Gus Potter

Ok. If you fancy let us see the drawing (include the weathering detail if possible) and a few photographs of what's been built so far. What's the beam span and confirm the loads if you can. Has your SE provided calculations?

That’s good news the SE is coming to site. It's also very encouraging to see your builder chipping in with their concerns, demonstrates competency. From time to time I use an unequal galvanised angle to support an outer leaf. They are prone to torsion and warping. Just as an aside, the angle is galvanised and the internal I beam is not. If there is too much moisture floating around the angle will become a sacrificial anode. Thus we could electrically decouple the angle an internal steel. Or we could paint the angle and make sure the drip above keeps it dry and protects the paint. I tend to plump for an I beam on the inside, especially if supporting floors, heavy roof loads down the inner leaf for example. You can use Cee sections, but again they are prone to twisting, torsional effects. Going into a little more detail. An I beam has it's centre of gravity in the middle of the section. There is a also a thing we call the shear centre. For an I beam the shear centre coincides with the centre of gravity. But on a Cee section the shear centre lies outwith the actual section profile! If you load a Cee section in the middle of the top flange it immediately twists. Now we can actually take advantage of this behaviour by making sure the floor joists for example frame into the web side, the flanges face towards the outside. But this makes it a bit harder to insulate as the inside of the Cee faces into the cavity. Below is an example where I'm using an angle on the outside and an I beam on the inside to support floor and roof loads. This project had a fair bit of steelwork thus the method I adopted of coupling the angle and internal I beam didn't add much to the over all cost. There are three thermal bridges, one at each end and one in the middle, but the coupling plates are thin and the work was to an existing build. Yes technically, thermally not perfect, but is does the job in the round. Part of the 3D steel model: There are three plates called F4. One at each end and one in the middle. The first detail shows the DPC arrangement etc. The next two show a plate called F5 welded to the back of the angle and a plate F4 welded to the I beam. F5 has a slotted hole to allow for tolerance. Below is a diagram of the shear centre of a Cee section: The shear centre is marked SC, the centre of gravity marked C. @flanagaj It might be worth you reading around this a bit (including the finish on the angle, galv or painted) and then ask your SE about it when they come to site so they can explain to you and the builder why they have designed what they have and explain to you in lay terms how it works. Well, lets hope they can answer your legitimate questions.

Hope this helps lift your spirits a bit. The following is a bit of "chat", but also serious at times. Firstly. Well done you for looking up some span tables, what you are doing is carrying out a "sense check", you've clocked that the joist span looks out with normal expectation. I agree you are right to question. Also @Roger440, no dafty is asking.. and I'm pretty sure @saveasteading, @JpManning et al may bring professional opinion to the table. The thing that disappoints me most is this radio silence you are experiencing. There is generally no excuse for this. This is a common complaint on BH, Engineers not communicating or just being downright arrogant. But on the other hand your Engineer may have fallen unwell, this happens more often than you think. I have a long standing Contractor on my books who is mentally unwell, I'm supporting him. His business is suffering, he is a sole company director and employs folk that rely on him for their income. It may be your Engineer is unwell? That said SE's in particular seem to be very poor when communicating with Clients. It's actually a core objective of the IStructE, ICE to communicate with your Clients. I would try and determine if this lack of communication is due to say ill health. You'll maybe feel bad if you give them pelters and then find out they are on their death bed. Ok your joist span looks.. questionable. But your Engineer may have taken the view that it's a garage thus, no brittle finishes on the inside, thus we can tolerate extra deflection, so long as the deflections are not too big we can handle that. If deflections get too big then they can introduce what we call significant second order effects. Us folk with knowledge of structural design get wary about second order effects when we relax standard deflection limits. What your Engineer may have done is to just to design the timbers for strength alone, relaxed the deflection limits, as it's a garage. But if I adopt this approach I'll always tell the Client I've done, why I've done it, get their approval and check to see if these second order effects are significant or not. Now if you have a flat roof on a garage and you can push the spans. Yes, the timbers may be strong enough (just to not break and fall down) , but if they deflect in the middle too much then we have to be very careful the fall is still enough so we don't get ponding of water or snow melt on the roof as this can be dangerous. I would try as best you can to establish communication with your Engineer. Then you can ask what they were thinking was when they designed your garage roof. The may say, I relaxed the deflexion limits to save you money, but neglected to seek your approval for this.

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!