Gus Potter

Good sketch. Can you drop the duct so you get some insulation over the top of it to mitigate the cold bridge? In parts of Scotland it regularly gets down to minus 15 -18 deg C. We have a 5.0kW stove with a bottom intake that can be ducted. I do have a duct from the solum space to hearth level and it pops up just under the intake but is not actually connected to it. When the stove is on you can really feel the air flow if you put your hand under the stove, but the cold air is drawn directly into the stove rather than over your feet / under the door. The rest of the room is reasonably sealed so when the stove is not on the room is ventilated.. it's not a passive house. One day I may connect the duct to the stove intake and see what happens.

Looks good and exciting to be moving to the warrant stage. From an SE point of view it looks like you have a fair bit glass there, big openings thus building stability is an issue? Your SE may have already expained? This could be complex / costly to achieve with ICF. Also you have the weight of the building on sand with some probably hefty localised loads. @saveasteadingmay be along to give some pointers here about building on this type of material. SIPS maybe good but check for availability of contractors to install and your preferred method of build / cost curve etc. Also, again, bear in mind that you may want to make some changes as you go. I would price up the twin wall TF as others suggest and compare. Lastly don't rule out a standard TF with brandered out walls for example to get the insulation thickness required. It may not be quite perfect but it gives you more scope to adapt as you go and it's something that local contractors are maybe more familiar with, so savings could be made here.

Surprisingly yes. Once you change the loads and the stiffness / positions of the beams framing in then you need to review the whole thing. If you move the steel supports you need to go back and check the bearings and so on. It can be quite involved. Then sometimes you need to redraw a lot of it, change the detailed specification and so on. Before you know it the clock runs up. @saveasteadingmakes good points.. good flavour of how things add up. I think your SE is probably doing you a favour here. In the grand scheme of things if you want to open it up more then pay the SE and enjoy the result. If you like the open feel then others will often too. When you come to sell you'll get your money back anyway?

Well done to you. Have you decided on a traditional weighted window with the ropes and pulleys or ones with what are called spiral balances. These are visible but a modern way of creating a nearly traditional sash and case window. If you are going for the ropes, pulleys and weights you need a good rebate to fit all the wieghts in, usually about 100mm rebate to be safe. Next is the glass and the type and shape of the window, astragals etc. I would make a sketch of what you want and send it out to some bespoke manufactures for a ball park figure as they will vary widely.

Remarkable response from an Engineer to dismiss a Client in this manner with no apparent explanation. If a reasoned explanation was given the there would be no need to "scoff" However here lies the rub and maybe "scoffing" was not the appropriate response. Yes the small buildings guide is under review. I know that @saveasteading has a particular interest in this so have included a link at the end of this text to download the latest guide available online. I also attach the document I have down loaded using same link. Page 3 of this document contains the critcal text that deals with the withdrawn aspect of "SBSG" In my view paragraph 2 is misleading. Many of the BS Standards have not been withdrawn as suggested. Some have, in particular the wind / snow code but much of the timber design codes are still valid but with a few nuances. It is for example perfectly acceptable by BC all over the UK to design to BS 5950 for hot rolled steel provided you take into account the latest available information in the euro codes. A specific example here is that the Eurocodes require a haunch sharp end stiffener check/ design in a portal frame when in the BS left this open to the designer to check. Paragraph two then introduces uncertainty and contradiction. It says that the designer should take care when using this guidance.. it does not say that you can't use it. BC say that this guidance has been removed from the technical hand book. So what! Provided you can produce a reasoned, valid and safe design based on the latest available information it is ok Just because BC have removed this from their guidance does not invalidate understood Science and Engineering skill. Paragraph 3 is pretty much a rant but finishes by saying that as Designer you can do what you want provided you can prove it is safe. In my view it is still ok to use the SBSG as a basis for design provided you recognise where the changes in wind load / snow loading may impact on the guidance. It still is a good document for preliminary design. In actual fact unless you live at a high altitude for example in the UK the Eurocode changes will have little impact on the guidance. The wind may have a slight differance but generally it is the dead weight of the roof covering and the access load / deflection under normal loading that will goven the design anyway. For any Enginner not to discuss and offer reasoned explanation to a Client when specifically asked is a disgrace to the SE profession. Gus Potter. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjD6Z7ftcn2AhWVQkEAHfBJARwQFnoECAcQAQ&url=https%3A%2F%2Fwww.gov.scot%2Fbinaries%2Fcontent%2Fdocuments%2Fgovscot%2Fpublications%2Fadvice-and-guidance%2F2020%2F02%2Fthe-small-buildings-structural-guidance%2Fdocuments%2Fsmall-buildings-structural-guidance%2Fsmall-buildings-structural-guidance%2Fgovscot%3Adocument%2FSmall%2BBuildings%2BStructural%2BGuidance%2B%2B.pdf&usg=AOvVaw2nnn0liJPfV762mn9NosnA 1226535124_SmallBuildingsStructuralGuidance(3).pdf

