Gus Potter

This sounds tricky! To add complexity often a crack will develop in the render / finish at each end of the beam as you transition to a different material. The detail of this needs a lot of thought!

An important thing to remember is that firrings get thin at one end. One golden rule is to make sure your fixing is going at least 2/3 of the thickness of the thing your are fixing (OSB in this case) into the strucural timber (the roof joists) until the firring gets to a sufficient thickness that it can be counted on to act as a proper substrate. For this to happen the thicker end of the firring needs to be properly fixed to the top of the joist. If I was to glue anything it would be the firring pieces to the tops of the supporting joists. This matters as often we use the roof as a stiff element that stops the roof and say dormer from twisting sideways.

Good point! No I don't think many elements were "designed" in the modern sense where we may do extensive calculations to cover higher point loads and settlement for example. Since man started putting up houses we have relied on tacit knowledge and practical experience. In other words we know what works.. but often it's almost impossible to prove by calculation. A 50- 60's house often relies on this knowledge base. Shallow founds can be quite common. They were building so many houses at the time that if the odd one suffered a bit from frost heave, near a tree it was not a major consideration. The important thing was to create employment ( East Kilbride new town is a good example) and to improve the living conditions of as many people as possible at the lowest cost. Incidentally this lead to what we call non traditional housing. The Builders (George Wimpey, yes this was his name, etc) were experimenting with new alternative construction methods.. some worked well, others less so. Remember that at that time we were trying to improve the basic quality of the housing stock.. an inside bathroom was a luxury in many cases. Another different case is in Victorian houses. The internal door frames are often made out of 6" x 2" timber, a goal post. From time to time if they had some extra load from above they would construct a shallow brick arch over the top of that (often called a relief arch) which acted compositly with the timber door frame. This is akin to a recent BH poster who asked about composite concrete lintels where the brick works together with a shallow prestressed concrete lintel. As a designer I love working on old structures as the challenges and nuances are fascinating. Often I'll refer to my library of historic design information to support my design assumptions when say BC or a checking Engineer ask for a bit of validation. One simple way to approach this is to calculate the weight of the existing building and the stress on the soil under the existing foundation and try and make sure that the new building doesn't exceed this load. When it does you have to think whether further settlement will occur, how much and how the existing concrete foundations have aged (often 50- 60's house). On Victorian or earlier houses with say brick spread foundations or big stones just laid on the ground this can in some ways be easier.. as stone does not age.. but the lime mortar does to some extent.

I'm not a spark, rather an SE / Designer. So here is a laymans question! Mind you I've see odds an sods hence why I'm asking. My though process is you have an incoming DNO connection rated at 100 amps. I guess as a layman that will be protected with a 100 amp sand type fuse just before the meter. This fuse is not really intended to protect you, rather it's to protect the electricity board cables. Sand fuses don't blow in the same way as say a fuse on a 13 amp plug. The sand adsorbs the heat and delays the blowing of the fuse. If you say have a 120 amp demand then sand will heat slowly and then the fuse will blow after a bit of time. Draw 400 amps and the fuse will not last so long. This is maybe why DIY shed welders wonder how they can get more bang for their buck! I think there is a table in BS 7671 ( the sparks regs) that explains how long it takes for sand fuses blow depending on how much you overload them. The cable that comes into your house probably runs to a big local transformer. That cable might have a 600 amp fuse at the eletricity board transformer end. Now I faced a similar dilemma. What the spark did was to fit a 100 amp fuse isolater switch just after the meter. Then run a thick wire armoured cable and split that at the consumer unit end, hence overcoming the 3.0 m restriction on the tails. I have more than one consumer unit in my house, one is mounted above the other.. long story but each consumer unit is capable of serving one dwelling. To be a bit different the spark and I agreed to wire the house using radial circiuts, it suits me but it's technically less efficient than using ring mains for example. Now a couple of days ago the spark phoned me and said my industry (can't remember if it was SELECT or NAPIT) body wants to inspect some of my jobs, can the inspector come to look Gus? Inspector turns up and gives my spark work a clean bill of health.

