Installation Guide

ROOF VALLEY FLASHING DETAILS
Most roof leaks can occur where water is channelled off the roof or where the roof
abuts a vertical wall or chimney. At these points, metal valleys and flashings are used
to assist the shingles or shakes in keeping the structure sound and dry.
Structural members that protrude through a roof
should also be flashed at all intersecting angles to
prevent leakage. Step flashing should extend
under the shingles or shakes and up the vertical
surface and should be covered by a second layer
of flashing (counterflashing).
Flashing should be pre-painted both sides using
a good metal or bituminous paint. Flashing strips
which must be bent to sharp angles should be
painted after bending. Metal flashing with
baked-on enamel coating is available in some
areas. Different flashing metals are available in
different areas depending on climatic variations.
It is good practice to use metals that have proven
their reliability under the specific conditions to
be encountered. It is important that metal flashing
have the same longevity as Western Red Cedar.
Valleys—Shingles
For roofs with slopes of 1:1 or greater, valley
flashing should extend not less than 178 mm on
each side of the valley centerline. For roof slopes
less than 1:1, flashing should extend not less
than 255mm each side. Valley flashing should be
center-crimped, painted galvanized steel or
aluminum Valley metal should be underlayed
with No. 15 (minimum) roofing felt, but is
optional when spaced sheathing is used. Shingles
should not be applied with their grain parallel to
the valley centerline and those extending into the
valley should be cut at the correct angle (Figure
12). Joints between shingles must not break into
the valley.
Valleys—Shake
On shake roofs it is recommended that a strip of
No. 15 (minimum) roofing felt be installed over
the sheathing and under the metal valley. This is
optional when spaced sheathing is used.
Metal valleys should be center crimped, painted
galvanized steel or aluminum and have a
minimum total width of 510mm. In some areas,
however, flashing width requirements may differ
and local building codes should be consulted.
Shakes should not be applied with their grain
parallel to the valley centerline and those
extending into the valley should be cut at the
correct angle (Figure 12). Joints between shakes
must not break into the valley.
Use minimum nails to hold
metal in place
Roofing felt
Valley metal
2.4m long
overlapped
150m at joints
painted both sides
Eave
protection
Metal to extend as far as
shingles or shakes
Eave protection
Open valley width
100mm to 200mm
depending on water
volume. Mark
anticipated water lines
(width of open valley)
valley sides with a
chalk line
Lead saddle over joint of
two valleys bent to fit
Typical saddle flashing
Keep nails well away from
the centre of valley
Fig. 12: Flashing Details for Shingle and Shake Valleys
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