Sparrowhawk

The buildup I had in mind was 2&4 from the first post : VCL (polythene sheet, stapled down) on top to stop any moisture getting into the space, and as a second airtightness layer. Glass mineral wool between joists Vapour permeable airtight layer (or VCL TBC) draped over joists and fixed in place to support the fibreglass, prevent wind washing and add airtightness Void So the timbers should be fine, it's whether to make the glass mineral wool able to breathe. While your earlier calculations used 0.32 glass mineral wool the stuff easily available here is 0.44 Knauf loft roll. It means the calculated U-value of the floor is 0.29, but is cheap. Good to know there's a way to plaster over it, thanks.

Yes there is, but 70mm -> 100mm has less impact than 40 -> 70 would have. If 70mm is significantly cheaper use it, else 100mm. Do the soffits have ventilation in them? And is there any ventilation in the loft to let out air that rises? If not, getting that circulation of air from bottom to top is your first task. I think you have a massive struggle on your hands with no destruction or redecoration possible. How long do you expect your parents to stay living here? As an alternative is to get an Air to Air heat pump fitted to provide heating and cooling (aircon) winter and summer to give them more comfort.

AFAICT this has to be attached direct to Ubbink manifolds (or distribution boxes as they call it) rather than between some 90mm duct and 75mm duct? Will be v pleased if I'm wrong. This was the kind of thing I've been looking for, but as 90 -> 75: https://www.paulheatrecovery.co.uk/product/zehnder-flat-51-straight-converted-to-90mm/ Genius John 😁 That reduces the upstairs supply manifold from 8 port to 6 port.

I've been unable to find 90 -> 75mm reducers in any MVHR semi-rigid ducting range. Got a link? Ditto for Y-pieces, which would be handy to ventilate a large cupboard off the room's duct.

I'm looking for distribution box manifolds that I can attach both 90mm and 75mm semi-rigid ducting to. The only ones I've found are Ubbink's which seem to be 75mm with an external converter for 90mm dia ducting. Zehnder's and all those on the BPC site like Quiet-Vent seem to be all 75mm or all 90mm. Any options I've missed?

Welcome! First your visuals are amazing. I think you rendered them in Twinmotion but how did you draw the building? It's hard to see in the photo but it's either turned black from mold in it or a build up of dirt. The lack of airflow isn't good, so you may want to sacrifice here and later when you can redecorate consider some internal wall insulation over this particular part. Remember that building regs expect a 50mm gap between the roof felt and the insulation, with free flowing air in here. I did knee walls last autumn and had significantly underestimated the impact it would have in winter. I used 100mm supasoft insulation as we use these for storage so brush against them. We shall see about summer overheating soon, and whether it's better or worse now. Others will have the knowledge to make suggestions, but you're spot on re rigid foam boards. For snug fit installation you can put strips of Gapotape down either side of the boards, but it costs an absolute bomb. With the badly fitted ones here I taped them to the joists with aluminium tape, so the insulation value isn't great but they are airtight. Thermal mass is a running joke on this forum but if budgets allow you may want to reach for denser insulation like wood fibre, which slows the progress of heat into the building in summer (see https://www.steico.com/fileadmin/user_upload/English_Media/Content/PDF_Not_PIM_EN/Brochures/STEICO_heat_protection_EN_i.pdf).

OK with no feedback on a breather membrane at the bottom I'll take it that's a silly idea and use polythene sheet above and below. Where this laps up the wall and is taped, you can't plaster onto polythene right? So it needs to be a small lap and plaster onto the Tescon Vana tape - or the wall replastered first and then this has to be done after?

Hi @JohnBishop, for temperature and humidity I've tried Sonoff, Aqara and Tuya. Avoid Sonoff, the one I had was more out of calibration than the others and dropped off the network more despite being closest to the dongle. My Aqara ones are excellent (this model) and give the finest resolution data. However they are more expensive than... Tuya, which is what most of my sensors now are because they were less than £3.50 each. Beware there are two models on AliExpress, IH-K009 and ZG-227Z. IH-K009 are slightly more expensive and have performed better, but I have no idea what the difference between them is. Zigbee range is surprisingly short (well it was a surprise to me) if you have more than plasterboard and timber walls in your house. I've ended up with a second Sonoff dongle in repeater mode 8m from the other to keep sensors in all rooms connected to the network. For plugs, I went with these WiFi ones preflashed with Tasmota (Esphome wasn't an option at the time). I currently have a temperature sensor and a WiFi plug automatically controlling my heated propagator.

