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Interesting stuff, early technology, not to be ruled out. As an SE I've always been interested in rock mechanics. It's a fascinating subject, not bedtime reading for all mind.

I agree. I've had a bit of a closer look. SE wise there is a sideways stability issue that may be questioned. This may be ok if the roof diaphragm is well braced and connected to the the main house wall. We can't yet see how you get into the extension from the house? Again this has SE implications. The drainage looks like it needs clarification and so on. Anyway, one should always not judge a job half done, thus I'm reticent to be too critical at this stage.

I think there are bigger thermal bridges than the steel post……just saying!

Post your SAP so we can take a look. I’m very surprised that a timber frame is failing the SAP. I would also assume that the junction calculations are taken from standard details rather than specific construction drawings.

Hi @bluebellcottage I really liked the Westcoast windows, but decided against them in the end. Our local installer was very helpful, as was Westcoast, but ultimately they couldn’t provide all the window sizes we wanted. Incidentally, a few months ago I spoke with an installer who dealt with both Westcoast and Rationel. He found that most architects specified Rationel but Westcoast was, in his opinion, the better window. Eventually, we opted for aluminium (Deceuninck) instead of alu-clad, purely because it was the only way to achieve all the openings we wanted using one system. If we had gone for Alu-clad, as was our original intention, then of the many, many systems we looked at, my first choice would be Zyle Fenster. They seemed better engineered and more robust than the likes of Westcoast, Nordan, Velfac, Rationel and significantly better value than Internorm or Norrsken (even though both are great windows). It would be worth a chat with @craig The Zyle Ecotherrm windows he can supply are aesthetically quite similar to Westcoast. Craig’s also extremely knowledgeable, helpful (and patient!) Just a really good guy. If I ever build another house and opt for more sensible window/door sizes, then Zyle would be top of my list, as would Craig 👍

Buildings insurance for the existing house has a (low) limit on the value of building work that can be happening (anywhere) on the plot (even though there is separate insurance for that building work). Land Registry won't split the plot into separate title deeds until you are selling to another party. I will continue to hunt around for insurers with a more sensible outlook!

While getting rid of thermal bridges is admirable you need to remember that you SE needs to connect the structure together to stop it falling down, or deflecting, shrinking so much that you don't end up with a duff house. Now if you go over the score with your mitigation of thermal bridges, this can make the detailing so complex it becomes unbuildable, I'll have to introduce work SE arounds for example, the build cost and detailing time starts to rocket exponentially. Your builder will charge you for what's on the drawings.. and if it looks hard, add a premium, but often never actually deliver what you are paying for. Keep the design simple. To do this you have to embrace holistic design, from the foundations / ground investigation up. This makes it hard for self builders who want to split the design into different stages which is common on Build Hub. The trick many miss is not to get an experience designer on board early, even if just to keep a watching brief on what you're up to pretty much from day one. I do this from time to time even though my real work may only start later in the project. it also gives you time to find out if you like me, and I you! it often gives us an easy exit route if we don't gel, little money / programme time, if any, is lost. It make a lot of sense at my designer end as if I've kept any eye on the earlier process I can often avoid having to sort out a mess before I start on my own part of the design.

Try and post your drawings, you'll get loads of targeted advice if you do. How refreshing to hear, well done!

