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Now the expensive bit begins. 10 weeks from submission is pretty good i think.

I've enjoyed reading the various reactions, and understand the range of views. We've called a meeting with Dan, and his office manager/finance person, for later this week to discuss exactly how the costs incurred on this stage compare to the very detailed quote he gave us - the costs are being tracked against the original quote, which was the 'target price' set out in the contract - so that we can see if labour costs are coming in higher than expected. HWMBO said that if the costs being incurred are in line with the quote, then he doesn't favour kicking off about idling about on site. I agree that after having examined the original quote very thoroughly indeed, line by line, we did feel that it was representative of an acceptable pace of work and therefore if they are on track with that we should accept that there isn't a significant degree of piss taking going on. However, the heater is now off, and staying off. When they returned to site this morning, I heard one of them comment that the workshop was colder inside than the outside temperature. Perhaps that will encourage them to hang out in there less. They are battening the outside of the house at the moment, ready for the renderboard to go up. I wonder if anyone has a view on how long it should take three men to batten the outside of a house that is 230m2? It's a simple rectangle - 11m by 8.7m. They've been at it for 5 whole days now, and I'm still wondering if they should have finished by now... The electricity bill is the subject of a separate email in which we very strongly made the point about how shocking and upsetting it was to see use of electricity at 58kWh per day (for the 70 working days on site that the bill covered), and that this demonstrated a failure to exercise proper stewardship of our resources. We have asked him to pay towards the bill, and will see what he comes back with about that. @Jilly we also made the point that this represented almost 100% of our anticipated annual electricity use for our entire house, AND that given that this is meant to be an environmentally conscious build of a low energy house, it is especially galling to see such shocking energy waste. I suspect he will offer us something, as this is an important project for him. Very much appreciate all of your kind and thoughful replies. Here is a picture of our house, for your enjoyment, with Milo the whippet for scale M

After a hair cut and a relaxing hot bath, I have thought about this. There is no surefire way to deal with it. So just call Dan up (hope it is not the builder Dan I know), and say. "Your lads have landed me a (expletive deleted)ing £1500 bill for electric". Probably no more needs to be said after that. I will say that no matter what you say to a Cornishman, the first or second question they will ask is "How much was that then". Then start to obfuscate to a ridiculous level. Answers should be 12 words or less.

You will learn a lot and get a certificate. Whether that makes you a skilled roofer is another matter. Not saying don't do it, but allow for learning more before and on the job. I assume you have some building skills already. Don't assume that you are saving £20k. Other jobs you can learn and do? Depends so much on your abilities, head for heights, stamina, boredom threshold, strength and endurance, coordination. I would say you cannot learn enough about bricklaying, heating, electrics so don't consider them. Yes painting and flooring. Allow for some errors. the university of Youtube will help. Groundworks, foundations, drainage? Some find it easy enough and some never will. Timber structure No, but inner studs and insulation etc maybe. Do though study every subject and do quality control, as the trades might not care as much as you do.

Folkestone WaterWorks Company. ? Folkestone Waterworks Company | The National Archives

All the time. I thought it was compulsory. Why do you think I started driving diesels. "Steal a little and they throw you in jail, steal a lot and they make you king"

Your logic is flawed here, IMHO, and gets worse the longer you intend to stay in this property. Lets delete solar PV from this equation for simplicity, as in the winter it will have little to no effect on heating, ( unless it is a considerable array ). Installing wet UFH into a slab you're already having, is a way to introduce ridiculously low heating costs, so in order to "justify" it, just get a calculator out and do the maths. Look at the costs of heating, coarsely, with grid cost 1:1, and then look at doing the same with a HP at 1:3.5 - 1:4. That's a 1/3 of the costs minimum, and the cost ( and inconvenience ) of panel heaters ( which you absolutely will NOT be able to sit anywhere near to ) and the VALUE of how you will live with each choice in your HOME. Then suffer furniture plans being definitive, and that's the end of the choices then, for me, anyways. Then factor in load shifting for an off-peak tariff like E10 etc ( 3x per day ) via the HP ( multiplied by the CoP ) and you should see running costs as low as a few pence p/kWh. Your proposed heating arrangement would soon be up at 50p/kWh eg 10x the cost. Now can you justify it? THEN, factor in slab cooling for the summer which you will get for free as a side-effect ( aka bonus ) of owning an ASHP, plus putting you furniture wherever you want. Also, the heat emitted by UFH in a low-temp slab is a thing of complete and utter beauty. The heat emitted from IR panels is, IMO, "ugly" by comparison. A colleague of mine recently installed the smallest IR panel he could buy, in his small home office, and after suffering skin issues ( he said his eyelids were literally cracking ) he has had to remove it and go back to an oil-filled panel heater. It matters not one tiny bit what you decide to go with, just my 2 cents. FWIW I have been installing space heating into passive houses ( or thereabouts ( or way above also )) for over 8 years now, and I would never ever steer away from wet CH, nope / nil / nada.

