Gus Potter

Quick reality check folks. Make things complex on site and you'll often pay for something that never gets delivered by the contractor. Wrapping the bottom of internal columns in Aroegell is daft.. because you need a small quantity (costs a lot) and someone has to go in the van to go and get it! That excercise just to procure the stuff could cost you £150 -300 or more which could pay for a lot of thicker insulation elsewhere at no risk. You may need fire protection so a bit of extra glass wool solves the problem and get you below the 0.7 U back stop value to stop regular condensation. The key thing that a lot of folk seem to be missing here on BH is that you can do a compensatory U value calculation. If you have a steel column poking out inside the house you need to make sure it does not drip with condensation. Again a back stop U value of 0.7 is about right with a vapour barrier to be on the safe side. There is a massive diference between an internal column and a steel column on the external wall in terms of cold bridging. An internal column is founded on the heated dumpling of soil so the heat loss is much less that the basic software is often telling you. You then compensate for the extra heat loss by beafing up other parts of the insulation envelope. But for such a small extra heat loss from an internal column.. it's next to nothing. This is a common sense approach that a lot of folk on BH are missing.

Oh and if you do this you will find that you are falling under the CDM regulations not least. Please spend some time investigating what you're getting yourself into.. hence the percentage fee rates I mention. How well are you insured to do this? It's not just to protect you it's also for your Client in case you get run over by a bus. You have a duty of care and while it sounds great to help folk out when you do so things have to be set up correctly.

To put a bit of an impartial slant on this.. @nod is highly experience, has time and also has a day job and contacts in the construction industry? Now I'm not going to cast stones as I use to be a Contractor and also had plenty of employees and subbies that I could chuck at my own stuff and make the money work. Nods figures are probably achieveable if you are set up this way.. but this is a self build forum and I can tell you (I do this as a day job) that Nods rates are "optomistic". But also Nod works like a fiend seven days a week! Nod has some serious commitement and deserves the reward. But often folk on BH have young kids so you can't do what Nod does. My hat goes off to Nod for commitment but most of my Clients just don't fit into Nod's mould and we need to reach a compromise and the build cost goes upas a consequence.

Given the size of this project and complexity my advice is to diplomatically extracate yourself from this. If you are intent on pursuing then you need to be commanding a fee of somewhere between 8- 12% of the build cost. Set out the deliverables, get paid in stages and get a good QS in right now.