For me this is a interesting challenge to design a solution. I appreciate that you find it far from interesting and it's a worry. Stage 1: One option I would be inclined to look at first is to install another beam or beams below the ones you have if it turns out they are so heavily corroded they are well below capacity. Remember we would look initially to design these for the latest loadings prescribed in the design codes. The following is based on using a trick we deploy when we are needing to support say a large opening in a historic building or repair steels, more applicable to you. The existing beams have a point of support on say the main walls. Thus in the round we know these are the strong and proven points. It's a reasonable starting assumption the walls locally will have pretty much finished settling in and around the existing supports, thus we want to put our new point loads at these positions. Let's say, as we don't have much information that the beams are supporting the ground floor flat but also an internal spine wall that runs up the building and it turns out there is a fair bit of load. It make the challenge more interesting. This is in a bit of reverse order. How do we calculate the loads and do some other thinking. Well the loads are easily calculated once we know the building layout, floor and roof span directions. From that we can calculate the forces on the existing beam/s. We would want to split these between permanent loads ( dead loads from the materials) and imposed ( live loads) from people, furniture, snow roof load etc. Next we would want to have a look at the existing corroded beams, try and identify their section properties when new and as they are now, corroded. We can then make a reasoned guess as to what their original design strength was and what it is now. The extra thinking comes for example as one obvious question is why has it not fallen down to date? Have the beams deflected a bit too much and shed load elsewhere. Remember a building does not often fall down until it has exhausted every alternative load path. This is what SE's often call redundancy, which helps stop what we also cause disproportionate collapse, like the domino effect. We would want to get a handle on this before we access any confined space. Any Engineer is going to want to do a pretty comprehensive dilapidations survey. This heads off any "adventure’s seeking to take advantage, but it also protects the honest residents if some further cracking occurs during the works. In summary stage one is doing some fag packet calculations, a survey and from that we can get a feel for how the building is "working". Stage 2: Again not quite in the right order but it easier to hold the narrative. Lets say we can install beams under the existing, then do some bolting etc to support the loads, maybe by stiffening the webs of the existing beams or by using other simple plates / angle sections. This means the new beam/s load the supporting walls in the same place, proven to have worked so far. The big thing is that there is a good chance you won't be able to get the new beans into the basement in one complete length. Thus splices will be required, which tend to flex a bit. Also critically the new beams won't take up the load unless we pre deflect them. For them to carry load the building would need to settle onto them.. high probability of cracking as we move up the building. There is a technique we use on historic buildings where we get the new beams in with a bit of clearance and then jack between the old beams and say the top of a new beam to pre bend the new beam so it takes up the load. We have calculated the loads so have a bench mark as to how much we need to jack / pre bend. We are only talking mm here so we would use say dial gauges. In practice what we do is jack it a bit then run up stairs and see if cracking is starting or if existing cracks are opening up, doors starting to jamb an so on. This takes time, it's not a one day job! Stage 3: As above and in reverse order. The new beams often need to rest on a new padstone below the existing one spreading the load from the existing corroded beams or we need a spreading arrangement. This is partly a detailing and practical thing. But once access is gained with a fair wind usually there is a way of applying the load to the supporting walls in the same place as the existing beams are. Again simplistically we just trick the building, it's sub structure into "thinking" nothing has changed above. But this is not an exact science and 99% of the time some minor movement will occur and that has to be communicated to all parties. Comment: Infilling the basement or sifting the loads to a different place invites lots of potential settlement problems and so on. You would need to investigate the basement floor and the soil under which is going to be less consolidated than the soil under the main load bearing wall for example. Construction safety is going to be the driver here in terms of a structural solution. I would look to have at least head height clearance for folk to work. Two means of escape from the basement. Make sure we have a good ventilation strategy during and after the works, avoid any welding, use of volatile paints etc and make sure there is compliance with all the regs relating to working in confined spaces. In summary it may turn out that the SE solution is not complex, it will likely need a diligent / experienced and well supervised Contractor. The hard part is herding the rest of the cats, project administration and agreement of where the liability lies etc. This goes along way towards explaining why many designers don't want the hassle of a project like this, the design fee has to be attractive not least.

The wife has just finished our vat claim i will see your 161 invoices @Benpointer and raise you 1057 invoices anybody had a larger amount than this.

I’m not sure I get what you want. you get a self build insurance for the new build and keep your original house insurance on the original house. what has the building work in the back garden got to do with the original house. are you splitting it into two plots ?

If I was pouring a slab in this weather I would have rolls of hessian stacking in an old bathtub of water, an hour after the final trowel up i would cover the slab in the damp hessian. the picture is just ring beams, but it was 28 degrees and the hessian cost pennies compared to the cost of the concrete the pump and the labour. cheap insurance really.

@Great_scot_selfbuild Thanks for coming back to me. Certainly doesn’t look too onerous to me. Good to get an insight of structure and content though. We’re early stages of design but trying to get ahead and be as prepared and organised as possible!

I saw these people the other day: https://anthonygold.co.uk/service/leaseholders-and-freeholders/conversion-to-freehold-enfranchisement/ May be worth another quote. Are the other leaseholders on board?

