Iceverge

Internet thinks woodcrete would be fine underground........ I was thinking of EPS however, it will perform every bit as well as an insulated raft as a foundation provided you get your thresholds right.

Any pics of the board install? It's very tricky to do well. In fact I don't think it's actually possible in real life. Batts and EPS beads are almost fool proof by comparison. What is the remaining cavity depth after the boards?

There's more to consider with MVHR too. 1. Noise from outside. 2. Filtered incoming air 3. Heat load ( how big a boiler you need) 4. The stability of the internal temperature. 5. Drafts. 6. Insects in the house. Hard to put a more accurate price on these. However as I posted elsewhere recently Airtightness and MVHR are far more important than extra insulation so perhaps they might be a better place to trim if you're really stuck for cash.

In the real world mechanical ventilation is a must if you value the quality of the air you're ingesting. I would never suggest anything else as a sensible option. MEV works well, but to have some control over the infiltration, you'll need humidity sensitivity wall vents (about £60 each). Say you have one per bedroom and living room maybe 7 in total=£420 Then add dMEV in every room with a tap. Maybe £70 x 5 = £350. A little bit of additional wiring and fitting and you'd have a well performing ventilation system for £1000. For a 200m² house it'll cost roughly 3000kWh of extra energy to be used annually. Say £250 extra annually on heating. Electric will be much the same. There'll be minimal servicing but allow maybe £70 per year for a dMEV needing replacing. £320 per year for a 200m² house isn't too bad. 20 year cost £7400 A bit of shopping around will see you buy a new MVHR unit and the bits for say £4k. Allow £2k for install for some reasonably handed builders. It'll cost you £40 per year in filters and the bearings will need to be done every 4. Allow £100 per year in maintenance. 25 year cost £8000. There's very little in it long term in £££. Break even is about 20-25 years I'd estimate.

Plain string with nothing tied to it is often fine to get pulled through a duct by a vacuum. Your situation sounds unfortunate but not to worry, we're all learning and in the grand scheme of things, it won't be a major life regret. The plan to dig, add an accessible junction box and run a bigger duct is probably the best options at this stage. This stuff isn't that dear.

It'll be fine. I hope you're using full fill EPS beads or mineral wool batts.

Congratulations on your new house. Perhaps more details of the current state of it might help us guage what kind of heating system is most likely to be most comfortable and efficient in the long run. Some houses are terminally unsuitable for an ASHP but this depends on, 1. Airtighess 2. Insulation levels 3. Window spec 4. Footprint 5. Occupancy patterns. Perhaps you could give us an idea of some of these. At the moment it sounds like a gas boiler might be best if that's what you currently have installed?

What about strip foundations and ICF rising walls?

I'd be putting that in the "pro" box for conventional footings. Nobody will care as much about details as you. Can you trench fill for the footings in dry weather? With good digger operator and it's one of the simplest footings you can make. Superb performance can be achieved with any kind of foundation so long as you look after the thermal bridging which isn't rocket science.

Our builder used timber bolted to the steel, cement board screwed to the timber and rendered over with sand and cement to match the render on the blockwork. Wish I'd insisted on using concrete lintels now. I'm not keen on having timber buried in the outer leaf of the house and there'll inevitably be some voids in there which means that moisture may be able to corroded the steel. Ideally I would like steel: 1. Completely encased in concrete for rust protection or 2. Under/behind some insulation to keep it warm and ensure no moisture condensates on it to start with..... What I would do in your case. 1. Tac weld or drill and fix some heavily expanded metal mesh to the web of the steel. 2. Fill the web of the steel with concrete entirely. May require some partial shuttering and then poking with a trowel but it's not rocket science. 3. Apply more expanded metal mesh over the whole lot. Use some self drilling screws underneath to secure to the bottom. Better still tac weld the mesh directly to the steel, (you'll need a MIG welder for half an HR). Let the mesh overlap well onto the blocks too to prevent cracking and fix it with a few screws. 4. This will leave a flush and well keyed surface to directly take a coat of sand and cement render. Following this process you will have 1. Steel complete encased in concrete. 2. Thermally uniform substrate for the render to avoid differential heating and cracking.

Our actual measured heat usage was a bit more, 3.2MWh/annum. Not sure of why the difference to PHPP. The insulated envelope of our house is essentially a 8.5mx13.5mx5.5m box so a good form factor like you say. We're quite a distance further south than you too. What was your blower door result and window spec?

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 Lose 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 our 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.