WUFI

Hello,

Normally, in timber elements we cannot have a water content above 20% M, or 18% for prolonged periods. There is also a limit of 200 g/m² for insulation or other hydrophobic elements.

But what about wood fibre? Do these values have to be respected for wood-fibre insulation—for example, in the case of a timber frame with interior wood-fibre insulation—or, as long as we comply with WTA Guideline 6-8 and the mould growth remains relatively low (mould index below 1) and the wall dries out, can we tolerate more than 20%? For instance, in my case at the critical point over 1 cm we reach between 165 and 135 g/m² and between 33 and 27% moisture content (which still seems high to me).

If so, are there still limit values that must be respected? Because in the following document: https://wufi.de/download/guideline/Guid ... 240716.pdf

It seems to me (on page 22) that says that there are no limit values.

Dear Alexandre,

This is not an easy question to answer. According to CSTB SimHuBat 7.6 (in France), 23% moisture content is permissible for non-load-bearing wood-based materials.

Until now, the WTA curve has actually been intended for softwood. However, many wood fiber insulation materials are even more durable than wood, but not all of them. If in doubt, this should be clarified with the manufacturer — for some materials, this is already known, otherwise testing options will soon be available.

Another point: for example, fire retardants can significantly increase the water content in M-% at the same relative humidity. However, the relevant evaluation parameter remains the RH, as this describes how easily the moisture is available to the fungus. Thus, the limits should be defined in RH values - and unfortunately rather individually for every material.

best regards
Daniel

More information can be found here - but the topic is still ongoing:
https://wufi.de/de/wp-content/uploads/s ... Report.pdf