Indy

1. Standard MVHR. Noted 2. Monoblock ASHP to UFH ground floor only. Cooling if possible. Noted 3. UVC as you say is ok. Bigger is better. Plan is 300L and 100L buffer tank is what I've been recommended. With 3 bathrooms and a cloakroom, we're on the verge of 300L being sufficient and we do tend to use a lot of hot water through the day with multiple showers. 4. UFH on ground floor is good. Noted 5. I don't like fan coils. Unnecessary complexity in my opinion. Provide space for A2A is easier in my opinion. This is the latest advice. A2A or split air con is what I had originally planned for. The discussion I've had with someone from an energy 'consultancy' who is putting together a full proposal for me is to go fan coils which will work out about 10k cheaper than air con. And the fan based radiators are 'as good as' internal air con and can get it down to fridge like temperatures. 6. Don't know. The question was to make sure that running ASHP in cooling mode wouldn't cause too many issues with condensation for the UFH embedded under the floor? 7. No wet UFH upstairs just UFH electric under tiles. On ground floor bathrooms too. Not sure on this one. We've gone back and forth a few times on this. The latest is that we have wet UFH in all the bathrooms on ground and first floor for sure. My wife likes to run the bedroom hotter than I like - at about 21-22C and is kinda insisting on having UFH. If we were to increase the insultation in the floor and have the fan coil units in the bedrooms - would that negate the need for having the UFH? The cost for UFH is coming out to be about £7k per floor, so the £7k saved would mean we can easily fund the fan coil units with that saving (8 x £500ish). 8. Include an electric spur for towel rads if you want them . ASHP runs too cold to do much with them. Yes, updated following advice on this thread 9. Don't know. Answered earlier in the thread, standard copper plumbing pipes. 10. No thermostats in individual rooms. I really like the idea of being able to set the rooms at diff temps - but would this work with the setup we have? I think the Fan coil units will have individual thermostats as well so this may be negated by having individual thermostats for each room.

To be fair, this is the document from the Structural Engineer and the architect hasn't yet finalised the drawings from his side. He's aware of my focus on airtightness and thermal bridging and my understanding is that there will be an updated set he produces alongside construction notes that should address some of these points? I'm happy to take onboard points where taping etc needs to be done and swapping of blocks to more appropriate ones and this can be in the pack that we use the main contractor who will undertake the build.

What would you suggest? In the process of finalising the BR drawings which will include construction notes. It's not set in stone as such but I don't want to start changing things massively unless there's a noticeable difference.

Nope - just a spec for now. Build starts in Feb next year.

What change would that mean if we wanted a bigger slab?

I do like your confidence but I have to say that my understanding was the same - i.e. anything related to cooling is not covered by the grant. I do know that PD doesn't cover cooling but this is one of those situations where it would be quite hard to police as the external unit is the same so how would anyone find out if you're using it for cooling as well as heating? As for PD not being applicable under sign off - something I'm acutely aware of. We have convoluted plans to do a number of things under PD as I have no desire to go back to planning for absolutely anything I don't have to - so we'll be building the house, get the sign off and immediately exercise our PD rights for a number of things - including a rear outbuilding, fencing, front boundary wall, ASHP etc.

