https://www.sintef.no/globalassets/uplo ... ort273.pdf
Walls with low internal vapour resistance
Several of the wall sections had no traditional vapour barrier and therefore relative low water
vapour resistance on the hot side of the insulation layer. This fact has however not led to
dramatic high moisture contents. In the sections W4and E8, both with a ratio between the
internal and external resistances of 7, the measured moisture contents are approximately on
the same low level as in the sections W1, W2, W3 with ratios between the internal and
external resistances of 35 to 62. In the sections W6, W7 and W8 however, which have equal
materials and very low resistances at both sides, the moisture content is higher and close to 20
weight% in wintertime both in the top and sill plates. Due to the difference in RH at the two
faces, the ratio between the internal and external vapour resistances has probably been higher
that 1, also for these wall sections
Air leakage may give high moisture content
In most buildings air leakage from indoor through walls and roofs represents a far higher risk
for moisture damage than pure diffusion. That seems to be true also for the test wall sections
when the air pressure is higher indoor than outdoor, which was the situation during the last
heating season. All the sections got the highest measured moisture content this last year, and
in several of the sections the moisture content was very
These test house measurements, during four heating seasons, show that moisture
redistribution in insulated timber frame walls may lead to high local moisture content in the
outer and upper part of the timber framing members. This is the case even for normally
“moisture safe” structures with high ratio between internal and external vapour resistances
and low build-inn moisture content. Air gaps in the insulation layer will increase the risk of
high local moisture content.
The measurements indicates that water vapour diffusion do not represent any high risk for
moisture damage, even for walls with relative low internal water vapour resistance, as long as
the external vapour resistance is far lower. In these experiments the walls with low internal
vapour resistance and a ratio between the internal and external resistances of seven or higher,
had the same low moisture content as “normal” walls with high internal water vapour
resistance.
Paluks lugeda ja aru saada õigesti- viimane lause ei ole parastamine, vaid lihtsalt fakti konstanteerimine.