Gus Potter

You outside corner post is going to get a bit of uplift. Depends on where you are in the UK. That is the SE starting point for wind uplift. How much of the slab can you mobilise to resist up lift? You SE is going to want to know how the slab is reinforced. Now even if you know that you can't be sure where the rebar is. If I was designing this I would want to make a base plate that is capable of alternative fixing, you start to drill a hole, then hit the rebar.

Just a few comments for a bit of fun. Things I like about the Yanks, oh can I include Canadians? 1/ I love the way they often do stairs. They knock up the structural part in cheep timber. Then when all the messy trades have gone they over clad in high quality timber. 2/ Yes when you have a big house the soil dumpling in the middle needs much less insulation. @saveasteading and I know that the majority of heat losses take place around the perimeter of the building. On a big house we will take advantage of that and insulate the perimeter more. Also take the perimeter edge insulation down to the top of a strip found if we have one. 3/ USA and Canada have a huge variation in climate. They deal with the different types of soil, the presence of trees and frost protection in a different, arguably a more pragmatic way. In the UK the default position from SE's etc is to refer to the NHBC guidelines for example.. we can end up with trench fill going down to 2.4m depth, then forced down the piling route etc, just to satisfy BC and to be arguably lazy. This all costs money. Yes, because our politicians who are making policy are generally complete idiots. But on the other hand no, because we often in the UK have this "conscience", for example we consider making reparation for slavery a good idea, forgetting of course it was the Brits that strove to end it. Our commitment to that apparently was absolved in 2015? We seem to also be making the mistake around this drive for energy efficiency, it's zealotry at times, but for many it just "feels good" and are happy to pay for that good feeling. Fine for some, but if you are on a low income, getting taxed to death then you may take a different view? I'm all for building energy efficient homes, but it's got to be pragmatic and evidence based for the UK in our political climate / approach which is not going to change drastically over the next few years. 4/ I have learnt a lot of the stuff I know about insulated rafts and their permutations from American and Canadian text / research. A lot of that is about designing cold stores, frost penetration, soil heave and so on, then reversing the physics at times to apply to the UK climate. It's actually good fun for me to see folk on BH coming up with all these new ideas. My job is to turn these ideas into reality by say calculation. Things I don't like about the Yanks / Canadians. A/ They sell us timber and sheet materials in converted to metric material sizes. B/ They post these videos of barbecuing sides of beef and shrimp, by 1100 hrs I'm starving. Now on the upside do you fancy Welsh Rarebit? To many, it's cheese on toast. But now you can do it with sourdough, chives, unsalted butter not least. Salted butter lasts longer by the way, hence why the salting for folk that could not afford to use it willy nilly. It's changed days.

Hiya Will. Welcome to BH! Your starting point here is to really understand how a flat warm roof works. Research this and it will give you a good basic understanding of the principles. It's essential that you have a impermeable VCL between the OSB and the underside of the insulation. Have a look at Alutrix type membranes. Once you get your head a round how a flat warm roof works that then pitch it up, as you now understand the basic principles. Key things that will change are that as you pitch the roof up to say 5- 35 degrees is that everything that is above the trusses will want to roll down the roof, like slip off. The fixings and roof make up need to be designed for this, what we call roughly rolling shear, to stop everything slipping off the roof! The fixings need to be carefully designed as the rolling effect causes them to bend not least. It can be done but you have to learn a bit more first. Much also depends on your actual roof covering, each type of covering needs a different set up. Give hybrid roofs a miss until you have learnt more. You're best bet is to post a sketch of what you think you may like to do.

If you want some better quality feedback then this is the way to go. There may well be a simple solution to this. You may not be seeing the wood from the trees. It maybe that someone on BH comes up with a simple observation?