Seen stuff on the millimetre wave drilling technique before. Seems like a really cool technology. Glad to see they are still moving forward and don't appear to have hit showstopping issues yet.

Environment How to unlock unlimited geothermal energy, anywhere we want Earth contains more than enough heat to power humanity many times over, but so far only a few lucky places have been able to exploit it. Now we may have a way to tap this vast clean energy source almost anywhere By Katharine Sanderson 21 July 2026 A geothermal power station in Iceland’s Hengill region, one of the few countries with natural geothermal reservoirs that allows it to turn underground heat into power Science Photo Library Deep under your feet, Earth is hot. Really hot. Some of that heat is left over from the planet’s violent formation. More is continually created by the splitting of radioactive atoms in the rocks below. In a few places, Earth’s hidden furnace dramatically makes itself known, bursting through the crust as volcanoes, geysers and rivers of magma. Spectacular stuff, but also extremely useful – if we can get at it. Conventional geothermal power works best wherever geology has done the hard work for us: where fault lines crack the crust and hot water or steam rises close to the surface. That’s why countries like Iceland, New Zealand, Kenya and Indonesia can turn Earth’s heat into warmth for homes and electricity for grids, while much of the rest of the world has barely touched it. Its appeal is obvious. Unlike solar power, geothermal doesn’t fade when the sun sets, and unlike wind power, it doesn’t stall when the air is still. Over the past decade, advances in drilling have begun to loosen geothermal power from its geological shackles. Some projects aim to improve on nature, creating cracks and pathways where none existed. Others are more ambitious still: they want to drill so deep that geothermal power could work almost anywhere. “Ultimately, the whole world is the goal,” says Matt Houde, co-founder of geothermal energy company Quaise Energy. That would turn it from a niche resource into something far bigger – a way to tap the planet’s hidden heat wherever we happen to need it. How we harness Earth’s heat To convert heat from Earth’s interior into usable energy, engineers pump cold water into naturally occurring reservoirs in hot rock. There, it warms up and returns to the surface as hot water or steam, which can be used to drive turbines and generate electricity. The water is then sent back underground to begin the cycle again. It’s a simple concept, and unlike fossil fuels, geothermal heat sources are practically inexhaustible on human timescales. “If you measure in terms of the energy stored within the Earth’s crust, geothermal heat exceeds by orders of magnitude all hydrocarbons,” says Houde. The trouble is that traditional geothermal requires three ingredients to work: heat, water and rock that is permeable or fractured enough for water to move through it. “Traditional geothermal systems are very constrained to countries and regions within countries where you have this unique combination of conditions,” he says. That is why geothermal has flourished in places like Iceland. Sitting astride the mid-Atlantic ridge, the country has those core ingredients in unusual abundance. The global oil crisis in the 1970s pushed Iceland to exploit that advantage, and geothermal now makes up over a quarter of the country’s electricity supply. That may not sound like much, but Iceland’s geothermal plants can keep generating whatever the weather, making them a steady backbone for the grid. “Geothermal is really well placed to be the glue that will make low-carbon electricity systems work,” says Iain Staffell, a sustainable energy expert at Imperial College London. However, most countries don’t share Iceland’s good fortune. They may have heat or water or fractured rock, but not all three at depths that are easy to reach. Traditional geothermal plants are limited to mining heat from less than 2 kilometres underground. Go much deeper, and the engineering becomes brutal. Drills must chew through hard, hot rock. The vertical shafts that connect the surface to heat reservoirs, known as wells, must survive punishing temperatures and pressures. Even after all that, the rock may still be too tight and unbroken for water to flow through it. A worker surveys the vast interior of a geothermal cooling tower in Monterotondo Marittimo, Italy Alessia Pierdomenico/Bloomberg via Getty Images Still, the prize is enormous. The International Energy Agency estimates that geothermal’s technical potential is around 150 times current global electricity demand, assuming we can exploit heat down to about 8 kilometres. Conventional geothermal typically taps pre-existing reservoirs of hot water or steam in permeable, fractured rock less than 2 kilometres underground, leaving much of that potential out of reach. The implication is clear: to expand the resource, engineers must drill deeper – and create the underground plumbing that nature hasn’t provided. Enhanced geothermal The first of the new geothermal techniques does exactly that. Enhanced geothermal systems target hot but impermeable rock, typically 2 to 10 kilometres underground. Engineers pump in hot water at high pressures to open or widen fractures and create pathways for fluid to circulate. This is known as an enhanced geothermal system (EGS), and it is