Hilarious. Was talking to the spark about the upcoming IEE 19 regs and said I fancied arc fault protection.. until he said you have two fuse boards and.. then pointed out that I have been at doing my own house for longer than I "predicted"... and I may be best spending the money on other things. I'l stick with diversity for now.. and upskill to selectivity next year. On my office wall hangs a hand line drawing of Bradwell Nuclear Power Station which is a work of technical art, a Hemingway hat and my Teady bear from when I was about 4, one Teddy suffices as not of Royal descent. I'm not sure what will be banned next!

Delightfull.. thanks for the heads up Onoff. Sparkies use a term called diversity. @Carrerahillmay pop up and explain in detail how this works from the IEE regs point of view and the theory. But in summary I understand (I may just know enough to be dangerous!) that although the sum of all your appliances may exceed 100 amps they are less likely to all need maximum demand at the same time. Also, the fuse (100A) in the cable head is apparently called a sand fuse and does not blow with a short surge. Then often at the local sub station there is a 600 amp fuse. But if you have say one of these electric Ferarris that do ultra rapid charging at some 400 amps? you may be on a loser and need separate phases for example.

Keith..Welcome then.. lot's of interesting stuff here. Don't panic! Draw what you have on a bit of A4 paper and what you had originally . External ground levels, the brick / block coursing, the kit, the floor, suspended or ground bearing slab etc. Take a photo or scan and post. Don't worry about scale as just draw the blocks and say their size. Lastly it's not a drawing test, just convey the info as best you can. Gus

