IanR

Pretty sure everyone would agree the position of the rebar within the beam should be where the SE has shown it in his section, that's why the OP has opened this thread and I have contributed with a means of doing so. If you believe I have said something different you need to go back and re-read my post.

You're over thinking it.

Tie in some short rebar pieces horizontally and vertically. Push the pieces a little way into the EPS. Spacing sufficient to keep the longitudinals robust for the pour.

By thickness EPS gives 60% of the thermal insulation that PIR does, so to achieve the U Value that 300mm EPS provides, you need 180mm PIR. I said 200mm PIR as I'd personally be buying that in 2 x 100mm sheets. When I cost compared for bulk order, I could get 100mm EPS100 sheets for half the price of PIR sheets and I was comparing BBA Certified EPS100 (load bearing) with an equivalent, but not load bearing, PIR. Looking at what each are retailing for today it still seems to have the same price difference. At the time (2016), and apparently still the case today, EPS formwork are not priced publicly by the various suppliers, but are offered as part of an Engineering & Supply bundle. For me prices varied widely between the companies offering such bundles and if the bundles included installation the incremental cost for installation was far higher than you'd expect to pay with local resource. The price I ended up paying, after looking at all options available, was the equivalent to paying around 10% more for the same m³ that I could purchase directly in sheet form, once I'd allowed a reasonable Engineering fee, so felt it not unreasonable as it included the EPS300 formers. I can see the benefit of buying a full package: Engineering, supply and installation, especially if it also includes the house frame on top, as that totally de-risks that structural build, but, you have to expect that to come with a large premium attached, and you'll be paying that premium on everything, ie the insulation, steel, concrete, UFH and labour. The best "full bundle" price I could get, including installation, was over 100% more than the price I paid using a local ground works company, PM'd by me, to install the Engineered raft by AFT, who supplied me the insulation from Springvale EPS.

I don't believe BC would accept it. Why do you want the outside ground at FFL level? What's your plan for the outside finish?

As per image posted on page 2 of this thread And in practice At the threshold locally bring the outside surface up to the FFL with linear drain against the threshold if exposed, or just tip the surface away from the door a degree or two if there's an overhang above. Level thresholds are no problem with a raft. Edited to add:

It's a BC erquirement for DPC above ground. DPC/DPM will be at the top of the poured concrete of the raft. (unless you are building a partial basement)

Well done, you must have crossed a lot of hurdles to get to this point! Lovely project! Will that be a "thick" timber frame with lot's of insulation to go with that passive slab/raft? Ignore the Portal Frame? - Have you got permission to knock down and rebuild? Even better if so!!! Re. Plant Room, assuming warm roof can you make any space above the 1st floor to house MVHR, and maybe UVC, Buffer? etc. If you can, then centalise your coms up there as well. Yes you can (and should) duct your ASHP under the raft. (pre insualted twin pipe from someone like Rehau) MVHR to external should be on same wall or roof plane, ideally 5m apart, 3m Min.

I'm also on clay and due to the nature of my build didn't even go down that deep, but as I was converting a cow shed the top soil was already gone, I just cleared away the old floor and hardcore that was underneath. I actually had to build up the outside around my raft. You need to clear away the top soil and any vegetation and as long as the clay you expose has > 100 kPa bearing capacity you can go from there. AFT can go lower than 100 kPa, but might need to change the build up. Top of the raft should be at least 150mm above ground level, but can be more. Under the insulation is typically 150mm Type 1 plus 50mm layer of uncompacted pea gravel or granite chipping with no fines.

No, I'm referring to an Insulated Raft. And while there are many terms used for it, it's the one most often used here and by the Engineers that Engineer them. A "raft" as it supports the full weight of the building. ie. all walls including external and internal load bearing walls*** sit on and pass their loads through it to the ground beneath, rather than a floor slab that sits between the load bearing walls. Then we're not comparing like-for-like. If you only want Building Regs performance, then standard foundation details would be the way to go, although 100mm EPS isn't going to achieve it. To meet the same U Value as a typical Insulated Raft then 200mm PIR would be required over a floor slab. But that still won't match the raft for psi (Ψ) values, further mitigation would be required. Insulated Rafts become economical when wanting higher thermal performance from your building. As an example (not mine), publicly available from https://www.advancedfoundationtechnologylimited.co.uk/projects/paul-williams/ For close to Passivhaus performance, or PH performance when combined with a Larsen-truss wall structure. This requires only a 450mm dig depth, if that's sufficient to clear the organic matter. ***sometimes with an additional, unconnected or partially connected ring beam for an external skin for Passivhaus performance Ref. https://www.advancedfoundationtechnologylimited.co.uk/our-products/passive-building-foundations/

You do need to pick one side or the other as the airt tightness side, and detail your roof structure into it. But I do like an external air tight layer, there are many fewer penetrations and no need for service voids, unless putting plumbing in the external wall. I have my air tightness layer on the outside of the structure and it worked well for me, although mine is timber-framed.