the most mature technology in geothermal’s new era. But this approach has a downside. Forcing water into deep rock doesn’t just create useful cracks. According to a 2023 review of the research, it can also disturb older, pre-existing faults that are already under strain. Many faults are held still by friction, like a heavy book resting on a tilted table. Pump water into them, and the pressure in their pores and fractures rises. That partly props the two sides of the fault apart, reducing the force clamping them together. If the fault was already close to slipping, that can be enough to induce an earthquake. An investigation commissioned by the South Korean government concluded that a nearby EGS project triggered a magnitude-5.5 earthquake in the city of Pohang in 2017. More than 80 people were injured and the earthquake caused an estimated 300 billion Korean won (£148 million) of damage, making it the most destructive in the country’s history. Is a broken jet stream causing extreme weather that lasts longer? Scientists are scrambling to understand how climate change may be interfering with the winds that carry our weather, with potentially catastrophic consequences Bill Ellsworth at Stanford University in California was part of the team that helped establish what role the geothermal plant played in the disaster. “In Pohang, they drilled a couple of wells that were a long way apart,” he says. The hope was that pumping water into one would fracture the rock enough to connect with the other, creating a route for water to pass between them and gather heat. But trying to force that kind of connection through the subsurface is risky, particularly if the drilling intersects faults that are already primed to slip. That is why newer projects are trying to be more deliberate, says Ellsworth. In Iceland, for instance, engineers try to create EGS reservoirs more gently without blasting them open all at once by pumping cold water slowly and at relatively low pressure. Over months, the cooling rock contracts and cracks, says Lilja Magnúsdóttir, executive vice president of resources at Icelandic energy company HS Orka. Iceland also has an advantage born of necessity: it is a seismically restless place, so the country has already invested heavily in monitoring. At HS Orka, that now includes using geothermal wells themselves as early-warning sensors. When magma begins to move, it compresses the surrounding rock, creating a telltale signal in the well. “It’s a really cool design,” says Magnúsdóttir. But even where EGS projects have learned to manage seismic risk, hard rock still makes an unreliable basis for a plumbing system. Fluid can leak away and contaminate groundwater, for instance. And the same fractures that make the system useful can also make it dangerous. Advanced geothermal One way around this is to stop asking the rock to carry water at all. Where natural fractures and reservoirs don’t exist, an alternative to EGS is to drill a sealed loop through hot rock. Engineers drill down, then sideways, until the boreholes connect underground, before lining and sealing them with steel and cement. That creates something like a buried radiator where fluid circulates, but never comes into direct contact with the rock itself. This closed-loop system is known as an advanced geothermal system (AGS), and it has been tested successfully in Germany, where Canadian energy company Eavor has developed a geothermal power plant at Geretsried, which began construction in 2022 and started producing electricity last year. Because closed-loop systems don’t force fractures open in the rock, they should reduce the risk of induced earthquakes. And because they don’t depend on continually pumping water into and out of those fractures, they should reduce it further still. In a few places, including south-western Iceland, Earth’s buried heat lies close enough to the surface to be tapped easily by geothermal plants. Water from this plant also supplies the nearby Blue Lagoon geothermal spa Dieter Telemans/Panos Pictures There is another possible advantage. If the working fluid stays inside a sealed pipe, it doesn’t have to be water. Companies can, in principle, use fluids that pick up and release heat more efficiently. Eavor’s working fluid is a company secret. The firm China Huaneng Group, meanwhile, has built the first geothermal demonstration plant that uses supercritical carbon dioxide – CO2 that is compressed and heated until it becomes not quite a gas and not quite a liquid. In that state, it is dense and flows easily, and is very good at moving heat. The firm’s test facility began operating in May this year in Zhengzhou, China. But these systems have their own difficulties. Eavor has had to scale back the number of wells it planned to drill after rock debris clogged parts of the pipe network. Its plant works, but not yet as efficiently as hoped. That points to a broader question: can closed-loop systems circulate enough fluid, and draw heat from the rock fast enough, to be commercially useful? “The jury is still out,” says Ellsworth. “Time will tell whether these ideas of having just a single closed loop will be actually successful.” And while AGS could be safer and cleaner than inducing fractures deep underground, it is still limited to places where hot rock lies within reach, usually a few kilometres down. To make geothermal truly global, companies will have to drill much, much