Hiya @Amateur bob Have raked back through you posts and made random comments for your digestion and general discussion. Reach for the Rennies if need be all. Your posts, generally copied, are in italic. “I’m looking at a different house design” Good.. different does not mean expensive. I would go back and really write down you requirements. For example I built a house for us that had three large bedrooms near Biggar. Other houses locally on the same footprint had 5 bedrooms but we always designed for there being just two of us living in it most of the time. We knew that potentially it could reduce the value as it was not really a large family house. When sold we got a substantial premium over and above a similar 5 bed as the folk that bought it were retired and wanted this type of house. Why does everyone not do stick build if its cheaper? A number of reasons. One is speed and speed often translates into the release of funds by a lender and valuation. Speed.. well roughly two joiners will build three accurate panels a day give and take. Some panels can be long, some short but I would price on 3 a day. You also need a good working platform and space to store the panels you have build on site. Take your average external panel as being about 3.0m in length to be safe. Internal non load bearing panels are just erected later on, often once the ceilings are up. The non load bearing panels need very little drawing effort. Internal racking panels are the same as external panels but with no vapour barrier. Two good joiners who know how to build kits on site £ 250 -275 each per day. That will get folks attention in the Central belt, my Mum lives in Dunning. To build a kit on site you need the panel drawings. I do panel drawings for Contractors I work with that do stick building as I’m often doing the whole design so all the cad / model files and so on are already set up with grids, levels and so on.. you need a bit of practice to do this well and most importantly you need to know what kind of joiner / contractor you are design for as one part of the job is to play to their strengths. It can be difficult initially to find joiners who will take the job on. That said I recently did a 250 sq metre + single storey house with complex roof where the Client specified stick build as this suited his preferred contractor. Cost to do the walls panel drawings about £1750.00 with a bit of prefabicated roof truss specification /detailing chucked in. Once you have the panels up you can then shop about for insulation and so on, you can change your mind! Stick building gives you more flexibility and choice. “Thanks for the reply so this design is fairly cheap to do if i dont open any of the downstsirs rooms up? Could you give me a rough cost for a house like this, average/basic spec” Would love to but prices are all over the place. The main thing is not to get to hung up on the timber kit. PeterW and plenty others on BH I think (and I agree) suggest that the super structural frame is only 10 – 15% of the cost of the job so even if you pay more for the kit in the round it’s not a disaster. “yes he budget is tight but would i not need joinery skills and time myself to do a stick build?” To build a kit for the first time DIY you’ll need to be fit! You’ll also need some joinery skills and an understanding of wood.. post for another day. “so a standard joiner can built these stick frame houses up to the spec of the kit providers?” No they need to be familiar with TF construction, know their way around the types of metal fixings and how to fix. Etc. “Our original design was 2 storey box shape as it was an easy design but refused, the next application needs to be materially different so i thought lowering ridge height would help planning and roofs in roof would be cost efficient, are those designs I’ve shown quite expensive? Dive back and review for example the Scot Gov permitted development rules, then see where you don’t comply and address as you can. It may seem like basic stuff but in doing so it will increase your confidence and allow you to get the best out of this. “They basically commented on the size and visual impact so i thought lowering ridge height would be a good place to start? no real limitations to plot size” Have a day out walking about the area, see what else is out there. Imagine you are a planner! Good you have plenty land as this is a real bonus. Also, when you walk round and about your land you can get a better feel for the shape, contours and so on from a distance rather than just standing in the middle looking outwards. ”This would be a cheap design as no dormer windows and use of roof for upstairs? “ Old rule of thumb.. allow 3- 5K per standard 1200 – 1350 wide dormer if new build. If attic conversion folks.. the price can be a good bit more. “Thanks for the feedback, is there any way to avoid these big steels for the vaulted ceiling? steel is not cheap just now” Don’t get too hung up on this for now unless you are going for daft / pretentious vaulting and huge spans. Concentrate on the layout that suits you. Your big construction savings often come from setting the building at the right height with respect to the existing ground, foundation design, drainage design, access, services and so on. The immediate value comes from getting the house to meet your dreams... just a great home to live in and.. in doing so you make it energy efficient, sit well in the environment for example. If you do this then the house will also maintain its long term value. All the best.

Hiya @notreadyforthis I don't want to cause you undue concern but I would again urge you to get your SE round for a look in the interests of safety and to set your mind at rest. Diplomacy is probably at the top of the list as you seem to be getting on ok with your builder? Interestingy the steel packer plates are probably not a major issue in themselves, but they provide a slip plane that your SE may not have designed for. What it suggests to me though is a possible lack of skill / dilligence in setting out / your builder not reading the drawings. It looks like you are taking a chunk out the corner of the building. When you do this it introduces a lot of overall building stability issues and it is really important to follow the SE's drawings to the letter. If the builder wants to make even what appears a minor alteration it can have a major impact on jobs like this. The builder should always ask the structural designer first if it is ok to deviate from the drawings. "Thanks for taking the time to comment. It gives me things to ask the builder about. I'm sure he'll have a good response but I can usually get a good read on whether he's trying to wing it. The beam where there appears to have been a cut is interesting as it didn't get delivered like that. i also note that the bolt holes aren't centred as they are in the drawings. These steels should have been ordered according to the structural engineering specification. I've got the docs which have all the calculations - none of it makes any sense to me though. The building regs guy has also been around to check it out - would he have raised any of the same concerns as you have or do they not check those sorts of things?" Don't rely on BC to be a Clerk of works.. it's not their job. Also the points I make re the connections and stability are of a more specialist nature that are more in the "wee world" of SE / steel fabricator / steel contractor types rather than BC. Cut BC a bit of slack as they can't know it all, just as SE's say don't know it all. Hope this helps.