You absolutely technically correct about the space frame! I'll try and reason out my thoughts. I do like your example of the racing car, same applies to certain types of boat construction.. solid timber, ply and plenty glue. You also not wrong and again technically correct. For a bit of context. I was delighted to be invited by @Square Feet to get involved right at the early planning stage of this project. My brief is roughly be the SE. @Square Feet Now referred to as SQ. The brief is fabric first, high levels of thermal performance, eco friendly all on a very tight budget. The house has to be elegant, play to the outstanding views, be functional for example. The budget does not easily allow us to just make the house bigger to solve design issues! Now lots of the materials we are thinking about using are for example hemp, wool based products and internal lime plaster. We need to take cognisance of the fact that some of these don't have the best fire ratings for example. The walls are going to be thick and that introduces structural issues around bracing the building against sideways sway under wind loading. We also have to be very careful to avoid condensation within the walls, could be a disaster if we don't set this up right. SQ and I have had a fair bit of correspondence initially. Then we had a preliminary design meeting for a day, just to meet face to face is very important. Our last meeting was structured so that it included me giving a one to two hour introduction to the basic structural design concepts, call that a "structures lecture". The objective is to allow SQ to see, follow and appreciate the types of things we need to do structurally so we can actually marry up the insulation etc with a structure that is not going to fall down, crack or protest later. The walls are going to be thick. If we want to use say Hemp and achieve as close as we can to passive house standards. The easiest way for me to describe this to SQ was to call it a space frame. It's not entirely correct, technically, but it's probably the easiest way to explain some of the basic concepts to a first time self builder. If I do this it means they have a basic understanding of SE stuff and this enables them to make better informed decisions. It removes some of the uncertainty that self builders encounter, gives them confidence. The house is going to rest on some ground that may have problems. I've plumped for a ground bearing slab at the moment. The slab is thicker than what you may often see. But on balance I feel it will allow me to reinforce locally without complex thickening at the edges or internally where I have point loads. While we use more concrete on the face of it, it makes it more buildable, easier to set out and arguably more carbon efficient, just due to the simplicity. The house is not heavy, single story. The design is very early stage. But I knocked up the detail below, just to explore for myself, not least, how I would fit all the materials together that SQ wants to use. CAUTION! The detail below is a concept to promote discussion, I know it will have flaws in it so do not copy! To explain the above. The inner timbers are vertical load bearing (the roof load). The outer timbers carry the vertical load from the cladding. The cladding vertical load is transferred back to the slab edge as the ply gussets are glue with a structural glue. The inner timbers are clad with structural ply, to resist the in plane wind loads (looking into the page). The glued ply gussets are rigid moment connections, unlike a standard truss used as a wall element. The sheet of more breathable ply on the outside also acts as a stiffening element, but if push comes to shove the ply can act compositely with the vertical timbers. The ply plates turn the wall element into a compound element so the wind suction and internal pressure loads get shared by the inner and outer timbers, then if I need to I can also increase the effective area of the timbers by utilising the ply, the ply turns the timbers into a structural Tee member. But in summary, yes it's not a true space frame, but close. We might say it's a version of the Larsen truss concept.. not really. Most familiar to folk will be the concept of using Posi joists as the vertical wall element or a flat timber truss, like on a flat roof, but as a wall element. But we only have the slab edge so we need to be a bit more crafty. To summarise. Technically you are all correct. I've used loose language. Once SQ and I get into the detailed design then we can come up with a name for this kind of bespoke construction that takes into account the types of materials we want to use and their nuances. But to finish I can tell you all, both SQ and I very much appreciate all your comments, every day is a school day!

It does. technically your SE may have designed the garage roof to provide lateral restraint to the wall, hence the built in joists and the bearing will be down the middle third of the wall. But hangers are not quite often as robust, the load path is slightly different. Practically, given your experience from what you have posted brickies are not your forte. The hangers are likely going to be all over the place level wise and you're garage roof will end up looking like a roller coaster. You are just digging yourself another hole. Now from memory your designer is not helpful, neither is your SE. If you want a bit of help with this then post some photos not least.

I would come at this in a different way. First would be to have a look at the design drawings, to understand what AFD intended. Are there any nasty point loads lurking about for example. @lizzieuk1To do that I would need to see the superstructure drawings ect, to get a feel for the loads. You may have design calculations, I would want to see them. Then my approach may well be to say, @lizzieuk1, well it's a localised thing, you are just short of the mark in terms of materials, it's just few sheets if that of insulation. Can we get an equivalent insulation off the shelf from a local merchants at a standard price, cut and assemble the layers to be equivalent to AFD design.

It looks like this is, on reflection, just an infill roof, like a small canopy that is constrained by substantial walls either side. Are we over thinking this? Vertical loads could be roof access, at a push, maybe snow dump coming off the higher roof. But the canopy looks like it has a good slope. I would go back and look at what is Architecturally pleasing, like your proposed joints earlier.

To add a bit. If you use traditional dowels, pegs then there is an old trick that was used in Scotland. We have lots of solid stone walls lined with lathe and plaster on studs on the inside. Timber wedges were driven into the stone work mortar beds. Then they were cut flush using a string line and the studs fixed to them. That is how they got the wall plumb etc. The spelling differs, as a traditional craft, but they are commonly called Dooks. But the secret was that they would dry the Dook's often near a fire thus they had a really low moisture content. Once they were driven into the wall they expanded. A traditional wall never gets below this moisture content and thus the Dooks always hold tight. You can use the same principle if you want to peg / dowel the way you are thinking. The dowels will need to be tapered as standard, but to get them really tight dry them out in an oven first. You could of course use a modern structural glue, but that may be cheating?

Are the posts just there to carry vertical load or is the beam and column acting to resist sideways sway.

But you have just posted one photo! You should know if you want folk to invest their time to help you then you need full inside, outside photos along with a good location of the property. Is it in Fife Scotland on highly mobile soils for example. Is it sitting over a tube line in London, is there vibration from a nearby road etc. Come on, you should know better than to just post so limited info. You have been on BH long enough to know better.