The following I hope gives you a flavour of the design but also the liability that lies with the designer and that, I hope, will help folk on BH get their head around some of the SE type fee costs. Well done @Alan Ambrose for digging out this article. The author takes one of the CPD courses on Eurocode concrete design I have been on and interrogates it in a bit more detail.. and makes a good job of it too! For me this is part of my day job so am familiar with the terms / design calcs etc and how the Euro codes go into more detail and the theory behind it.. such as restraint conditions, ageing, restraint at slab ends.. a long list. But for all on build hub for the critical thing to take away from this is the bit at the end of the article copied below. "Firstly, the design need to be realistic. Blindly throwing reinforcement at it can do more harm than good. Good detailing is particularly important for complex geometries. What’s more important is to try and have simple geometries in the first place". In other words you can have a fab house but keep the underlying structure as simple / stupid and buildable as you can. That drives down cost, reduces risk and lets you spend your cash on the thing you get to see and enjoy. Hiya @SteamyTea If I could I would give you a double cup award.. I've learnt loads from you.. For all there are some folk like Steamy and to do a name check @MikeSharp01 who are fantastic educators. I'll give it a go and try and cover some of the concepts for folk on BH. but excuse the spelling and grammer please! For all the below applies to lots of other things you might do not just basements. Ok take a simple concrete reinforced beam spanning between two walls loaded from above. The bottom of the beam is in tension and the top in compression. Concrete is quite "stiff" which means that under compression is does not compress much. The bottom of the beam is in tension. Concrete is not so good at resisting tension so we introduce steel rebar in the bottom of the beam which has lots of tensile strength and now we have a reinforced concrete beam. But steel is quite stretchy compared with concrete. For it to work the steel rebar needs to be bonded to the concrete at the bottom of the beam. For the beam not to fall down the tensile forces in the top of the beam need to balance the tensile force in the bottom steel rebar. But to achieve the balance the steel needs to stretch first thus we get cracks in the bottom of the beam. The same principles applies to basement walls. Call this behavoir primary cracking. To limit cracking we add more rebar area so the steel does not stretch as much. In other words when we design reinforced concrete we make sure we have enough rebar so it does not fall down.. then check that we are limiting the amount the steel stretches by so we limit cracking. Now it gets complicated. In a reinforced concrete wall we have a large area of concrete that as @Alan Ambrose article points out undergoes a number of "experiences". Concrete goes through a number of phases when you pour it in to say a basement wall. Broadly speaking cement (part of the component in concrete) needs to start getting it's act together within 4 -8 hours ( temperature dependeant) and this is covered in the BS standard for example. This means that the chemical transition gets underway. This causes a lot of heat which makes the concrete expand. After say 24 -48 hours the concrete starts to "bind".. the aggregates, cement any additives and we get what is called plastic shrinckage.. which can be quite a lot.. in other words the concrete is still in quite an excited state for a better word. After a bit of time the concrete starts to dry out and we get what we call drying shinkage. On a raft slab.. say on an EPS raft slab we also get funny behavoir at the slab corners call "curling".. which is basically all of the above having a laugh with us. @SteamyTea The secondary reinforcement is primarily intended to deal with the behavoir of the concrete during the curing and drying out process. It is a bit of a guess but if you look after your concrete for say a month after it's poured you can do a lot to help yourself in terms of getting what you have paid for. Quality of workmanship is key. I've copied below a bit out of one of my specifications that I wrote for a self builder for a floor slab. The idea of this is to provide simple instructions for what you can do on site to address what is a very complex problem. Designer liability: From the above you can see that this is fraught with liability if you are say an SE / designer like me. My PI insurer goes nuts and wants to know exactly how much liability I'm taking on. @Alan Ambrose article deals with Eurocode design which if applied well results in lean and cost effective design.. but it is predicated on all the Contractors etc doing their bit very well.. the construction industry in the Uk is not often up to this standard. So when it goes wrong I'm for example the first easy target. Now folks if want to pay me for taking on that liability then I'm fine with that.. but the only way I can do that is if I come to site often to make sure that the contractor is doing "EXACTLY WHAT I REQUIRE" no if's or buts! However while that sounds great you will need to pay for an experienced contractor who is used to having someone like me holding thier feet to the fire. Self building is about finding the right compromise.

It's this thing where folk think PH and you need to eliminate every cold bridge.. even columns that are internal.. it looks great on paper but the cost outweighs the benefit.. your door handles are a cold bridge for example. Building houses requires a common sense and practical approach. Yes you do to you achieve a back stop U value. For a column like this that is founded say 450mm below finished floor level then it may achieve the back stop U value anyway with the fire protection and associated air gap. Yes it usually is enough.

Yes.. some of that mesh looks really conjested. I would send some photos to your SE before pouring and make sure they are happy with the layout. You'll need to be right on the ball with the concrete compaction. Scottish BC may ask for photos of the rebar.. if they don't match up with the SE's design you may have a problem! Be safe and get approval for this now from the SE and then you can sleep soundly!

I like this approach.. it's like passive stack ventilation simple and effective. No maintenance. In principle I'm all for PH type houses.. what I'm not in favour of is designing in elements that will require costly maintenance in the future and possible early replacement.. When I see folk doing this I think vanity has taken over from sanity. Off now to support England at the footy.

Are you able to get some work in the building trade even part time at the weekends? This is where you will be able to supplement your academic learning with hands on stuff. If possible get work local to where you want to build.. much of self building is about contacts.. the folk you know, the ones who do a good job and have "flexible methods" of payment. It is possible I think. I'm a firm believer that if you work hard you generate your own luck. Also, at times, you may feel that this is a mountain too high to climb. Do it in small stages.. get to base camp first then plan and prepare for the next part of the ascent. I wish you all the best and keep BH folks updated if you can.

plus 1

Love this solution.. so simple but very accurate!

