Thanks for the link.
I think I've seen this before on Construct Ireland in a less developed form when Joe was starting to feed back his empirical data.
All of what Joe suggests about the drawbacks of the single leaf wall seems to be fair comment.
However most of the inner leafs I have inspected haven't had serious issues with damp build up behind them unless it was water ingress from outside.
The argument that the vapour barrier is ineffective works both ways - vapour moves back in to warm rooms.
As for the graph Joe cites, it looks informative but its not the kind of HVAC graph I need to see.
P. 7 shows discrete measurements of different metrics
P. 10 shows projected moisture build up to 2014
P. 11 the graphs seem to be misplaced on atop the other by accident.
(there seems to be nothing in this on the drying out effect of prolonged cold, dry spells)
The implication of this is that the variable membrane prevents moisture build up whereas as a plastic one doesn't.
But im my experience a normal wall whether cavity or hollow block seems to prevent moisture build up because it can get away on the cold site.
I don't understand Joe's findings, where the permeability of the construction seems to prevent moisture escaping on the winter months unless the external wall has a sealed face.
Oh yes, on Page 7 there is a note under the cross section
"Figure 6: A screen shot of a dynamic display of moisture movement in the wall
(note: this wall has a plastered face between block and insulation
so is not directly comparable to buildups studied below)"
Good job we don't build them like that in Ireland so, Joe.
We studied HVAC and moisture control build up under Gerry O'Brien in Bolton Street back in the eighties.
The graph I need to see is the one where maps temperature against moisture content at the correct relative scales.
Its able to show visually (to use visual creatures, architects and designers) where the overlap and therefore the likely dewpoint occurs.
Dewpoint is where vapour, able to migrate through a substance, becomes moisture, which isn't, and which then causes reductions in insulation value.
The issue tAFAICSis not to decry ventilated interstitial spaces but to use them to take away the moisture preventing it building up in the construction to unsustainable levels.
This is where the current super-insulation and super-sealing strategies seem to start tying themselves in knots for what appears to be very little gain.
Proper ventilation is what houses and constructions supporting human beings require, not sealing.
Breathability is what traditionalists have been arguing for decades, and current knowledge supports it.
You "check" the moisture getting in on the "in" side, and make sure its can get away on the "far" side - thus it cannot build up.
I like where Joe is going with his research, but graphs have to be supported by empirical studies showing real consequences and verifiable cost benefits or they are only paper exercises.
And in all these new technologies, we have to factor in the results of moisture and bacteria moving through new restricted constructions and ventilation systems.
Has anyone done a bacteriological study of MVHR ducting and filters yet?
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matter at hand.