Iceverge

Delight is pushing it!! Given the labour and uncertainty involved in renovations it's a pragmatic decision.

Probably not. Maybe if you were to have a lighter superstructures like timber frame. Have you considered a basement?

As an aside 3G, Airtightness and MVHR were always going to be included for the comfort, noise, air quality and building health aspects. Payback was considered but it wasn't really ever up for discussion given the other benefits.

OK here are some numbers for our 185m2 house after having a play with PHPP. Out annual heat demand is 2625kWh. Passiv windows with 3G , 200mm EPS in the floor (u = 0.16) , 250mm EPS bonded beads in the walls (0.15) , 400mm Cellulose in the attic. (0.1) Airtightness 0.31 ACH50. Here are some Airtightness figures. 0.31 ACH = 2625kWh 1 ACH = 3012kWh 2 ACH= 3586kWh 3 ACH= 4170kWh 4 ACH= 4716kWh 5 ACH= 5537 kWh 6 ACH= 5861kWh Now I play the same game but step back the other fabric of the house individually to say a bregs basic house of a few years back. Floor U 0.3 = 3103kWh Wall U 0.235 = 4005kWh Roof U 0.175 = 3159kWh Double Glazing = 3387kWh Loose MVHR = 5365 kWh Keep the airtightness and MVHR but use the poorer figures everywhere else 5918kWh MVHR and airtightness are the biggest wins. Then come glazing and U value. This isn't as straightforward to generalise as window areas vary, a bungalow will have much more wall than a 3 story town house. Insulation has to be improved all together really. Not much point in adding 50mm to the attic insulation when its already at 500mm. It only reduced the U value by 0.008W/m2K. However if you add 50mm to 100mm wall insulation it takes it from 0.4 to 0.26. 16 times more of a difference. I concluded in out house for the above insulation types the ratio of increasing the insulation in the following ratio was the most economical. YMMV depending on construction specifics. 4 Floor 5 Walls 8 Roof Hope this helps.

For any UFH you need lots of insulation in the floor or otherwise too much of the heat will be lost downwards. The more the better but start at 150mm PIR or 200mmEPS. This means digging up the existing ground floor and lots of labour. For an old leaky house you need high power heat emitters for quick response. Radiators are the easy way to do this. If you go for UFH you need to have it in a thin screed and closed spaced pipes.

I think it's 400mm for 12.5mm plasterboard. Maybe @nod will have the definitive answer.

This is a terrible idea. A terrible terrible terrible idea. Sliding sash windows are on my list of an awful way to build a house. I'll play with PHPP in the minute to give you some numbers on the importance of Airtightness.

Good stuff, we built with blocks too. Plans ( scrub off your name and address ) are always appreciated for a nose!

BUT I'M LAZY..........

Are those flanges strong enough to take a reasonable load like a big TV?

Fabric first. This really means a good form factor, good insulation (including thermal bridges) and AIRTIGHTNESS!!!!!!!!!! Get these right and you can burn baby Panda's and still have a very low impact house. Congratulations on the decision to knock and rebuild, It's absolutely the right one. I too had no experience in building but like @jack says you'd be surprised how quickly you'd pick it up, especially as you have a technical mind already. Plumbing, MVHR, Airtightness are all jobs that can save you £1000's and with the products available don't require any extraordinary skills. Have you decided on a build method you'd like to use? The best one of course will depend on the house design, location etc. At the moment my favourites are Stick build on site Masonry Maybe ICF but I'm still reading about it.

Most builders would who supply would just quote for the whole thing eg "extension" not the "extension + pile of unused crap in the garden" so I would say the material not used is rightfully theirs. In theory these who are better at reducing waste and taking the offcuts to the next site can offer a more competitive price in the first place so I don't think you're really loosing out.

I think I actually worked for a company that his company eventually bought, but that's neither here nor there! Are those metal webs the same as the ones @Jenki has?

By the time you've paid someone to do it properly spray foam would be just as economical. @JohnMo used it in his roof. Maybe he could review my idea and comment.

Roughly how much per m2 are the blocks? Did you use them for internal walls too? The idea of screwing to the metal webs is a great one. Someone in here was faced with drilling and concrete screwing hundreds and hundreds of holes for battens for cladding insulation. Different EPS ICF. Can't remember who. As an idea one could use the thinnest EPS ICF as a structural wall. Then using timber frame cable ties add an external masonry leaf and use EPS blown beads for the cavity. It might be a relatively economical method of getting to very good U values and Airtightness with a durable external finish. It'd be also excellent for thermal bridging with the ICF.