds (or seams) are loosened and the remaining material is bent upwards with help of a board and then supported (for instance with a short piece of wood that is jammed between the board and the roof batten). The new roof covering is then pushed as far as possible beneath the board and is tied or sewn under cover.
The topmost layer should be made of very fine reed that is packed loosely under the supporting board. Then the supporting board is removed and the covering layer is dressed with a legget. The mended surface of the roof is then visibly sewn on two or three roof battens.
Repairing the Ridge
When the ridge of a thatched house is damaged minor damages can be mended with an extra layer of reed placed on top of the damaged area which is then fixed by sewing or binding. However, it often makes more sense to re-thatch the whole ridge. In this process the upper bottom layer should in any case be checked and re-thatched if necessary.
Repairs on the heather ridge are easy. Normally the original heather, which is already shrivelled, can just be replenished with fresh heather. After 2-3 years the wire (chicken or rabbit wire) should be retightened so that it lies tight against the ridge and protects the heather against storms.
