Bitpipe

Well, if your builder uses the wrong glue (most will default to cheapest unless otherwise instructed) then you may end up with a squeaky floor later on. They won't have to live there and good luck proving that that was the issue and getting them to fix it. Same goes for tapes, sealants, fixings etc. Because premium products are more expensive and they will quote assuming bog standard. If you then ask for the better product it's 'extra over'. Oh yes, builders will buy from the BMs that give them a decent discount but more importantly good payment terms. They will not spend an hour on the internet to save you 20% on insulation or sockets etc. Whatever it costs them gets passed onto you, with a small margin. We specced EPS 200 under the basement slab and EPS70 to basement walls. Groundworker had never worked with it and said that I needed to take care of it. I found a buyer who got me a great price (on commission from me) and had it delivered to site.

I just used a per m2 estimate going into planning and to guide the architect on gross floor area, scale etc. The QS plan should be able to initially work off your planning drawings and make assumptions on cost of structure (assuming you know what you want here) and the first and second fix which is pretty generic. If you give them detailed BR drawings then they will be more accurate but this assumes you've decided on construction method etc. We ended up with a 25 odd page spreadsheet, one page for each stage (e.g. preliminaries, ground works, structure, roofing, windows, etc etc..) and we were then able to use this as baseline for supplier / contractor quotes. Was also great to be able to give a contractor a fairly accurate quantity for things like plastering and flooring as the QS calculated all those measurements from the drawings. As we got quotes, we tweaked the spreadsheet and most things were cheaper, a few more expensive. Made it easier to decide if we had budget to push the boat out on fancier stairs etc.

Yes, 2015 so things have moved on but I suspect the majority of architects are still in the same position.

While salt is used to recharge the ion exchange resin in the water softener, the resulting softened water has increased sodium content but not salt itself. Our old Quooker was on the hard cold feed and we were descaling it every year, eventually the tank seal got damaged with the repeated servicing and it failed. Quooker replaced it for £250 and we hooked the new one up to the soft cold feed. Guidance is that provided the hardness does not exceed 400ppm then the residual sodium will not be an issue. We measured our hard water with a testing kit and came in below that level. I would absolutely not use soft hot water as the tanks are designed to work on a pressurised cold feed and also DHW is not potable.

My architect designed us a great house and got us through planning, inc. navigating around an initial refusal. He freely admitted that they had no skill in low energy design, just standard regs. It worked out for us as the house design was fairly traditional (a gable ended cube) and the low energy specialist timber frame company (MBC) took care of all the detailing - however we 'built inwards' from the approved plans so the interior is a fraction smaller than if we'd 'built outwards' from the original floor plans. That said, it was not really an issue - only the single story utility was a squeeze to get a run of standard 600m units in but we managed. Architect was really interested in what we did but said that there was just not enough demand from clients for them to specialise. Most of their work is commercial or domestic extend & refurb - even a whole house 'build from scratch' is a rarity.

My only experience was selling our original residence (that we moved out of and into the wreck that we eventually demolished and rebuilt) after we rented it out for 36 months as sale market was flat. You get CGT relief on the % gain while it was your principal residence, I can't recall if we only paid CGT on the value between moving out and sale or if it was the whole gain from original purchase to sale. CGT does takes into account money you spend permanently improving the property (e.g. extensions but not maintenance) so your rebuild costs would be eligible. You also get to include costs of sale & purchase. There is a calculator here to do the sums. https://www.tax.service.gov.uk/calculate-your-capital-gains/resident/properties/ Strictly speaking, the 0% VAT self build scheme applies to a home you live in or holiday in but not sure how HMRC determine this for a single house. https://www.gov.uk/vat-building-new-home/eligibility

Thermal mass is a myth. Forget that. As said above, you can build passive / low energy standard in any style and with any fabric from ICF to TF to brick & block. Very good insulation, thermally efficient design (no cold bridges), high levels of airtightness, MVHR etc are key. Standard building regs are not ambitious and you can do so much better with minimal or no extra cost. The trade off with TF vs blocks is the cost ratio between materials and labour and the speed of build. The latter may be a factor if you're living in expensive rented while the build happens. That said, the building shell is only ever about 20% of the cost - everything else from there on is the same.

I'd negotiate a break point at the PP granted stage. For our 400m2 demolish and rebuild in Berkshire, this was about £5k back in 2015. This is where their local knowledge and experience will pay most dividends, from there on it's more generic. We went solo post planning as our architect had little experience of basements or low energy build and was only really prepared to do a traditional set of drawings (block & block) plus discharge planning conditions etc for a further £15k. As we were planning on using a TF company, they would have just recycled the detailed drawings from that firm which in themselves were adequate for BR. However it was amicable and they popped round occasionally to see how we were doing, helped us out with a few referrals (groundworks, BC etc...). We also got the CAD but once the TF drawings were issued, they became the reference. Most trades just estimated off the planning PDF. Do you have a particular build methodology or performance requirement (passive etc)? Are they experienced in this? Many architects are surprisingly traditional in approach to build fabric irrespective of how impressive their designs are. You sound quite hands on already, organising surveys etc, so I'm sure you'd be capable of PM - if so, a full tender exercise is kind of pointless, better to invest in a solid QS estimate once your detailed design is available.

