Lisø PhD Dissertation Manuscript - NTNU

LisÖ et al.
Table 1 Ranking of £ashing types according to the percentage
of building damage cases associated with the different types of
£ashing (based on 175 investigated assignment reports)
Type of £ashing Building
damage
cases (%)
A Window, windowsill and weatherboard
£ashing (upper and lower). Door
£ashing (upper and lower)
B Parapet £ashing (including balcony
£ashing and balustrade £ashing)
C Chimney £ashing 9
D Wall £ashing and horizontal £ashing 6
E Roof £ashing and ridge £ashing 4
F Other types of £ashing 13
Damage in connection with weather-protective
flashing is most prevalent in coastal areas, which are
subject to strong winds and penetration of driving
rain and snowdrift.
Table 2 presents a ranking of typical weak points irrespective
of the type of flashing.
Evaluation of results
This paper presents a ranking of damage in connection
with the design and construction of flashing. However,
the survey presented has some limitations. Analysis is
based on NBI’s project archives and thus cannot
aspire to represent a complete and definitive overview
of damage associated with weather-protective
flashing in Norway. In geographical terms, a majority
of the cases of damage are near NBI’s offices in
Oslo and Trondheim. This is due to the NBI having
easier access to building damage assignments in
its vicinity. Furthermore, the ranking has not been
evaluated against the amount of different types of
flashing. For example, there are usually many more
metres of parapet, windowsill and weatherboard flashing
on a building than, for example, for a chimney
flashing.
Despite the investigation having quantitative weaknesses,
it must nevertheless be regarded as being an
important qualitative step towards identifying problem
areas. The presented ranking of flashing types
and typical problem areas were in good accordance
with the Norwegian Association of Ventilation- and
Tinsmith Companies own comprehension of typical
problem areas (S. Tybring Haug and T. Opheim,
personal communication/interview, Norwegian Association
of Ventilation and Tinsmith Companies, Oslo,
2003). Evensen (2003) used interviews as a method
for the mapping of typical flashing construction/workmanship
failures. The results from the analysis presented
herein are in good agreement with results obtained from
Evensen’s interviews with a number of tinsmiths and
other actors in the construction industry dealing
with the planning, design and construction of weatherprotective
flashings.
Table 2 Ranking of typical weak points irrespective of the type of £ashing according to the number of building damage cases associated
with the source of damage. A total of 175 case reports were investigated.Two or more weak points occurred in several reports
Typically weak points (source of damage) Number of building
damage cases
I Fastening. Screws and/or nails puncture the £ashing, thus providing an opportunity for
water penetration. Insuf¢cient construction/workmanship and/or anchoring are also
a common problem
II Jointing.Overlap joints are very common and frequently cause leaks. Always use
welted £ashing, possibly combined with a sealant, and without clipping off the
corners of bends in the £ashing
III Drainage from the £ashing. Flashing must be inclined if build up of water pressure
against joints and/or connections is to be avoided
IV Turndowns along the facade. Short turndowns make it possible for the wind to force
water underneath the £ashing
V Ends and corners of the £ashing. Lack of three-dimensional thinking when shaping
the ends and corners of £ashings can easily lead to leaks
VI Finishing-off. Finishing off with insuf¢cient drip edging prevents water being directed
away from the facade, resulting, for example, in a moist or soiled facade
VII Ventilation gaps. Air access to ventilated cavities, in both inward and outward
directions, must not be blocked
VIII Tightening layer behind the £ashing.Weather-protective £ashing usually forms the
rain shield (drainage £ashing) of a two-stage tightening. A poorly executed tightening
behind the £ashing can easily cause leaks. Besides which, the wind-barrier layer
behind the £ashing must withstand moisture loads
IX Holes. All puncturing and perforation of £ashings provide opportunities for leaks 10
X Flashing edges. Flashing edges must have a wrap-over if corrosion is to be avoided 9
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65
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