Warm batten internal wall insulation mitigations

[FrankHouse]

I'm extending and renovating a Victorian property with 9" walls and am planning on using the warm batten method of internal insulation with 100mm of PIR fully taped and detailed on all external walls. With 25mm battens over the top to create a service void. The insulation will be foam adhesive and screwed through the battens into the wall. I like this method as it keeps my timber inside and all of my wiring as well.

 

I have read a few recent and not so recent posts and realise that this warm batten method may not be the current favourite for some people but I don't think there is a perfect solution for my situation. There are some perpendicular internal walls, adjoining cavity walls, steels all of which complicate the situation and I don't want to externally insulate and cover the exterior façade. 

 

It seems to me that there are some symptoms of issues that will arise from this method and if I can treat them individually then the method should be sound.

 

Floor Joists - I have cut back the floors to allow the insulation to run from ground to roofline. The only exception is the joists entering the external walls. I don't see there being a significant issue if they are expanding foam and taped. My only concern is that the timber may be cold and damp and therefore rot. Its treated and I cant see it being any worse than the 120 year old exterior lintels which seem to be OK. I am considering making up some long angle brackets which will bolt to the wall and protrude well into the room. If there were any rot at the end they would offer extra rigidity and maybe by me another 20 years? Am I over thinking this bit?

 

Internal perpendicular walls - I understand there could be some moisture ingress through these points as its not possible to tape around the corners, although I could put an internal DPM up if anyone has experienced damp in these corners? I'm hoping that the walls wont be cold enough to suffer condensation. I am installing an MVHR system so the house will hopefully be well ventilated. Has anyone else had damp issues in these corners and was it due to external moisture or condensation? Did anyone put up a DPM behind internal plasterboard in these locations?

 

Failure of brickwork due to moisture - I am not that convinced that this is an issue, I know the bricks will effectively be outside a heated house but the brick barn at the back of the house is of a similar construction and I don't think shows any adverse effect other than maybe requiring repointing more frequently. Surely any cavity wall outer leaf is in the same situation being out of the heated envelope?

 

Driven moisture through the wall - this is another one I am not sure of. Surely if the rain is driving hard enough to penetrate 9" of brickwork it would possibly form on the inside surface of the wall. As the PIR will be taped to the floor PIR it shouldn't penetrate the internal layers and will just be reabsorbed back into the brickwork at some point. I would guess that the majority of moisture in a cavity wall is condensation from leaking internal air which hopefully wont be an issue for me as I am in control of the taping and sealing of my internal envelope.

 

So do I need to add the joist hangers and vertical DPM to internal walls and is there anything else that people have experienced that will change my mind?

[Annker]

@FrankHouse Understand this is an old post but if you get the @ notification I would love to know if you went ahead with the IWI as outlined in your post and if so how it has performed?