Alternative to breather membrane?

[Anonymous]

We are trying to look for methods/ products that remove the need for a breather membrane to our timber frame building system. It would speed up the build, remove another plastic element and allow us to factory fit support for the cladding (battens). We have a spruce plywood skin externally with 280mm warmcel and another ply skin internally for the walls and roof. Any body got any thoughts on this?

Mike Jacob mentioned using diffutherm boards without a ventilated gap in another thread – but not sure if this will get through building control though? But for timber cladding with a ventilated void how can we protect the timber? We could buy our plywood pre-tanalised – would this provide enough protection? or another pre treatment?

any ideas appreciated..

bruce,

[Anonymous]

Not a suggestion, but a point. Building regulations only require adequate performance, rather than enforcing a particular approach.

If you can provide calculations to show that interstitial condensation will not be a problem with your build-up, then you have met the regulation.

[Anonymous]

still not sure i fully understand the function of the breather membrane – my presumption was that it was to protect the structure against moisture from the outside condensing on the outside of the structure? how does it relate to the interstitial condensation – i thought that was a separate issue relating to internal vapour checks ect?

[Anonymous]

the diffutherm board is good for render but we wouldnt use it for timber or panel cladding as we already have adequate insulation and our main motivation is removing the number of building layers.

So there for – if the breather membrane is purely to protect the membrane from small (?) amounts of moisture then we should look for a treatment that will protect and still breath. So tanalised might do the trick?

[Anonymous]

Hi Mike

Yes – all of our wall roof and raised ground floor Uvalues are 0.14WmK have been worked out using Build Desk software and made allowances for thermal bridging (different percents for walls roof and floor 9-15%). So presumably with the taped joints for the air tightness we should be cruising…

I have been doing a bit of research talking to various manufacturers of the wood and tanalith and it seems like its no problem, just need to clear it with building control and hopefully e have removed another building layer,,,,,

bruce.

[Mike Jacob]

Hi – for sure any repeating bridges would form part of the U value calc. I was wondering mainly about junction detail scenarios I.e non-repeating bridges? I haven't seen any detailed drawings of facit build ups – maybe it would be fine (from a ph point of view) but maybe not..

[Anonymous]

I have just been looking at boron based timber treatments – anyone out there had any experience?
Much less toxic than tanalising which contains arsenic and would pollute all our wood waste.

[Anonymous]

My main focus at the moment is the breather membranes –
I have been researching and trying to understand the origins, reasons and realities of breather membranes and it seems very difficult to get clear answers.
The first question as you raised is – do we need a breather membrane at all? Can any one give me a clear answer on what its for? is it:
a) to protect against moist air from the exterior condensing behind the cladding?
b) to protect against moist air from the inside condensing on the outside ?
c) both of the above?

Our condensation risk analysis using BuildDesk says there is no risk of either surface or interstitial. Does this mean we dont need a breather membrane? (attached)

[Author]

Posts