Good suggestion as a starting point. The justification for the 665mm comes from general guidance for small buildings. Once you move away from the the general guidance these simple (but also conservative) rules no longer apply. Yes agree on looking at wind posts. Your SE may well have gone for the simple option to save you money. What is also important is you maintain overall building stabilty so it does not blow sideways in the wind, or lean over if things are a bit off the vertical plumb. Suggest you go back to your SE and ask them what needs to be done to meet your requirements and the cost implications. A good SE will be able to walk you through the design issues and explain in laymans terms what it is all about. Then you will be in a position to make an informed judgement. Communication is the key!

For me I would weigh up getting a bit of professional advice (say £300 - £400 + vat) against say a days builder's labour and materials that could prove a waste of time.. or make things worse. I hope the following helps a bit. Take an old building like yours 1920's. Door frames tended to be made out of 6" x 2" timber with bricks over. The bricks and timber interacted a little so developed what we today call composite action.. in those days they knew it kind of worked but could not quantify it. Window frames were more sturdy timbers and these too interacted with the surrounding walls. I see this a lot where folk are making open plan spaces and wonder why I want to introduce wind posts and other stuff. But I point out.. hey you now have PVC windows which are very flexible.. some silicon and plastic DPCs which create slip planes.. so now there is no interaction and things start to bend / protest. For me I go back to the way to when the building was constructed.. try and understand what has changed and when.. then try and work out what to do next.. in a cost effective and buildable way. To do this well you need to examine the whole building to get a feel for it and then look in detal at the windows / doors etc.

Hiya. Sorry if I caused a lot loss of sleep, that was not my intention. Indeed, I did not have the full picture as you fed the info in dribs and drabs. For all on BH.. If you have structural concerns then for someone like me to make reasoned comment I need to see where all the loads come from and where they go. If I can't see enough I need to be very cautious.. and this may seem heavy handed at times. @Mulberry View I've copied and pasted some of you text and comment in line. "Is directly from Pasquill's design, which has been agreed with my engineer. The whole of the first floor is in the same principle. Are Pasquill's design engineers not capable of engineering this? " Yes they are. In fact Pasquill's started out just down the road from where I live and I used to work with them on and off. Their lead Engineer was very talented, the owner a talented business person. As I understand they merged with one of the big outfits. If they have the same quality of design team and leadership then they are more than capable. But just to be sure, my SE spec'd 195x47 for the Ledgers for the first-floor joists after examining the scheme before it was signed off. The same principle was used for the roof ledgers, so they are probably overkill. Not looked at that at my end. If I deviate from their designed scheme, will they underwrite it? If you were the engineer here, would you underwrite it if it hadn't been installed as designed? No. But.. in the heat of battle on site sometimes the builder needs to adapt. A good one will often get it right.. often over compensate. Just because there may be a deviation from the design doesn't always mean disaster. The main thing is to spot any deviation early.. check to see if it is ok, if not fix it.. often a belt and braces solution is adopted. Everyone is happy and it all gets signed off. I think you know the answer to that, so for that reason, I have installed it to the absolute letter. So what could I have done differently? Questioned Pasquill? Questioned my SE? I am a ruthless worrier, so I have done both and both times the same verdict was returned. For all. If you have any doubts then ask questions. The easy way is to send photos to the design team and say.. am I doing this correctly? This is the safe and cost efective way of doing things. Fun Fact - My First Floor has been engineered using predominantly top-chord hung Posis and cleared for the 750kg loading needed for a large bath upstairs, along with a 2.3m high 2.6m wide 3-sided triple-glazed Oriel Window. I can't imagine what that will weigh. You can work it out pretty quickly to get a ball park figure. All the best with the project.

@ETC good detail. The vertical strut at the joist end seems to be missing from @Mulberry View? This omission of this dramatically changes the forces in the metal web for example. Best just to seek clarification.