Low Impact Development Manual for Michigan - OSEH - University ...

Example eave detail for sloped roof
Source: Roofscapes, Inc.
the green roof system, including vegetation must be
calculated as permanent load. Extensive vegetated
roofs weigh between 60-150 kg/m2 (13.0-30.0 lb/sq.ft.)
depending on the thickness of the vegetated roof system
build-up. Trees, shrubs, and construction elements such
as pergolas and walkways cause high point loads and,
therefore, have to be calculated accordingly.
Wind uplift
A vegetated roof must be tight to the roof, especially in
cases of strong wind. When designing and installing the
vegetated roof, safety measures against wind uplift are
to be considered.
This is especially important when the vegetated roof
provides the load for a loose laid waterproofing and root
barrier. The actual influence from the wind depends on
the local wind zone, height of the building, roof type,
slope, and area (whether corner, middle or edge) and
the substructure.
Roof drainage
Vegetated roof systems store a major part of the annual
precipitation and release it to the atmosphere by transpiration.
Depending on the thickness of the vegetated
roof system build-up and rain intensity, surplus water
may accumulate at certain times and must be drained
off the roof area. The number of roof outlets and the
penetrability factor, or more precisely, the water retaining
capacity of the vegetated roof system build-up, has
to be adjusted to the average local precipitation.
Roof outlets are to be kept free of substrate and vegetation
and have to be controllable at all times. For this
purpose “inspection chambers” are installed over the
roof outlets. Due to safety precautions, roof areas with
inlayed drainage must always have two drainage outlets
or one outlet and one safety overflow. For facades and
roof areas, gravel strips, gullies and grids provide fast
drainage of rainwater into the drainage system.
LID Manual for Michigan – Chapter 7 Page 309