Iceverge

Hold fire on the render until this is sorted. You may need to remove the boards. You need to have a 100% weather proof later over the timber frame before proceeding. The outer layer of render board is only really to deal with 99% of water. The one under this (tyvek house wrap) needs to deal with the full 100%. Do you currently have windows and/or a roof on? Has the tyvek been properly lapped at all junctions? Did you tape it? This sounds strange. The vented cavity behind the render board should be able to freely drain away in case of any water ingress. It certainly shouldn't pool behind it . Can you do a quick cross section sketch of what has been built please?

Zoom out please and take more pics. Is this the inside or outside, ground floor, first floor or flat roof. It's hard to tell unfortunately. A few drawings/sketches would help too.

Sorry, I'm a bit confused about this. Do you have more plans and pictures to help please. Is the picture above the first floor or ground floor? Is the wall being battened an external wall or internal? Purple passive and other airtight paint is expensive, much cheaper to use a membrane or a parge coat where you can. It's of limited benefit to apply until you're absolutely sure you've filled every hole you could poke a pencil through first. My advice is to make a DIY blower fan once the windows and doors are in. The get some Illbruck FM330 and fill all the big gaps. Then use a sand cement parge coat to do all the flat surfaces that might leak like un rendered blocks. Then spare the airtight paint for the junctions and hard to reach areas.

You could use a breathable insulant like woodfiber and screw it directly to the wall and lime plaster over the top.

As I remember it's your Airtightness layer too. I would tape the DPM to the membrane such that if any drips run down the outside of the breather they end up outside the building.

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.