Installation Guide

MANSARD ROOF DETAILS
The mansard is particularly well suited to
renovation work on pitched roof houses because
the upper story can be enlarged without adding
extra height to the structure. The conversion of a
pitched roof bungalow to a mansard provides a
floor area on the upper floor that can be identical
to the main floor area.
The low downward slope of the mansard roof line
acts visually to reduce the scale of a building and
helps to eliminate a boxy appearance. This
technique is used frequently on large commercial
projects, particularly those near residential
neighborhoods It is also a common solution to the
problem of avoiding a monotonous appearance on
flat-roofed frame apartment buildings.
Properly used, a mansard roof can strengthen the
design without substantially increasing
construction costs. If raised up above the level of a
built-up roof, the mansard can screen out roof
penetrations or mechanical equipment.
The variety of mansard roofs is practically infinite.
One of the most widely used (and misused) roof
designs, its proportions and scale are very
important and care should be taken to avoid a
mansard roof line that is either too skimpy or too
generous.
Two of the most widely used roofing materials on
the mansard roof are Western Red Cedar shingles
and shakes. Cedar shakes, with their heavier
texture and solid appearance, are perhaps more
frequently specified for mansards although shingles
are also used, particularly when a lighter scale is
desired. The light weight and ease of application of
shingles and shakes contribute substantially to
economical construction. They can be installed
over light framing—usually spaced battens—thus
affording a considerable saving in both materials
and labor as opposed to cladding that requires a
solid base. This cost saving factor, combined with
their excellent insulating qualities and attractive
appearance, contributes to the increasing
popularity of shingle and shake mansard roofs.
Construction details for typical mansard roofs are
shown in Figure 6.
Fig. 6: Shingle and Shake Mansard Roofs
4
Venting
Flashing
38mm x 90mm Curb
Panel sheathing
or spaced battens
38mm x 90mm
spiked to joists
Cedar shingles
or shakes
Cedar shingle or
shake siding
Cant strip
Built-up roof
Joist
Flat Roof Treatment
Venting
38mm x 140mm cap
Panel sheathing
or spaced battens
38mm x 38mm at
610mm O.C.
Cedar shingles
or shakes
Cedar shingle or shake siding
Plumbing vent
Built-up roof
Joist
Flat Roof Treatment
Flashing
Venting
Joist
Adding a second story
38mm x 90mm curb
Flashing
38mm x 90mm spiked to joist
Spaced battens
Cedar shingles or shakes
Cant strip
Built-up roof
Joist