TerryE

I really do wonder why it is still popular to include a garage within the fabric of the house. If you price out the cost per m², then this is bloody expensive off-road parking -- especially as most people end up using it as an inefficiently laid out glory hole because of the hassle of getting a modern-sized car into a standard garage opening. This is especially in your case where the turning circle for access doesn't even comply with highways guidelines. My advice is to lose the garage and use the space for something more functional. Modern cars don't really need garaging in the UK; using decent powered gates can provide secure and a lot more cost-effective off-street parking. As @Weebles suggests: really consider losing the split levels. These are a real PITA for construction and will add to costs. Also a big downer in terms of mobility access. Yes, your site has a gradient, but any competent architect should be able to do the cut and fill calcs so that you can level the site at least covering the foundation area and parking. (Extend this level area in front of the kitchen. Even if you don't want to park here regularly, having this as overspill when friends and family are using BR 2 and 3 is really useful.) This amount of moving soil and levelling within the site is cheap -- and a lot cheaper in terms of overall build costs. It only starts to become expensive if you have to move a lot of soil and subsoil off site. I see that you have a "wood store". Why? If you are planning a wood-stove then where are you going to fit it? Your plans don't seem to facilitate one, or is that what is shown in the living room? Wood stoves are very fashionable but IMO totally impractical for a new build conforming to decent build standards. The minimum practical output of a wood-stove on tickover is about 3 kW. This will rapidly overheat a room the size of your sitting room even if you are attempting to build to minimum compliance to current BRegs. You or your architect need to do the heat calcs and consider the implications. Also search this forum, as there are many topics discussing the pros and mostly cons of using a wood-stove.

Just to endorse what Jeremy is saying, IMO the key difference in my build was that the build was airtight by design rather that by construction fix-up. Examples here are: On each floor the joists were hung off the TF panels, decked out and the next floor on panels sat on this decking. There was a air tightness membrane wrap from the inside lower panel, out and over the joist ends and back inside and up the upper panel. This sealed all joist ends for air tightness, so no taping up around joist ends. All other interfaces were properly taped and sealed by the MBC airtightness crew. None of my trades were allowed to penetrate the filled panels. Where penetrations were require Jan and I had a standard procedure for fittting an airtight access pipe: drill through inside to out with a 1m × 15mm drill; use this hole to core out the 25mm (say) entry and exit holes; feed through the 25mm abs pipe and seal properly at both ends; one of us then insulated and sealed the inner pipe bore when the electrician (or whoever) was done. Our biggest residual leak by far, IMO was down to incorrect sealing in fenestration, which is fairly easy to identify and fix. One issue that we did avoid -- thanks to reading Jeremy's early posts on this -- was to place our inlet and outlet some 5m apart high on the same gable wall so we don't seem to get the gust pumping effect that some installations experience, as any wind-gusting impacts the inlet and outlet equally.

I sent the test report to my B Insp and he was really happy with it. The requirement is 10 and I think 14× better or thereabouts is a reasonable margin. Don't you?

Good. You understood what I was trying to explain. Jan read it and said that I was clear as mud. ?

Put a small horizontal rafters bridging across between the pitched rafters leaving at least 100mm between the top and the ridge beam. You can now insert 50mm Celotex flush with the base of the rafter leaving a 50mm up-and-over airgap under the breather membrane. And add another 75mm celotex bonded plasterboard or equiv across the rafters. Note that you really need to dry line the room with 50 or 75 mm Celotex bonded plasterboard as well to get acceptable thermal performance. Nowhere near passive, but at least not bloody freezing in winter.

Pete, we got 0.6 ACH on our first test as well. Even so, after going around the windows we found and fixed quite a few leaks on some of our Internorm seals later so we are probably quite a bit less. A double check is well worth while, IMO.

Raft vs piles, etc. You really need your SE to advise you on this. As @JanetE said we used and MBC passive slab and they / Hilliard Tanner required that we did a Geophys survey which involved coring down in the 4 corners of the slab and taking regular core samples at a range of depths. The result of this was a clean bill of health for a passive slab. The type and depth of sub-base depends critically on this survey and in some case it will lead to the conclusion that this type of slab is just not suitable for the site -- e.g. if there is any differentials across the site. As to doing the slab, UFH, etc. in one go I would endorse this approach to anyone. Yes, you have to do careful prep and take create care over getting your levels right, but this was still a case of the slab crew turning up on day 1 and leaving on day 8 with the slab all finished and power-floated ready for tiling and the UFH loops all installed. Job done.

