Breathable walls without MVHR

[Clare Nash]

Hello,

I have just got back from a very interesting trip in Germany looking at energy saving or passive houses built using local materials (specifically Schwarzwald larch shingles, timber frame, breathable insulation). I interviewed the architect (highly skilled, trained as a carpenter and master craftsman before becoming an architect and fits the MVHR units himself as doesn't trust anyone else to do it correctly!) and he was explaining to me that the problem with breathable walls (which he uses extensively combined with MVHR) is that if you don't combine them with MVHR then in summer the walls build up with water vapour, they store it, then in winter when we have dry winds which dry the internal environment, this vapour then expires into the room. In breathable walls in this country we always use a VCL or airtightness membrane on the inside so presumably this stops this happening. But I found it interesting that we are really concerned about keeping the internal moisture away from the walls (hence the VCL) and not especially concerned of the moisture build up from outside in the wall itself. Just wondered if any of you had any thoughts/experience on this or perhaps I have got the complete wrong end of the stick (my German is still pretty good but not perfect!)?

[Tom Foster]

Clare or anyone interested if I reply to this rather old thread? It's interesting but full of misconceptions, maybe by the German architect, I think.

[Anonymous]

Please do reply FosterTom, I'm interested 🙂

[Alex Rius]

Was there any concensus this breathable walls without MVHR discussion as to what is the right answer? Thank,s Danny

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