I would urge you to get this reviewed by an SE say before you go any further. I can't see quite enough from the photos but.. That connection in picture two where one beam is framing into the web of the beam that seems to extend outside is highly questionable. It looks like someone has made a mistake and been cutting, altering the connections on site. The bolts look like M12 diameter, possibly undersized.. not just to carry the vertical loads but also to prevent other things from twisting. The beam has an unexpectedly large notch. You have some top plates on the steels but the spacing of the welds looks quite large. Also, you seem to have a couple of beams in the depth of the floor above. This coupled with the steel section sizes suggests you are holding up a fair bit of load and that the load is not always centred over the beams. In picture three the beam seems to extend outside so can't see how it is all supported. I know it's not finished yet but it looks like the works are quite extensive. I would at some point expect to see much more tying together of the steels, timbers and masonry so that the overall assembly is stable and safe globally. The padstone supporting the steels seem to be cast in place. This is often acceptable and can be advantageous at times, have done this on my own house for example as it can really help tie the brickwork below together. However I would also want to have a look at these in closer detail. Sorry about the above but I would get this checked out professionally by an SE for example.

Hiya. Yes I think your SE has put a bit of thought into it. Can it be changed? On the face of it you would move beam 9 to line up with beam 12 and that would open up the stair well. But the load from beams 9 & 10 would move from roughly the 1/3 point of beam 8 to its mid span so the bending forces not least in beam 8 may increase, I'm not sure though how much they may increase if that much as you will have to support less floor area. I can't give you a definitive answer as I don't have all the info.. but ask your SE the question as it may be simple to change. They may be a bit peeved as I think they will have put a good bit of effort into this.. so you may need to part with some cash. But if you don't need the floor space the extra light may offset any aditional SE fee. But perversly if you are going to sell the house on the every sq metre of floor could count.

@RJHumphrey What a stunning looking place. This rendering.. do you really have to do it, even if the other walls are half or a bit worse you will knock value off it, not just financial. It would be a real shame to render a beautiful place like that. Technically if you render some walls then you'll have to design for a wall that breathes and others that don't. The interfaces at the corners will be complex to say the least. As an over view always look at how you are going to say wire and plumb the place. Work out how you are going to do this and maintain / alter at a later stage and the practicality if you have insulation placed hard up against the stone. Remember for example that electric cables placed in insulation need to be heavier or need shorter cable runs which may be hard to achieve. It's not easy fitting 4.0mm cable into a 13 amp standard socket. Yes there are different views on whether you insulate these old buildings with an internal frame, a cavity between the walls and the stone or an insulation system with no cavity. But structurally you often need to tie the old walls into say a mid floor.. often with a chapel and this means complex penetration details at these levels which are hard / costly to achieve. Yes if you have an internal frame with a cavity you to some extent create a bridge layer when doing you U value calcs.. but in practice you are talking about a cavity with trickle ventilation not a howling draft. In the round you may want to take the hit on the reduced U value if you have a cavity but the buildability savings especially at the corners and floor often off sets this. Use these savings to load insulation into the floors and roofs where it is easy to do, more buildable? The key for me.. if that place was mine..well it's not.. but I would look first at the pointing, external drainage and the general weathering details. Pointing is the key as even wind driven rain will be mostly shed by good pointing. If you want to experiment find a bit of that river stone, dry it out in the oven and put it half submerged in a bucket of water. See if the top gets wet and the split it in half. Observe. In summary when you insulate you make the stone wall cooler. Generally the humidity is higher inside the building and this air that contains water gas gets into the wall. At some point in the wall the gas turns to water.. called the dew point. Now the dew point in an old wall is hard to predict as it is a natural material made up of a mixture of random rubble and dressed stone. But you can be sure that you will shift the dew point inwards when you insulate. From a buildability point of view it is very quick to put up an internal timber frame, at the worst case it is also a reversible process and easier to intervene if a localised problem occurs. Look at this in the round.. you can create an energy efficient house but energy efficiency and eco friendly is also about making it easily maintainable and adaptable over its 50 plus year intended life span.

Back on topic. Probably telling my wife that our alterations would take 2 years to do worst case 3.. in 2017.. still not finshed. Not overspecing (putting in more) the insulation.. just got the latest fuel bill in from Bulb.

