Lisø PhD Dissertation Manuscript - NTNU

A possible objection to the presented method could be that the index does not
include the effects of wind. The moistening of e.g. a façade material is of course dependent
on geographic orientation and wind conditions. But, in the end, the relative potential of a
climate to promote frost decay or frost damage is basically guided by the two climate
parameters included here, namely freezing events and rainfall.
6. The way forward
In Norway, about 100 stations cover the normal period, and have well enough
observational programs to be used. Another 100 stations have long series that, though
partly outside the normal period, can be coupled to the normal period. The next step may
be to look at shorter series of a choice of stations that have a more frequent observational
program. During the last 3-10 years, automatically recorded hourly values of temperature
and precipitation at some 30-40 stations exist, but the quality of the hourly precipitation
data has to be analysed. It is of interest to look at those data to find out whether improved
climate indices may be compiled.
An important goal of future work is to further develop the index to provide
quantitative information on the connection between climatic exposure in different regions
and durability of different porous, mineral building materials (as indicated in this paper).
This work will also include analyses of the influence of frost period lengths on the
assessment of frost damage risk mapping.
Field investigations and laboratory testing of different materials are needed for
validation and further improvement of the index. An important issue to be addressed is the
connection between frost resistance and suction rate, especially of interest for clay bricks.
Research to address these issues are currently in progress as part of NBI’s research
& development programme “Climate 2000” [19], along with several other approaches in
the pursuit of design tools using climate data and strategies for risk management of climate
change impacts [20]. This is particularly important with respect to the preparation of
additional Norwegian appendices to international standards associated with the various
types of climatic impact. 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 (based on historic weather data and scenarios for future
climate development under global warming) and their impact on building enclosure
performance. The index can be used as a tool for assessment of changes in decay rates due
to climate change under global warming incorporating data from regional- and local-level
climate change scenarios.
7. Conclusions
Frost resistance of brick, concrete and rendering mortar is tested according to
internationally standardised methods. Test methods are given for different countries
(dividing countries in far too coarse national-level climate zones), but there exists no
classification of local- or regional level climate zones for frost durability assessment
purposes. Frost decay assessment methods are also needed in the planning and design of
high-performance building enclosures. A relative potential of frost decay or frost damage
of mineral materials exposed to a given climate can be expressed using a simple index
incorporating information about number of freezing events and 4-day rainfall sums prior to
freezing events for the different months of the year, based on multi-year records of daily
air temperatures and rainfall data. The principal advantages with the presented method are
that the results are based on long-term series of climate data that are readily available. The
method will be used as a foundation for the further development of a frost decay exposure
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