I have a small project on the go. I'm replacing an existing conservatory and putting a solid structure on top and bringing that into the house insulation envelope.. but retaining what is a good solid base. The base (substructue and floor) is worth about 20k as it is elevated. The planners fought back but I played the sustainablity card.. as per the small print in thier guidance. That make the project viable. @allthatpebbledash I think that for the extent of the work you are proposing retaining the existing founds will not be cost effective. One reason is that you may want some open plan spaces.. that often introduces point loads that the existing founds were never designed for. Now you may need extra pads and tie all that in.. this is expensive labour wise not least.

It's a fascinating subject. For all on BH there are some general recommendations in the design codes, say for movement joints in brickwork / concrete blocks but mostly it's left up to engineering judgement and that is based on looking at the whole design holistically. Movement in buildings is one of the dark arts.. it's taken me 40 years to grasp the basics and I still learn from day to day. A green oak frame is just a hard wood timber structure and we have a good idea about how this will move about and how to detail the other bits of the building that are connected to it and allow for the diffferential movement between the materials. All houses move about, bend in the wind and settle for example. Take a passive / semi passive raft foundation. It sits on a thick layer of insulation which is a bit "squashy" and here we that into account. When designing I look at the materials, what needs to be supported, say walls and glass and how they behave and interact, then say OK.. how can I force the movement (which I know is going to happen) to a place where I can control it better and how do I design the movement joints to cope with this particular structure. A simple example may be where you know you have tiled floors transitioning to say engineered wood floors. The common sense thing here is to force the design so the movement takes place under the door threshhold where it can be hidden and not crack the tiles. Probably because the folk had loads of experience and understood the materials they were using. Sadly in the modern world this is often no longer the case. Do you know if these buildings have fallen down? Mind you they may have masive cracks in them?

I assume you have gas hobs etc and showers running off a gas combie boiler and not on electric. Potentially do you have 4 ovens running on xmas day.. make it make sense please or is BS 7176 not all DEI?

I have, good solution! Eating some humble pie at my end. Hopefully still pals?

I'm trying to get my head around how this is an economic build. Yes go for the wow factor.. I love oak frames. They live, breath and move about, but ICF walls are stiff for example. Then you need to sit them on some kind of foundation, could be a raft and all the time you add unwanted weight. For me a small oak frame building should almost "float" on the ground and move with the ground and it's nuances. But if you take this design approach and then go putting in sensitive finishes such as large format tiles on the floor then you need to either spend more money in the ground or re detail your finishes. There is often no free lunch. But with a bit of eccletic thinking you can often have your cake and eat it.. if you put in the work to understand the building, the ground and put in plenty movement joints. Incedentally when designing raft foundations we might choose to make them very stiff with lots of rebar.. say if there is a mining risk. Here we want the raft foundation to "stay together" so the whole house tilts a bit without breaking it's back. But we also may design them to be quite flexible as the ground may settle differentially (a different depth of good load bearing clay from one end of the building to the other|) In some ways an an oak frame is suitable for a flexible raft (often cheeper) as we just take the view.. everything is moving about so let's live with that. So long as it does not fall down then it can be ok to have a house that cracks a bit and lives! Maybe that is an eco friendly approach to design? Well a plus + for that getting an SE in early. Good designs are about taking a view on things, exploring options, ruling out others, review, develop and review again. You have done the right thing gettting an SE on board early. This will allow you to look at the design holistically from the load bearing ground up. There are great savings to be made by adopting this approach. Mnay Build Hubbers don't do this. Cracking observation. That is giving me food for thought! Why.. because @saveasteading has tackled a really complex roof on a steading conversion. They got a competant local joiner to template the really difficult joints, some of the hip angles and joints were hugely challenging and then they executed the work effectively. Ok that was done in soft wood but you could easily do the same in green oak. The connection design is similar.. dowels or bolts. Oak is stronger than soft wood thus the connections (which often govern the design) are easier to make work. My gut feeling is that a local joiner may not have the heavy tools / fabrication facility to cut complex rebates say in green oak.. but for a simple oak frame it think it may be doable on site.. after all a simple oak frame is just like a traditional cut / purlin type roof.. with 1/3 checks in the timber for the ceiling ties, half checks at the ridge and so on.