My suggestion is that if you are going the architect + PM route , then engage the engage both of them before you contract the TF+foundation contractor. The architect should take the lead in the TF engagement but you now have two other control agents and everyone needs to be on the same page.

Jane, You've engaged at a good point in your cycle. There is almost a numbing amount to learn. As you say "we", I assume that you and your partner are doing this together. The more that you can work together and share the load the better. I think the fact that Jan and I worked as a partnership was one key to our success. If the finances work for you and you aren't trying to crash timescales, then one of the things that we found really hard to get in the early days is just how long everything is going to take -- at least a year longer than your most pessimistic expectation. Just getting your first application approved is a long journey, and then you might need to amendments, then clear the preconditions to get ready to break ground. At the same time you've got to decide your approach: Do you want an architect, or do as some of us have done and to the overall design yourself and used an architectural technician for all of the documentation sets? The former is probably less risky and it seems that you've already chosen this path, but even if you go the architect route then you should spend some time first getting your brief and specification in place, so that the place is truly yours. Do you want to hire a project manager or do you have the time and skills to do this yourself? What broad specification do you have in mind? Tour the area and look for recent new build example that might give you ideas. Learn to use the local planing authority (LPA) online system and look up the planning history on these builds. Lurk here and research the topics that you think that you need to understand. Review some of the major topic threads and blogs and decide which posters are providing the sort of info that you need. Ask focused Qs when you need to; the more that you show that you've reasonably researched a topic, then the more focused the answers will be. Many members will be happy to let you visit their properties and talk face-to-face about their approach, issues, etc. So just reach out. And good luck!

Just a brief codicil written just over a year after we moved into the house - gosh, how accurate this modelling turned out to be as built. Our house is a 300mm twinwall TF on passive slab with a local natural stone skin, and it essentially performs as per this simple design calc.

Perhaps the most important thing here is to indelibly mark the centre line of the studs on the inner slab before you cover it with insulation board etc. You can strike verticals from these makers simply, and this saves a lot of "hunt the stud" games later. You may need to refresh these makes occasionally if the fade from foot traffic, etc. but worth doing IMO. Also make sure that you or your electrician leaves at least 50mm gap to the nearest stub if dropping any vertical cabling runs during first fix -- this just moves them out of the fixing danger zone.

I made up three, all of which used the same routing guide and bit: a three slot jig which I used for routing door hinges and the door liners. Door hinges are traditionally cut asymmetrically, but I decided to centre my middle hinge and offset the top and bottom hinges by the same amount -- because of this the same three slot jig could be used for left and right hung doors and left and right liners. I only had to remember to offset the top of the jig in the frame by the door head gap when cutting the frame hinge cut-outs, and I just used a 3mm spacer for this (or occasionally a 4mm if the liner head wasn't quite true). You do need to get the spacing and dimension in making the jig accurate to better than ½mm. A dado jig for cutting the heads A mortice jig for rebating the lock plates and keeps. Just google youtube router jig door hinge etc. for example how-to videos. As well as the router set, you will need a set of decent chisels and a sharpening system, and you will also find a Trend Corner Chisel pretty much essential.

This isn't a DIY job IMO. It was a shitty 3-man job with the blowing kit, etc. So you have to include this in the pricing. The MBC crews like most small crews seemed to have too lax an attitude to HSE for my comfort, but this was one job where everyone got fully kitted out.

Oh, interesting. Why so when the U-values are comparable? Was it decrement delay and better sound insulation? Did you have a direct comparator to draw the comparison I wonder? I did do a +/- comparison at the time, and which I've since chucked, but in the end it was for more intangible reasons really: One factor was (at the time) MBC had a lot more experience of twinwall construction for this U-value spec, and so our slab and TF were well in their comfort zone = less risk. The profile with its pumped cellulosic filler is intrinsically more air tight, less risk of voids and accidental bridging and better Ψ values. The OSB3-racked pumped-cellulose construction profile is just more solid and has better racking strength, IMO; we have a warm loft giving us a three storey house, so this was quite important for me. The high decrement delay factor is also a good bonus, IMO. This is so high that we can effectively ignore the sidereal heat cycle in our worst case heating calcs.

