Gus Potter

Thanks for the compliment, much appreciated. The amatuer point, well I still qualify as that as this sort of stuff is complimentary to my day job.. SE / Architectural designer. Great succinct writing. The house I look after is big. I forgot to mention that it also has a large "garage" which has space for a few cars and a games room. That has it's own boiler that runs off oil. I think Clive's thinking was to have options.. switch from a big LPG tank to oil if the price changes. He really future proofed the place. But that comes at an upfront cost. @MuellarIn terms of protecting your asset (when you come to sell) then connecting to the grid, even if you have a small main fuse is probably the sensible thing to do. But you do have the standing charge. Much will depend on the value of the house cf the capex cost of connecting to the grid. That said if you are a bit strapped for cash then you could set up your own of grid system and get grid connected later, so long as you plan for it then you may have options.

Thanks for the heads up. I'll mull it over.. see if I can come up with a anything that may be worthwhile, most of you have already claimed the good ideas and given sound advice in my mind. For all. That's the great thing about BH.. the sharing of ideas, a bit of maths, design principles, Architectural, Goetech, Electrical ( long list) design, innovation and not being to afraid to be off the mark from time to time. I always appreciate BH as if you're a bit off or say something silly you don't get ripped to death.

Feel for you. Best to redo it in the long run.. unfortunately.

Hi all and @Muellar Here is a bit of a story but some ideas for you to have a look at. I'm and SE and Architectural designer but here is some of the stuff I've picked up along the way. Servicing a site can be expensive.. a decider often. I look after a house for a great friend who's husband died. It's around 500 - 600m^2 and well out in the country. We ( the husband who was the techy guy) both did a self build at the same time (mine was a lot smaller) but Clive (the husband) who was a scientist / technologist say like @SteamyTea and @Alan Ambrose were well ahead of his time and brought loads of info to the table as he use to work in Finland / Sweden etc. In some ways the bigger the house the easier off grid is to do. The house I look after also has some 5 acres of land so plenty scope to "do stuff". It was Clive that got me into UF heating systems /off grid stuff / electrical diversity and trying to get the maximum kVa out of a transformer on a pole that is several hundred meters away (voltage drop see later)... and that was 30 years ago. This worked for us as we were well out in the sticks and we use to have power cuts for days at a time when the temperature was regularly -15C and at one time hovered between - 19 and -23 deg for three days in a row.. even our drink froze / the diesel vans did not start, my German Shepard got a bit cuddly and that was a great experience big dogs are warm! This is the Scottish Borders I'm talking about when we used to get hard winters. Basically we flew by the seat of our pants and hoped it would work in the Scottish climate. We had no internet to research and a set of Y fronts each! they came before Speedos I think. .. for the younger these are male under garments that we use to wear. I'll come to the off grid stuff which I love later.. on my bucket list. Ok what Clive did was to have a LPG gas generator for when the power went off. My power cable which was right at the end of the line was a 95mm^2 aluminium three core cable, each core! What the electricity board was to connect all the cores together so we got single phase (220 -250 volt) but delivered through each of what could have been a three phase supply. This mitigated the voltage drop. But the big cost saving was me digging my own track and backfilling. DNO obligations, diversity and demand: My level of understanding is pretty basic @ProDave may chip in to clarify. Also @Carrerahill is off line at the moment, but I'll see him early next year and he does this stuff as a day job. Anyway @Muellar I would come at this from a different direction. Generally the cable that comes to your meter is protected by a main fuse. These tend to be sand fuses and work in a different way from everything after, usually the tails to the meter. I'll call it a sand fuse as there is a table in BS 7176 that lays out how they perform. @ProDave can you correct my interpretation if my laymans explanation is off the mark? Now lets say you have an 80 amp sand fuse. That is the one in the meter box that has a seal on it. Up stream you have a DNO cable ( belongs to the lekky board) which they are interested in protecting and everything up stream of that only. Your in house system is of little interest to them. Now a sand fuse / breaker does not blow like a fuse / MCB you have in your consumer unit. I'm trying to find the BS 7671 table but you could draw several hundred amps through a sand fuse over a few seconds before it blows.. and that is why you should not tamper with it!. Sand fuses work by heating up and then they blow, the sand stops the fuse blowing when say you blow a socket in the house and you get a surge of current.. but the MBC's etc on your consumer unit stop you getting killed as they trip quickly.. hopefully. The stuff in your consumer unit works on miliseconds.. the sand fuse in minutes. Now say you had an 80 amp sand fuse and you were drawing 100 amps.. it may last a few minutes before it blows. The whole objective of the leccky board fuse is to protect their equipment and not yours. Where I live here is a local transformer that has a fuse rated at 600 amps. but it I think serves 10 -15 houses. The electricity board apply diversity depending on the number of houses. Again their fuse at the sub station is not the same as the ones we have in our consumer unit. Ok lets put some sums to this and why. Copied from internet to be lazy.. In the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts. Now your supplier has a legal obligation to meet the statutory voltage range... and that is easier said than done! @Muellar this may lie behind the quotation you have. Try and get to the bottom of this. If you have long cable you get more voltage drop prid pro on on the cable area. It may not be the amount of kVa that is the sticking point... could be their obligation for voltage? If the cable is too thin / long it causes a voltage drop that could expose your suppplier to a claim if your appliances stop working. The sums are Kilo Watts = Volts * Amps. Say you have a 15 kVa transformer up steam. It's the current that overheats a transformer generally. How many amps could you draw if you were the only customer at 216 volts. ? 15000 watts / 216 = ~69 amps continuously... like for an 20 min to an hour say . Transformers are designed to cope with a surge in loading and that is why they are oil cooled and have fins for example. But if there are other folk using the same transformer it gets more complicated. A good example here is that you get a DIY guy that likes to do a bit of welding. They may be drawing a lot of amps but only for a few seconds. In summary I would try and understand what is lying behing the quote from the Electricity board. Most of their Engineers are quite helpful and will be happy to share their technical knowledge. You could ask the question.. can I have a 40 / 60 amp fuse, all sealed so it protects your network? Funnily they may be more than happy to engage once the find out your plans for off grid / with a bit of back up. They may support you a lot as they could use this as part of their environmental accreditation? Sell it to them! Write to the head honcho! Many ex council houses have 60 amp fuses so this is quite common. @SteamyTea has done a spread sheet on diversity.. but I would start with the main fuse to get this issue out the way and then you can play with you off grid stuff to your hearts content. To finish the DNO . I would love to have another go at doing an off grid house. OFF grid! Love this but the key for me is to do it and still be able to sell the house when you move on. Another poster has made the point that it is a neice market. True.. but if I was doing it I would keep it as simple and stupid as I can and keep some data on performance and an operation and maintenance manual. Make sure you future proof things like underfloor heating pipes.. the things that can't be easily changed. @SteamyTea Combined heat and power is fantastic. If you have a bit of ground then grow some willow, encourage wildlife and as it grows like fury it could well be enough to keep you warm in the winter. I'll need to stop here.. but @Muellar love your idea. Don't forget.. you can write to the head honcho of the leccky board.. lay out your case and they may suppport you! Get your ducks in a row and you may get a nice surpise and support.. this lunch won't be free but..

