Lisø PhD Dissertation Manuscript - NTNU

LisÖ et al.
Figure 4 Recommended design of a window installation in the
outer side of a cavity wall
Figure 5 Recommended jointing of windowsill £ashing.
Jointing must be located between the windows
transition flashings also apply to balcony and top flashings,
as well as flashings around ventilation louvres.
Balcony and/or balustrade flashings are often penetrated
when antennas, sunroofs, windshields, etc. are
installed. Such devices should be fastened to the in- or
outside of the parapet/balustrade without perforating
the flashing or, alternatively, furnished with grommets
and/or collars.
The most common fault with regard to parapet flashing
is the design of the jointing. Overlap jointing,
often combined with nailing of the flashing at the top
edge, can easily lead to leakage (Figure 6a). Few
problems have been registered whenever welts have
been employed (Figure 6b). Folded joints (welts)
48
Figure 6a The top of the parapet is formed as a ‘gully’. Overlap
joints and nailing of the £ashing from above render the structure
prone to leakage. Sealing solely with mastic is not effective in the
long term. Source: Norwegian Building Research Institute,Oslo
Figure 6b Jointing of parapet £ashing with double-raised welts
(i.e. a double standing seam), and with possible sealant in the
welt, provides a watertight joint
incorporating a sealant are water resistant and permit
thermal expansion/contraction.
Parapets and gables with elevated projections of varying
widths can provide challenging tinsmith work. With
parapet projections, it is vital that flashings and roofing
are formed in such a way that the sealing is not damaged.
To diminish the visual impact of the parapet flashing, it
is common practice to reduce the turndown along the
facade. Too short turndowns make it possible for
wind to blow water in under the flashing. The
parapet flashing for multi-storey buildings should
be drawn down a minimum 150 mm along the facade
(Figure 7).
Parapet flashings should act as outer rain barrier in a
two-stage tightening, i.e. there must always be a tightening
layer behind the parapet flashing. When the
tightening layer under the flashing is missing,
water ingress can easily arise. Also, in cases where
the roofing material has not been drawn across the
parapet under the flashing, water can enter under