A breakdown of a Passive Eco Wall for an nZEB build - Traditional Style Timber Frame Series (part 2)

In part two of the Traditional Style Timber Frame Series, our Group Technical Director, Niall Crosson, describes the 'Passive EcoWall' system designed by Ecological Building Systems. Along with providing Passive House levels of insulation, this system is designed to allow maximum breathability of a timber frame wall, allowing moisture vapour to easily migrate to the ventilated cavity on the outside.
Pro Clima Solitex Adhero
Self-adhesive, peel and stick, windtight monolithic breather membrane
www.ecologicalbuildingsystems...
Gutex Multitherm
Natural wood fibre T&G external insulation board
www.ecologicalbuildingsystems...
Finsa SuperPan VapourStop
Airtight vapour barrier racking board for timber frame walls and ceilings
www.ecologicalbuildingsystems...
Dämmstatt Cellulose
Blown-in cellulose fibre insulation
www.ecologicalbuildingsystems...
Thermo Natur Thermo Hemp
Natural flexible insulation made from hemp fibres
www.ecologicalbuildingsystems...

[@drkarlwoods722]

Gypsum plasterboard is not 'breathable', so strictly speaking this is not a breathable wall.

[@niallcrosson5859]

Hi Karl, thanks for your comment. The Passive House Eco Wall combines a vapour retarding racking board on the inner warm side, which is our Finsa SuperPan Vapourstop with a very vapour open external woodfibre insulation board and breathable insulation between the studs.
Finsa SuperPan Vapourstop fulfills 3 functions:
1) timber frame bracing,
2)Airtightness,
3) Vapour control.
In our climate in Ireland and the UK it is common to use vapour retarders internally to reduce the risk of interstitial condensation in winter months or when moisture levels within the building may be high. This wall "breathes" to the outside through the GUTEX MULTITHERM board which has a very low vapour resistance factor µ of just 3. Finsa SuperPan Vapourstop on the other hand has a µ of 1150. These are the core elements within the assembly which manage vapour transmission and breathability. Sadly in some projects end users apply a vapour tight membrane or barrier inside and a vapour resistant insulation externally. This greatly reduces drying capacity and breathablity leading to great risks of mould, structural degradation and moisture induced issues.
In the Passive House Eco Wall specification gypsum board has little role in this process internally, though its worth bearing in mind gypsum board typically has a µ of about 10 and is relatively thin, therefore if is relatively vapour open too. On the other hand, if the gypsum board has a foil lining on the reverse side, then it is very vapour tight and wouldn't be considered breathable.
Of course where assemblies are diffusion tight externally it can be useful to allow some "back breathing" seasonally internally. This is where our INTELLO PLUS Intelligent vapour control membrane is often used instead of the FINSA board, and this is compatible with non foil backed plasterboard. Lots more details about our INTELLO can be found here:
www.ecologicalbuildingsystems.com/product/intello-plus
Sorry for the long response! Hope this is helpful.
Details about the FInsa board can be seen here: www.ecologicalbuildingsystems.com/product/superpan-vapourstop
And the GUTEX board here: www.ecologicalbuildingsystems.com/product/multitherm

[@igg5589]

Actually gypsum IS VERY breathable (for moisture vapour). That's why under it always goes vapor barrier (i.e. polyethylene) to stop moister going into insulation materials and structural elements