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The PIR will be adhered to the masonry with a foam seal around the perimeter of each board, along with a coat of liquid airtightness membrane. As you mentioned, continuous MVHR ventilation with auto-humidistat will be controlling humidity levels also.
The external brickwork will be properly re-pointed with lime mortar, and the walls in question are south-facing, so very unlikely to ever soak through (they haven’t in the 8 years I’ve been in the house).
ectoplasmosis-
MVHR ventilation with auto-humidistat will be controlling humidity levels also.
Does this work through trickle vents in each room venting out in to central spaces, or does it rely on you having doors open, or are you running ducting pipes to each room? Feels like it will have to shift a significant amount of air if the external surfaces of the room are made airtight?
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I reckon you'll be alright but I don't really fully understand MVHR or fully understand all the Changeplan/Ubakus etc. wizardry - I'm getting my head around it at the moment. Although someone on Buildhub said Changeplan puts the dew point in the insulation with IWI even if you spec 5mm of insulation, so hopefully you've got figures from Ubakus/somewhere else too.
There's only so much I can do right now before the point above about planning and EWI is resolved.
Howard
Fox
Have you got a plan to deal with the moisture from that internal air flowing through timbers or breaks around partition walls, sockets, joints etc then condensing when it meets your wall which will be colder due to the IWI?
My worry with this setup would be that the PIR will simultaneously stop your walls from drying towards the interior and lower heat flow through them, reducing their ability to dry and upping their moisture content. Which will speed up the rotting process of any timber in the wall.
This coupled with the point @apc raises about the lack of an external finish to keep rain out of the wall does seem to present some risk factors for interstitial condensation to me based on what I know so far.
Not wanting to poo on your parade at all and hopefully this is helpful*. You've clearly done a lot of research and IIRC you're getting a MVHR system which might make this theoretical internal moisture exactly that?!
*In due course I'd quite like some constructive criticism on whatever system I decide on because this stuff is flippin' complicated 😵💫