Dunc

I haven't got a spade in the ground yet so not best placed to advise on future economies. But I have been through the "what can we afford" question very recently. What do you want to achieve in three key areas: Style: Architecturally interesting or simply functional? Performance: a bog standard building regs house? A passive house? Build: will you do any practical or management work, or do you want a project manager or main contractor to do it all? Talk to architects/designers. Some we spoke with gave us expected costings in the £3000-£4000/sqm. These were architects whos portfolios clearly show "flair" (balconies, ovehangs, fully glazed walls...i.e. expensive things to engineer) and/or who work most often to passive standards. Others suggested lower costs per square meter and clearly work more with self builders who have a tighter budget and want a nice, but fairly simple house. Even these latter types started at >£2000/sqm. I think unless you're very hands-on, the lower end of the range is not going to be achievable. YMMV. Cost per area doesn't usually include the plot itself. Or the professional fees associated with that...I'm rapidly finding that I didn't budget for all sorts of things that do add up. £180 just to register the address, for example. Fees for servitude to get services to site. Site surveys of various sorts. Insurances... I think self build is a bit like the stock market; it's an investment that contains an element of risk.

thank you @Dave Jones. Not sure I can use Marmox thermoblock as these require the sole plate to be at lest the same width as the block (100mm seems to be the narrowest availalbe). The MBC frame has 89mm verticals.

Do you just need to cross a road, or is the main under a road? Could you use a moling company to go under the road?

I suspect this is a typo from the architect; it's already on my list of things to check, but thanks for pointing it out!

Thanks for the thoughts! @saveasteading keeping the blocks dry was exactly the point of trying to find an improved design. Mannok have a variety of examples (for traditional cavity wall block construction) on which I based my sketch. @Dan F they do, but were very reluctant to send the groundworks team this far and this was reflected in the eyewatering quote. Odd since they've no problem doing the TF bit... @Kelvin will look into the Weber render. Yes, I noted your issues in sourcing I'm looking in to that. @Russell griffiths Duly noted. This is the architect's drawing; hasn't been through the Engineer's hands yet.

I would love to use a raft but can't find anyone willing or with experince to install one up here (NE Scotland). I'm not brave enough to DIY it!

Architect's current foundation detial. Can I do better in terms of thermal bridging? Although the actual product is not specified, Forterra's thermalite trench blocks are 0.24 W/m.k below ground (i.e. when wet). A dry aircrete block seems to be closer to 0.17-0.18 W/m.k but obviously needs to be kept dry. I've trawled previous threads but haven't found a foundation detial for the MBC twinwall on a non-raft foundation. @JohnMo's ICF detail seems helpful so I'm wondering if something like this is possible and worth the effort? @Kelvin I belive you used Mannok's high strength 7 - presumably you need to keep that dry? Were they the full 300mm width? Would I be causing problems for lift& slide door threasholds later?

Following with interest...

My build will have an attached garage. If I put the consumer unit in the garage can all of the electrical cables from it be fed through a single duct through the insulated house wall (300mm cellulose fill) and then sealed? Perhaps using one of those mulit-cable conduit seals such as https://www.filoform.co.uk/filoseal-hd-re-enterable-duct-sealing. Or am I better to find space to put the CU inside the thermal envelope?

Looking at options for MVHR. Brink Fair 325 is looking promising for my needs. However the switching seems heavily biased towards using wireless switches which are rather expensive. The unit is supplied with a single manual rotary switch but I'd like to be able to fit boost switches to bathrooms and a loo which does not have a window. Anyone know if simple sprung rocker switches can be used with this unit?

The Home Insurer. Came out cheapest for us...haven't needed to claim so no idea if they're any good

That's exactly what I've done.

bit off topic but @Kelvin can I ask what size velux you have in those upstaris areas and what heights are the short and tall (false) coombs?

I've been struggling with this recently too. "design, supply and do all the work" is apparantly a big ask. I've contacted everyone on @garrymartin's list and more. I only found 2 willing to get even close to your requirement: MBC will design, engineer (subcontrated), supply and install from -150mm MOT to concrete finish, but the underbuild is still your job. And presumably will only do this if you're buying their frame too. Econekt will design, engineer, supply and install, but only starting from the formwork. All underbuild, service install, and the blinding layer are your job. I don't see much value in this proposition as getting the blinding layer flat with services in the right place will be half of the critical part of the install (the other half being getting the formwork square. Happy to be corrected on this). Everyone else I contactetd are desing/supply (+/- engineering) only, no install. AFT will design, engineer & supply but no longer send someone to site to supervise. Greenraft are similar to AFT but claim to have a network of installers...except in the highlands. If you can find a groundworker who has experience with insulated rafts (ask the suppliers who they've worked with) then you're probably good to go with any of the desing & supply companies.

I was going to suggest @Trw144 price may reflect the power of bulk buying? but then @haythorn_1 is buying 2x my area and looks to be more expensive. It likely depends on how many non-windows (lift& slde/paito/entry doors) there are. My internorm quote (April 2024) for 22.4m2 (1 lift& slide, 1 front door, all else T&T) was £939/m2 + fitting + VAT! At least delivery is included in that price 😕 GBS and Zyle are coming in at about £800/m2. Rationel, NordVest and others looking a little more sensible at <£700/m2 (+ fitting + VAT) but it's all rather eye-watering. Performance wise, GBS, Zyle and Internorm have average Uw values around 0.75 W/m2K for my window list. That drops to 0.85-0.89 for the less expensive ones. So for a 0.1 W/m2K hit in Uw at a peak difference of 30K (-10 C out/20C in) over the area (22.4 m2) that's only 67 W difference ....is that about right? If so, I'm not seeing how I'm ever going to realise the benefit of the extra investment up front. Have I missed something here?

