ABSTRACT
Building design should combine maximum usability with low damage risk and do that at affordable costs. Damage risk in that context is defined as the probability a failure event happens, multiplied with the severity of the consequences, when happening. In structural design, risk acceptability is extremely low as consequences may be very dramatic. In building physics related design decisions, risk acceptability lays higher as consequences indeed affect durability, comfort and energy efficiency but hardly are life threatening.
The probability a hygrothermal failure event may happen depends on many factors, such as the actual outside climate, orientation and slope of a surface, the inside climate, workmanship quality, design clarity, etc. Advanced heat, air, moisture tools, used to evaluate building enclosure parts on hygrothermal response, typically separate these parts from the building and handle all factors mentioned as deterministic by definition. Hence, such approach cannot explain the variability in hygrothermal response, seen in practice, of a same type of enclosure part, applied in buildings with seemingly analogous usage. To clarify risk, the paper uses a roof damage case. That case shows how thermal performance of an enclosure part may be connected to the whole building heat, air and moisture response. This is done, using simple tools.
