My house is a (non-listed) late 17th century stone farmhouse. It has a bathroom that was added as a single storey extension possibly around the early 20th century, constructed in solid brick. Originally it had cement render which I have replaced with lime render.
I am now proposing to extend one end of the bathroom, which will require new footings and two new walls, one of which will extend an existing wall.
The proposed structure of the walls is 100mm concrete block - 50mm cavity - 100mm PIR insulation - 100mm concrete block. It is then proposed to finish the exterior with a harled lime render and silicate paint and the interior (above the level of the suspended floor) with moisture resistant plasterbord/insulated tile backer boards. I am then suggesting to insulate the adjacent wall to the same thickness using PIR insulation so that it matches the new wall.
Given that I have spent a lot of time making the main house as breathable as possible, this all feels a bit strange. However (a) it is a bathroom and will need waterproof walls (and humidity control using an extractor fan) and (b) it is not part of the main house.
Any views?
In particular, what about the insulation on the existing wall - should I use PIR or, say, wood fibre or would that only make sense if the internal surface is breathable (i.e. not tiled)?
Also, would I be better to ditch the PIR insulation altogether and have a mineral wool-filled (150mm) cavity and go for lime plaster internally except in the wet zones?
I am now proposing to extend one end of the bathroom, which will require new footings and two new walls, one of which will extend an existing wall.
The proposed structure of the walls is 100mm concrete block - 50mm cavity - 100mm PIR insulation - 100mm concrete block. It is then proposed to finish the exterior with a harled lime render and silicate paint and the interior (above the level of the suspended floor) with moisture resistant plasterbord/insulated tile backer boards. I am then suggesting to insulate the adjacent wall to the same thickness using PIR insulation so that it matches the new wall.
Given that I have spent a lot of time making the main house as breathable as possible, this all feels a bit strange. However (a) it is a bathroom and will need waterproof walls (and humidity control using an extractor fan) and (b) it is not part of the main house.
Any views?
In particular, what about the insulation on the existing wall - should I use PIR or, say, wood fibre or would that only make sense if the internal surface is breathable (i.e. not tiled)?
Also, would I be better to ditch the PIR insulation altogether and have a mineral wool-filled (150mm) cavity and go for lime plaster internally except in the wet zones?