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Unless you've got a sizeable solar array and batteries, solar wont generate much electric in the winter when you need the electric the most to run the heat pump. You're probably better spending your money on sorting out the heating system you've already got to get the lowest running cost you can. Once you've done that you can choose how much or little you heat the place.

Two things arise in my head from this - I may have missed something as I did have some wine last night. Firstly, if it is a big problem why has it not been sorted out - stupid to ask I guess but hey. Secondly, if you do have a blower test result then surely the leakage must add to the MVHR losses and be a calculate fraction assuming the MVHR holds the pressure difference roughly constant. From this it must follow that you can reduce the MVHR setting by the pressure test ACH when you are setting up the MVHR as part of the ventilation strategy. Might this then go some way to explaining why people find that when using MVHR they can back off the flow rate and still be comfortable because all they have done is got to the regulation ACH flow rate including the fabric losses.

Plus you can look back to that point where you had perfectly flat, boarded walls and think "If I'd have "turned right" and accepted a mate's proffered help on the tiling..." Guess you turned left and had a go himself? 😡

I've done loads of things commercially. It kept factories going. There is still going to be an end of life cost in demolition, but that might be 30 years because you've fixed the roof. We always fitted a steel over-rail system first because direct oversheeting won't fit and the existing fixings will clash. Then you can use any metal profile you want. BUT it's not easy. Don't fall through the roof, and don't make dust.

Hi BB, yup thanks for reminding me about that link tucked away in PM's.. will open it up tomorrow. Tbh there was rather a huge spanner in the works, for me, a few pages back when the talk was of £700 bills, rather than £70, in order to bet the results you guys are wanting. Bottom line is expenditure, after all. I did mention I've got used to listening to my Lp's seeing my breath.. with hottie on & sat upon my mini leccyB. So I really am up against it with the Rapidly rising cost of electric. If & this is a big if.. I could get some solar panels up, then the HP 'ON' idea, becomes somewhat more feasable. Maybe I need to explore this avenue. I've one end of my cottage South facing (albeit an eaves end, so no roof position options). I'll measure up my max potential area. Big Thanks all, Zoot

Change that to medium blocks inside and outside and you get to 0.18. That's a nice calculator actually by Knauf. It is fairly optimistic with the values it's allowing for the airspace behind the plasterboard though but it'll get you through regs which I'm getting the impression is the aim. Hemelite blocks are a small bit cheaper too. Superglass is a bit cheaper again than Knauf. £51.37 inc VAT per m2 for the blocks and insulation.

I know the dilemma well. I actually used to work in Microsoft back in the 1990s. I have a dual boot system and spend most of my time on Linux with LibreOffice, but then boot up on Windows and use Excel only when I absolutely have to. It makes life a bit of a pain, but for me it's worth it. Ventilation losses are a big problem for the whole industry. Unless you've got the results from a blower or pulse test, it's pretty much guesswork anyway and then you've got just a few options on methodology - you've got SAP based on storey height, location, exposure etc. or BS EN 12831-2017 or CIBSE methods and they usually treat MVHR differently so I'm not sure MVHR would correctly be an extra leak on top of ACH.

Just been to Stairbox in Stoke. Long drive, but worth it. Looked at lots of design options in their showroom and an expert on hand to help us design the stairs. We haven't taken delivery yet (two week lead time), but so far so good.

The cladding is something we don't want to change.

Unless this is a strict planning condition you may find render is more acceptable to future purchasers and lenders. Probably cheaper and quicker as well.

Thanks Gus. Yes, there is felt under the tiles, and it's generally in good shape - we don't see any water in the loft anyway. I had a dry ridge installed not to long ago too. The single-storey extension we're building at the rear will make access a little more difficult, so I'm just trying to make sure it's in as good shape as possible while I can still access it relatively easy. And yes, due to the extension we are skint so I'm glad to hear it can probably last a few years longer! Some of the houses in our street are council owned and they had new tiles not too long ago so the council must have thought they were reaching the end of their life, or a contractor persuaded them to reach that conclusion anyway.

I have put the numbers into the knauf calc and I end up at 0.19. The other issue is that I am using timber clad and not render.

It won't be a can till the metal roof goes on @Nickfromwales

I looked at earth tunnels when we built but came to the same conclusion as @Gone West. Minimal energy gain with the drawbacks of mould growth in the pipe and high install costs. As usual sitting down with a calculator and a biro very quickly dispells incompletely though out ideas. Passive stack was another. There's only 3 practical options really. 1.Trickle vents and extractor fans if you don't care about indoor air quality, noise, thermal comfort or energy use. 2. Humidity sensitive mechanical extract. Upgrade to humidity sensitive vents if possible. Good IAQ. Some energy loss. Minimal maintenance costs but some cold spots in the house. 3. MVHR. Excellent IAQ, minimal energy loss, best thermal comfort, no cold spots or noise. Higher maintenance costs may not be offset by lower ventilation losses.

I have the 350 m3 version, works very well for me. Super simple unit, been running for four years without issues.

But is very poor for airtightness. PIR boards are routinely installed terribly with lots of thermal bypass. There's plenty of threads on here to look at. For the same U value ........ a Wet plaster + double dense block + mineral wool batts will far outperform a Thermalite, PIR, Dot and Dab Wonderwall (don't sue me Oasis) As to the "lost" floor area just push the walls out by the same mm.

Try and get away from aircrete. I think you can get .18 with medium dense and 150mm cavity from memory. Maybe dot and dab improves the score slightly

Are the regs super strict now with walls having to hit .18? I seem to remember this being the case and swapping some cavities from 100 to 150 in 2015. Saying that new build sites round here still plugging away with 100mm cavity albeit with thermalite blocks. Now I'm thinking maybe you can exceed .18 if you offset elsewhere.

Pics please!

I did Durisol ICF, used ready mix and a pump lorry, me, my assistant, ready lorry driver and pump lorry driver, was the full team. Someone else near me did the full pour via a mixing hopper and Tele handler all on his own, mixed it, poured it. So you don't need a full team, makes life easier and faster. Durisol or Ecobrix are easy to fill you are only filling 5.5 rows deep at a time. No special equipment needed just OSB support patches are cut joints and corners, so very DIY friendly. Concrete pump (36m boom) was £560 for 8 hrs. I did my build during COVID restrictions, which included the Durisol training centres being closed, so I had the build manual to rely on. Just followed the steps laid out in the manual and zero issues. Note: I like to read manuals, many people don't, Durisol now a Ecobrix manual is very comprehensive.

4m max potentially get it down to 2m with different svp position. Nothing set in stone yet. When i read the regs its asking for 18mm in 1m for fall

Not trying to put you off but with all the positive stories on ICF maybe it's worth highlighting that it doesn't always go completely smoothly and it might be worth checking out some cases which were a bit difficult so you know how to avoid those situations. I think @ToughButterCup had a somewhat bumpy ride with his.

Maybe opening a can of unnecessary shaped worms?

Is there any reason not to use 7.3N blocks for the outer leaf? We are having vertical wood cladding on the upper floor and brick below. I have plugged some options into the calculator. If I use a medium dense or dense block for the outer leaf, I have too use a celcon or thermalite for the inner leaf. Is that typically the norm?

Guilty, and it was EPS (Nudura)