Haddock78

Hi, we have a separate annexe to our house, built in 2019. It consists of a single-room bedroom/kitchen which has electric heating, and a tiny corner (~2x2m) shower/wc. The bathroom has a very basic manrose extractor fitted and no heating. Even when the rest of the annexe is a comfortable temp the bathroom is like a fridge. When the extractor is running it feels like there is more cold air coming in than going out (I'm pretty sure it's not running backwards...). On windy days it definitely backs up. What would be a better solution? Just a higher spec conventional extractor or something like a single-room mvhr unit? There seem to be a lot of conflicting opinions on how well they work - does anyone have any positive or negative experiences with them, and any recommendations for specific models? Anything more elaborate seems like overkill in such a tiny space. Thanks

Apologies for the slow reply. Thanks for putting that together, certainly helps to visualise it and some food for thought. We're still waiting to get someone round to talk through what is possible, and at what cost! Though I would guess we would have to get to the 0.15 in the present building regs? No idea how much headroom we would have to potentially lose before it is considered a justification for achieving the less stringent U values?

It's actually detached ( I think Steamy Tea was just using a picture of a typical Cornish Unit house, nothing like ours thankfully...!) with a pretty steep pitched roof. One single and one double dormer at the front and a flat-roof extension - of indeterminate age - midway along the rear. We think the tiles were replaced in the last 20 years and they seem in ok condition apart from not having been cleaned in a long time. Most of the ballpark reroofing figures appear to be about replacing the tiles. I've no real idea about the practicalities and how much it would cost to keep the tiles but replace the rafters/battens/felt to provide more space? With the present plan of doing the insulation 'between and under' we are looking at losing 115mm on the sloping ceilings. Not ideal but not the end of the world, we're midgets anyway. We only moved in in October, so can't say for sure about overheating - but the temperature definitely fluctuates significantly with the weather between mild and cold/windy conditions.

Ha, yes! Probably if we had the money that would probably be the best option here anyway... Tbh I'd assumed that reroofing would be out of our budget and doing it diy/pieceal was going to be the only way. Maybe its something we should revisit: We'd like less ugly and better insulated dormers, the soffit and fascias are shot and pv was definitely on the plan. ?

No, we had it checked alongside the survey and it isn't.

Hi Iceverge, yes, I've definitely read so much stuff on here and elsewhere to get the message about points 1,2 & 3! Some photos attached (random foam/tape/plasterboard to temporarily block up holes where old cupboard was removed). My thought for conventional buildup was for: Sloping Ceilings - 50mm PIR between rafters/100mm PIR under/VCL/15mm Plasterboard Dwarf Walls - 50+mm PIR over studs in eaves/100mm between studs/VCL/PB My alternative was to use the same for the SC, but change the DW to: PB/VCL?/100mm Woodfibre Batts between studs/100mm WF Batts over/80mm Woodfibre board to hold the batts outside of the studs in place?? My rough calculations suggest a comparable U value (~0.15) and about 1/3 more expensive than the PIR option. Comments I've seen suggest WF doesn't need a VCL on the inside face, but wondering if I could continue PIR VCL along top of WF and then down outside to meet VCL under/over insulation laid in eaves. At present the eaves have glass wool, but mostly destroyed by previous plumbing work access and full of dead flies. Quite keen to replace it as well.

Well almost - a smidgen north of the Helford. I'm not sure about changing it to a warm roof. I assumed that as it is (probably) non-breathable felt I would have to leave the full 50mm below? Sorry if I'm misunderstanding what you are getting at.

Hello all, we recently moved into a very neglected 1950s chalet style house, in the far south of Cornwall. The in-roof upstairs bedrooms are eccentrically insulated with a random mix of old glass wool, loose polystyrene sheets and - mostly - nothing. Knowing nothing much about insulation or building regs a few months ago, I now know a little more but feel ever more confused... Our rafters are 100mm deep at 600mm centres (ventilated roof). I'm assuming there is no real option in the sloping ceilings apart from PIR to get to, let alone exceed, building regs (I think at least 150mm is going to be needed)? As we have more space behind the dwarf walls I was wondering if there was any mileage in fitting wood fibre insulation in this area? I've noted the various comments/topics on thermal mass/decrement delay as well as the claimed ability of wood fibre to store moisture. Or is it pointless to mix the two and we should stick to PIR for the whole thing? Many thanks for any light you can shed.