Why?

No get this check by an SE. @IanR and all. Please don't dish out this advice / suggestions without knowing about the design philosophy. I respectfully suggest that you need to know not least about rebar anchorage, bond length and how that changes depending on the embeded depth in the concrete even if giving general advice on rebar. For all and at say @IanR there is some great general advice here on BH but a lot is contradictory when talking about raft / ground bearing slabs. The main reason is that the ground varies from site to site so needs a bespoke solution. It's not just the ground but often the slope of the ground and the water table. Funnily for me as a designer it's not the concrete slab or the insulation it sits (Kore etc) on that is the hard part to design. The really hard part / that risks my PI insurance (and your house) is often how much you need to dig out below the slab or raft! This is where the main risk lies.. in the ground under the insulation.

Nothing "thick" about your query. Good spot! Check with your SE as they should have provided this dimension. It's important for both top and bottom bar. Often on a raft found the top of the ring beam is in tension (hence the top bar) when we design for say soft spots or want to shed load (called partial fixity) from column point loadings for example. The detail you see with the top bar is probably the SE making sure the corner of the building doesn't sink (critical desing case) with the weigh of the external leaf if there is a soft spot at the corner.

Will be up for a bit, I'm researching some stuff I need to dig out for tomorrow, I'll drop you a quick note.

That's a good starting point recognising that some folk can shine a bit. There are good an bad eggs in life. Ah.. dealing with the public! or is it worse being a sub contractor for say McAlpine or a smaller firm that use you as a subbie. Seriously Nick we probably have a bit in common. If you fancy chewing the fat then PM me.

Good point Nick. To add a bit. If you nip down to you local B&Q and look at the floor slab you see what we call tied (call these sawn joints) joints at 4 - 6 m spacing. About every 18m you'll see a movement joint, tends to have metal armour each side with a big bead of mastic. B & Q slabs are mostly ground bearing slabs, no rafts. As an aside when I'm designing pallat racking systems we try as best we can not to sit the legs straddling the primary movement joints. Ok so 140 m sq. Say it was a rectangle 9.5 x 15 m ~ 142m sq. You could probably do this as a ground bearing slab with a few sawn joints or non at all if you up the anticrack mesh density. If well laid and cured.. looked after then with a screed on top then it can work as you point out. I'm cautious as while it worked for you on that site it won't apply to all slabs. You make a good point about intermediate and ring beams. These if not detailed and understood properly can tend to lock the slab edges and say the middle in position. This locking effect increases the shrinkage stress in the slab that cause trouble cracking wise. It's a great job as self building and renovations for example test you skills, for me the more I learn the more I realise how much I don't know! Indeed. We may have a fair bit in common. I was a local building Contractor for 20 years before trucking off to Uni to become a Structural Engineer and Designer. It's almost a natural progression for those of us who enjoy their job. You build stuff following other folks designs, realise you can do better at times, learn, improve and implement.

To add a bit to my last post. Structural raft foundations and ground bearing floor slabs shrink (mostly) and move about. Sometimes we need to split these up if you have a big house. It's quite common to various kinds of joints when designing industrial building slabs as they tend to be big. Optimised design is also looking about how the slab will move and shrink in terms of what we are putting on top of it. For example, we need to think about resting glazing on the slab or near to, positions of walls and so on. No point in having a massive slab movement joint right under your lovely large format kitchen tiles or sensitive glazing. Bigger slabs can move 15 - 20mm, no tile decoupling matt is going to cope with that. True optomisation results from holistic design. But it's hard (impossible?) to plan down to the last detail on a self build. The secret is to build in flexibility / options and that way you generally make overall savings.