deeper. Supercritical geothermal The deeper you go, the hotter Earth gets. Go deep enough and water crosses a strange threshold. At about 374°C (705°F), under sufficient pressure, it transforms into a supercritical fluid – akin to the CO2 in the China Huaneng demonstration plant – and can carry far more heat than ordinary hot water or steam. “There are a few countries where geothermal does provide a sizable mix of the energy supply. But strictly the heat itself, which is fundamentally what geothermal energy is, is actually available anywhere if you go deep enough,” says Houde. Supercritical temperatures are usually found at depths of at least 5 to 20 km, and often deeper. The rocks become harder the further you go: basalt or granite rather than the softer sedimentary layers often found closer to the surface. This rock chews through even the hardest tungsten carbide or diamond drill bits. Then there’s the time spent not drilling at all but instead replacing worn-down drill bits or equipment that begins to fail at higher temperatures and greater depths. These delays quickly push up costs, says Houde. Quaise Energy uses millimetre waves, a portion of the electromagnetic spectrum, to laser through hard rock found at great depths Quaise Energy Quaise, which is based in Houston, Texas, wants to get around this by drilling in a different way – without using a drill bit at all. Its plan is to use conventional drilling for the upper part of the well, then switch to high-powered microwave energy once the rock becomes too hard. The hole would be lined with corrugated steel, helping the microwaves travel downwards. When that energy hit the rock, it would heat it until the rock cracked, broke apart or even vaporised. “There’s no drill bit mechanically destroying the rock here, it’s just the interaction of the energy with the rock,” says Houde. The rock would be reduced into a fine ash that is purged from the well with a nitrogen-rich gas and collected at the surface. Quaise isn’t alone in pursuing non-contact drilling: Slovakia-based GA Drilling is also trialling laser- and plasma-based systems, and carried out its first field tests in 2023. Once the hole is open, Quaise wants to create a deep, EGS-style reservoir. Water would be sent through fractures in superhot rock, picking up heat before returning to the surface to generate electricity. In principle, it is geothermal freed from geography. Rachael Tremlett/New Scientist Quaise’s test holes are still just a couple of kilometres deep, but the company sees them as a proof of concept for something much larger. Its first planned superhot geothermal plant, located in Oregon, is intended to come online by 2030, accessing temperatures up to 400°C (752°F) at a depth of 3 to 5 km. A potential future site would push deeper, potentially to 10 km. “By 2035, we want the first superhot well producing energy at a depth greater than 10 kilometres,” says Houde, who thinks his company’s technology could transform any region into geothermal country. But there are still serious uncertainties. One is whether such deep wells can be kept open under the immense pressures found kilometres below ground. “It’s unclear whether that is possible,” warns Ellsworth. Houde accepts that the hardest engineering lies ahead. “I think it’s very viable for getting to these initial depths to prove superhot geothermal,” he says. “I think it’ll become increasingly more challenging to push the frontier on how deep we can go.” Iceland offers a glimpse of how these different strands of geothermal might converge. Instead of simply resting on its laurels as one of the world’s great geothermal success stories, the country is fast becoming a test bed for what comes next, says Magnúsdóttir. Its deepest geothermal well – the second well by the Iceland Deep Drilling Project, a consortium of the country’s leading energy companies and its energy authority – has already brushed against the promise of superhot geothermal. It was completed in 2017 and goes down 4.7 kilometres. “It is the first well in the world where supercritical conditions were confirmed in the geothermal well,” says Magnúsdóttir. Icelandic operators are also using EGS techniques to get more from existing fields, stimulating deeper faults to reach another kilometre or so of heat. Next year, the Iceland Deep Drilling Project plans to drill its third well. “There, they just have to go down to a little over 2 kilometres to reach supercritical conditions,” says Magnúsdóttir. But even at that relatively shallow depth, the engineering challenges remain fierce. The main problem is well integrity. At such high temperatures, the steel casings that line the well can expand, deform and fail. In Iceland, engineers have been testing fixes, including flexible connectors between sections of casing. This sort of engineering will be crucial if geothermal is to win over investors. Projects are expensive up front and slow to prove, and often need permits before developers know whether a site will work commercially. But the reward for patience can be unusually durable. “It’s very, very costly,” says Sanjeev Kumar at the European Geothermal Energy Council. “But once you’ve drilled that hole in the ground, that lasts for over 100 years.” That is the promise and the problem in miniature. “We know that very deep geothermal energy would be fabulous if we could reach it,” says Ellsworth. “We just don’t yet know if it’s possible.”