Thanks for the detailed reply. Just to make sure I understand, I'm going to break it down step by step - and please correct me if I've got this wrong. 1. Standard MVHR - no cooling added 2. ASHP with cooling function - may or may not be eligible for grant but if we have only 1 unit, then we can put this outside without going back to planning and do it under PD rules. 3. Heat pump cylinder - 300 to 400l for 3 bathrooms and 1 cloak room. 4. Wet UFH heating on the ground floor 5. Can I also put fan coils in certain rooms on the ground floor with the wet UFH? This will make them work as air con units in the summer when we run the ASHP in reverse. 6. Any modifications needed to the ASHP to make sure running in reverse doesn't cause issues? 7. Wet UFH only in bathrooms upstairs, and not bedrooms? Will the fan coils work enough on their own to provide heating up to say 22-23C to keep the rooms at that temp? And what temp can they cool down to in the summer? 8. I currently have towel rads that run off the ASHP and then an immersion element that can be turned off or on. I assume this is the equivalent of electric towel rads? 9. Stupid question: the fan coil units will have plumbing connections to them I assume - i.e. a pipe coming in and a pipe going out? 10. Why not have thermostats in the rooms? Or can we replace the thermostat with the fan coil unit which I assume will have some sort of manual control on it rather than running of a central system? With regards to floor insulation - we did speak to the architect about adding more but his opinion is that BR regs are pretty good these days, and coming from my baseline of a 1930s semi with no cavity walls at all - it's going to be a massive step up. This is what I have so far Floor construction: U Value = 0.14 W/m².K 65mm. sand: cement screed 500g. Polythene separation layer 120mm. Celotex XR4000 insulation Polythene DPM Concrete beam & block floor to manufacturer's design Wall construction: U Value = 0.15 W/m².K Render 100mm. Thermalite Hi Strength 7 blockwork 50mm. clear cavity 100mm. Celotex CW4000 insulation 100mm. Thermalite Hi Strength 7 blockwork 12.5mm. plasterboard on dabs dry lining, plus skim Pitched roof construction (insulation at rafter level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters fully filled with 150mm. Celotex XR4000 insulation 25x47mm. battened services void beneath rafters Celotex PL4060 (60+12.5) insulated plasterboard plus skim Proprietary felt support tray Pitched roof construction (insulation at ceiling level): U Value = 0.11 W/m².K Roof tiles 25x46mm. treated tiling battens 25x46mm. treated counterbattens LR Breathable roofing membrane 150mm. rafters Unventilated loft space 19mm. plywood decking or flooring plywood for loft storage 75mm. Celotex GA4000 insulation above ceiling joists 150mm. ceiling joists fully filled with 150mm. Celotex XR4000 insulation Visqueen High Performance vapour barrier 12.5mm. plasterboard plus skim COLD Flat roof construction: U Value = 0.11 W/m².K GRP weather surface 18mm. plywood deck Firrings to give 1:40 fall 195mm. joists with 150mm. Celotex XR4000 between joists 90mm. Celotex GA4000 insulation below joists 12.5mm. plasterboad plus skim

Pertinent details of our build 260sq m masonry build to BR standards and emphasis on airtightness. U Values Floor: 0.14 Walls: 0.15 Roof: 0.11 Doors/windows: 1.2 Wet UFH heating on both floors – ground and first. 22mm system for the first floor due to height restrictions. Missus likes feeling extra warm all the time - wants temperatures of upto 22C in the rooms. No carpets through the property. Tiles in the living/hallway etc and then engineered wood in the bedrooms Digital thermostats for each bedroom, study, living/dining area (8 in total) ASHP – most likely 10kW 3-400l UVC MVHR Solar PV – 16 panels (7.1kW) Solar battery storage – maybe, depending on price but 5-10kWH battery to be added later. This is generally straightforward and easily speccable. Where things start to get confusing is my desire to add some sort of cooling to the property. This would be in 5 rooms (4 bedrooms + living/dining area) or 8 rooms (adding studies) if we can find a system big enough. Plan A – add a separate air con system using a 5-8way multi split system. One big external unit that sits outside and wall mounted units within the rooms – both to be added in 2 years time when we regenerate funds. Part of the build would be to have power and ducting/pipework to allow the external and internal units to be connected so that we’re not ripping open walls again. Rough cost of £10-£15k for a system like this. Plan B – get a heat hump that runs cooling as well. Not eligible for grant but price difference won’t be that much. Dissuaded against this as running heat pump in reverse means issues with condensation. Plan C – get an MVHR system that also does cooling. BPC quote for standard MVHR parts is £5k for Zehnder Q600(parts only) and £20k for 2 x Q600s with Enthalpy exchanger and ductwork for cooling option. Not going to be as good as active air con but the price differential is quite significant. Plan D – get a Fan Convector unit/Fan coil unit. I’ve picked this up reading these forums and had no idea of the existence of these. But it seems that this look like radiators and can be floor or wall mounted and can do heating as well as cooling? Does this mean I only get the standard MVHR unit, wet UFH heating on ground floor and then install these FCUs in the bedrooms on the 1st floor? Do they work like air con in the summer and radiators in the winter? What additional pipework do I have to get done for these – if I decide only to get the pipework done now and the actual units added later? Make it make sense please! Would really appreciate some guidance as trying to find a company that pulls this all together in a simple package has been an exercise in futility mostly. They all want to quote or sell products that they stock and not really looking at what would be the most effective option – both in terms of installation and running costs. Thanks in advance.

Would love to hear more on this from others. We've been back and the quote has now come back at £22k ex VAT for the 4 bathrooms. Mid to high spec in terms of finishes. 2 x shower rooms 1 x bath + shower room 1 x guest WC This includes all fittings, vanity units, mirrors, storage and tiling/adhesives but not the install, internal lighting as per design and build out of the rooms (enclosed shower rooms, seating in one shower area etc). In terms of brands, they seemed to indicate these are quality fittings that will last under Hard London water for far longer than the base spec Grohe/Gerberit stuff. Is it too high and worth looking at alternatives? Personally, I'd like it to be under £20k if possible as installation will also be a decent amount.

