Rob000

Ok thanks Mike, but is K5 on the outside and no PIR on the inside (but still a VCL) going to make any difference to the moisture at the bottom of the cavity? It still has nowhere to go? Or will moving the dew point further out remedy that? I've had a look at wood fibre, which may have the advantage of warming up and drying out the existing cavity insulation (if it needs it), but haven't seen anything yet that confirms your can use brick slips on it.

Thanks Mike, I didn't realise brick slips were an option. I think I'll reduce the inside insulation to 50mm PIR, get a survey of the cavity wall insulation done (and remove and replace is necessary), and do an additional 60mm or 70mm of K5 externally in the summer/early autumn. Having done a bit more research on AVCLs I think I'm going to use a non-combustable one and batten off it too create a service void rather than lapping it up (the a2 rated ones I've found are foil based so the less you can scrunch them up the better). I'd feel far more comfortable fitting downlights under one that wouldn't potentially take a fire all over the house.

Hi, We are renovating our 1950s detached bungalow. I'm currently trying to figure out the best approach for insulating the whole ceiling and the new walls and would welcome advice from knowledgeable members. Apologies in advance as this post is a bit long but I'm not sure how to condense it. Walls The original walls are brick cavity (approx 60mm) and have loose fill insulation (possibly mineral wool but I haven't taken a close look yet). There is a small amount of old rear extension wall that is brick and block with a cavity (55mm), which also has the loose fill in it. The new walls have a 100mm cavity with 90mm PIR or similar in it (I'll add the exact type later). I don't know how good the existing cavity wall insulation is but wouldn't be surprised if it is patchy. The ideal upgrade given all the work we are doing would be external insulation but as it would change the look of the building we'd need planning permission which takes on average about 6 months here and me and my family of 4 are currently living in a caravan in our garden so I'm not sure I'd get away with it. My first idea was 75mm PIR covered by constivap membrane secured with 63mmx38mm cls timbers to create a service void (the orientation of the timbers varying depending on what's going in the void and on the wall) and covered with plasterboard. A friend then suggested I look at multifoils (insert groans here) and I discovered that for a 10mm thicker build up (50mm PIR, 25mm batten, ybs super quilt, cls, plasterboard) I could further improve the total r value by about 1.2 (although the foil would be compressed to about 30mm rather than the full 40mm wherever there is a socket or switch). Any thoughts on the pros and cons of these two options (u values, airtightness, vapour control) or any potentially superior alternatives are welcome. Please note I don't want to shrink the rooms any more than I would with the options above. Roof A warm roof would require planning (see above). The pitch is only 22.5 degrees and the majority of it has 90mm rafters. The roof was replaced a few years ago so it's got a breather membrane. There are a number of tricky corner sections in the rafters which makes PIR tricky to install in the rafters and the shallow pitch and small rafters would make a ceiling PIR install also very tricky. I am keen to have some kind of service void to avoid having to massively increase the size of cables because they are running in insulation. I've investigated using multifoil as the airtightness layer/vcl on to of the ceiling joists and putting rockwool on top and was advised by the multifoil manufacturer that (despite their drawings for flat roofs showing otherwise) it was best to run the multifoil (if using it as a vcl) beneath the joists to avoid interstitial condensation - I couldn't get to the bottom of why though. Is that accurate? I thought the vcl was just supposed to be on the inside of all insulation so can only guess that it might matter because a joist could be a cold bridge where it sits on the wall plate? If the vcl needs to go from underneath I reckon I can create a service void by stapling it up the sides of the joists and taping over the staples with an airtightness tape. Can anyone forsee any issues with using multifoil? Would I be better using a breathable hydroscopic membrane instead as I'm putting rockwool above or will that not matter? For info, I'm also installing a MVHR.

Hi, we are renovating our bungalow and are upgrading our insulation and airtightness as part of the work. I've found some helpful posts on this forum so thought I'd join up to ask some questions. I might also be able to help with electrical questions as I'm an electrician.