Lisø PhD Dissertation Manuscript - NTNU

interesting to compare those results with our own for these
four stations. Driving rain numbers from Hoppestad for
Oslo, Bergen, Trondheim and Tromsø are shown in Table
4. Note that the built environment around the stations in
the late 1940s was likelyto be significantlydifferent than
today, and the Bergen and Trondheim observing stations
in Hoppestad were not in exactlythe same locations in
these cities as the observations used in this study. Some
differences are therefore to be expected. For comparison
with our values, it is appropriate to use the wall indexes
(I y‘s) from 901, 1801, 2701 and 3601 to represent driving
rain from the east, south, west and north, respectively. The
annual driving rain totals from 1946 to 1950 (in mm/yr)
shown in Table 4 are roughlysimilar (at about 500 mm/yr)
for Oslo, Trondheim and Tromsø, with approximately
four times as much in Bergen (at just under 2100 mm/yr).
With the exception of Oslo, our values (obtained by
summing the four directional values in each row) are
somewhat higher than Hoppestad’s.
We must be cautious, however, in trying to draw any
firm conclusions about absolute driving rain totals
derived from these methods at anygiven station. It is
the relative magnitudes of driving rain values versus
direction at and between stations that are relevant in this
comparison. The relative magnitudes between stations
shown in Table 4, then, could suggest that Oslo has
comparativelyless total annual driving rain than is
implied byHoppestad’s results. The relative magnitudes
for total annual driving rain at Bergen, Trondheim and
Tromsø are, however, quite similar in both studies.
Furthermore, the directional dependence at Oslo is also
verysimilar in both cases, with perhaps a slightlylarger
component from the south in our work. For Bergen, the
1974–2003 data yielded a relatively greater contribution
from the east and less from the west than is found in
Hoppestad. For Trondheim and Tromsø, the relative
directional dependences were qualitativelyverysimilar
in the two studies.
5. Recommendations for further work
One important goal of future work is to determine
how differences in free wind-driven rain loads affect
ARTICLE IN PRESS
J.P. Rydock et al. / Building and Environment 40 (2005) 1450–1458 1457
Table 4
Driving rain values (in mm/yr) from Hoppestad (1955) compared against driving rain wall indexes, I y (mm/yr), for Oslo, Bergen, Trondheim and
Tromsø for the analysis period 1974–2003 (in italics)
Location Annual driving rain bydirection Total annual driving rain
North I 360 East I 90 South I 180 West I 270
Oslo 163 153 163 149 116 142 47 39 489 (483)
Bergen 157 210 120 772 1129 1328 688 323 2094 (2633)
Trondheim 84 75 53 81 91 140 301 417 529 (713)
Tromsø 51 68 22 30 202 349 174 277 449 (724)
moisture uptake in walls with ventilated wooden
cladding. This is a necessaryelement in incorporating
a driving rain wall index into design guidelines for
buildings in Norway. Research to address this question
is currentlyin progress at NBI/NTNU’s experimental
building site in Trondheim. Data on driving rain and
moisture uptake are obtained from several instrumented
test walls with different ventilated wooden cladding
configurations. An automated weather station and
driving rain gauge provide supporting weather data.
A second goal of future work is to develop simple
algorithms for assessing how local topographical characteristics,
especiallyin hillyor mountainous coastal
terrain, alter driving rain exposures determined from
observational data at weather stations. This is an
important element in putting into practice use of
regional driving rain information at specific building
sites awayfrom the locations where the data are
gathered.
A third goal of future work is to use the method to
evaluate changes in driving rain loads due to climate
change under global warming. In order to do this, we
must incorporate data from climate change scenarios
into the methodology.
This paper is a part of the NBI Research &
Development programme ‘‘Climate 2000’’ [8,9]. An
important aspect of the programme will be the preparation
of a thorough overview of the relevant climatic
loads that should be taken into account during the
planning, design, execution, management, operation
and maintenance of the built environment. The ‘‘robustness’’
of the Norwegian building stock will also be
addressed as part of the programme, including the
development of methods for classifying different climatic
parameters and their impact on building enclosure
performance.
6. Conclusion
The principal advantages with the presented method
are that the angular distributions of driving rain loads
obtained are high resolution in terms of wind direction
and that the results are based on long-term series of