Ugh, this thread.... Should be compulsory reading for all. It's got it all. Overtrading owner, Corns with massive chips on their shoulders desperate to make a point -that Emmet's needs akikin' and an owner too polite to put soom bloody stick about. And all I can do to help is wince and clutch my wither. There's no point in telling you to go down there and - in a staged but convincing way- lose your temper by bringing two verbal bricks together smartly such that there's an involuntary intake of breath on their part?

Why on earth would anyone spend a shed (or in this case a barn) load of money on a house but pay peanuts to get it designed. If you’re going to invest a large sum of money in your home invest in a good architect. He or she will save you money in the long run.

Looks like a piece of flat strip steel so it will not support the wall above it. Definitely needs a lintel. Had it been an angle section steel with the leg upwards behind the bricks then it would have been ok.

Even if you don't plan an A2W ASHP, may still be worth putting the UFH loops in case the other methods aren't as effective/sufficient as hoped. How much m2 in your thermal envelope? What is your plan for cooling? Cooling is one thing UFH does very well, but you can't do with electric UFH, towel rails or radiant panels.

Being pedantic that is an estimate not a quote, it’s good you are keeping an eye on this and need to take him to task if the estimate over runs.

The Brickies I borrowed from my mate Wouldn’t do any loading or clearing up I’d to do all the setting out and lay the foundation blocks and load all 9000 blocks Two Brickies and a young lad would get through about 2k worth of work Saturday and a Sunday Start at 9 am away for 230 Very quick and neat The Brickies dad and uncle where my Tuesday and Wednesday gang Age 67 and 73 Old school 730 am start 430 finish

It came from 1.27 of part F. However, having just re read it i think i misunderstood. Its been a long day. Purge ventilation rather than boost as i stated means opening the windows.

Hi all I'm in the commercial ,industrial pipe fitting business. But im not here for that although i could be useful to other members . What im after is general building skills to take me through my projects . Cheers Will

I do feel sorry for my mum. We got her the simplest mobile phone we could get but it's still so much more complicated than her landline phone and causes her no end of stress. Just keeping it charged is a problem - I would bet that whoever signs off these massive industry changes has never even considered that. The switch to digital TV was a while back when she could take on new things but now Sky are dropping some SD channels and while they offer a free upgrade to a SkyQ HD box, she definitely won't be able to use it. Heck, I can hardly use ours.

4020÷14÷5÷12 = 4.8kWH So that sounds like a 3kW fan heater on 12 hours a day. Over a weekend replace it with a 1kW heater. Tell them the old one wasn't working when you visited.

I asked my builder why he didn't have any sockets in his site van for a heater or kettle and he told me he didn't want his trades sitting around. He said they can sit in their cars if they are cold. I learned a lot from him. He also put a lot of effort into ensuring trades never had to go of site to get materials. Every day before closing up he asked everyone what was needed for the next day and personally went to buy it on the way home if necessary. He said if you let trades go and get stuff they will be gone hours on your time.

Get an old mop and bucket and lather it on, then wet the floor til it’s sopping and then lay your SLC. Depending on the manufacturer you may need an extra 1/2 litre of water per bag, mix with a whisk and let it stand for 5 minutes, mix again then pour. Squeegee to move it and a spiked roller to get the bubbles out and flat it off. @Nickfromwales anything to add ..?

Agree with this, but I thought that it was on daily rates If its on a fixed price and you have accepted that then idleness is hurting the pocket of the employer. If dailys then the idleness is hurting your pocket.

@Omnibuswoman Nothing to do with this at all, but was wondering what sort of MPG you get from your car, both running around locally, and on a long M4/M5//A30 run. It is one of the vehicles on my short list. To do with this thread. I hope you have optimizers on those PV modules, going to be a bit of shading on them, all year round.