Often I may come over as a bit of a crusty / sceptical. In mitigation I designed and installed my first UF heating system some 30 years ago.. long before this came more main stream. I'm an SE and designer now.. still learning lots. But many of my Clients are folk that want to build say an extension (some are big mind) the odd new build and some really big barn / church type etc conversions. Most don't have a bean to rub together.. every pound is a prisoner! They have a mortgage and want to protect their asset. Often I say.... hey look you can have fancy controls, systems but lets also look at the value of these when you come to sell. Lets also look at the maintenance costs.. the reality of sticky valves, ducts getting clogged.. who can mantain all of that and at what cost. For example I have some Hive controls... nice graphs on my phone etc but if I want to move house it's difficult to transfer the ownership.. in fact a nightmare. Now many modern systems have software, controls that are difficult to maintain after five or so years. Now if you have plenty of cash to splash and want to make an environmental statement or just like techy controls then on you go as far as I'm concerned. If you are happy with the maintenance and potential loss of value when you come to sell. If that is what you want then I'll get that into the design. Mind you during the design process you may change your mind and come round to my way of thinking! Especially once we start to look at build cost /benefit in detail. This is a good point. Old crusty ends.

Now here is the rub. Personally I would live in a house that has some element of air heat recovery in terms of ventilation at a push. But not having windows that open is beyond comprehension. What happens when you have wet dog, want to dry some extra washing on the bannister..or just want a blast of outside air. This is not a home to me.. it's an extension of a crappy sanitized office. Ok you want to have MHVR and a wood burning stove. But I will bet my last cent that you won't change the rope seals every year on the stove door! A rope seal kit is about 12 -15 quid.. but most folk won't do it. As @SteamyTea says.. these wood burning stoves can be a killer. Always have a CO alarm in the room. Design your house and systems to last and look at think how you are going to maintain it and the cost of that. Be practical and not just aim to meet the regs. That is good design that will protect the value of your property and make your effort worthwhile and rewarding in the long term. Remember when you come to sell, some hard arsed surveyor is going to look at all this and may well write down the value if they can't understand what you are up to! This is not Fred Dibnah.. folk need to get a mortgage. Does any one think the same calculations and controls will work the same way in 20 years time? Any takers?