1/ Non vat registered. Well the current vat threshold is £85k and equates to two or three modest extensions a year for a builder if they do nothing else. Now if a builder is experienced in extensions they should be doing a few more than that. Ok if they are not vat registered then questions need to be asked... such as.. are they a limited company.. if so be very careful before you part with money up front. If not limited find out if they own their own house so in the worst case you have an asset to go after. However they may be starting out on their own but do have sufficient experience so don't rule that out and take care... but generally there is no free lunch here. Its a red flag this for the unwary. If you have to make up front payments only risk what you can afford to lose. No vat / cash = more risk for you. 2/ Your SIPs panels have to sit on a pretty level base and can't be altered. Watch your payment schedule to the ground worker as unless you are absolutly on top of the found setting out and levels then you are inviting a lot of grief. 3/ Word of mouth recommendation. Ask not least your Architect and the folk that are putting up the kit. They maybe will know who builds good bases / underbuldings and who to avoid. All the best.

Hi all. I can't quite see where all the supports are to the steelwork but there are plenty things that could be going on here and the SE looks like they have spent some time thinking this through. It's looks quite elegant really even though you have a bit of cantilevered floor that with hind sight you may not have chosen at the Architectural stage. Let's start with the basics. A steel beam is designed for "pure bending" called its moment capacity (Mc). This is often where the steel starts to yield and fail but the beam does not distort or twist sideways. Beams can also fail in buckling where they just twist and distort and collapse suddenly. Often you find buckling (Mb) is the governing criteria. We call this (Mb) the buckling capacity of the beam. Long beams buckle easily so what we do is to fix floor joists, floors or other beams to them to prevent them from distorting / twisting / moving sideways and thus we increase the buckling capacity as we shorten what is called the effective length.. that is simplistically the distance between restraint positions. If we do this well we can in cases increase the buckling capacity up to the Mc capacity and thus get most bang for our buck. Lets start with beam 8 and lets assume there is not much restraint from the floors as the joists span beam 9 to 7a. The SE may be using quite a stiff connection from beam 9 to 8 to stop the twisting / provide torsional / twisting restraint to beam 8 thus increasing it's Mb (buckling capacity) significantly. If you don't do this then often you need a heavier and deeper beam. They may also be using beam 12 to further reduce the effective length of beam 8. As you come up the stairs on your left hand side there is the stringer with spindles above and behind the stringer there is a space before you seem to find the first potential support. It actually looks like the end of beam 11 is supported by beam 7a. Thus beam 11 spans from 7a to beam 10.. it is beam 10 that is holding up one end of beam 11, 7a the other. Now for beam 10 to hold up the end of beam 11 it needs to act as a cantilever off beam 8, but if beam 9 was not there then beam 8 would just twist and it would fall down. I think the SE has designed a very stiff connection between beam 10 & 8 and 8 & 9 so that 9 & 10 act as a continuous beam, supported at one end by the outside wall and by beam 8 at the joint. Lastly you also find that where beam 9 rests on the wall the SE has made sure there is enough back weight to stop this end of beam 9 lifting upwards.. like ballast in a boat. That looks like one possible hypothesis but a caveat is that we have not seen all the info, support detail and the global structural design. Lastly the diagonal bracing. I have touched on a few but not all the facets of this but you can see that the steels will be doing a lot more than just carrying the basic loads. Everything will be wanting to twist, bolted joints will slip here and there so I think the SE has introduced the diagonal bracing to stiffen things up. Also the diagonal bracing may be providing global stability to resist wind loading. In summary don't remove beam 10 or any other for that matter without asking your SE! Also don't let your fabricator / metal worker change the SE's connection design in any way without asking. If you have read this far then thanks. Gus

To excuse the pun. Rather than interfering with your neighbours tiles can you create a rain screen effect. Here you would fix maybe a metal channel type section to the good bricks, could be timber protected by dpc. The rain screen would belong to you but over sail the neighbour's tiles. You could run Code 4 lead vertically, say in 900mm lengths so manageable and easier to fold neatly. That may be enough to solve any problem and allow air up behind the "rain screen" lead? If you are using lead don't forget to coat with patination oil on both the front and back of the flashing. You would need a wee nifty bit at the top but if it looks promising in principle the you should be able to devise some kind of capping flashing?