The main disadvantage of course is that the built up profile is deeper than the Larson strut design. If you are constrained on the external footprint, then this involves losing maybe 75mm of the insides of exterior walls. We made this change after we had planning approval, so took this hit internally. Even so, we don't regret this decision at all.

We achieved under 0.6 ACH on our first test which was the contracted MBC value, so our airtightness / insulation crew didn't bother going round the fenestration looking for leaks. I like @JSHarris tester and might do that, but to be honest I found that a gentle wind outside creating a pressure drop across the house was enough to be able to feel the slight draft you get with the back of a hand on a couple of windows and a door that the Internorm installers didn't properly adjust . I did adjust these to tighten the seal, so we are now probably well under the test value.

@epsilonGreedy, In another thread From wonky shelf to self build in deepest Cambridgeshire @Lots2learn talked more about his goals and explicitly stated: So much of the advice is consistent with his wishes. His stated U-values for walls etc. whilst not quite passive class are good enough to have a well insulated and energy efficient house -- that is with the exception of his slab design which is outside the general spec of his other house components. This makes little sense to those of us who have completed our houses. I don't think that anyone here has suggested a complete change to what was been done so far, for example switching from a foundation + beam and block floor to a passive floor. I see this as an issue of making constructive suggestions going forward that can rebalance the design. So if he wants to have UFH then replacing the blockwork with something like Tetris insulated blockwork is a option that is worth considering, IMO. Also the detailed build-up of the floor profile is important. The SE has to be willing to sign it off and his chosen builder has to be comfortable / competent doing it. Are you going to have UFH or not? If so then how are you going to profile this up? However it is done, the TF sole plate has be set above the internal FFL and DPC otherwise you risk wet rot of the sole plate and the compromise of the entire TF -- as I keep saying, the devil is in the detail. Even if a classic radiator-based CH system is employed, a solid concrete floor significantly constrains the radiator placement as BRegs prevent you placing inaccessible joints in the slab, so need to design your CH topology and lay your runs unbroken before the pour. Off the top of my head, I can't think of any members with new-builds of this class or better that have decided to go with a radiator solution for the GFL. So the decision of UFH or not, upper floor heating approach, etc. really needs to be finalised at this stage before foundations and ground-floor finish are completed. In another topic, I described the whole process of self-build a bit line skiing in front of an avalanche. There is just so much to do and to lean and to get right and there is a logical sequence to be respected. I am not saying I am good at this, but at least I was good enough to complete my house within spec and near enough to within budget, so all I am trying to do here is to help others avoid mistakes that can be avoided.

Your electrician will have to factor in the derating of your wiring runs it your cables are running in an insulated medium. This has a dire impact on the maximum approved current. Basically the internal resistance in the cable causes it to generate heat. This can radiate / convect away if adjacent to an air space, but when embedded inside insulation, this will heat the cable increasing the resistance ... So insulating the service void is not a good idea. You could drop it down to 25mm, say, which is still enough to run cable and pipework, so long as there is mechanical protection over the cable - which also impacts the rating but not by nearly so much.

@epsilonGreedy, if you look at the elevation profiles then the beam and block would need to be dropped another 50mm to accommodate the screed. You can't have the internal FFL above the sole plate without courting disaster. The sole plate is anchored on a DPC at FFL. The devil is always in the detail. ?

I fitted all my own linings on our MBC house. This is a case of shopping around, online or local BMs. The main issue that you will have is quality. We bought our liners in bulk from a local BM early and I then stacked them properly (horizontal with spacers) for over 6 months in our case, but there was still enough warping to be a PITA, so maybe consider the extra to get a decent slow growth redwood rather than the typical cheap but far grown pine. MDF is no good since the linings will get knocked around through life and MDF just isn't knock resistant enough for this use, IMO. Also remember that the quoted dimensions are nominal and the actual are typically 5mm less as a result of planing. The other complication for us as that we used 12½mm plasterboard on most walls but the halls were a fire safety corridor and need 15mm pink plasterboard. Hence the frames are not all the same depth. I bought a fairly cheap planer-thicknesser and this was invaluable for truing up the board surfaces and planing to depth. If I were ever to do a house load of doors again, then I wouldn't bother buying cheap liners, but instead go for decent grade planed wood. You will end up routing all of the hinges, locks and keeps and some head mortices, so it is well worth spending a few hours making up the full routing jigs for these.