We have a 300l Joule direct UVC with 2 X 3kW immersions on a simple time clock that runs for 2.5hrs per night. The immersions are set to the max of 70⁰. The TMV blends everything down to about 50⁰ for the hot water manifold. From experimentation I reckon that the cylinders average temperatures is about 30⁰ when useable hot water stops coming out of the tap. From this storage capacity is.... 300kg of water X ΔT (70⁰-30⁰) X 4.2Kj/kg/K = 50.4Mj or 14kWh. This covers our daily usage of 10kWh just fine however if there are guests over we need to run the immersions for a few hours in the afternoon. If we were to store at 50⁰ we would only have 7kWh and need twice the storage volume.

I have to endorse the comments on wet underfloor pipes. We have a Passive build and our contractor suggested we wouldn’t need much heat and panel heaters would do the trick. I am so pleased we initiated on underfloor heating pipes. Experience has shown that 3 hours overnight on Octopus Go tarring does everything we need for the next 24 hours. We put in an inexpensive electric flow boiler rather than Willis, but the idea is the same (long story about our plumber not really liking the Willis and this was a compromise). The savings with a heat pump didn’t add up for us, we spend about £1 a night on heating and with a COP of 3 that would save 66p a day which takes a super long time to recover the costs of a heat pump. We can add one later if needed. The concrete acts as a great heat store and I don’t think we would have got there just heating the air.

Youve got a number of contentious issues where both installers have differing views. Youve also got a few defects identified by the new installer that the original installer has accepted. There's no absolute guarantee that the new installer is competant/trustworthy but out of the pair of them he'd definitely be the one Id be inclined to trust over the other

You have mentioned the inverter a number of times. Apart from a few different features, there really is not a gnats cock between them. Unregulated DC goes in, regulated AC comes out. They disconnect when they need to. The more important thing is how the modules are wired into it i.e. are the separate 'strings' within the inverters limits, is the inverter wired into the most used phase in the house, or in the case of 3 phase, is the largest/most productive string/s wired into the most appropriate phase (3 separate inverters is so much easier with 3 phase). Why I suggested that you do a simple sketch and state what you want the system to do i.e. help run the washing machine, charge the car, heat the DHW...

All valid points from everyone. This is a build to let hence I cannot claim the VAT back which I knew from the beginning. That's quite good statement as i have already bought materials changed design and not used them. It hurts. I once bought £300 of timber completely the wrong section and cursed myself, but ended up using it later in the build, one of few times an error turned good. Yes, white matt paint all over, and might end up with £15m2 laminate on the open plan ground floor, what am I going to do with all those natural stone and porcelain samples i got of the internet! Recuperating this week while my plaster boarding guys make the inside look beautiful. Down but not out.

It means the PSTN, Public Switched Telephone Network is being turned off. In simple terms no more hard wired analogue telephone service. No normal phone plugged into a socket on the wall to give you a hard wired telephony signal. This is the telephone equivalent of analogue switch off, already suffered by televisions and mobile phones. So if you want a "landline" aka hard wired home telephone, it will be a VOIP phone, Voice Over Internet Protocol, so it will only work with a broadband internet service, and in the event of a power cut unlike a hard wired analogue phone, will be very very unlikely to work. I believe the switch off plans have been put on hold due to lots of complaints about things like alarms that call for help, old people that just need a phone that works without needing internet, loss of functionality in a power cut so the vunerable cannot call for help etc etc.

We’re doing the same. 12m x 8m is huge. Ours is 10.5m x 6m and after pouring the foundation yesterday it feels pretty big. We went for 80mm insulated panels and roof with insulation under the slab and under and up the foundation. Our total cost including groundworks, floor insulation and installation is well under £40k ex VAT.

Ha! Ooh, good shout. Having lifted the thing, it appears to be a brick-lined weir for surface water, that then discharges into a pipe under a road, and finally infiltrates under a field (I think). No idea what the acronym might be, but it seems to be serving that purpose. Yeah, it doesn't match any extant water companies, but it is close to Folkestone. Folkestone Waste Water Company? Sounds plausible. No-one seems to know that it exists, or where it leads - Southern Water (the sewage company for the area) don't have it on record, National Highways don't have it on record, and Dover District Council only know that there's a gulley which they empty, but otherwise have zero information. Funny how this stuff gets lost to time!