@Kelvin that's very generous of you, thanks! Will keep this in mind, though we're months away from digging. @JohnMo thanks for sharing this, appreciated! It is looking like I'll probably have to go in this direction ultimately. Cost wise, it's interesting. The EPS formers aren't really very expensive (<£10K from all the suppliers who quoted on my 138m2 GF build) and really I'd be buying nearly as much sheet EPS for standard foundation insulation, other than the thickness of the upstand. Suspect this will be more than ballanced by the cost of insulating blocks (marmox, mannok etc) - roughly £2k for my permieter, assuming I only need 1 block wide (MBC frame is 300mm wide - maybe it can overhang and I can have more upstand insulation internally?) The concrete slab component may be 40mm thinner in the diagram above than a kore raft, which on my build would only be 5.5m3 , so £825 less. Both require 2x A393 mesh layers. The underbuild for the kore raft would be 800mm deep MOT3 & 50mm sand blinding on my plot. For me that's 110m3 so about £5k. No idea what trench dimensions or blockwork would be required for a more traditional found (my perimeter & internal load bearing walls are about 80 linear meters). Then there's the top screed layer in the trad build. I really wonder if it will work out pretty similar materials wise, and I'd be happy to pay a small premium for the easy to achieve U value of 0.1W/mK. It's just the lack of experienced contractors that causes the issue. Or my lack of bravery to go DIY 😕.

Apololgies for lack of clarity @JohnMo Insulated raft as in Kore/AFT/GreenRaft type system, such as https://www.kore-system.com/products/kore-insulated-foundation/ Similalry to you @Kelvin am in conversation with Greenraft and they claim to have worked with a couple of installers up here, but have failed repeatedly to provide contact details. While several suppliers are keen to assure me that it's so easy as to be DIY-able I'm not prepared to take the risk on such a critical component! MBC's quote is eyewatering so I may have to resort to something more traditional with a trench, insulated blocks and upstand. Do you have any idea on the thermal performance you achieved? (U, psi?)

Just rounding this out having finally managed to speak to the right people at Highland Council who confirmed what @ProDave and @Jenki said: A static caravan on site during a build is considered a temporary Permitted Development, and the van must be removed on completion of the build. However, the waste water management (installation of water treatment plant and soakaway/outflow pipe to water) comes under Building Control therefore requires either a separate warrant if doing in advance, or should be included in the main build warrant submission and will be subject to inspection.

Can anyone recommend a groundworker with experience of installing an insulated raft fondation in the Highlands (Inverness) region? Really struggling to find anyone who has even heard of this, never mind done it.

One risk with silicone is that paint doesn't stick to it so if you end up with even a thin smear left on the adjacent wall and want to paint that wall in future you may have issues. Only because of that risk I'd go with CT-1 smoothed with a square cornered silicone profiling tool and then paint it.

Forgive some daft questions: Why is Tret bottomed out at 20 when r is either 0 (Tret from UFH =20) or 1 (Tred from rads =20)? Again at the extremes of the graph, why are TretUFH or TretRads different from TretCombined when r is either 0 or 1? i.e. when the entire flow (r) is going to either rads or UFH alone why is the "combined" return temp not the same as the one open circuit? ta.

Just to be clear, I meant "Building Warrant" rather than "building regs" - sorry I can't edit the post or title. In Scotland, Building Warrant approval is requierd before starting construction; this is different from England/Wales. I'm asking about what I can do to facilitate living on a site that has full planning approval but beofre starting construction of the hosue and before we have submitted our building warrant application. The Highland Council have a specific exeption in Planning Permission for temporary accomodation on site: "Living on Site During Construction: Self-builders often want to reside on site in temporary accommodation (caravans) during building works. Providing detailed planning approval has been obtained for the house, we consider this to be ‘permitted development’ during building works and you do not require planning permission for this aspect. We will however require the temporary accommodation to be removed once the house is built." From https://www.highland.gov.uk/downloads/file/22985/self-build_guide Sounds like Utilities are likely to be OK and that it's worth a phone call with Building Standards dept. to clarify stuff. In my case I have SEPA approval for a sewage treatment plant with direct discharge to a water course. @Jenki are you saying that installation of the STP was prior to BW sign off but the drainage field required inspection, or both STP and field were subject to inspection? thanks

What can I do with my site before I achieve building regs approval in Scotland? We want to put a static van on site to live in during the build. Logistically it would be useful to have this in place sooner than later in the overall proces. So before we achieve building regs approval can I: Get and electrical connection made? Get a water connection made? Install the sewage treatment plant and outflow? Anything else it might be useful to do?

Possibly not the same thing as we're in Scotland so must submit for building warrant before starting. Our architectural technician has quoted: Stage 4 Preparation of Building Warrant drawings based on Approved Planning package 3500 Submission of application, start forms ,completion 89 each Dealing with building warrant points 250 Engineer’s certification and design details in regards structure (Allow subject to quotes from engineers) Allow 2200 TBC Drainage Design Allow 675 SAP 375 EPC 190 CDM Pre construction Plan 350 all + VAT I think this assumes that the foundation and timberframe design will be done by the engineer and the TF supplier, respectively. We then have the option on: Constructional package, precast, steel, window schedule etc. 850 This provides construction based package for build combining engineers package to architectural technician's package So I'm expecting to spend £8675+VAT to get through building warrant. I suspect the submission of start and completion forms to planning will be 2x£89 that I can easily save. Other than that, I'm expecting to just pay the money to get it right.

@kandgmitchell May I ask: how big is the raft (square meterage) and roughly what shape (simple rectangle vs something fancy)? I've just had my quote from MBC for ours and nearly fell off my chair... thanks