I love @SteamyTea post above. In a few lines he spells out what you need to do and why. Don't forget the saving that you will make on the standing charge for gas and electricity.. it maybe only a pound a day but that could pay for maintenance of a generator. changing the filter and so on. That's my tuppance! Combined heat and power (CHP)..it's a no brainer in my mind.. there is a massive amount of heat to be extracted from the exhaust gases of a generator. Mind you it needs to be done safely..I would make sure I put all that gubbens in an out house. I think this may be an advantage prid pro quo.. provided you design your house more as a box, like a long house.

My thoughts are. Safety on site is paramount. This is works on an old unstable structure and this happens in real time. Sometimes it is not possible to safely brace a structure during demolition and you need to take it down to ground level. This is good evidence of you working safely. Did you leave the existing founds and masonry below ground? If so then it is argueably a repaired wall rather than a new wall structure. Let's see that photo they have of a "cleared site".. to qualify as a complete wall removal they must have a photo of the ground from above.. rather than just one taken from an oblique view! Wall removal means all of it right down to the top of the founds! Complete removal means the founds too. Bet they don't have a photo of that! With my SE hat on. Now you have left your neighbour with a potentially un supported party wall. That party wall may have a chimney breast. If you are end terrace then your house (and the roof) may have been butressing the rest of the houses in the middle.. I could make a bit of hay with that as an SE. I would go back and distill down why you did what you did , why you did it (on advice from the builder and BC) and then maybe get an SE to back you up. If there is still some evidence that an SE can work with then they may be able to help. In summary I would get all my ducks in a row before responding to the council. Ideally any response you give has to force them to incur expense (eat into their time..) or take a pragmatic view and that will concentrate their mind. The low level planning / BC officers have managers who look at the cost / time sheets.

Hi Joe. Have a look at how an OH cowl works. When you live near say trees and say have a down draft (positive wind pressure on the roof) the vertical sides still cause a draw due to the Venturie effect. It works in all directions wind. I think it's rare that these cause "whistling"

No because you have not provided any drawings! Fesse up and share your drawings. Folk will then chip in and in return we may also learn a bit from you. Them's the rule of the game!

Good advice. In a standard cavity wall (say 50-75mm cavity) the two leaves act together. When doing calculations we derive an effective thickness of the wall. A bit like this bit from the the BS code. But the strength of the wall as @Iceverge say rapidly decreases exponentially the thinner the effective thickness. There are other kinds of masonry walls. Solid walls are say built with English Garden bond. These you can't really take down the inner skin in any practical way. There is a wall called a collar jointed wall. Here the cavity is no more than 25mm and fully filled with mortar. One key thing here (collar wall) is that the wall ties are much thicker and more robust. Ancon do a wall tie for collar jointed walls. A collar wall tied with the right ties acts like a solid wall so you get more bang for your buck. It's a good idea to value you time. £20.00 per hour seems reasonable. That's £160 a day. A trade rate up near Glasgow can vary from say £100-120 a day for an inexperienced labourer up to say 220 - 250 a day for a good experienced joiner( chippie)... more for a spark and techy folk. Now if that is all through the books and you are doing an extension there may be vat and an extra contractor profit / overheads to go on top of that. When you look at it this way it can be good or bad! If your time spent on site is doing some work then you win a watch. You efforts are tax free and not subject to contractor profit for example. Any time spent keeping an eye on the builder is still worth while as it can head off disputes and extra claims for cost later on. It can help keep the quality of workmanship up too.

True enough but we need a starting point. I suppose it's like asking a farmer for directions. "If you want to get to there don't start from here.."