I think I can safely say that during the last 8 years of the build, I've had that feeling that you report once a year or so. I've just had my second new hip put in during the build. Doing a self-build is a hardening off process. It's one where you have to make thousands of compromises that you didn't expect to have to when you were in the planning phase. But it's quite important, I always think, to remember that being able to do a self-build is a privilege which many people can't do because of the planning regulations or for other reasons. Self-building is a real test of character. And in the end the only thing that matters is that you just bloody do it.

It's never easy, everyone has to sacrifice doing a self build, they can be a money pit. Spend your time getting the best price, you can do that sitting down. Search for best price, check online, ring for best price, play one supplier of the other, huge savings can be made. Paint white throughout, can you close off sections, to do later? Basic not flashy. Ex display kitchen and bathroom? B&Q flat pack all save money and don't really mean compromise. Don't scrimp on things you cannot change later, like insulation, windows etc. Do you need a stove now - no Do you need a flashy kitchen and multiple bathrooms - no Do you need a heat pump installed at a stupid price, so you can save £5k. Shop around eBay etc, you will be supposed what's available for half price of less. Do you need more than one toilet, shower or sink - no, except for completion you need the accessibility bathroom complete. Do you need curtains and blinds, maybe, maybe not. Floor covering, just seal the concrete floor if that's what you have to stop dust. You are likely to need, electric install certificate, ventilation performance certificate, boiler installation certificate, air tightness certificate, drains test. I had to sell cars and all sorts to finish ours, it's what you do.

Glass half full time There are many, many people worse off than you. Struggling a bit to build your own home is par for the course. Just sit back and enjoy the ride, as you can't get off until it's ended. Buy materials now, if you fear they may go up, but then repent at leisure if you find they then came down instead, or something better came out. Timber and inert stuff won't really matter, but if you extend over time then your salary(s) will chip away anyways. You will need an electrical completion certificate, same ventilation and drainage. You'll need a very basic kitchen with an oven and hob ( free-standing crap 2nd hand electric job will suffice ) and one bathroom. That's it really. Heating can be via plug in radiators etc but sense should prevail around what you 'don't do' before occupancy, as moving in when massively incomplete is progress-suicide. It is what it is, so preserve the bathroom(s) and flashy kitchen for later down the line, possibly funded by a remortgage post completion? Concentrate on the fundamentals, and leave cosmetics for now. Function instead of form, and invest wisely in the infrastructure as it will be daft to have to redo anything such as heating or hot water. Run cables for PV, install later etc.

This is thought provoking .. I wonder how many people have ever ‘wasted’ some of their employers money? Maybe left the heating, lights or air-con on when it wasn’t required? Used a company vehicle or fuel for their own use? Taken something home from work?

+1 Depending how thick the concrete is and if this area will get any vehicle traffic (during construction so large vehicles). You may want to construct a brick chamber, two courses of engineering brick in water bond. I would only suggest this if the area is getting considerable traffic though, as probably be 3-5 days work with a temporary diversion for the pipes required as well. I was on a job where this was required as there was regular tractors near this area, and the owner of the existing pipe specified, also meant the new chamber had no flex in it with the older fixed pipes.

As @Iceverge and @Nickfromwales, have commented: I have UFH in-slab with 3 UFH loops heated by a single Willis heater @ 3kW. The main advantage of in-slab UFH (this sort of approach) is that you have a huge thermal mass within the house's warm envelope. In our case this means that we can do all of our heating using cheap-rate electricity: if you can accept a ~1°C ripple on your house temperature, then it doesn't really matter what time-of-day you dump the heat into the house; just do it when the electricity is cheapest priced. No ASHP at the moment, but I will put one in when a can get a decent price. Iceverge found out about this approach too late and hence has to do a lot of his heating at peak rate prices. As to H/W this can depend on your use. We take short showers and the odd shared bath, so the electrically heated SunAmp approach works for us. @ToughButterCup in one shower probably gets through as much as Jan and I do in a couple of days. 🤣

It's very ironic that they are building a Passive House... I think we need a 'conciliatory hug' icon.

Yes just two courses of engineering bricks (more waterproof than regular bricks). I made some long bolts from 12mm stainless steel threaded rod and nuts and embedded them in the concrete "head" down after levelling it. The mix was stiff enough they stood upright on their own but might need support. The bricks had holes in so were easy to drop over the top of the bolts when laying them. Just had to cut a few bricks where the holes or mortar joints didn't line up. DPM then drilled clearance holes in the wall plate. Big washers and nuts. Warning: I tripped and fell over and nearly impaled my head on one of the bolts when laying bricks, so make sure to put lengths of 40mm pipe over them as soon as the concrete is set until they are safe.

