Iceverge

Ok, that helps. Looking at those rafters I guess they are ~150mm so something like 100mm insulation between them , ( I would use flexible batt insulation) and then as another 100mm below across the rafters. A/tight membrane then. 22 mm *50mm battens and plasterboard. I assume the roof ventilation is happening below the sarking by the way.

Buying a sheet of this here or a plank of that there is a recipe for getting rinsed. Try to buy say at least £2k worth of materials at a time. Ring 5 different BMs and give them a list as long as your arm and get an itemised quote from each. Then you can pick and choose the ones that are doing the best deal or get the handiest one to price match. For some reason delivery never seems to be much or anything extra either.

Fire resistance i think. Do you have any pics of the roof today as it is. Might give some clues as to the best solution.

Something denser than PIR and metac would be better for noise. Cellulose or Rockwool maybe.

EPS beads or fill fill mineral wool solve a myriad of problem here.

airtightness tape?

Sounds like their thinking hasn't been updated since the days of high temp heating with emitters that loose heat to the room quickly and then turn off again. And in houses with terrible fabric that required constant heating to stay warm. Low flow temp heating effectively self balances anyway. As the temperature of the room approaches the temperature of the emitter then the energy transfer to the room slows down to almost nothing.

Yup

Can you switch to 150mm EPS beads save yourself lots of time money and have a better performing wall? You can just put a strip of dpm on the outer leaf if the wall, 150mm from the ground then and let the beads go right down to the bottom of the cavity really mitigating any thermal bridge.

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You'll have to weight up the cost. Crushing may be impossible if there's too much rebar in it. The time you might spend sorting it and loading it on a flatbed is probably not worth it.

Get an experienced operator with one of these and start smashing. Salvaging anything will be more hassle than it's worth.

Very interesting. A couple of questions if you don't mind. What is your wall buildup? What is the interior volume and occupancy rates? Did you use bog standard trickle vents or something else?

If you can I would build a literal model before committing to the design. Some card and sticky tape and a few hours will give you a great feel for the building. It's literally child play.

Did you take any measurements of air quality post construction? This study suggests at children did less well in under ventilated classrooms in the US in 87 sample cases. Ventilation Rates and School Performance | Indoor Air Quality (lbl.gov) Separately, using historical examples to justify the natural ventilation of buildings often ignores the influence of a fireplace as an active ventilation device. Open fires used to run for 18hrs+ per day in houses and probably 24/7 in hospitals. They used about 2/3 of their energy simply to drive smoke and air up the chimney. Even at 7kg of coal per day this would equate to about 35kWh/day or 10% of our annual MVHR usage.

Seems a shame to cover up all that lovely wood with insulation now! I assume the boards at the base will disappear once the concrete has cured further?

I doubt there is ever an economic case for wool as a house insulant. Theres too many steps involved for something that can be done well with other materials. It's a shame more people don't realise how bloody excellent it is as clothing however. Wool socks and wool jumpers are tremendous. Always warm, never sweaty. I wear them every day. Something like hemp would be far more economic as an insulant I suspect. It would sequester loads of carbon too and can be grown really easily. Unfortunately processing facilities are tough to find.

On the design of MVHR units I have a couple of suggestions to the manafactuer's. I think both fans should be kept at the warm side of the heat exchanger. This would prevent them from ever getting cold and developing mould on the blades which kills pumping efficiency. The unit should be more easily serviceable. Mine required 10 screws and the front of the unit to be taken off in order to access the heat exchanger and fans. There's no reason this couldn't be done with over center clips or similar to make a 1hr job a 5 minute job. A quick wipe down with a microfiber cloth and vacuum of dust etc could be done by anyone then, not a trained professional etc etc. If maintenance isn't easy then it doesn't get done.

@SimonD what specialist technique did you employ to ensure natural venting was adequate? Do you have any monitoring of the air quality as this is too often pitiful in non mechanical ventilation systems. I drew our house so that every bedroom, living room and kitchen has 2 operable windows (T&T) on walls facing different direction to ensure good cross ventilation. Similarly the upstairs hallway. However we did employ MVHR. I dismantled it at the weekend to clean the exhaust fans and heat exchanger as it was growing some kind of mold on the exhaust side of the unit. I think due to not having the unit perfectly level on the wall bracket which was causing the condensate level to be too high. Time will tell if that corrects it. As for the complexity involved, I was surprised by how simple it was really. 2 fans, made in Germany and a digital speed controller essentially. To the point it would be pretty easy with some OSB, foam and off the shelf fans and a heat exchanger to make one yourself.

I'm aware you want timber as a finished floor but I wonder if how it'd affect thermal performance of the UFH if one was to put the two layers of OSB on top of the profiled EPS. Something like: 50mm EPS DPM 100mm EPS 50mm EPS with profiled boards with UFH 11mm OSB x 2 layers, glued and screwed. Finished flooring. I'm just wondering could it be an alternative to a concrete floor for those who want UFH and are limited in the space build-up or those who like me are not a fan of the hardness of concrete floors.

Interesting. Please keep us updated with pics. Have you considered moving the DPM above one layer of EPS to prevent it getting punctured? How do you plan to run the UFH?

Good stuff. What was the build-up of internal wall insulation in mm and order of layers? It's a less covered method here. Any floor renovation?

Well done on getting planning and welcome. Pics and plans always welcome! I think @Kelvin is a fellow heb homes builder and there may be a few more about too.

Concrete is normally cheaper than screed but needs care to get a good finish. You could omit the screed altogether and just put two layers of OSB glued and screwed together floating on top of the insulation. This could give you up to another 50mm to play with and certainly wouldn't crack.

Your scheme is to try to emulate the effect of trapping a layer of gas between two planes like a double or triple glazed window. This only works if there is no convection. In your case you want to actively promote convection above the insulation to ensure the roof can dry out. In reality anyway you will find it impossible to create a layer of air between two materials without any convection and a layer of simple mineral wool would aid the insulative effect more than your DIY cavity. I don't quite understand this. There is a case for a low emissivity (shiny) barrier for heat protection in very sunny climates with no ventilation below the roof covering but it makes almost zero difference in a heat retention setting.