Iceverge

It needs some scaling and rebalancing to work aesthetically for me but that's personal. At the moment it reminds me of an apartment building. I'm guessing a floor area of 400m². A 7 figure project I would say. The east/south east is highly glazed. You'll have high energy bills unless you think about this carefully.

A house is like a boat and a passive house is like a boat with no holes in it. I can never underestimate why people argue that a boat would be better with holes in the hull. You can still fit whatever engine you like.

Have you done much research on this or is it just hunches? Gut feelings can be pretty unreliable when it comes to building, partly because we're at the recieving end of a century of commercial interests presenting their product as the newest and greatest. If you really want to get informed then you'll need to dig beyond any "opinions" of professionals and infomercials. If you don't you're going to overpay for a substandard house. For instance here's a report about cellulose toxicity with a screenshot of the summary. TOX-74: Cellulose Insulation - National Toxicology Program https://ntp.niehs.nih.gov/go/tox074

Hollow core planks here too. 75mm concrete. 150mm planks. 140mm service void was as tight as they could manage it. 12.5mm PB and skim It is dead quiet with carpet over the top. Next time I think pozijoists, thinner and easier to work with.

There is the land use case re growing Hemp and other considerations. What I should have pointed to was the lower greenhouse gas emissions over a lifetime than concrete. https://www.researchgate.net/publication/271608819_Life_cycle_greenhouse_gas_emissions_of_hemp-lime_wall_constructions_in_the_UK

Use 150mm rafters at 600mm CC with full fill batt insulation. Batten and counter batten above a taped/sealed breather membrane to give the required ventilation gap. Airtighess membrane below then 50mm counterbatten at 400cc to suit plasterboard with a mineral wool insulated service cavity. U value 0.21. Same as your PIR. Make the rafters thicker for better performance. No cutting at all and almost zero waste. Better for noise, fire, summer heat protection, thermal bypass, airtighess and windtightness, thermal drift and offgassing.

Welcome, a mate is building with hemp/timber frame at the moment. Materials are about 5 times € vs dense blocks and EPS beads. It is much nicer to work with however and environmentally more sound.

@Patrick used closely spaced boarding instead of ply which I prefer TBH as any moisture under the Zinc has somewhere to dry to.

No sorry, thermalite Vs standard 7N blocks. Rockwool (other brands available) or EPS beads is practically the best solution here I would say. If they had wanted better performance then I would have widened the cavity. Given they're extending to a solid walled house going much better with insulation on a small extension won't make much difference due to all the thermal bridging interfacing with the old walls. They could put some insulated plasterboard on the internal walls including the "internal" wall that used to be the external one. All this pales into nothingness without a solid airtighess strategy mind you. Another option to materially improve things at this stage is decent triple glazing Vs double.

The difference in swapping to dense blocks is about 15mm of rockwool. The wider the cavity the less % difference the blocks it make.

No that'll be fine. Almost all the heat loss is stopped by the rockwool anyway.

Blown beads. Leave the cavity run as low as you can. Right to the foundation if you can get your SE to agree. Don't cross the cavity with the DPM. Have a separate DPC on the outer leaf. This will give some allowance for mortar droppings not to bridge the cavity above DPM as they'll just fall to the abyss harmlessly. Then fill the cavity with blown beads. If you have a line of aerated blocks in line with the floor insulation you'll get performance matching an insulated raft foundation.

Or don't bother with foam if you can manage it.

It could be done for the living areas where there's plenty of circulation with doors open etc. However for the bedroom's without ensuites they'll be a ventilation dead end when the doors are closed and would suffer high CO2 levels at night. Well planned the ducting is quick easy and cheap to install.

Kooltherm £££££ Another steak dinner for the Architect and a week in the Rivera for the Kingspan salesman.

If there is a continuous layer of mineral wool as per the cavity at the outside of the steel it'll be fine.

If bothered you can counter batten your service cavity internally at 400cc. You tube has shown 1200cc rafter spacing so I wouldn't worry about it falling down.

Mineral wool batts or blown beads. 250mm cavity here with blown beads. Have you seen the denby dale videos from green building store? Also @tonyshouse did a blog.

A big gas boiler and a thermal store would work I would say.

Interesting I hadn't seen that. I had it pictured as a variable intake duct.

I wouldn't bother.

Have you done the calculations on stainless steels ties? Over a wide cavity, the difference is tiny in heat loss but dramatic in money saved. We used these guys ship but I don't know if they ship to the UK. http://www.vartryengineering.com/products/extra-long-wall-tie-large-cavities.html

@JtG Have you measured your DHW use? Heating a large UVC with a cheap time of use tariff has the cheapest lifetime cost for low volume users with my sums. Heat pump DHW is only really cheaper over a lifetime for higher volume users. On another point, an ESHP (all in one) DHW heater can be set to extract heat from the house or the outside. I've not been able to find any accurate data on the COP of said tanks Vs inlet air temperature so I'm undecided which I better. However at full chat they will tend to over ventilate a house. A simple operable butterfly valve or two in a duct could make this switchable season to season and fine tune it for best ventilation/COP.

I have most faith in EPS. It is 98% air so suffers almost no thermal drift unlike other insulants. When clearing out some old abandoned sheds I found some EPS that had been outside, wet and tangled in briars and scrub for at least 30 years. It was in perfect condition. In a thermally and UV stable setting I think it would last forever. In fact it has crossed my mind as an environmental concern.

That would work too. I'm just exceptionally cheap.