One of my mentors was Professor Ian MacLeod of not least Strathclyde University. He taught me about the importance of having a robust energy mix that could withstand environmental and geopolitical shocks. He has been lobbying the Scottish Gov for years about this.. fell on deaf ears. It's often overlooked but folk don't realise that natural gas is used to make the precursors for things like plastic.. heart valves and so on. Ineos at Grangemouth in Scotland is prime example. Wind turbines make electricity but no byproducts for say your electric cars.. that need also needs a lot of plastic and faux leather. Coal fired power stations make fly ash that we use in low carbon concretes and as a retarder! So we now buy fly ash from China.. who are building apparently a new coal fired power station every week..

Great comments from all. Interesting to read all the views. For the budding loft converters a few observations. As a designer your starting point is to establish what folk want out of their conversion, what will meet their primary needs and then, aspiration. Next is to get down to brass tacks. You have planning constriants; ridge height, eaves alterations, what you can project from the roof.. dormers or Velux or in some conservation areas.. mme. From a BC compliance point you look early on at how you get a stair up and fire protection. A critical dimension is to see if you can get the clearances for the stair in terms of head height. Lastly you have a look at what kind of headroom you can achieve in the rest of the proposed converted loft. If your Clients are all six foot six plus then you need to say.. hey you are quite "blessed" but you ain't going to enjoy this even if you comply with the regs. On the other hand you can be "blessed" if you are of shorter stature. Everyone on BH is blessed! Next you delve a bit more into how you may insulate, do you need to replace the roof, get any drainage to work and so on. You look for booby traps that could burst the ball. Now have a look downstairs and where you can support load by means of load bearing walls. What are the Client constraints... do they want to live in the house or move out say. This then gives you a flavour of what to explore structurally. Once you have got this basic information you open your SE tool box and see what will work best, not just in terms of pure structural design but also what will best fit the local contractors. Good design is also about designing something that is elegant and buildable at a reasonable cost. That is the art of structural design. Next you iterate and go back to the Architectural side of things and this lets you design Architecturally in the knowledge that what you are doing has a sounds structural footing. Now you may then want to use Glulam beams..maybe an oak ridge beam for a feature if you have enough height, use sistered joists, steels, cold formed steel.. sometimes very little structural "extras" are required and this feeds into the Architectral design. which is the bit you see at the end of the day. In summary your starting point should be as above and as each attic and floors below are often different it is almost impossible to say "this is the way". If anyone wants some pointers then the best thing to do is to post some sketches thah show for example the span, height to the underside of the ridge, walls below. Rough it out on a bit of A4, take a photo and post. Don't worry if they look a bit rough.. you want to see mine! Lastly while some materials may best on paper to use.. say steel, glulam, cold formed steel the design decisions can be driven by the type of builder you have available. Say you know a great joiner that buys a lot of wood and gets a good price. You may want to play to their strengths and use Glulam that they can buy using their regular account, rather than steels that they may have to pay "punters" prices for. At the end of the day this can work out cheeper for you.

From an SE point of view that house look reasonable structuraly efficient = lower cost and fairly buildable. There are good few cross walls on the ground floor so easy to stabalise the building. Floor spans are modest and so on. The gabled parts of the roof will probably need girder type trusses but there is plenty available support for them. If you like the design then you could start to tweek it but the structural cost will start to rise significantly if you really want to open it up. And if you do that then you need to go back to the drawing board and start afresh. There are plenty ways of doing a 1 1/2 and 1 & 3/4 storey house. Enjoy the journey.

Ha ha.. you are not supposed to tell folk that I'm an SE.. cats out the bag now.