I can confirm that they are useless for problems that arise. Ours relied on the Year 1&2 clause in that any issues discovered in that time period are responsibility of the contractor (unless contractor has ceased to trade in that time period).

@HerbJ used a low profile on floor wet UFH system on upper timber floors in his build from memory. I have wet UFH on my ground timber floor - basement underneath so GF is suspended timber joists with 16mm screwed & glued OSB. I did manage to get spreader plates down onto the joists before decking but the idea @ProDave has above looks good. On top of the OBS I have two layers of ply (12mm & 9mm) plus the resin floor system (4mm crumb mat, & 6mm resin) so it's quite a sandwich but all heats up perfectly well with a low temp system (35o).

You'll need to re-think your ensuite to move that 110mm pipe from where it enters the study, unless you have the floor depth to run it horizontally until it hits the corner.

You're welcome - do share more about your location and the project - hopes, dreams, constraints etc. We're all here to help!

Unfortunately you do need to proceed at risk in the initial stages and spend some money. Simple maths exercise - either take your budget and divide by £2000 or £2500 (depends where you are in UK and how much you can get involved in the build, PM etc) to get a m2 of you house (i.e all internal floor area) OR take your proposed house design and multiply the floor area by the same number and see how it compares to your budget. If the resultant house is too small for your taste or the budget is way over your resources then you need to stop and think of a plan B. If you choose to refurb, reduce your budget by 20% and repeat the above exercise. For architects, make sure you compare apples to apples. Most architects will agree a staging process where the initial stage (usually the most creative) is based on the plot design, high level concept sketches etc. When you settle on a scheme you progress to the next stage of detail design which enables you to submit drawings to planning. At this stage you can start to get costings but again, if you work to a rough £/m2 budget then you know if you're in the ballpark. Once you have planning you can then proceed to building drawings (SE gets pulled in here) or in our case get a TF company to do all the drawings etc. Building control get involved at this stage to make sure the scheme is compliant and you can then start to get tenders from turnkey contractors or PM it yourself. At this point a QS detailed estimate is invaluable. You don't need to use an architect for every stage, some self builders have a clear idea of what they want and just use a technician to get the PP drawings and drive it from there on - we took over post PP but the architect completed the first few stages and we were very happy with their scheme. Also WRT refurb vs full rebuild, remember that the frame of a house is usually only about 20% of the overall project cost. Was 16% in our case. The rest you will spend either way (roof, services, interiors etc) but refurb will attract 20% VAT unless you're eligible for the 5% scheme (but that has a lot of strings attached).

Don't have a spreadsheet that high level but was in a similar position when we bought our plot with a tired 1950's detached 3 story house on it. At this initial 'either / or' stage then you're better off working to a £/M2 figure. Talk to architects and builders. Find local people who have done similar (self builders love to share stories). A couple of questions based on our experience. Is there a fundamental problem with the existing (aside from general condition) i.e. is it badly orientated on the plot, very poorly insulated etc? Do you have a scheme for the re-build vs the refurb, has an architect done some thumbnail sketches ? How radical would the refurb be? We have friends who basically ended up with about 3 walls and a slab before building back. In our case the existing was at an angle to the large garden behind it and was not cavity built. While we could have rectified that somewhat with refurb and extension, would have been a lot of work. The clincher for us was that a new build is zero rated for VAT, has fairly predictable costs and complexity (cost) can be designed in or out according to your budget. We were able to build a high performance (i.e. low energy), aesthetically pleasing house, well orientated on the plot in a reasonable time frame (12 months construction). Also included a basement which would never have been an option in a refurb. No-one could give us a fixed price for a refurb, new build elements (extension) were easier to cost but the problem with a refurb was you don't know what you're dealing with until the house gets stripped back and there can be surprises that cost a lot of money. We spoke to quite a few people who had completed projects and many said that they wish they'd been brave enough to just knock it all down and start from scratch. We certainly did not regret it at all, however it's a leap of faith to do it. A QS is indeed worth the money and are are often not that expensive in relation to the overall budget. However they will only work off a reasonably detailed set of drawings, which as you say also cost money and imply you have already received PP. They're best employed to get a working costing of the final scheme and to look for economies / opportunities to save money and to keep track of costs. I'd caution that if the cost of drawings or QS is putting you off at this early stage, you'd better get used to spending a lot more on services before a spade goes in the ground - it's one of the often forgotten costs in a project. However one benefit of demolish and rebuild is that all services and access is in place, often one of the largest 'starting costs' in a new build.

Does it have a coin operated vibrating mechanism too?

Yes the dehumidifiers kick out quite a bit of heat. When we were in the caravan for 18mo we started using the gas fire but the floor was damp and cold each morning which was due to the water vapour generated by combustion condensing out overnight on the floor. We switched to running a small dehumidifier which kept the inside dry and warm. When the house was up we also had a major humidity issue when laying the resin floors (in June) - needed to keep windows closed to minimise dust but moisture was condensing our and 'raining' on the curing floor causing a bumpy finish. Running some big dehumidifiers for a few days ahead of a rerun made a huge difference.