The unfortunate reality is that from time to time companies cease trading during the course of your job. We need to be pragmatic and say. Let's first understand the design intent, where the forces go and then seek an equivalent solution, it happens a lot! To interpret @Square Feet question a little further. If you are a self builder then you need to seek out designers that will explain to you what is normal industry standard liability that they will take on and what is not. Often designers are not as transparent as you may wish. I'm just up front about where my liability starts and ends. Each project is different, particularly on self builds. If a Client wants more cover then I'll phone up my broker and say, how much is it going to be to extend cover, then leave it up to the Client to decide what they want to do, pay the extra or not. One great example here is that one of the warranty providers asked me for contaminated land insurance. Now the fee for a contaminated land design may be less than 1.0k, but the clean up costs could be hundreds of thousands. There is no way I or my insurer's can take on this liability for such a small fee, it's just bonkers!

Don't cry and don’t apologise for a long read, you want to see what some of myself and others write when we get keen! As a bit of background I also design rafts, ground bearing slabs and everything in between. I share some of the stuff I do on BH, but also want to see what my competitors are up to. I've had a look at AFT's design details and I can see that they know their stuff, some of their designs are very elegant. Olaf is mentioned. He strikes me as being a very knowledgeable Engineer with excellent creative skills based on first principle design. If you are short on your modules then you can improvise. There are a few key steps to this. 1. When you improvise you have to be very careful you don't change the load path down through the insulation for example. The diagram below is probably more complex than yours. The hatch below the slab shows XPS insulation, the bit up the sides is PIR insulation. The key bit is that I'm stepping the XPS so the load transfer from the concrete goes down to the hardcore below in direct bearing at 45 degrees. The extra rebar you see and the square links are due to the fact that this raft is supporting point loads from an oak frame, and the raft rests on some engineered fill I've designed. The external plinth course, only extends some 5 - 6 courses above ground level and is deliberately decoupled from the main structural frame, partly for thermal performance for example. Now if you can get your head round this then you are well on you way to being able to sort the problem yourself. 2/ Next is to understand what insulation you could use to improvise. You want to get this off the shelf. Insulation is primarily specified with a certain compressive strength at 10% compression. EPS is very squashy, even though it seems initially it has the same strength as other insulations. If it squashes too much before carrying the load then it will compromise the structure, too much deflection for example, which will crack your concrete. Don't get caught out, check to see the insulation you use to fix this is not more squashy than AFD insulation specified. Post the AFD detail you have and let us all have a look. My gut feeling is that there is a simple and justifiable fix available to you without any drama. Keep your head up!

Title problems can sometimes be fixed with negotiation? By all means get in touch with me, you can find me easily on the internet or DM me. But in the round my preference would be for you to share as much info on BH as you can, to benefit other members. I without doubt don't know everything! I enjoy learning from others on BH. Stick with BH for now.

I appreciate what you are saying. A common complaint on BH is about SE's over engineering founds or say BC coming out and saying they need to be much deeper. For all. SE's don't deliberately over engineer your founds, if they did it would be a lack of duty of care not least. They have to balance what information is available against the risk. Often the reference point is say the NHBC regs, maybe BC regs. These in lots of cases can be very conservative. Often a Client has spent little time or money on even understanding the ground, the trees (species and height not least), looked at the local and wider topography, possible perched water table, the topography and where ground water may be flowing form and to. @Bonner if you are serious about buying a site that may have "issues" then you need to find a good SE that can help you. I have commercial Client's that keep me on a "retainer". They can phone me up for a 30 min chat for free, it usually ends up much more as we touch base, ask about family and so on, then get back to business, it's good fun. If I need to chip in and commit in writing then I charge a fee, which they are happy to pay as they appreciate the value I bring. Over time I teach them and they can progress under their own steam.. it might seem to the cynical I'm doing myself out of work.. but the more successful they are, the other parts of the design come my way. Now in terms of trees. The key thing is to learn about how they grow, different root depths, types of roots and how they influence the soil depending on soil type. Next is to understand ground water and typical soil profiles in the areas where you may wish to buy a plot. @Bonner Here is a play. Sometime it's best not to be discrete when pitching for a plot! If the plot is a bit blighted you figure out you own solution, don't tell anyone. Put you own value on it but publicise potential issues so your competition backs off! It also brings the seller to the table to spell out what challenges the plot presents. If they are that nosey and raking about about on BH then it's fair game? OK how does that apply to a first time self builder wanting to buy a plot. In the current market there are fewer plots with "clean hands", the ones available often command a premium. The ones with mucky hands are often avoided by developers, but they present a great opportunity to self build. They go a a lower price, but if you don't want to loose you shirt then you need to find say an SE like me or really know your onions. Your best bet is probably not me !, try and find someone local first. You need to find a local SE or a designer that really knows their stuff. Now the fee is going to be more, but a good designer will make sure they wash their face fee wise and will steer you towards the right price to pay for the plot.