Moisture content of EPS

[Matthew Smith]

A calculation for a brick masonry/airspace/eps/vapour barrier wall construction in Lisbon (S facing with internal temp fixed between 18 and 24) is returning moisture contents for the EPS layer above those possible from 24hr immersion tests, and they seem to be increasing indefinitely by the same order of magnitude each summer, 100kg/m3 and counting. It is not the same with EPS from the North American or Lund database but it still rises above the value of 0.6 (Lund) and 3.05 (generic North American) given for 100% relative humidity in the moisture storage function curves. I know the inputs are a little odd but I am just practicing with WUFI; I am still trying to find my way round and am very confused. Please help.

Yours,
Matt

[Beate Stöckl]

Dear Matt,

the EPS insulation from the IBP-Database has no defined moisture storage function.

But for numerical reasons WUFI simulates a moisture field over the whole structure for each time step, so it must assign a certain low moisture content even to materials which nominally don't have any appreciable moisture content.

Therefore WUFI uses a so called internal default moisture storage function which is approximated based on the materials porosity – especially for insulation materials with a high porosity this default moisture storage function is too high. Because of this you can get a too high moisture content in your EPS material, which is unsuitable for an evaluation. The materials without a defined moisture storage function should only be assessed on the basis of the relative humidity which always shows reliable values.

But even so a moisture content of 100 kg/m³ seems to be very high. Maybe you can send me your WUFI-Project and I can have a look on it.

Best regards,
Beate

[Matthew Smith]

Thankyou, Beate, that clears it up for me. If you would like to see the project, how would i get it to you?

Yours
Matt