I used local ground works (it's what took most of the cost out of the full bundled price), but they did have experience with warehouse rafts. ...and it thought I was being vary fair. Here's why: Tweaked again: 300mm eps = 200 pir as insulation. Similar cost. same dig as no screed Optimised insulated Raft needs just 1 layer of the A142 mesh. Raft has a shallower perimeter at walls than a strip foundation - less dig, less muck away Raft is poured in the weather. That's a risk. - Yep there's a risk, not sure how much more than collapsing trenches in the rain. Both should really adjust timing to suit weather. Is that regarding thermal bridging? - I think we may be saying the same thing. Extra insulating material to break the walls from the heat sink strip foundations. It can be mitigated to a reasonable extent, but at extra cost not required on an insulated raft. Rather than gut feeling, where's that extra cost coming from, have I missed some costs from the list? I'm assuming PM'ing is the at same cost for each, ie. DIY or local groundwork team. There's nothing tricky with an insulated raft, as long as they can read a drawing.

This is a good point. You may need to design your UFH around how you need to prop the ICF. Would need some robust oversight during the build phase. I was wondering when to bring this one up...

Definitely, at the very least you'll be better informed when discussing with your own SE. If you can, break Engineering and Supply away from installation. My experience was that when the bundle included the installation as well the premium went up even further.

An insulated raft doesn't need to cost more. Doing a high level A to B costing from strip foundation + floor slab to a raft: Both require 500mm soil cleared - neutral cost Raft doesn't require additional 1000mm x 600mm trench so saves on dig and muck away Sub-bases similar cost, raft probably a little more with perimeter drain (Ø100 perforated pipe) Both have 100mm thick concrete floor with mesh. Roughly same cost and labour except a Raft likely has a higher spec concrete so + £8 / tonne Strip foundation typically 1000mm x 600mm v. raft integral ring beam 300mm x 500mm - raft requires less concrete, so overall a saving on concrete Depending on edge detail the raft doesn't require the brick or block courses up to ground level Raft will typically require rebar in the ring beams, which strip foundations do not so there's additional labour and steel, but not a huge amount. Both require same DPM 300mm EPS100 is about 2/3rds the cost of 200mm PIR, but EPS300 is required under ring beam + formers for edge section. Price should be similar, but, access to edge formers may come at a premium. UFH for both would be the same. Raft requires no screed saving ~£35/m², but does require power-floating so + £250 labour + machine hire, but a saving overall for the raft. To compare like-for-like the strip foundation requires further work and cost to mitigate thermal bridging that for the the insulated raft is designed in. I'd love to spend the time doing the above properly, but a raft comes out cheaper when you consider parts & labour....but....an insulated raft requires more Engineering/Design than a strip foundation so an additional £2K to £4K - not having a screed easily covers that. The problem in the UK is that optimised insulated rafts tend to be wrapped up in and Engineering and Supply bundle, that carries a premium margin. If your own SE will Engineer an equivalent raft and you can access the required formers then it should be cost effective. Being armed with "what it should cost" when negotiating price with one of the specialist firms should also help bring the price down. When I costed mine, one of the better known companies wanted 2.5 times the cost I ended up negotiating with another top tier specialist. Agreed, wrapping the Engineering and Supply up tends towards a premium price, but most companies will negotiate. I'd hope your SE would be happy to work with a specialised raft company if that's what you chose to go with, without charging you twice for the foundation design. But, someone (you or your architect) needs to manage the interface between the two and as both may require the same surveys etc. for different reasons, avoid double-counts and perhaps you get this organised ensuring it provides the results both need.

I can talk of similar experience, 465m² raft without any expansion gaps. 100mm thick, single layer of light weight mesh and UFH pipes set within that 100mm depth (no screed), increasing to 300mm deep x 500mm wide integral ring beam around the periphery. Seamless resin floor finish across around 275m² and tiles elsewhere without a sign of any movement. Although with a thermal expansion coefficient of 0.00001/°C I'd not really expect it to move that much. I see a temp swing of 18°C to 22°C of the floor across the year which would equate to about a 1mm change across its 26.5m width.

