I'm starting to think about improving our "thermal envelope". Our floor is already a new slab within 100mm PIR below the screed and 25mm PIR up stands (for the underfloor heating).
Solid brick walls, no signs of damp/moisture ingress, the majority of the brickwork is already pointed in lime mortar, where it's been bodged by others over the years with cement, will be rectified soon.
I'd like to attach the insulation direct to the wall, in a couple of overlapping layers of PIR, both taped, and continue it up from the ground floor, through the intermediate floor cavity, up the first floor and into the loft space, before battening it all our, for a service void, plus noggins where we'll hang the TVs etc, and finally attaching plasterboard to the battens.
I'm confident that taping both layers of PIR individually and having a couple of layers overlapping will give me a solid airtight VCL, from slab to roof space. My concern is around the first floor joists which are pocketed into front and back external walls. I can keep the detail around them as neat as possible, trimming the PIR and taping, but my concern is the joist end that will be on the cold side of the insulation (pocketed into the external wall). The wall is expected to be much colder than it currently is (as that means the insulation's doing the trick), but that also means it's at more risk of damp, right?
The front wall is pretty thick, around 330m and the joist is pocketed in my around 100mm, so there's still ~ 230mm of masonry to protect these joist ends...
Ideally I'd reseat the joist ends on the warm side of the insulation, but I really don't want to replace all the downstairs ceilings if I can help it... I've seen some recommend an injection of boron paste into the joist ends to help, but that really seems to be a mitigation of a symptom rather than the cause.
Am I over thinking this? Should be I be detailing around the joist ends differently?
Solid brick walls, no signs of damp/moisture ingress, the majority of the brickwork is already pointed in lime mortar, where it's been bodged by others over the years with cement, will be rectified soon.
I'd like to attach the insulation direct to the wall, in a couple of overlapping layers of PIR, both taped, and continue it up from the ground floor, through the intermediate floor cavity, up the first floor and into the loft space, before battening it all our, for a service void, plus noggins where we'll hang the TVs etc, and finally attaching plasterboard to the battens.
I'm confident that taping both layers of PIR individually and having a couple of layers overlapping will give me a solid airtight VCL, from slab to roof space. My concern is around the first floor joists which are pocketed into front and back external walls. I can keep the detail around them as neat as possible, trimming the PIR and taping, but my concern is the joist end that will be on the cold side of the insulation (pocketed into the external wall). The wall is expected to be much colder than it currently is (as that means the insulation's doing the trick), but that also means it's at more risk of damp, right?
The front wall is pretty thick, around 330m and the joist is pocketed in my around 100mm, so there's still ~ 230mm of masonry to protect these joist ends...
Ideally I'd reseat the joist ends on the warm side of the insulation, but I really don't want to replace all the downstairs ceilings if I can help it... I've seen some recommend an injection of boron paste into the joist ends to help, but that really seems to be a mitigation of a symptom rather than the cause.
Am I over thinking this? Should be I be detailing around the joist ends differently?