It's made by DAB Pumps S.p.a. Will be something quite cheap and basic as I didn't specify it. I bought these: The Shelly Plus 1PM goes inside the button and the button intercepts the power cable of the pump. So the pump is plugged into the mains, but via the button. Then I set up the three motion sensors pointing towards the three taps which I wanted to activate the pump. Managed to hide them all quite well so you don't see them.

They are not unrelated. I would present myself as 'extremely worried' , show the bill, and say you need to take a raincheck as you are running out of money. It will slow the build down, but to me it's the only way to get control back if you are not on site. Everyday they are on site piddling about you are haemorrhaging money unawares. Say you need prices as its got out of control. Let him sense your panic so he panics that he might lose the job in the nicest way. I ended up with a day rate, so I was there constantly. I really wouldn't trust anyone otherwise, its too open to accidental or intentional abuse. All the best.

I have people on daily's and it's a bit of a nightmare even with my site next door and me visiting site every day. I couldn't do it with a remote site, too many people take the piss.

break out the concrete, couple of clay to plastic collars, fit a Y and a new chamber. A mornings work tops.

https://www.dimplex.co.uk/product/edel-hot-water-heat-pump Best to have plumbed to outside air, but you could configure to take the waste air from the MVHR possibly Cylinder2go will do custom, not sure they are any different in price

Yes, two 65mm standard bricks and two standard 10mm beds of mortar gets your the 150mm. Use cement screws to screw down through the wood into the block (into drilled holes). This is how mine turned out In mine the dpm is under the slab and comes out and terminates at ground level. There Is a second dpm that sits under the insulation, laps up the inside of the two bricks and gets joined to a dpc which is between the brick and the timber frame sole plate

I seem to recall the guidance for even a wired cable is up the wall to a junction box then in through the wall. I ignored that and ran the cable they supplied through conduit up through the slab and up into the house where I wanted it, and the engineer that came to connect it did not complain at all.

It depends what load each prop is carrying but probably not, the blocks especially would be vulnerable to a point load. Your builder should be able to make an assessment of the load, with the effect of the weight of any floors or the roof needs being considered. Note that Strongboys should be limited to 340kg (acrows are much stronger but due to the eccentric load on the acrow prop it is reduced a lot), which is around 150 bricks or so. Easily solved though, either remove a few blocks and prop off the ground or use thick timber sleepers to spread the load. Be cautious as a prop failure (at either end) would be Very Bad.

I would suggest it needs a concrete lintel and because the clay liners have been broken it will probably need the chimney lining (although that's probably a good idea anyway).

While the external materials and finishes are very strongly "Suffolk Barn", I don't see that from the form. Roof Pitch on both main roof and mid-stay porch, need to be steeper, in the 45°-50° range, and for a traditional timber structure it appears too wide. Max width of the main structure would be 6m. To get to 10m wide would need a lean-too. I imagine you have a height restriction to combine the current width, 2 full stories and 50° roof pitch. For me the form would appear more in keeping with a modern, portal frame style barn, but that would mean walking away from the Suffolk tile, black cladding and red brick plinth.

this is too funny…. Only because my planning has been delayed a year to survey again the bats that I also don’t have 😂. Used to like those furry critters. Now not so keen

