Gus Potter

You can never have enough books.

Your comments are valid. When I was a building contractor.. to provide a bit of context. I employed 7 - 8 men full time and many of them were long standing and loyal.. but I paid them well. I also pulled in sub contractors. Depending on the seasons I could have my core guys and then up to 20 folk working.. but I was still small fry, just a local rural builder (Scottish Borders) that had contacts. But make no mistake.. I could have bought in a TF from say the modern equivalent of MBC, Pascills et all for one off jobs but the service was not that great, maybe because they view self builders as a one off and generally inexperienced Clients. They add an extra profit margin. For all.. when I was a builder I could have knocked up a TF on site faster than saying going to a TF company, many of the builders I now work with do so I was not that special! I made that happen by starting the kit as the brickies were putting in the under building. The great thing is that all the guys worked together so the joiners on the TF would check the brickies work and eat their lunch together in the site hut. Sometimes if the roof was simple we would get prefabricated roof trusses and make sure they fitted on the walls. Some of the kit roof designs I see on BH are just not suited for the prefabricated application and I can see that a stick built roof is the best and most economic solution. I can be done this stick build thing and often more smoothly and in you time frame! But for all on BH the main barrier to this is that you often don't get the right design team in place and spend enough on professional fees and taking advantage of their contacts and are willing to pay for a few panel drawings for what is a one off project. The thing that irks me is that folk expect Builders to price jobs for free. Sometimes I say to the builders I work with when we have say a tricky renovation / refurb job.. hey the Client will pay you to sit down and work out a real price!

What a great post Nick. I spent the first 20 years of my carear stick building TF's before I became a designer. To knock up TF studs on site you need to set up a good saw bench. We used to make one from timbers that suited 4.8 and 6.0 m timber lengths. The chop saw (a top quality one and expensive) got mounted each day on the bench and taken home at night. To cut all the stud lengths / noggings you use stops / marks on the bench. The other main tools were a passlode nail gun for the 90mm long framing nails and I used a air driven nail gun with a compressor for nailing the sheeting when making the panels on the ground for the first floors. For two story houses you adapt the panels to make them manually liftable.. and as you say no need for a crane! I work with a lot of builders (do the TF panel drawings) and we use this method as they win jobs! It's not just that they win jobs.. they get less hassle as they have much more control over the process / delivery and that leads to management savings and that less hassle makes them more competetive. The more competetive they are the more bread and butter work flows my way. Yes you do, in fact you can often achieve a better build as you can account for the variation in the underbuilding and things being off the square. The savings can be significant in terms of buying the timber. I understand that @saveasteading has done a deal with a merchant to basically buy a pallet /s or so of timber off the boat.. cutting out many of the middle men. Ok set that advantage aside. As a self builder cash flow is everything at times. Stick building can smooth the cash flow way. Yes agree. Larsen trusses as well can be knocked up on site. You can do it the slow way using nail plates from say Tool Station or the quick way using ply gussets nailed with a nail gun. You can also make the Larsen trusses bear on the edge of a raft foundation with a bit of diagonal bracing. Again here an experienced joiner will "smooth" out any minor dimensional errors that may have manifested in the underbuilding. A TF fabircator cuts you no slack in this respect, they are not that flexible if you get your found a bit off the square or level or want to move a window or door late in the day. First the upsides.. 1/ You don't have to stump up a big wad of cash up front and hope the TF turns up when you hope it will. You pay for the timber and once it is on site it belongs to you. Then you look after it, dry it slowly until you are ready to use it.. this reduces the shrinkage and cracking you get later on, that has hidden cost benefit. 2/ You don't have to worry about the TF company going bust. 3/ Self building should be an exciting journey, at times you change you mind.. well quite often. Stick building is much more flexible in this respect. 4/ If you can find the right joiner to do the TF then they will often introduce you to all their pals who do all the other trades. Down sides.. 5/ You need someone to do a TF panel drawing and coordinate the main services that might clash with the TF. I do this as an SE / Designer / Ex builder.. but it comes at a cost.. it's a fair bit of work to think it all through, there is no getting away from this cost unless you are able to design and draw a timber frame with the panel drawings and connections economically.. That's it for now but hopefully you can see how I think @Nick and I may be singing off the same page. Mind you we don't always agree at times! In summary. I would always want to compare a manufactured frame with a stick build for domestic one off jobs. Don't forget that we are doing one off builds (extensions or houses) the TF manufactures need to sell mass market to known and big spending Clients who they work with day in and day out. They have invested millions of pound in ther factories.. your self build / extension is the cream on the cake profit wise. Where they really make their money is selling you insulation and the "service" etc. Now if you look at @Nickfromwales.. it seems to me that here is someone with loads of experience who may have something to offer.. I suggest PM him?

Posts over lapping. Lucky you can get to both sides! Good tip, also go and create an account for youself on the British Gypsum website and use their deisng tools, you can print off the calcs and so on. To make this relevant you'll need to download the White Book, it has good details and laymans terms guidance etc.. Remember you need to fire protect the perimeter joints around the wall edges so have a look at that too as to how you detail that out.

50 years expererience talking here from @saveasteading, not to be disregarded.

Hi @Mike DC Are you trying to fire protect the party wall in an attic conversion? Can you provide more detail as we are all guessing here. If you want to get a bit of free help then you need to provide more detailed info.

Agree, this often works. The word goes about you are good folk to work for and folk will be helpfull, especially in a rural area.

This can be easyish or horrible in terms of builability. Do you or can you get access from the neighbours side? If you have access from both sides then it can be pretty straight forward as @nod says. If you only have access from your side..it can be a challenge to understate!

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!