- Q.We are getting a lot of
jobs with Mansard-type roofs. The roof covering is
concrete tile, but much of the roof has a slope of only
2:12. What precautions should we take?
A.According to the
National Roofing Contractors Association, the
minimum slope for a concrete one-piece barrel tile
or interlocking flat-ribbed tile is 4:12. For flat
shingle tile, it is 5:12. The CABO One and Two
Family Dwelling Code prohibits the installation of
any concrete tile on slopes less than 3:12, except
with the permission of the building
official.
The best precaution is to use some other type of
roofing on the low slopes. However, if a uniform
appearance is desired, a double-layer of 30-pound
roofing felt, set in mastic or hot asphalt, must be
laid over the sheathing and under the tiles. This
effectively forms a waterproofing membrane. The
concrete tile would then be cosmetic and would
protect the membrane from the sun.