Progress! Well done. Here are a few nuances about raft design which I hope helps. When designing these for say a less experienced Client; self builder or someone (say a cabinet maker or mechanic) that want's a small industrial unit I'm always keen to understand and make the Client aware of the potential for selection of builders and how their skill set is reflected in the prices you get back. . I also want to know how experienced the Client is, have you done this before? how much do you want to get involved in the technical design and decisions that underlie the final drawings and specification that I produce. This can have a big impact on the actual cost. Ideally you want to make the job easy enough so more builders can price.. get a bit of competition going. To try and explain briefly. For a reinforced concrete slab to act properly as a raft we need to for example control the thickness... ideally it should be of even thickness...but definitley not too thin in places. The slab can end up being too thin if we don't specify a level tolerance for what is is sitting on. Now if I say on my drawings that the EPS or insulation under the slab needs to be between +0.0 mm and minus 5.0mm then most local builders would think I'm nuts and add on a cost, tell you that your SE is an idiot or worse just not do what you are paying them to do. Let's select a general tolerance of 0.0mm to -15mm for how level the EPS needs to be. This is still quite a big ask when the winter rain and snow is running down your neck! That said we don't want massive low spots as it stops the raft from sliding as the concrete shrinks. If you make it harder for the slab to slide during curing and drying out a bit then this can make the cracks worse. We may want to put a screed on top of the slab with underfloor heating pipes. Here we need to control the how level and flat the top of the slab is. We may say that from a datum no point of the slab is to be more than 5.0mm higher and no more than 10- 15mm lower. If the slab is too high then you run into trouble with the cover on your UF heating pipes, particularly if in the heat of battle on site you need one pipe to cross over the other. Now there are some folk on BH like @nod and @saveasteading that are highly experienced at this and can work to tighter tolerances... but they know their stuff! If you are a novice at this then tighter tolerances are not for you! On paper I can make a raft pretty structurally efficient (I've a tool box of tricks and different design methods) but your chances of building it for reasonable cost as per the specification are probably pretty low unless you have a lot of experience and can adequately supervise (needs experience and time) and monitor the delivery. A properly optimised raft is one that performs structurally, is designed to suit you skill set in terms of access to builders, amount of suprevision, location, finance, surface finishes and so on. The motto is .. keep it simple!

Yes as the plastic introduces a slip plane which destroys the composite action between the masonry above and the lintel. If you bend a beam (also a composite beam.. composite lintel) downwards then there is compression in the top, tension in the bottom. When you balance all the forces within the beam you'll find not least that there are axial shear forces along the length.. the top of the beam is in compression so it shortens.. the bottom is stretching getting longer.. so there must be some axial shear forces in there. If you put a cavity tray in then the longitudinal shear force is not transferred between the brick courses above and the concrete lintel.. add a bit of water to that.. as that is what cavity trays are for and you have a good slip plane. Hope that makes sense? In this case you need a non composite lintel. This is roughly how a composite lintel works.. but you often need sufficient masonry each side to act as bit of a buttress to the imaginary arch to be on the safe side. If you look at the manufacturer data for composite lintels they give you this information on the number of bonded courses of brick you need over the composite lintel to make it work. Many manufactures data tables use a safe working load (SWL) which has the factor of safety (FOS) built in. This is fine for normal day to day stuff but watch out when you go for the longer spans as the deflections could cause other issues with say bifold doors below or sensitive renders. Always check to see if the lintel manufacture shows their loads as the total load or a UDL load (load per metre run of lintel) In the round I often use non composite lintels as the extra cost outweighs the on site risks of bad workmanship, folk making late changes (an enthusiastic heating Enginner coring / slapping holes in the theoretical arch etc) to the design or propping an faffing about.