Aye on the top line full poke for about half an hour to and hour but we have and always have has a contractural obligation to supply to the EU..so they take some of our power and leave us looking daft and our pensioners freezing. I studied this at uni and we have never had 90GW able to cope with a 4 hour peak supply under our own UK steam that was available soley to us without breaching our EU contractural obligations. We have signed up to make the French / Germans cosy! Now even if you take pure peak delivery. Some of that comes from the Scottish Hydro.. (pump stograge) but once the head water is exhuasted it takes time to pump back up... days The 90 GW is bollocks! @SteamyTea We do not have 90 GW reliable supply in the UK. It is far from a non story. We are in / close to shit street! For interest.. I worked on the construction of Torness Nuclear Station and then designed some stuff for the decomissioning of the Bradlwell Station. As a point of note. Biomass takes time to crank up.. oh like a coal station..it takes time to heat up. Wind turbines.. well you don't get peak wind over a whole large wind farm. Twenty years ago we had from recollection some 64 GW of balanced supply. There is no way that has jumped to 90 GW.. even if it had the transmission system has not kept up.

@SteamyTea Had to look that word up! In retort. Genetic algorithsims. I had a dabble in this at uni as we were looking for a way of getting to grips with cold formed steel distorsional buckling behavoir.. but the Yanks / folk in AU got there with a "simple solution" that did not require massive computing power. For the novice (me) mathematician.. we have numbers called imaginary numbers... it's to do with calculus... which us as SE have a interest in? For the remotely interested. An imaginary number is something we introduce to an equation at the beginning to make it work.. and at the end it disappears again! I'm not shitting you! And now you may be wondering why you trust folk like me to design your house! It's ok in my day job I'm grounded.

Hope this helps. There are three generic types of sewers. 1/ A private sewer. This serves your own house and belongs to you.. so you can do a lot. Now if you have a detached house this could run to the sewer in the road. Or you could be at the top end of a terrace.. if so there should be a rodding eye that allows for rodding of the drain along the back of all the other housese down stream.. you need to bear that in mind... keep the rodding eye accesible. 2/ A public sewer. These belong to the water company. These tend to be found along the line of a row of terraced houses at the back. But be aware that these can be deep if you live at the downstream end of the terrace. On occasion I find that these are not economic to get build over permission for if deep. I have seen sone at at least 3.0m which make a rear extension far from viable moneywise. 3/ A main sewer. These are big sewers (call them pylons in electricity terms) and tend to be very problematic to build near. Recomendations. Spend a £100.00 or so and get a utility search from an approved waterboard company.. could be Cornerstone etc. If you have 1 or 2 then it looks promising .. but check the ground levels. If 3 then make sure you get the place for next to nothing to cover your risk.

Bit of general comment from me re slab thickness and UFH, pipe abrasion / expansion, concrete slab shrinkage and stuff. Excuse the spelling and grammer please as I'm off duty. I'll start with my plumbing / concrete hat on, also bringing to the table that I've been "experimenting / sefl building" with different UFH designs for the last 30 years. Ok if you have structural slab you probably want to put the crown of ( the top of the pipe) UF pipe say 40-50 mm below the surface. This allows for a sensible construction tolerance and the unexpected pipe overlap when you make design changes at the last minute. There are some that advocate for less but this is self building.. cut yourself and the builder some slack. **This is self building.. you generally don't have the same control over workmanship as say on a major contractor project.. keep things simple stupid. If you are anal and want to tie down your builder to tight tolerances then you either need to be able to check this or you will end up paying for something that never gets delivered. I see this all the time! Now if we have a simple ground bearing slab on say EPS then I would put the anticrack rebar mesh near the top of the slab. I have on several occasions tied the UFH pipe to the mesh.. with zip ties. Now this can be great thing to do yourself. It gives you that feeling.. here we are putting in the pipes that are going to make our home warm.. it's romantice and gives you a spurt of joy / keeps the spiits up. I say this as I've done this and felt it more than once. Get the builder to lay in the mesh and tie down your own UF pipes! A good way of getting it right. Now lets look at the behavoir of the concrete and the UF pipe preparation. Most UF pipe is rated to 10 bar (it decreaes depending on temperature). I tend to pressurise the UF pipe to 4 bar and hold that for a couple of days. Now I lay the concrete. The concrete has plastic shrinkage ( first 7/ 8 -24 hours / then drying shrinkage. My own experience tells me that the concrete shrinks a little (a mircon of two) away from the pipe and the rebar. Pretty much all heating sytems have a pressure relief valve set at 3 bar. In the round my view is that pipe abrasion can be shown by calculation to be negligeable / none at all. BUT .. SE hat on now. If you have a concrete slab is a structural raft with big point loads then you can still put your UFH pipes in but I'll tell you where you can't put them. Generally it's not to onerous but you'll need to pay me a bit more to do you a couple of drawings.