I have been talking to 2 solicitors about my Leasehold to Freehold enfranchisement. Already rejected a couple of others due to geography or other things. One has quoted £1600 and the other about £9500. I am not the sort of person that would usually gravitate towards the cheaper option in any scenario. But the difference here is huge. For any solicitors that might be reading this... #1 Is this gulf common? # Do solicitors respond well to a haggle # If the figure is based on a formula that is open to the customer how are the numbers derived. # I thought there was another question. It'll come back to me

The youngster may turn out to be a better fitter, be more meticulous, work with you out of respect, and do a good job. Just speak with him and explain your concerns, and see how he responds. Sounds like the product isn’t a top shelf option and the repeats are the fleas coming with that dog. For want of a better phrase, Champagne job on lemonade money? Feel free to tell me to FO, I have thick skin.

Thanks both Redbeard & Nick, found helpful info through this thread - so grateful. For anyone else in same situation, this is what we will use: fire rated aerogel strips on the steel, and the cold roof will have fire rated rockwool (cold roof), and fire boards internal areas, on the outside, we are aiming to clad with bricks around the steel to go up all way on the corner.

Maybe I'm an optimist but to me the hardest problem you have to solve here is to get everyone to agree how to move forward. In a way, winning the appeal for insurance would help a lot with that as it will take the details somewhat out of your hands and into the insurance companies. Still, while you wait for determination there well worth getting the SE in to do a proper assessment (which should be easy to agree).

Quite so. I've just reread the original post. Concrete cracks, steels corrode. Newish walls can be removed again. The managing agents were not technical people, so their comments are probably irrelevant. So the residents' trust perhaps need to get a fund together and start from scratch. A good local SE will be a starting point. A free first visit for a quote. Then a solicitor (there are construction specialists) to formalise the process, get insurance etc. Then sort it. The value of all properties will then increase by more than the cost, esp for those who can't sell. OR. Is there a local big developer/ landlord who might buy the lot and sort it out... takes the risk and makes money?

Fire Resistance.

Thanks a lot Nick that is helpfull, yes all steels are galvanised and painted with anti rust paint, steel not holding second floor, only carrying a small mono pitched roof on top of a bay window. What is FR?

I'm sure I've seen some photo's but can't find them. They tend to show a forest of brand new screwjacks which I believe we have purchased. It's useful to have this sort of feedback as it demonstrates there are alternatives that need assessment before a design decision is made. Just to qualify my approach I'd say using foamed concrete would put an extra 3kN/m2 load on the existing basement floor/sub grade. I'd say that was pretty nominal in the great scheme of things and likewise, horizontal loading on the existing basement walls would be resisted by the existing external ground. Access to pump could be via one of the ground floor windows of the affected flat. Mind you if the costs come in too high it might be just as economic for leaseholders to club together and buy that flat leaseholder out. Remove the floor and put a simple steel stair behind the front door to give access into the basement. It's always worth thinking outside the box!

To put it into real life context, in the Steading we left a significant proportion of 600mm original wall exposed internally. This was for aesthetics and a historical nod. That would never pass Passivhaus which is an extreme target. I have no intention of sacrificing lots of money and aesthetics for the certificate that comes with a few % energy benefit. But many do and it's their choice and money (never regained in £ payback). We did get respect from the bco who agreed it was a good design feature, and we balanced the insulation by extra elsewhere. You are building all new, so can more easily tweak the insulation. Should be easy enough esp with a proper analysis with expertise. You say lots of insulation. What products?