Is the temperature dropping as much in the lounge overnight as the bedrooms? Has the lounge had the heating on for longer than half an hour to heat up the fabric of the room more? As you say the lounge and kitchen will have a lot of heat input from ovens, TVs etc over the day. I am guessing that your house has 100mm of mineral wool in the cavity which is the bare minimum required to pass building regs. This gives a U-value of around 0.28 which is very poor today. The maximum roof U-value in England is 0.18 and the maximum window U-value is 1.4 Assuming these numbers the room will lose around 75W an hour through the walls, 35W through the window and 30W through the ceiling with an outside temp of 3C. If for example the bathroom or hall are not heated then further heat would be lost to these areas. I assumed a room size of 3.5x2.5x2.4m and 1.5sq metres for the window. These will give a rough idea. You can probably double the heat loss including ventilation losses, but this would be a guesstimate. Thus the room will likely need around 2-300W of energy to keep a constant temperature during the night. I am assuming a 21C internal room temperature and 18C differential to calculate heat loss. The heat loss is directly proportional to the differential, so if the outside temperature is 12C as it has been during the day recently, then the heat loss halves versus 3C night time temperature in the last couple of days. The day also benefits from solar radiation and heat generated by activity in the house thus requires a lot less heat input. Assuming that the room has a volume of 20m3, that is roughly 24kg of air. The energy required to increase the temperature of 24kg of air by 1C is roughly 24Kj. So to heat the room air by 3C requires 72Kj or only 20Wh of energy. However, assuming 120mm of blockwork/plaster. The outside walls of the room weigh around 1500kg. The specific heating capacity of this would be around 1Kj per kg. Thus to heat the walls up by 3C would require around 4500Kj or 1260Wh. I don't know what size of radiator you have in there but say it has a 3-400W output. It could easily warm the air by 3C in half an hour (20Wh required versus 150-200Wh of output), but you would need to run it for 3-4 hours for the walls to be up to the same temperature as the air. Once the walls are up to that temperature then you will only have to overcome the 200-300W heat loss, but initially you have a large deficit to make up. Net net at 3C outside during the night, if the heating was on for 12 hours, I would expect it to be actually running for around 75% of the time. (Very dependant on the radiator size assumption). The size assumption just affects the time the radiator runs for, the amount of energy required to heat the room is the same it can just be provided faster by a lager radiator/higher flow temperature. Basically you cannot run the heating for half an hour and expect the temperature not to drop quickly on a cold night. If you ran the heating for 4-5 hours in the evening I would expect to see much less temperature drop as the walls would be up to temperature. Their relatively high heat capacity would lead to a more constant air temperature. Basically set the thermostat at 21C at 5pm and leave the heating on until 9 or 10. It would not run constantly, but it would run a lot of the time whilst the walls warm up. Then I would expect a much steadier temperature during the night. However, the poor insulation levels of the house mean that even then I would expect it to be somewhat colder by the morning as you have quite a lot of heat loss at 3C outside. If the walls have not heated up and are materially colder than the air in the room, due to their dramatically larger heat capacity they will take energy from the air and cool the room down during the night.

The combi will have a cold mains feed, teed off in 15mm before the control group. The hot outlet of that will be 15mm pipe to the low use outlet and that alone. One pipe one outlet. DHW will come from the UVC for everything else. As above re flow of mains through combi. As long as the rising main gives the UVC what is called “cold mains priority”, eg the 22mm feed from stopcock to control group uninterrupted, then you’ll be as well off as you’re going to get. To maximise the preservation of the flow rates the outside tap should come from the rising cold mains BEFORE the first ( aforementioned ) stopcock. The cold fed domestic appliances and the WC’s should all then be fed from the softener cold outlet, with the softener being the very first thing off the stopcock. Stockcock > double check non return valve > drain off cock > 22mm tee. Off that tee comes the 22mm feed to the softener, and the 22mm cold feed to the UVC control group. Some may call this a bit OTT, but with a promise of no more than 2.1 bar and expected struggles with max flow rates, do this and max out your situation is my advice and what I would 100% do if this was one of my client’s full M&E projects. Soften everything other than the kitchen sink cold, American fridge cold feed, possibly the utility cold, or any other cold outlet routinely used for human consumption. Combi-mate conditioners can be used for treating the raw ( hard ) cold feed before these outlets / appliances ( like a boiling / chilled water faucet ) for max results. As always, follow the specific MI’s ( manufacturers instructions / installation advice ) for the items you wish to purchase, so knowing right now what is going in is paramount for this design to be right first time. MI’s can be downloaded for most common devices. Running 2 showers simultaneously will need a household discipline of no other significant outlets being used in parallel during shower times. Both combi boilers and UVC’s are cold mains dependant so ultimately use that cold mains potential and nothing else to push the hot water to the outlets. Starving them obviously had a detrimental effect, however with the static body of pre-heated DHW in the UVC, you will benefit from ‘same temp’ showers which just speed up or slow down, whereas with a combi they would just go cool / cold. Good quality thermostatic shower mixers for balanced pressure cold / hot systems is vital. Do not cheap out there. 28mm is OTT imho, as the above splits the 22mm main at the stopcock already. I would say allow space to add a 200 or 300L cold mains accumulator if there is room in a garage / ground floor space, and have that in the pipe run between the 22mm priority run and the control group so it’s only ever fortifying bathing / showering / mixer taps. Consider that as a parachute option for the eventuality of when the new mains becomes live and you have the system finished, you’re not happy with the max flow rates for the 2 showers together.