Roof Shape and Design

Roof slope

The higher the roof slope, the less rainwater can penetrate the roofing and the less time is needed for the roof to dry after a shower. 25° Roof slope => up to 15 years
30° Roof slope => 10-20 years
45° Roof slope => 25-45 years
50° Roof slope => 45 years and longer
(Source: Vakfederatie Rietdekkers,


Valleys tend to cause several problems. If you cannot avoid them in your design, it is at least necessary to adopt special measures to achieve a durability of more than 12-15 years.

Dormer Windows

Dormer windows should be positioned with sufficient distance to valleys or other dormers, so that the exposure to moisture of the intermediate areas does not become too high (cp. illustration 3). In the case pictured the roof areas between the dormers and the valley of the portico will only last a few years.
For the durability of a dormer its slope plays an important role. It should not fall below 38° according to the Rules for Reed Thatching. If the angle of inclination above a dormer is too low, the rain water cannot drain properly; rain penetrates and soaks through the roofing.

Stalk Inclination

The slope of the canes is a result of the relation between the thickness of the roof covering and the length of the canes used. In general, the slope of the reed canes should not fall below 30°. If the slope of the reed stalks is lower than 30° water from dew and rain cannot drop freely from stalk to stalk. Instead it penetrates the cover and soaks through the roofing.