Thread resurrection! I've had a quote from Solarcrest using the Airflow system - coming in to 2-3x more expensive than others. They do offer a turnkey service and full compliance to the relevant regs but not sure whether that uplift is justifiable?

If I knew the secret - I would have used it myself. We were searching in SW London/Surrey borders so the opposite end of London but demand for large plots that are suitable for redevelopment is fierce as there are lots of people like you (and I) with the same thought process. Where we ended up by accident was buying a bungalow on a large-ish plot that we'll demolish and rebuild. It was a probate sale and the owner had lived here for 50y+ (essentially bought and never moved). I'm not sure how scientific this is but a couple of builders have said if its £2k/sq m for the ground level, then factor in additional £1-£1.25k/sq m for an additional floor - IF you don't change the structure too much (i.e. a box above a box). When you get into fancy steel structures and glazing/skylights etc to be added - then those numbers don't apply anymore.

£112k for skylights and glazing seems quite excessive I have to say! Unless they are full PH spec, 3G with solar film etc etc.

Welcome to the forum and your criteria looks very similar to what I had in mind when we started our search - 4+ years ago. What you're going to find is finding properties that haven't been maxed out already in London with the potential for space that you're after (in effect trying to double the floorspace) are very few and far between. Most of them have already been extended and the best shot would be a probate sale where an owner has lived in a property for several years but didn't need to extend as the family had left etc etc. The architect rule of thumb is not too far off - but it really depends on where you are as a lot of places with a proper London postcode will have a London premium also applied to them. £5k/sq may be a bit toppy but the number is definitely between £2.5k - £5k somewhere, based on the extent of work and the level of finish you go for. If you multiply that by the number of sq m you want to add - you're already somewhere between £250 and £500k. At that level, it becomes easier to just build a 200sq m house from scratch at about £2k/sq m (save the VAT)- which would be newer, more thermally efficient and designed just the way you want it to be. And the cost to do the work has shot up massively over the last 4-5y, especially since COVID. With the recent market adjustments, I've found that its actually cheaper in most cases to buy properties that area already done up.

This is a good shout as I'm in the process of finalising the bathroom design on mine and had missed off adding UFH and the towel rads are currently fed off the ASHP. Will go back and incorporate these changes. We've also got a lot of glazing in our design though I'm loathe to change that - it all looks so pretty!

Ok, just had a better look at ours and it’s closer to £22k than £21k, but it does include tiling all the way through all of the rooms and a wet room floor in the 3 bath rooms as well.

The initial post indicates that it already has planning so I'm sure these things would have been considered already?

In the process of getting bathroom designs and quotes and we've had the 1st one come through. £21k for 3 bathrooms (all 3 have showers, 1 has a bath and shower) and a guest WC. This is parts only. I don't know if this is too low or too high but it doesn't include installation. Do I get an installer from the bathrooms company or would this be something the main contractor would be able to do as part of the larger overall build? Also - the brands listed in there are new to me and not the usual ones I see in high street shops - AVA, Faeber, Vado, Kaldewei. Are these any good or any recommendations on brands?

This looks fantastic and I'm going to go the opposite direction and say why not build the space if you can afford to. Whether you need 13k+ sq feet is debatable but I'm all for space. The other points already raised also ring true - if you can afford to build a house of this house, then its unlikely you'll be living in a static caravan for 2 years especially with kids in tow. Also, I would want a specialist concrete builder doing the E2E project management on this rather than risk taking parts of it on yourself. Sounds like a lot of structural elements to consider and be done right. Following the thread with interest.

So you were right on this point - the quote came through yesterday and it's £1530 + VAT. The quote did come through with the VAT added to make it £1800ish though a follow up phone call from them sorted that out. This is only for the original movement to the outside kiosk, and the movement back inside the house would be a different task and quoted for separately. I did ask if there's a way to reduce the cost if we do all the work (which we are already in terms of digging the trenches etc) and the lady said we could use an Independent Connection Provider. Have others used this and does it work out cheaper? One comment to add - fairly impressed with the speed and customer service from UKPN. Both the surveyor and the person sending the quotes through have been nothing but helpful and quick to turn things around.