Hello Will. I've not been about much as busy with the day job and trying to get a bit own own house done before Xmas. Excuse spelling and grammer please.. just knocking out my thoughts. I can see you have put a good bit of work in trying to get to the bottom of this. Well done you! For me that is the benchmark. We want the mortar to be no stronger per say. Ok they seem to be taking things seriously. Insurance companies per say.. delay, deny, defend.. a pattern of behaviour which I see on a regular basis. So nice of them.. as they know it will cost you lots! They are chucking enough at you, getting some testing done to see if this will head you off at the pass. Did the report give an interpretation of the results and the knock on consequences SE design wise? Well done you! Smart thinking. And here is your simple way in I think. When we design masonry cavity walls we allow for the inner and outer leaf to interact. This allows us to take an overall effective wall thinkness.. both the inner and outer leaf work together.. which gives us an overall effective wall thickness. This means that both leaves have to reach the design standard. Also the wall ties are critical as is cavity width.. something to check later to make sure the ties have the correct embedment each end. Now if the inner leaf is sub standard and is contributing to the effective thickness of the wall then someone is going to have to prove that the cracked inner block and mortar with extra air is still able to meet the design codes.. and that will cost them a fortune! Now the questions I would be asking are: OK we have a BRE report. But has an SE had a look at this to check to see how the wall was initially designed to resist the vertical and importantly the horizontal loads and if the inner leaf still is able to contribute to the effective thickness of the wall.. especially for lateral wind load. THIS IS I THINK YOUR WAY IN at least expense / risk to you. In som way they have started the forensic process. The NHBC et al do this, get a report that is confined in scope with no interpretive element.. the knock on consequences. I would go back to them and thank then for the testing. Then say can you give me a structural Engineers report supported by calculations that check both the inner and outer leaves for wind loading and slenderness under vertical and horizontal wind loading.. give the information we have on the cracking in the inner leaf and the mortar findings. They need to provide you with an interpretive report. what does the testing / findings mean?.. and I guess at that point they may shit a brick! My gut feeling is that they are intending to appear they are doing something and racking up your percieved risk aspect. It's a game they play... gambling odds. This is going to open a can of worms as the SE that has to sign off on this will want to know lots more! The main thing here is to force their hand and not spend any of you own money at this stage. For me this is a structural safety issue.. and that concentrates minds. Now as a word of caution. If you instructed me to go full pelters to win as much as possible on your behalf then we could find lots of other issues. As and SE I can't sign off on the stuff that suits you and ignore other stuff I find. Depending on how things pan out you may have to make a declaration to your home insurer and you must make sure you don "blight" the property by a simple administrative error. Now say it turn out that these defects are prevelant over the whole structure? What then? That's it for now. Don't act in haste here.

This is going to take you time to sort out.. allow for 1 - 2 years, if sooner then you have won a watch. For all if you have this kind of thing get a hold of the NHBC and the Blockwork folk. Make sure you identify the blocks! Each well known manufacturer has a different scratch pattern on their blocks. The scratch pattern identifies the manufacturer and the block strength. I've screenshotted the scratch pattern for Themalite so you can see what I'm on about. But.. what's going on here @Will A.. are you declaring all the info you have. If you want a bit of advice then can you expain how the petrographic test came about? Who paid for that? Where are you in terms of the NHBC / Builder?

In my own house I have a mix of products. The windows and pass doors are Origin.. Its high end stuff and expensive... they have performed well to date. SE wise and in terms of large areas of glass.. its a mine field. Very few of the glazing suppliers will give you the data I need as an SE to design an adequate system. My arse.. the glazing system needs to be integrated with the structural design. If not the guarentee is void. The glazing system is a big ticket item and thus you need to get an SE involved early (pay your SE a little more.. it will be money well spent) so they can guide you on the selection of the glazing system and how you fix that to the structure so the horizontal and downwards vertical deflection of the stucture is compatible with the glazing system. Armed with this information from the SE will help you select the right glazing supplier. Express Bifolds are a mass market outfit.. there is one up the road from me and they don't give away too much and that often leads to trouble later on in the build.