Hope this gives you some pointers. Lets start with the abbreviation.. ICF.. insulated concrete formwork. For walls the insulating blocks act as a shutter (formwork) to hold the wet concrete in place while it sets and then cures. The blocks themselves for walls make no contribution to the structural stength of the concrete wall. The choice of insulating wall medium has no bearing on the strength of the wall to resist the vertical an horizontal loads. The choice of block has no real bearing on the amount of rebar you need in the walls. Not quite, but let's keep it simple for general costing purposes for now. Some complex behavoir can happen at the bottom of the wall, depends on how and if it (the wall) is positively fixed to the floor slab. However it when it comes to the floor slab things change a lot. If your insulating blocks go down the walls and continue under the structural floor slab then the building is supported by the insulation, which rests on the ground below. What SE's do to design this is to look first at the ground.. how squashy is it, one property they look at is it's elastic modulus... a property of squashyness! Next step is to look at the insulating blocks.. how squashy are they. Hopefully you as an SE find the insulation is more squashy than the ground below. If so plane sailing. You design for the most squashy layer which is the insulation, there are other methods but this is the most common and practical for domestic design. Thus if you have an ICF block rated at 300 kPA at 10% compression (30 tonnes per square meter at 10% compression) you first say how thick is the insulation? Say 300mm thick so 10% of 300 = 30mm settlement to get your 300 kPa out of it. Now 30mm settlement is too much to tolerate normally. Also, you may have insulation that creeps a bit over 25 -50 years.. bit of a worry. Lets go for a figure of 2% compression and see what load we can put on the ICF blocks. Thus 300 * 2% / 10% = 60 kPa = ~ 6 tonnes per square metre all nicely spread out. Closer but we need to watch out for point loading and so on. Now there are many ways of carrying out the next steps to determine the shape and form of the supporting slab that sits on the insulation. But basically you strike a balance between the thickness of the floor slab and the amount of rebar you chuck at it. The easy way to get your head around this is to think about a bending a ruler. If you do so the top is in compression, the bottom in tension. Thus the thicker the ruler the less force on the tension side. Now concrete is good in compression but poor in tension so we use steel bars which are bonded into the concrete to resist the tension force. Thus for your ICF floor slab if you make it a bit thicker you'll often need a bit less rebar. But there is no free lunch as you'll need to pay for a bit more concrete. But the secret is often in reducing labour steel fixing cost, reducing complexity and avoiding on site errors. Lastly designing a ground bearing slab on ICF is not the same as designing a concrete slab that you may see in a multi storey carpark. The slab interacts with the ICF and ground below and thus the design approach is different. In summary @Ben100 if you choose a higher stength insulation under your floor slab you'll maybe use a bit less rebar and concrete, but you'll lose some of the insulation properties so will then need to make it (insulation) thicker to achieve the same u value.. and making it thicker will result in more movement.. who said self building was not fun! The best advice I can give is to seek out the most practical and buildable solution for you. Always start with the simple stupid. See how much that costs and then if you have spare cash explore further. Your simple stupid option is your bench mark. The weight of steel you need will much depend on your slab and another of other factors. To get the best out of this you'll need to post some pretty comprehensive drawings so folk can see what you are proposing. All the best.

Hiya. Yes if you can post some drawings then folk will chip in with value added comments. The main thing is to post so folk can see the roof space, plan view and sections and where the load bearing walls are below. You probably have plenty options but to get some practical SE type input then the drawings are required. Also let folk know if this is your "forever home". There is probably lots you can do at this stage so now is the time! maybe?

And there lies a potential problem. That is a big opening. When the wind blows on the glass the frame around about need to resist the loads. The central pane of glass is vertically spanning. The bottom rail prevents it from moving in and out. At the top there is a gap and the fixings are subject to a lot more bending force. For fixings to realise thieir full capacity they also develop a "second order" tension effect. They can't develop the tension as the compriband compresses and the frame at the top will bend upwards / twist under wind loading. One thing that stops the movement and saves the glazing companies is that the plaster board, masonry check outside / or the mastic lasts just long enough to make it very difficult for the home owner to complain. Bifold doors can be even worse as when they are open they rely on the top part of the frame to stay rigid, it does not have to be windy to cause a problem. It's a dilemma once you start to delve into it!

Nod.. see when you are sticking on the external corner beads for rough cast do you mix in a bit of old gypsum plaster to flash set the dabs on the beads?