MVHR airflow is low and will only extract from your wet rooms (baths, kitchen, WCs etc) but may help. Your dehumidifiers will be much more effective though.

7600mm2 required between rooms for airflow which is normally 10mm clearance at the bottom of a standard 7600mm door. This is independent of how the house itself is ventilated (window trickle & extractors or MVHR).

As said above, if you build to passive standards your house will have quite a low heat requirement. Low temp UFH is therefore an ideal method to deliver that heat requirement. If you have an insulated slab, the UFH pipes are fixed to the mesh ahead of the slab pour and the slab is heated as a single zone. Saves cost on another layer of insulation & screed etc. If you use an ASHP, this can be reversed in summer and the slab can be cooled to just above the dew point. If this is not of interest there are other ideas above on how to generate the heat for the UFH and also your domestic hot water (DHW). Your bedrooms should not require separate heating but you can make provision and install later if required. Nice to have warm bathroom floors if tiled (low power electric ufh is good option here) and towel rads for warm towels. MVHR is a must in a passive standard house as you'll have high degree of airtightness through use of ICF and will likely spec decent windows without trickle vents etc. While MVHR is not good at moving heat around (very low airflow) it does ventilate very efficiently with minimal heat loss. You can consider introducing additional heat (or cooling) to the MVHR system, just be aware that at best it will act as a trim and not the main source of warmth.

Quite a few here are all electric, if your build is of a passive standard then your heat requirement will be low so low temp UFH plus a ASHP would work well. Has the advantage of running in reverse in summer to cool your GF. PV will help also - you have a nice south elevation that would work well with in roof panels.

Unless you're achieving a passive standard of insulation & airtightness you will likely need heating in the bedrooms. We have not needed it and only have UFH on ground floor - nothing in basement and low power electric UFH and wet towel rails in upstairs bathrooms. However, laudable that you want to maximise the insulation and airtightness. which really needs considered from day one and closely monitored to make sure it's not compromised. The most challenging aspect are floor / wall interfaces and your roof space if you're having a cold roof. For our timber frame build, there is a layer of airtightness sheet that is taped to the top of the inside wall (which itself is airtight) and goes out around the floor junction and back inside where it meets the inside bottom of the upper wall. Everything taped with the special tapes. Others can advise on how you achieve this with brick and block. Windows and doors have compriband tape and are taped on the inside to the inner airtightness layer. There is a service cavity of 50mm battens applied to the interior wall to minimise penetrations through the airtightness layer. Any penetrations through the walls (like ducts for lighting etc, are sealed and taped on the inside. Obviously for passive standard, which I get you're not trying to achieve, you need to forgo cat flaps and letter boxes, also window trickle vents and traditional extractor fans (using MVHR instead).

Homebuilder's Bible has a good chapter on how design impacts build cost. To quote from memory... A sphere has the minimum surface area to volume, but not easy to build Next most efficient is a cube - i.e. to enclose 100m2 of floor you need 40m of linear wall (10m x 10m). Rectangle is less efficient, the same 100m floor may require 50m of linear wall (20m x 5m). Angles increase complexity and reduce usable space. Gable ends maximise room in roof space and simplify roof construction. Walls are cheap, glass is expensive. Slopes, difficult access, laying services all cost extra money, but often the land is cheaper as a result - same if planning will be tricky to get. Then, considering the structural build method, some are low cost material but high cost labour (brick & block), and the ratio changes as you move into ICF and then timber frame. Speed of construction can be desirable if you have expensive accommodation costs during the build or high financing costs. We built a basement, which on the face of it is an expensive idea, but it turned out to be one of the more economic parts of the build working out as £1000/m2 and it also acts as the foundation system for the house above. However that was highly dependent on the ground conditions and site access etc, which in our case were all favourable (but you need to spend ££ to establish this before you start). Then you have global FX rates, supply chain issues, local and national labour costs & availability etc.

I agree to both the above, we spent what we had, some things did not get finished and when more money came along, they did. The end valuation we got when converting to a high st mortgage (from the Ecology self build one) equalled the original site cost plus what we spent so I consider that a win. For me, self build is about getting what you want, where you want at a price you can afford. It was never about profit. What was very useful, and something of a reality check, was (post PP approval) getting a QS to itemise the build elements and do a cost plan. The 'book' costing was about 30% over our available budget so I was able to see where to make savings, either through value engineering / design simplification or some good old fashioned negotiation and bargain hunting.

As ever 'it depends'. But you're correct that the oft quoted build £/m2 is associated with the works themselves, not the preliminaries. This may or may not include site prep, clearance etc. We used an architect to get planning (took 2 goes) but since we were using a package timber frame, did not use him for the detailed design stage and did our own discharge of planning conditions etc. Commissioned a SE to design basement and the frame firm used theirs. We were the PM vs using a 3rd party. Some here have not even used architects, doing their own design and using a technician to do the drawings, others have used professionals to oversee the whole process.

I tried to add pv to front roof as NMA but it was rejected, however was able to do it under PD.