Should the membrane between the joists and under the fibreglass be vapour permeable, in case the insulation ever gets damp (dripping pipe or whatever)? If so, what's the cheapest one I can get? The layers I'm thinking are: VCL (polythene sheet, stapled down) on top to stop any moisture getting into the space, and as a second airtightness layer. Fibreglass between joists Vapour permeable airtight layer (TBC, draped over joists and fixed in place) to support the fibreglass, prevent wind washing and add airtightness Void

And where did you find installers that know and care about such things?

I like this idea. Is Marmox strong enough to replace chipboard in the floor build up, or needs that on top of it? Longer term the floor level will be raised in this room by ~20mm; it's a half/half mix of old suspended wood floor and (we think) beam and block. Which is probably uninsulated. I thought lifting the floorboards would show me a cross section of the beam and block but they whacked 2 joists across the join so going to have to try harder to determine its make-up and if there's any insulation in it.

My wife agrees I was explaining last night how I was trying to prove it'd meet building regs for BC and got that look. "You're not planning to put in an application to insulate the floor, are you?", followed by "stop being a stickler for the rules and get it done". Well that's me told.

I agree. Whether I notify BC or not I'm trying to get it to meet the required U-value of 0.25W/(m2K) and got myself in a right tangle with Ubakus I will try and recalculate with other insulation materials, but I haven't understood properly the perimeter/area ratio stuff used in England for floors. Like perimeter of whole suspended floor, or just the current room?

I'd love to, but unfortunately the joists are 100mm deep and then the void below is 100-130mm, less than building regs now require. I'm loathe to dig it deeper because the foundations are super shallow, but more because we're living here and I've got too many other things to do I hate digging

That would be idea 2 I think, with VCL being the proper term which I didn't know for "airtight non-breathable membrane" (something that keeps water vapour in the house and stops it from getting into the void)? I've edited my original post to clear this up. Interesting, is that to be belt and braces? So 2 stops water vapour and air moving down and around the PIR, while 3 stops air and water vapour coming up from the void? Any brand alternatives you can suggest? I'm unclear if a cheaper VCL is just thick polythene in this case or it's something more fancy and reinforced.

Because the joists and space below are shallow, I'm limited to 100mm of insulation so going to have to use 100mm PIR between our ground floor joists to get the best U value I can. Previously I'd planned to use the Ecological Building Systems approach of loose insulation and 2 membranes: I've come up with 3 ideas for PIR insulation, from least to most work: Install boards using Gapotape (or home made equivalent as that stuff is seriously expensive. I'm experimenting with expansion joint foam and aluminium tape) and tape joints between boards with Tescon Vana. Don't tape between boards and joists. As above, but then put an airtight non-breathable membrane VCL over it all. Any poor fitting boards can still let cold air come up to floor level Put the airtight membrane VCL below the PIR boards and over each joist. No cold air can make it to floor level Which approach has the least drawbacks?

Am I correct in thinking that when you do a radial ducting system it's the max pressure drop of any of the ducts that matters, not the sum of all the pressure drops? A simple calculation on duct length and flow (assuming straight ducts) gives: The total static pressure is getting close to what a well designed system should have as its max, before adding plenums, bends and more, so I'm assuming I've done something wrong.

Not wishing to derail this thread of sauna-porn (those Polhus ones, phwoar) but how do you find using an IR sauna? It sounds more practical, and hopefully easier on the wallet too.

Welcome @Mash! You are sensible doing it all at once (and I assume moving out while the work's ongoing?). We're doing a smaller renovation of an extended 1920s house while living and working in it, which has slowed progress a lot.

I shoved a layer of plasterboard offcuts between the rafters. Today's assessment is it's made the sound problem worse not better 😂 I haven't added any fluffy stuff yet as waiting for heating engineer to do his stuff, as I don't want to risk it getting wet as he moves the cylinder.

Welcome Graham. I hope you'll share your build here as it goes. There's a lot of skepticism about straw bales on this forum; me I'd build a straw house if I could for the carbon footprint, but mostly as I like the aesthetic they end up with. Fingers crossed that the warrant doesn't take as long as planning did.

"P = Length of the exposed perimeter (m)." Clarifying that the exposed perimiter isn't 36m (the length) but we involve the thickness too? I hadn't taken that into account before, which would explain some odd numbers I was getting 🤡

It is, the options on the Kingspan calculator are very limited (only this material, only 450mm joist centres) so it's going to come out better than the other. But - I was hoping to verify on 2 calculators that 100mm PIR plus flooring would at least get me to 0.25?

You're so lucky with that joist depth. My entire joist + void depth is around 200mm.

It is German, and I can't see what they're using for permiter/area, if anything. Kingspan by contrast required those two values before calculating the results. They only have an option for "floor", not ground floor. I can choose the space at the bottom to have air or earth in it, but AFAICT restricting what's at the bottom to those two settings is the main change vs modelling as a "wall" or "roof".