Ahhhh, you need to factor in the value of having a new project to interest you into the cost-benefit mix.

Technically, yes but safer if you have 100mm. Have a look at the blog posts a number of us such as Jeremy and myself on warm-slab construction which uses this approach. The risk is that you really need a slab crew that are used to working with embedded UFH -- which isn't the case for most jobbing builders. The devil is in the detail here and I've seen recent examples posted on the forum where members have shown how their builders made of total mess of doing this. The slab needs to be reinforced with mesh rebar. A typical method is to snappy the UFH runs directly to rebar to place it. The height of the rebar mesh needs to set correctly with correctly centred spacers. You need the correct structural grade EPS/PUR otherwise the spacers get punched down into the EPS during pour especially if the concrete is barrowed rather than directly pumped. If the rebar buckles then you might find the UFH breaching the surface and getting damaged during power floating. If the crew know what they are doing this is all pretty straightforward, but a lot can go wrong if they don't. It is essential that the pour and the slab as a whole is checked and to spec before the TF is scheduled. Whoever you contract to lay the slab needs to have the contractual obligation to guaranty to lay the UFH within it to spec. I know of at least one member who ended up getting his slab broken up, removed and relaid because of quality issues. Should you have such quality failures, then you want to ensure that you aren't financially liable. The slab perimeter should be level to 5mm or better at the perimeter otherwise the TF crew will have problems truing the sole plate for the TF. In my own experience as a PM (I was IT and my main job was as a tech manager / CTO , but I did enough PM to be aware of the main risks) I always found that interfaces between subs was this biggest black hole on any project: both subs claiming that their bit worked and the other was at fault. Here we have a three-way potential nightmare: the slab, the heating system and the TF. I mitigated this risk myself by choosing a single specialist supplier to cover all three. My other main subcontractor was my builder who did all of the groundworks, drainage and the external stone skin and slate roof.

Are they still willing to install old dual tariff meters? How are the financials of that playing out? In your case with PV, this would mean that you in essence operate in one of two modes: (a) (summer) zero grid draw; (b) (winter) E7 low rate only draw. What is your predicted payback term? I (and I suspect others) would be interested in your calculations. Certainly in my case with mode (b) only, I can't make a cost benefit case with current battery technologies. If the liquid metal / salt technologies come on stream + ½ hourly pricing so I can optimize purchase periods then it might be viable in the next 5 years -- about the same time that we'll switch to EV.

EPS has a lower thermal performance than PUR: you need deeper panels to get the same performance.

As @Dudda discusses, have you though of using one of the insulated block + beam solutions instead of trad block and beam. This would improve the U-value of the floor slab significantly. Also UFH is so much easier IMO because it leaves your heating source options open and avoids all of those rads everywhere, though you might need to augment the 1st story with with some vertical low temp rads. Our airtightness measured is 10× better than your design goal. Improving the air tightness makes a big difference with a decent MVHR. I see no reason why you can't achieve factors improvement with a TF house. This would have small or no cost impact, as this doesn't involve fundamental design changes but more quality checking and attention to detail in the construction phase, and doing all of the required taping up before or during 1st fix. This will make a big difference on winter nights even with gentle winds. We have a blow cellulose Larson strut twinwall which avoids many thermal bridging issues by design and implementation. The as-built performance of a single-wall+ slab PUR critically depends on the fit and completeness of the PUR panels to prevent gaps and internal air circulation in the panels. Again, this is a case of you inspecting all panels closely and using however much foam gap filler is required. As @ProDave suggests, trying to cut your wiring into the back of the Kingspan insulated PBoard is going to be a total PITA. Most single frame + insulated PBoard profiles that I've seen set the insulation 10mm or so back from the CLS front to leave a wiring gap, but yours doesn't. I did ask about the garage for a reason. If you use it for storage and not for a car as most people do, then you only have off-street parking for one car. Garaging a car adds little or nothing to its life. Even if we agree that the basic TF design is now locked in, you've got a mountains for design issues to resolve before TF erection and ditto before 1st fix. It's a pity that you didn't find the site a few years ago.