Hi @lizzieuk1 and welcome. What are your building performance aspirations? - Building regs, better than building regs, Passivhaus'ish, PH Certified, PH+? If your SE is happy to Design an optimised Insulated Raft, and you can get hold of the required insulation, including formers, at reasonable pricing then it should be a cost effective solution, as long as your soil has the required bearing capacity. When comparing prices ensure you are comparing like for like, ie. same U Value, psi value, and have covered all costs up to finish floor level. A strip foundation with B&B floor is going to require mitigation on thermal bridging, and a screed, to get close to an insulated raft, so those costs need to be included. When you add up the costs of each, an insulated raft will be less dig, less concrete, likely cheaper insulation, no screed and thermal bridge free by design, but you will have to pay for Engineering and you may struggle to find ground workers that will install, although DIY is definitely possible. Unfortunately Insulated Rafts remain a niche product in the UK and it's often the case that Design and Insulation are rolled into a premium price, you need to shop around to get a reasonable price. Ask your SE to share details of the insulated rafts he's previously done, does it look similar to the rafts engineered by the "specialist" insulated raft companies? ie. Advanced Foundation Technology Ltd., Kore, Tanner etc. Or is it a standard raft with the insulation on the underside, ie. 250mm thickness and several layers of heavy duty mesh across the whole raft. If it's not "optimised", only putting the thickness where it's needed (periphery and under load bearing walls), then it's going to cost you more. Nothing about your site sounds too much of a problem, but for an insulated raft you will need a soil investigation including bearing capacity. I've assumed the hawthorn hedge has been "managed" and not left to grow free. They can have really deep roots if allowed to grow, but I don't think they spread that much.

That's exactly what I thought on the Northern settlement with the last property on the Northern side of the road. Boundary set to stop a sub-division of the plot. I have to disagree. The Boundaries are set by the Local Plan and aren't subjective, once set. While there maybe grounds for Appeal, that wouldn't be one of them.

Their reason for refusal indicates there is no mitigation to it being within Green Belt, and the plot therefore resides outside of the defined settlement boundaries. Check that's the case in the Local Plan and that the Core Strategies, CS1, CS5 and CS7 all indicate that development should not be allowed in this position. If the LPA are accurate with their reason for refusal, and there's been no boundary or policy change since, then don't waste anymore time on this plot.

In this context, it's one and the same. The LPA's Local plan will have a set of maps included that define the "settlements" and their boundaries. In the rural context, the NPPF's "village" is within that boundary. As an example from my LPA, an infill at "A" may be considered, but "B" would not. Key:

I did say the difference is subtle. I have assumed you obtained the CLEUD due to a continuing breach of planning law (for either 4 or 10 years, depending on circumstance). The CLEUD makes that breach "lawful" and immune from enforcement, while the breach continues. The minute the breach discontinues, the 4 or 10 year continuation is broken and the clock is re-set. Whatever the circumstances were, the required breach period is now 10 years due to a change in April 2024, so it would take another 10 years of breach before becoming immune from enforcement again. I've taken your statement "rebuild our dwelling", to mean you requested permission to knock-down/remove the existing (immune from enforcement) dwelling and build new. The removal of the existing building would constitute a ceasing of the breach, the existing CLEUD would therefore expire. I have assumed that what is now a dwelling was not previously an "approved" building with a different use, that you have converted to a dwellinghouse. There may be other options around a Change of Use. If in doubt, hire a planning consultant and allow them to go through the planning history on the site.

Hi and welcome What's the reason(s) stated for refusal of the infill application? That would have been the only route to a planning approval, and it's been tried and refused, but can the reason for refusal be mitigated? Infill in greenbelt, within villages, is permitted within caveats, but not outside a settlement boundary. The NPPF covers this in basic terms, have a look at 154. e) & g) https://www.gov.uk/guidance/national-planning-policy-framework/13-protecting-green-belt-land The LPA's local plan may have local policies that build on the NPPF. The infill application should reference them both in the submission and the Officer's report. If the Infill application was well put together, the reason for refusal sound, and there's not been any changes to the local policies since, then it's not worth pursuing. If in doubt, find a local planning consultant that has had previous success with the LPA.

There is a subtle difference. The development was not "made lawful" by the CLEUD, it just became immune from enforcement action. If at any time you cease the breach in planning, ie. you knock the house down, then the CLEUD expires. Rather than clutching at straws, they are correctly applying planning law. Have you tried for retrospective planning, since gaining the CLEUD. It would be pragmatic for the LPA to now approve a retrospective planning app. Although that doesn't mean they will.

Don't they come under F1/F2 Uses? There's not a PD Class for Change of Use from F to anything other, so Planning would be required. Classes Q and R are specifically for Agricultural buildings

They have "Geothermal" in their title, how deep are those piles going? Surely typical piles for housing would require there to be ground water flowing beneath the building, within the depth of the piles, as there won't be any direct "solar gain" or geothermal heat transfer. There's not much info on the site linked, do they have any technical info available online?