Good point. I get a few folk a year and look at stuff ourselves where these cracking sites come up. Then you lift the bonnet and find all sorts. Most of the issues with these dilapidated things on small sites lie around servicing it and associated legal burdens. My mind set is like you perhaps.. ok lets go back to the beginning and see where the problems really lie as above. The seller want to sell.. you want to buy! Now here you need a bit of good faith but at the same time you don't want to incurr full on professional fees each time you look at a distressed property. You can get around this by either doing a lot of learning.. and by that I mean a lot or keep someone like me on a retainer, basically phone a friend. I have a couple of Clients who work this way. One is based in Glasgow who does both commercial and residential property development.. and we often chew the fat.. probably 1 in 5 to 10 projects end up getting taken forward to the bidding / financial negotiation stage. Remember one of the many common laws of business.. turnover is vanity.. profit is sanity! What you say is right.. it's about managing the seller's expectations... but not giving away just how you are going to make the project financially viable as some of these folk will just pinch your idea and advertise again using your hard work! It's a mucky business! For all though. Sometimes you see a property with a nice clean title and a friendly seller that is just stuck. Case in point. I worked on one years back where the public road was subsiding into and towards the house that was built lower down the slope. The highways were claiming that the house owner was liable... which basically made the place unsellable. The solution was in effect to use the first floor of the house as part of the stability system to retain the road retaining wall.. kept the highways department happy and that made the project fly. One trick here was to dig out quite a lot of soil and replace it with EPS as this reduced some of the soil loads behind the retaining wall . The off street parking was then built on top of the EPS which also served as great insulation to the semi basement wall. I'll do a sketch sometime for all. To conclude.. usuallly it's a service thing.. but sometimes the project can fly with innovative Enginnering.. which floats my boat! @Jimbobjones Good luck and hope you can do a deal!

Thanks for all the useful comments folks.. will mull it all over... lots to learn!

To add a bit. When we want to build on rock to get going we need to get a feel for how the rock is laid down and it's properties. We start with the compressive strength. That would be if we found a homogenous piece with no cracks, no weathering etc and crushed it in a test rig. Usually that gives a big number. But we need to know this number if we were to bolt a steel column with a thick steel base plate directly to the rock with a bit of grout under it. Here we have a higher localised compressive stress, like under the heel of you shoe. But often rocks have cracks in them. It's not solid rock. The cracks can be filled with other material. What we also need to know is how the cracks are spaced and their approximate width. We also need to know the direction of the cracks and plane. Rock (depending on type) can crack in 3 dimensions so it takes a bit of working out. Think of say leggo blocks. If all the leggo block interfaces are horizontal, vertical, interlocked and nice cubes.. they will carry more weigth. But if the leggo is slanted then they can slide over one another thus will be less able to bear load. If we have wide cracks in the rock filled with say clay/ silt / organic soil then the water gets in and this all acts as a lubricant which lets the blocks of stone slide more easily. When resting a building on sloping rock we need to work out if the rock will peel away / slide towards the open face or not and to make a judgement we need to look at the above not least. If it were to do so it would pull your supporting columns with it. Generally most rocks can take lots of load. Even if they have cracks they are fine so long as we have some confinement. If the rock is reasonably confined against sideways movement it can't go anywhere!

Love this! Watched the video, brilliant, love how direct glazing is explained and the cost element for example. This is the sort of stuff I enjoy, fraught with potential structural problems, reg compliance and legal burdens. In Scotland, not least the Church of Scotland, WRI etc have been selling things like this off and they can go really cheep. Sometimes you can pick them up when folk have bought them off the church say, lost their shirt and have to sell on! If you want to buy something like this you need not just to get all your ducks in a row (lots of research and learning) but also spot the elegant and cost effective design solution. Up front this is often getting the site services and foundations sorted out. There are bargins to be had but research and engineering solutions are the key. To be honest you often need to have an SE on board that also knows about drainage and all the rest that has lots of experience before you put in a bid for these things. You then need a good solicitor to wrap up the deal legally! In terms of cost anything that cantilevers often attracts extra cost. Building straight onto rock.. often a joy. I've done the odd build on rock in Scotland. Often it's not the rock (even some slightly weathered rock.. will often happen with Tuff) but BC and the NHBC that cause an issue as they bang on about frost protection. Often they just need a bit of education about frost heave, how ice crystals grow, their water demand and grouth rate. Don't forget it's just a house you are building which is pretty light weight. Funnily there are lots of houses in the UK built on rock.. extending them can be easy at times once you get your head around the common constraints and convincing BC that you don't often need to dig out the rock to put concrete back in the hole!

