2.1 Roof Shape and Design
2.1.1. 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, www.riet.com)
Illustration 3: This house has
a roof pitch of 55-60°, which
has a positive effect on the roof's
longevity.
Illustration 4: A house with an
extremely low roof pitch.
Illustration 5: The roof area of
the low-pitched roof 6 years
after thatching.
2.1.2. Valleys
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.
2.1.3. 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.
Illustration 6: Here the problem
is that the run-off rain water of
the dormer and the valley are
funneled together.
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.
2.1.4. 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.
Illustration 7: Provided you use reed of similar length, the thicker the roof covering gets, the lower the inclination angle of the reed will be.
Illustration 8: Two serious mistakes:
1. The low inclination of the dormer cover
2. Using short reed with a thick roofing in the upper part of the roof
The result: The reed is almost horizontal; water penetrates the roof and makes it moist throughout.
Illustration 9: The pitch of the roof might be even higher than 45°, but the inclination of the individual reed stalks is just 12°, whereas 30° are recommended. The result: Damages from moisture intrusion.
Go to Proper Ventilation of Thatched House…
Back to overview.
