The fact that they are covered in moss will allow them to absorb the suns rays therefore defeating the.
Flat roof with stone chippings.
Stylish and practical stone chippings can help to suppress and control weed growth when used with landscaping fabric and membrane.
Gravel is used on flat roofs for two reasons.
It also provides protection from foot traffic.
Roof gravel provides a protective layer to flat roofs reducing the weather damaging effects from uv rays and heavy snow hail and wind.
The chippings are put on the roof to reflect the suns rays in order to protect the felt.
Stone and slate chippings are a great alternative to gravel offering flatter textures to finish potted plants and borders.
Whether your roof is constructed from a standard 3 layer asphalt or from rubber based compounds or even sheets they are all susceptible to the growth of moss.
To protect the underlying layer of roofing materials as is the case with built up roofs burs.
To weigh down or secure the roofing material as is the case with single ply flat roofs.
There are different types and weights of gravel used on flat roofs for these purposes.
The chips act as a barrier between non solar reflective felt and the sun basically help prolong its life span of the felt if its green mineral on your new roof you will not have to chip it as the minerals are solar reflective.
Two common problems faced by owners of flat roofed properties are the build up of moss or silt and the free movement of improperly secured gravel chippings or pea shingle from the surface.
These issues are not something that you should encounter in the natural lifespan of your flat roof so should be taken as a sign warranting investigation.
Gravel to protect built up.
Roofs covered with stone chippings do tend to grow moss quicker than a roof coating with no stones because the chippings provide the moss with the perfect growing area.
Chippings should only be used on roofs at less than 10 as complete adhesion at steeper pitched is not possible.