Hi all. I've had a bit of a rake about on BH and read around some of the great stuff you have been posting about AI and how that may fit into the self build market, conversion of farm buildings to domestic and building extensions. For me I started out some 40 years ago in construction before we had computers and the internet. Quotations were typed out and sent by post! To provide a bit of context I now work for myself as an SE and Architectural Designer. Prior to that I worked and trained mostly with a cold formed shed steel company that sold a lot of buildings in Australia and the UK. They were the biggest supplier (of CF sheds, some we turned into houses etc) by a long way in the UK. My role there was to develop some the engineering calcs, do a bit of R & D and design raft slabs etc. But the funny thing was that it was almost a software company that sold steel sheds via franchises and this is done via the internet.. a web site. To summarise.. AI I think is just a natural progression that needs to be used as a tool like any other. But I'm struggling to work out where to go next! At the moment my bread and butter income comes from designing extensions, loft conversions, knocking a lot of holes in walls to form open plan spaces. The other part of my portfolio is what I call "whacky and challenging stuff" for want of a better word. This could be anything from an interesting self build, farm building conversion to the odd bit of dispute work say against the NHBC. Now technology we know moves fast and I've been trying to get my head around whether AI is a threat to my income stream say over the next ten to fifteen years.. and then I'll probably hang up my boots. Here is a link to the RIBA where they talk about this: https://www.architecture.com/knowledge-and-resources/knowledge-landing-page/no-turning-back-41-of-architects-now-using-ai?srsltid=AfmBOoqSGRmmzU3V9DcDtLc4hEeimXg3_kxSkilpP1ux1xJ6xEoRjH8O To save anyone but the very keen reading . In summary there are a lot of mixed opinions and some Architects are dabbling with AI. There is some interesting points on design responsiblity, copywrite, who is training the model and providing the data that AI learns from? There is an element of justifiable nerviousness. Another rough quote I saw elsewhere was, AI is not a direct threat to say the Architect / SE in design experience terms but it could make you much less competetive if you don't use it.. like we use excel or word.. which is a strategic business threat. If you go bust then.. Personally I know I have to get my head around this in some form or another if I want to still be in business in say 5 or 10 years time... but where do I focus my learning effort. At the moment I see this panning out as having access to better (cheeper) SE visualisation and Architectural rendering of finishes. This could maybe extended to show how say a traditional cut timber roof works to act as an aid to the contractor when pricing. Funnily I use a pretty high end structural steel and timber detailing package that does all the 3D stuff and produces the fabrication drawings anyway. But it is an SE package and does not do Architectural renders for example. Often I'll add some screenshots to a complicated 2D SE design drawing so folk can see how it fits together. But could AI know just how to pitch and angle a screenshot to capture all the tricky bits that a builder needs to know? I just can't see AI at the moment helping me design a padstone at the end of a beam on an 120 year old stone structure, with 5.0 metre bifolds under with some lateral stability problems. Then you have the temporary works.. propping and so on.. all to be cost effective. But where is can help a lot is in basic visualisation if it is cheep! As a one man band my unique selling point is my experience and the fact that I wear two hats, SE and Architectural designer. This make me competetive financially (one stop shop) as I am able to "see the whole design picture", and this is attractive to some Clients.. but not all! Now scale that up a bit to say a small Architectural practice. Again they have a USP but I think it will be the big outfits that may, as always wil use this first.. which at the moment puts it out of reach of the self builder. I'm tying my ownself in knots here as am just learning! I think AI will be at first low cost but then the software fees will rack up.. and this has to get passed on in some form or another. The question is.. Will it make self building / extending more affordable? Personally I hope that there will always be a need for a designer like me, small and in a niece market. But one hard law of business.. how much do you cost! In ten years time someone may call me an "Artisan Designer".. I hope! Maybe a way of explaining my raw thinking is to refer to Adam Smith, The Wealth of Nations; circa 1776 where he explains the division of labour. AI is in some ways doing this.

Stunning! Your hard work has paid off.

I could have worded that post better. Still pals I hope?