INTRODUCTION
Over the last few decades, more and more attention has
been given to moisture control in building envelopes. One
aspect of moisture control that is still not completely understood
and solved is the so-called solar-driven vapor movement.
An instance of such movement happens when rain is
absorbed by porous cladding such as brick veneer. Heating of
the wet masonry due to solar radiation will induce inward
water vapor flow, especially when the interior space is airconditioned
at lower temperature. These water vapor flows
can be important and lead to moisture accumulation in the
back wall. Sustained exposure to high moisture content may
lead to the development of mold and rot growth, corrosion of
fasteners and reduction of the thermal insulation value. The
occurrence of inward moisture flow due to solar radiation is
more prevalent in mixed and hot climates, but may also be
observed during the summer in cold climates. To avoid such
problems, the amount of moisture diffusing through an envelope
must be reduced (Tsongas and Olson 1995) or allowed to
dry out quickly (TenWolde 1989 and Sandin 1993).
The first mentions of summer condensation or condensation
due to inward flow on vapor barrier sheets were in-situ
observations. One of North America’s premier building scientists,
Neil B. Hutcheon (1953), clearly identified that “Hot sun
on a wetted outer withe can still drive water as vapour back
into the inner withes, producing wetting by condensation
there”. Hutcheon recommended the use of ventilation cavities
to promote air circulation providing drying conditions for both
winter and summer seasons. Then, more observations from
field testing were reported. Wilson (1965), TenWolde et al
(1986) and Straube (2001) observed that moisture accumulation
on the interior side of assemblies occurs in constructions