Indy

I looked into this and seems an impressive product and would get rid of a lot of the hassle with regards to getting builders to do the right thing. I've had a quote from them - looks like they do it solely based on floorspace and it's coming in at just a shade over £3k ex VAT! Seems like a pretty high number and I'm sure there are cheaper ways to achieve the airtightness?

Can I ask for an opinion on the option to go for a Lewis deck on the 1st floor ? This would be covered with a thin layer of screed which gives the floor a little more solidity, acoustic insulation (which I want to prevent noise transferring across floors) and a little better fire prevention capabilities. This was something the architect and I had discussed a long time ago and agreed but due to the whole process dragging on far longer than anticipated - was mostly missed in the pack I have so far. The SE design will need to be redone, the 1st floor height has been done at 2422 to account for normal floors and 22mm UFH system, whereas Lewis deck would mean I need to give up an extra 27mm of headheight as the system with UFH will come in at 52mm vs the 25mm of the existing option. Has anyone does this and does it really work? This is the one we're considering LEWIS-Metal-decking-brochure-2022-EN-web.pdf

Thank you @Iceverge - that's a really terrific input and lots of food for thought. I will admit I don't know what the difference is between yours and the one I posted originally apart from the areas where there's greater insulation and wall depth, and therefore assuming U-Values must be better. I take your point about buildability and cost as well. The tough part will be how do I get this all incorporated in my BR drawings as it could mean redoing a lot of the work that has already been done and I'm really at a point where I want to finalise the pack and start tendering the work out!

No, there is a room behind it which is my study and this gives extra headroom and there's a skylight in that room on that flat dormer. Because I hate creaking stairs in our current house and the original thought was to build an ICF house with concrete stairs, walls and floors. Moved away from this due to cost reasons but decided to keep the concrete stairs requirement. This would go well with the Lewis deck and screed floors that I'm planning for the 1st floor. Have the option of either though - and my initial quote of a pre-cast staircase wasn't as horrible as I was expecting. £4k including delivery but it would need cladding and installation etc. Getting quotes for timber stairs ranges from £3-4k for pine to about £10-12k for hardwood oak stairs - so the differential isn't as large as I was expecting, though this is all desktop research for now. We'll finalise which route to go when we get firmer prices back on either option and the SE designs/calcs we have cater for both.

Same for us - it's really there for wow factor more than actual utility. It will come on for about a week between Christmas and New year (based on the usage of our current gas fire) when we have friends and family over for entertaining and showing off. Not really meant to be the primary or even secondary heating system.

I am keen on having an airtight house though we're working towards a target of 3.5 at the design stage. It's something I will discuss with the main contractor and stress on as the build goes on. However, we do like to open the windows from time to time and the sliding doors are pretty non negotiable I have to say. Wood burner is something I like (as do both the boys) so I guess it will stay but I've been told you can get chimney stacks that aid airtightness when not being used?

What alternatives should I look at? Somewhat by design - given that BR is already a huge step up. I'm not too keen on losing internal space and we're limited on how far out we can go as we need to leave a 1m gap on either side of the property from the fence line. I have to admit I will need to spend time understanding all of this - though I assume VCL is a Vapour Control Layer?

I have heard the same re cost of wet plaster vs dot and dab being the same from a contractor I spoke to - just a little more work for the plasterer. However, my architect is convinced this was more expensive and would increase the drying time by several months - which would mean we couldn't paint the property or to expect cracking for at least 6m afterwards. So we changed tack to parge coat and dot and dab as a compromise.

Yes, wet UFH currently planned on both floors.

Taken your advice - separate thread started here

Following the recommendation on another thread, putting up the details of my build here to ask for recommendations on things can be improved. We're not aiming for a Passivhaus level of spec, as the law of diminishing returns means that the payback probably is not worth it. Aiming for a Building Regs compliant comfortable family home - and this is going to be a massive step up from a 1930s semi with no cavity wall (where we currently live). Ground floor is Beam and Block, and First floor is 225mm posi joist, Lewis deck with screed (for more stability). 2 sets of sliding doors (4.1m wide each) at the back which is West facing. Putting in ASHP, MVHR, in roof Solar panels (battery to be added later), 300l water tank + 100l buffer OR 400l water tank (3 bathrooms and cloak room), UFH heating on both floors including bathrooms, some form of air con in the 4 bedrooms and living/dining area (5 in total), Towel radiators with electric element in bathrooms. No carpets in the house - tiles in the hallways and living/dining areas and engineered wood in the bedrooms. My main questions are: 1. Given that this is a block and block build - how do we target airtightness? The 2 options I'm looking at are either Parge coat and dot and dab plasterboard (cheaper and faster to put up) Wet plaster though I've been told this will be more expensive, take longer and also reduce thermal efficiency which means speccing thicker insulation in the external walls. 2. What are the other things that are easily addressable given the details below to make it more efficient, without drastically altering the spec? Floor construction: U Value = 0.14 W/m².K 65mm. sand: cement screed 500g. Polythene separation layer 120mm. Celotex XR4000 insulation Polythene DPM Concrete beam & block floor to manufacturer's design Wall construction: U Value = 0.15 W/m².K Render 100mm. Thermalite Hi Strength 7 blockwork 50mm. clear cavity 100mm. Celotex CW4000 insulation 100mm. Thermalite Hi Strength 7 blockwork 12.5mm. plasterboard on dabs dry lining, plus skim Pitched roof construction (insulation at rafter level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters fully filled with 150mm. Celotex XR4000 insulation 25x47mm. battened services void beneath rafters Celotex PL4060 (60+12.5) insulated plasterboard plus skim Proprietary felt support tray Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters Unventilated loft space 19mm. plywood decking or flooring plywood for loft storage 75mm. Celotex GA4000 insulation above ceiling joists 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation Visqueen High Performance vapour barrier 12.5mm. plasterboard plus skim COLD Flat roof construction: U Value = 0.11 W/m².K GRP weather surface 18mm. plywood deck Firrings to give 1:40 fall 195mm. joists with 150mm. Celotex XR4000 between joists 90mm. Celotex GA4000 insulation below joists 12.5mm. plasterboard plus skim

Thanks, all valid points. I'm in the process of getting quotes and a lot of them come with the Surrey uplift applied. One quote we had for all the heating/cooling/PV/MVHR/UFH/basic automation was in the region of £80k! I'll be doing my own research and possibly getting the designs done separately and then get the builder to do it. The answer to the other question is that I won't be doing too much myself - until the money runs out I guess! Young kids and a very hectic job means I'll have most of the work being done by a main contractor, though my plan is to do as much procurement as possible to find the best prices on things.

Ground floor is beam and block floor. First floor will be posi joist - 225mm deep.

They will be sliding doors and that cannot be changed. SWMBO has said so and that's the end of the matter. The chimney was put in at the very early stages when we wanted a log burner, and I'm not sure anymore. However, I've been informed that we must build it to comply with the planning as it's part of the approved plans including the stack. Not sure what the alternative would be.

Very warm, very quiet and did not need a lot of heating to come on - even during peak winters. We were on floor 3 (out of 4) so had heat coming from both the top and bottom which made it even better.