Lisø PhD Dissertation Manuscript - NTNU

LisÖ et al.
Figure 9b Flashing detail at a roof/cavity wall junction
Figure 9c Recommended designs of a connection to a
concrete wall.Variant (c) is evaluated as being the safest against
water ingress
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conditions. Ridge flashing must be designed and fastened
so that it will withstand the local wind loads.
Heavy wind loads on the roof ridge may also blow
rain and snow in under the flashing. Achieving the
necessary ventilation in the ridge of a ventilated roof,
while at the same time preventing the ingress of rain
and snow, makes great demands on both design and
workmanship. Detail solutions depend on the type of
roofing employed. Figure 10 shows an example of a
ridge design that provides for the ventilation of
large roof areas while preventing the intrusion of rain
and snow.
Chimneys and other openings in roofs
Sealing around chimneys and other openings in roofs
can be difficult. As for flashings in general, it is important
that the flashing should not be the sole tightening
layer, but should primarily act as a rain barrier. Moreover,
where openings pass through a roof, the flashing
will protect the sealing layer underneath against mechanical
loads exerted by snow and ice. As a rule, a fully
clad chimney is the safest solution with regard to water
leakage and should always be used in the most
exposed/unsheltered areas. In Norway, exposed or
unsheltered areas usually means coastal and fjord
areas northwards from the South and West of the
country, as well as cold and windy inland areas in
South and North Norway.
The sealings of openings in roofs or walls are vulnerable
points, even when a separate tightening layer has
been installed beneath the flashing. Figure 11 shows a
case of damage due to the flashing end not being
inserted deep enough into the notch of a brick
Figure 10 Continuous, longitudinal ventilation louvre along the
ridge of an insulated, ventilated pitched roof. Source. NBI (2000)