Application
To bind the reed a thatcher needs the rounded needle, the shuttle and a needle with an eye and a barbed needle. Thatching, in most cases, begins at the eaves of the right gable on the side facing away from the prevailing weather.
On the lowermost roof batten the butt ends of the reed bundles are positioned facing downwards. Then, their ties are loosened, so that a firm layer of about 10 cm of reed can be positioned with the required roof overhang.
As a first coat a layer of about 30 mm thickness should be attached to the roof battens. This coat helps to prevent that the pointed ends of the reed bundles are driven under the lathing.
Ties and the so called bending tension fix the first courses to the roof. The tension is generated by raising the bearing edge at the eaves by 5 – 7 cm in relation to the level of the lathing (a so called eaves board is used). „Kniep” is the German term describing the difference in height between these two levels.
The pressure of the horizontal sways places the individual reed layers under tension which causes the characteristic bend in the originally straight stalks. This bend is transmitted to all following layers. That is why mostly short reed is used for the first layer as it can more easily adapt to the tilting board
The roof covering should have an overhang of at least 0.5 m all-round. The eaves projection (measured from the masonry) should measure between 0.15 m and 0.30 m. The projection at the verge, however, should only lie between 0.15 m and 0.25 m. The visible front end of the eaves should be at least 30 cm thick. In Northwest Germany the front of the eaves runs mostly horizontally whereas in Mecklenburg-Vorpommern very often it is in an angle to the main roof (Mecklenburgian Eave). The angle from the eaves to the main roof should not exceed 85°.
With a pin layers of a thickness of 10-20 cm (and with a width of approx. 1 m) are pressed against the roof with the help OF SERVERS
The butt ends of the first course (also called brow course) are then moulded and dressed with the legget. Now the sways (iron rods) are placed on top of the first course and then tied.
From a reel the binding wire is threaded through the needle (which is mostly curved) and is then inserted in the reed layer above the roof batten. With a second needle (with a hook), inserted below the batten, the binding wire from the curved needle is caught and is pulled up from under the reed. Then the binding wire is cut off, one of the ends of the wire is bent into a loop, the other is pushed through the loop, the wire is pulled tight and knotted, so that it presses down the layer of reed.
Per running meter 5-6 bonds are necessary. The distance between the bonds should not exceed 25 cm (20 cm for very steep roofs) (According to the Rules for Reed Thatching).
It has to be taken care, that the following layers are placed staggered to the preceding layers.
The reed roof covering should at least have a thickness of 0.3 m measured vertically to the face of the roof. When thatching, the thatcher measures the thickness of the roof with a scale on his needle.
In this way layer after layer is placed on the roof till the thatcher reaches the ridge. As the different layers overlap each other, the ties lie inside of the roof covering. After the binding the individual layers are dressed with a legget and thus brought into a flush position with the surface as a whole. If possible, the whole length of the roof should be thatched in one go.
Valleys (where two roofing planes meet) should be 1.5 times thicker than the main area of the roof. In some cases the ties of each layer are covered with 500 bitumen board. The slope of roofing planes meeting in valleys should not fall below 40° (according to The Rules for Reed Thatching). The valleys receive a rounded layer of thatch and can be broadened with the help of an additional cross lathing. If the reed roofing in the valley comes in contact with a differently covered roof area, the reed of the valley should overlap this area.
The covering of a hip should be rounded. Directly on the hip the stalks should run parallel to the hip rafter. Then the abutting stalks should be brought into the normal orientation.
The verge of a thatched roof bears the brunt of the weather, so that strong winds can cause damages. To avoid damages a so called weather board (gable board) can be used. There is also the possibility to use a narrow weather board or none at all. In this case the verge should be thatched with the material of the roof covering and it should be thatched against a tilting board.
It should be paid attention to the fact that the roofing has to have an overhang of at least 15 – 25 cm over the gable wall and that the reed stalks should not be placed in an angle of over 45° to the verge (according to The Rules for Reed Thatching). If the reed is applied without a tilting board it should show an angle of 5° to the verge. Furthermore, for the verge reed with fine stalks should be used.
Dormers can be thatched in any shape. Joining areas should be rounded and should be 1.5 times thicker than the main area of the roof. Dormers should have a pitch of at least 40° (According to The Rules for Reed Thatching)
The transition between the dormer and the main roof area should measure 0.6 m – that is why a sufficient distance to hips, valleys, verges and other dormers is necessary.
The design of the side gutters of dormers should help to lead off rain water as far as possible and in direction of the main area of the roof (see section 4 of The Rules for Reed Thatching)
Connections with other roofing materials and rising parts can be either concealed or overlying. When working with metal the concealed flashings lie under or in the reed layers and are invisible. If the overlying version is used the flashing plate lies on top of the roofing and has to be fitted in accordance with the „Rules for Metal Work in the Roofing Trade”.
Either single or double junction plates can be used for the flashing to the masonry structure. Upper flashing has to be water-tight. The problem of flashings at rising parts can be solved using constructions as for example projecting walls.
When designing the chimneys the respective regulations of the construction authorities (building regulations of the individual federal state) have to be taken into consideration. Chimneys in buildings with soft roofing have to leave the roof at the ridge and have to have a height above the ridge of at least 80 cm. Chimneys should keep a distance of at least 1 m to valleys, hips and dormers.
Furthermore, chimneys should be fire-proof, sufficiently heat-insulated, tight and resistant to wear from heat and smoke. For chimneys in houses with soft roofing the thickness of the side walls, measured 50 cm below the surface of the roof, should not fall below 24 cm for fire safety reasons.
The rendering coat on the exposed surfaces inside of the house should have a thickness of at least 5 mm. Chimney and thatched roof should be joined undercutting the masonry of the chimney. If this is not possible the joint should be a side wall connection. The connection at the eaves and at the ridge has to be in accordance with the „Rules for Metal Work in the Roofing Trade”.
