NailBiter

The calculations are coming out fine, I respect your opinion but you really don't have enough info here to know if this house will be cold or not. Thermal mass is an accepted term? https://en.wikipedia.org/wiki/Thermal_mass Splitting hairs feels like a waste of energy (pardon the pun)

It doesn't have to be but we believe we have good reasons to build it that big. Good tip on the ICF counterparty risk, I believe we are fairly well covered as we are using one of the big suppliers so the funds will only be sat with them for a very short period (less than 24 hours hopefully) before we take delivery of the blocks. I'm also told they have a whole yard full of the stuff if we need

Majority of the house is earth sheltered so this is less of a concern. We will also have a very large solar array and everything is electric. The main trick is to ensure everything is a deferred load and that we have a lot of thermal mass to reduce temperature swings. We originally specced a ground source heat pump but with modern high quality ASHPs, a MVHR, a passivhaus certified architect, good glass and 0.15 U-rating the calculations seem to say that this is totally unnecessary. I suspect once you look at it per person we will be above average efficiency. Yes we do have a lot of embedded carbon in the build due to all the concrete and ICF but our house will last 100 years (I'm currently writing this from a house that was built 125 years ago) unlike the 30 year life span given with some of the other approaches (e.g. SIPS, stick built etc) Also don't forget some of the spaces (e.g. workshop, garage, courtyard, terrace) aren't heated (or are barely heated in the case of the workshop). That figure includes everything included in CIL

Ouch that is unfortunate timing! Price rises are inevitable going forwards, the world is less at peace than it was before. This is why doing to big work up front whilst it is still affordable to do so. Instead of building whole phases entirely I want to first fix every phase at once. This is a very valid point, cheers, I'll check into it a bit more. The VAT exemption seems to mainly apply to things you'd do before first fix or materials (which I have plenty of room to store although not sure if that would be ok, best check). I'm sorry to hear that, something similar happened with our neighbours. I'm aware of the risk and the house has been built to sustain 3 generations in a cyclical way. As the annexe becomes unused there will likely be teenagers keen on having their own privacy. If the housing market doesn't improve soon they will likely be part of the boomerang generation. As you can imagine in a house that large there is plenty of flexibility and all of us are used to living in houses in various states of repair. Thanks for taking the time to share your experience it is very much appreciated.

Also don't forget if you have a CIL self build exemption there is still one more step to complete! Well done on getting this far! We'd all love to hear more about your build if you are willing to share.

I hear you and I'm also nervous my arrogance is overwhelming my better sense. I believe I can make a fairly cohesive argument for what, how and why. My understanding (which could be wrong) is that I can get building control sign off for each section presuming that section is complete (e.g. I can't get sign off for a bedroom that accesses off a landing with no bannisters put in). I think a lot of the stress of doing bits yourself is when you are forced far outside your comfort zone under time and financial pressure. I'm hopefully able to avoid the worst of that with the benefit of clever phasing and patience. Or so the theory goes anyway. Hope you get to the finish line soon mate, wishing you all of the luck (well not all of it, I need some too but a lot of it).

Very astutely put - the time-money-quality trilemma. Hoping to fall sacrifice time in favour of money and quality. Our architect is fantastic (and patient), our substructure and superstructure frame builder is a digital native with a can do attitude. We have a high quality value engineer and project manager coming in. All of our team know each other from previous jobs and work well together. We definitely have time for a phased approach but I'm preferring to go all out on the substructure and superstructure and then focus in from there. There is an emergency fund but it would require selling or mortgaging other family property. We can dip into it but it will hurt and be the point of no return. Thanks for taking the time to say hello

May I ask the reason it wouldn't be something you specify? We still have time to change so it could be very pertinent for us. For us it was always going to be ICF, we did consider PolarWall for a while and Alan was extremely helpful. Ultimately it came down to local availability, local support and finding a builder who we got along with.

Exactly this, we can go out to builders with packages and we can take advantage of quiet periods in the market as we can be patient. That should benefit both our team and ourselves.

That sounds good to me thanks. If we can get to water tight inside of 1 to 1.5 million I will consider myself incredibly lucky. Fit out will not be cheap but it is at least something we can do ourselves as a family lowering costs somewhat. The current design calls for using Nudura on the Lower Ground and Ground Floors. The 1st floor is partially Nudura but partially steel to try and reduce weight. It may be that we can reconsider this somewhat if the drillers come back with a positive report. We have planning drawings done, we have 1st phase of geotech drilling done, 2nd in progress and we have a basic structural model being worked up. The goal is to do the reduced level dig (the house is on a plot that slopes in two directions) in March / April with a view to starting the foundation ASAP.

Good to be here thanks for the welcome. Long term lurker (small renovations), first time poster. This forum has great people and great info, looking forward to being part of that.

We are right on the border between Dorset and Devon so possibly even closer to you. If I'm not a divorcee living in a box I'll invite you round when done. This house is being built for 3 generations of both my partners family and my family (5 people, extra on the way) and includes an Annexe, a Flat and what we call the Winter Garden which links the two buildings (building A: house, building B: flat and annexe). Large yes but I believe excusably so (the architect politely disagrees). The workshop, courtyard and the garage are about 200 m2 of that too. The combined building is a rectangle that is 42m long, 10m wide and it gets thinner as it goes up. The basement is 500m2. We have planning and we have gentlemen on site forming the access route. Geotech drilling round 2 is currently ongoing fingers crossed for a good result. Planning required a ratcheting approach that took 3 permission across as many years. I didn't want to leave too much to chance and didn't want a refusal. Why not build something smaller and extend: 1. CIL costs would apply to any extension but not the initial build. This is a not insignificant saving of something like £200,000 for the whole build. 2. The site is beautiful and I want to get it landscaped before completely the entire building beyond first fix (we don't need all the space yet). 3. With inflation nothing is getting cheaper, we had a windfall and we don't want money losing value in the bank. 4. Due to the layout of the building (flat, annexe, winter garden, house, 1st floor house south, 1st floor house north) it is easy to take on piecemeal. 5. My family ran a small building company but this is far beyond our capabilities. Once we are water tight we are back inside our comfort zone. 6. VAT exemptions provide further savings. The goal is to try and get substructure and superstructure finished externally inside of about £1 million to 1.5 million. After that I will be starting to run out of money so need to prioritise carefully and not give up my day job! I really don't mind if I'm still plodding on this project in 10 years time as long as my (extended) family are happy and comfortable.

Hello all, I hope you are well. My name isn't important but you can call me NailBiter. This is an exciting / stressful process and I'm a born worrier / overthinker. Hopefully by sharing in our successes and our troubles I can help build my resilience and possibly help solve some problems you or I are having. Despite our architects best attempts at protecting us from ourselves we have designed an utterly massive house (1200m2+) over 3 floors (including basement, garage, workshop etc). This is going to be quite some feat to pull off building this house without bankrupting ourselves. Good luck to you all and good luck to us too. Cheers, NailBiter