Apologies if this is an obvious question - but would this show up on a drainage search from when we bought the property? Or a separate call to Thames Water to find out the location of drains on our plot? This is what I have though this doesn't show any details for lines running under the plot.

What can I do at this stage for the drainage planning and finding out where the sewers are? I assume the builder will do the relevant checks before starting to dig up the foundations but if I can help with some planning earlier, I might as well.

Thanks - waiting to receive the quote via email and hopefully it will come in lower than the rough £2k he mentioned while on site. One more question - do I provide the cable or is that provided by the utilities company? As for 3ph, yeah - that's what he said. None of the other houses in the area were 3ph. I guess if the difference is £4k vs £5.5k - then it might be something I do to future proof. But if its £4k vs £8k - harder to justify. He did say that you can get a second feed to the property so a 3ph is not the only solution. Noted, especially the point re airtightness. So all we need to do in this scenario is to safely cap the existing connection and have it moved to a common spot so we can locate it in the future. The water meter is located on the driveway to the front of the property, next to the line with the neighbours. Though it is on the opposite side of the plot where we'd want the TBS. Is it common practice to have all 3 utilities next to each other or would it be ok to leave it where it is? Noted on the duct but I'd want to retain the working Virgin service, at least until Openreach cable up the area. Would I be ok to move the existing Virgin cable or extend by adding a coax coupler (?) and extending the length of the cable to end up where we want it to? And thank you, very informative and useful

Not starting the build just yet - planned for early next year (Feb/March) but planning what I need to do wrt utilities. Current plot is an existing bungalow with gas, electricity, water, virgin media coax. Plan is to demolish and replace. What I've understood so far is that we need to get the utilities moved to a temporary box on the plot BEFORE we demolish. Trying to piece together the whole process so hopefully some more experienced members can help. Electricity Given that we're in the SE, our operator is UK Power Networks. I contacted them a month ago and their guy came to do a site survey today. The drawings on their system indicate that the supply cable runs horizontally across the plot and then under the next door neighbours' house. Guy said this wasn't the case most likely and used his handheld scanner to confirm that the cable comes out to the front driveway which makes the movement much easier. Cost would be £2k to do the initial movement of the cable from inside the bungalow to an outside temporary supply and then another £2k to come back and move it back in the main house when it's built. Me to do the groundworks (i.e. digging up trenches) but they would supply and lay the cables. Here come the questions: 1. Can we leave the supply in the TBS they plan to place on the plot permanently and avoid paying the £2k a second time? 2. Would my builder/electrician be allowed to pull the main supply from the TBS and into the house without paying UK PN for the privilege? 3. Is there anyway to bring the initial cost down? £2k seems like a lot to relocate a cable less than 10m on a suburban plot. Can I supply the parts and dig the trenches and get them to only do the bare minimum? 4. On the topic of 1ph vs 3ph - looks like the supply runs across the road from us which means that a 2 way traffic light system would be needed costing about £2k on top of the £5.5kish for the actual pulling of the 3ph cable. Is 3ph really necessary if we don't want the 22kW car chargers. House is a 5 bed, will have ASHP, Air Con, Solar PV, UFH, MVHR etc. 5. Are we stuck with using UK Power Networks or are there any alternatives (cheaper) that we could use? Gas We have not yet decided on whether we move away from gas completely. Even if we go down the route of ASHP for heating/hot water, we may retain gas for the kitchen and a high efficiency gas fire (vs say a log burner). 1. Is there a similar process to get the gas supply moved to a temporary box and then routed back into the house? 2. Would we need to have the temporary supply moved to inside the property afterwards or could it be left on the TBS being made permanent. 3. Who do I contact to start the conversation re gas connections? British Gas? Water I do not know yet where the water mains run but to have the drainage etc designed - seems like there is a cost of £100 ish to Thames Water for them to do the design work and come back to us with a price? 1. Are they the only ones equipped to do the work or do I have choices? 2. Is there an easy way online (even if not free) to find out water connections, drains, sewer lines etc using a map? Internet The idea is to have the connection coming to the house either via the TBS or utility (both located on the same side of the plot luckily). 1. What do I need to build to future proof either Virgin or Openreach coming into the property supply? 2. No Openreach yet (Dec 26) but Virgin Media supply exists. Do I need to contact them to arrange for the movement of the cable or can I move the coax myself (i.e. builder) to this TBS box?

I'm loving all these ideas - the pull out drinks fridge and the double drawer dishwasher are now on the list of things I need but can't afford! Please keep them coming so I can fantasize even more... Have taken a note of all the changes proposed and will be reviewing with our designer over the weekend and come up with a new plan.