I can see how you may think this is jobs for the boys as the process if far from transparent. There is another thread that talks about the planners being corrupt. When I first started out 40 years ago as a builder there were brown envelopes flying about... before that we had the Polson scandel... which was corruption on a big scale. The planning and BC process is much more professional these days in the spirit of things but the basic delvery of service is very poor. A lot of these young folk are graduates but have no sense of business etiqette. They have not been taught professional manners.. even just to say.. I got your email.. I'm busy. In my view the "corruption" occurs at the political level ( by directing funds and resources.. with a pension pot).. we have lots of this in Scotland, its not cash.. or a free holiday or getting photographed with a call girl. For me I work with builders.. who are on my tender list. They all know I play off a straight bat... but in return they will get a crack at some good profitable jobs. BC and the Planners.. some are just totally incompentant.. but I don't think they are corrupt like the old days. @ThomasB The SE needs to pull up their socks. To put this into context. We as SE's carry a lot of liability. £80.00 to £120.00 per hour is not an unreasonable fee. Your Lawer will charge you more and do less.. funny thing is that it take less training to become a Lawer than an SE or an Architect... and folk moan about our fees!

To add context. Prof Hasseltine wrote a lot of the brickwork design codes and has acted for the NHBC. I had the privalge of working for the "other side" and found him and his reporting to be wonderful. He agreed with me.. the NHBC lost he case. What stuck me about him was his pragmatism and the way he as an educator was able to distil complex issues down to something that the layperson could understand.

Sorry to hear you are not satisfied with the service. As an SE myself I write my reports for a particular audience. I could write a report that deals with say complex structural behaviour that is intended to be read by other professionals who would be expected to have a basic knowledge.. even then I would summarise my explanation so it could be understood on a basic level by a lay person... who could be a Judge. When I write a report for a Domestic Client I ensure that I explain not least: 1/ Why I was there... the context of my appointment and the concerns that have lead to my appointment. 2/ What I saw when I arrived (photographs). Who the movers and shakers are.. You the Client / Builder and so on. 3/ What background research I had carried out before I attended site. 4/ What I was able to observe visually. If I take any measurements what were they, sometimes this is not easy as folk have furniture / the garden is full of stuff! Now that sets the scene. The detail: What can I see and also what are folk telling me. Frankly I tend to take everything folk tell me with a pinch of salt! I listen everyone and look at the evidence. Construction disputes are a bit "excited" at times. My report: There is a recognised SE reporting structure which I follow but then adapt for my audience. I'm a guts and all SE with 40 years construction experience under my belt so most of my reports use simple language and I take pride in using simple stupid basic English. I got my inspiration for simple English from Professor Barry Hassletine, who is in my view an exponent of this art of communicating.. and I'm still learning. For example a builder or the NHBC may need to read this. The NHBC are an insurance company so we need to make it simple for them, many builders have a higher level of understanding.. but not all. @ThomasB.. your builder seems a bit streetwise hence bringing in an SE. And here I smell..shite as you probably do! If there is testing required then this should agreed..what needs tested.. the scope and who is going to intepret the results of the testing. Who pays for this? In the round I can see why you may be naffed at the £700.00 but that is not bad for a basic report well written.. but it seems you are not pleased with your SE's command of simple English? If you want to take this further then post the report and more detail.. who is going to front the cost?

You can potentially save yourself a pile of cash if you post some sketches. You seem to be at an early stage. Here we look at the overall design, areas of glazing and so on (this is for structural stability.. side ways wind loading for example) and try and look at the insulation strategy and how we do the SE work for this to make it buildable and economic. The rafter spans you are talking about are modest.. no need for expensive I joists unless these can save you money on insulation... you may have a preference for what kind of insulation and roof covering you want? Sometimes we over engineer things so we make the buildability and insulation less costly for example. The best advice I can give you on limited info is to try and figure out what stops your house moving sideways when the wind blows! If you have massive area of glass then these are sensitive to sideways movement and reduce the available walls that can resist the wind. If I was teaching student Architects..(I do teach some and they in turn reciprocate) I would say.. bear building stability in mind and you'll have a good chance of actually getting your design built!

Help ma boab ( Scottish expression for surprise / aghast)! This needs investigating properly. Agree. Send them your marked up photo as I think this will grab their attention. Also send a photo unmarked. See what the NHBC and the manufacturer say first.. let them do some leg work before you get an independant SE involved.. which may not be required... but you may want a second opinion anyway.. will be cheeper for you if the donkey work is done by those who build it and underwrote it. Question is.. that's the bit you can see.. what about the rest that you can't see! Sorry to say it but..

Have had a look at their website and signed up for the download. "That’s why we're simplifying the path to Passivhaus ownership, by taking the complexity out of the build process." Now that would be refreshing if they can actually deliver what it says on the tin. From their website.. A People Centred Approach Founders Clare and Ross Booth share how their people-centred approach and compact Aberdeenshire team... Aberdonians tend to be of practical mind with their head screwed on the right way.. sounds hopeful.