Gus Potter

Ah.. there is a bit more to this fire protection stuff. Often on BH you see folk questioning.. why do I need all this protection? The protection is also required for the fire fighters that have to put the fire out. You need to avoid sudden collapse that put their lives at risk.. they could after all be your sons and daughters fighting the fire. A designer and you as the home owner also have a civic duty enshrined in UK law that dates back to the fire of London. Your fire is not allowed to set alight your neighbours house. Your house insurer may take a dim view and not pay out if you have a fire and it turns out you have not got a grasp of this. Lastly any designer that your employ such as myself take the view that your are just a custodian of the house and we often design for say 60 years. My primary qualification, says on the tin is a "Civil Engineer" so that means my primary duty is to the public, not yours! Yes, you pay my fee but my statutory duty under the law is to the public not just you who may be using the structure for a period of time.

I'll try and chip in here, some comment may not be specific but I'll try and outline some of the issues. Excuse the spelling and grammer as I'm off duty. To provide a bit of context. From time to time I get involved in representing Clients who are having difficulty in bringing the warranty providers to the table as they refuse to play ball when a Claim arises. The modus is; delay / deny /defend. By the time I get called in things are often serious and relationships have broken down. But that is not the case here and my experience also allows me to look at things holistically. Now, I also very occasionaly get involved at the stage where the self builder is trying to obtain a warranty later in the day.. in other words the build has started but the mechanics of the self build funding / lending require a warranty from say the NHBC / ProteK et al. Now nothing has gone wrong here. All that is happening is that the Client is playing catch up and often needs to get a warranty in place so they can obtain more favourable lending. Again no one has fallen out at this stage and the aim is to negotiate an equitable warranty deal. One key starting point is that BC approval is totally different from and not in principle related to what is an insurance policy you are taking out. Local Authority BC often write, when they give approval, words to the effect that the Client is responsible for a building regulations compliant design. In effect this means that even if local authority BC miss something it's not their problem. So yes, if you want a warranty the rules are different as you are entering into a financial arrangement with an insurer. In fairness they do pay out if conditions are met. To get a feel for what's going on let's put ourselves in the warranty providers shoes. For some of the stalwarts on BH.. go to the toilet, compose yourself come back and read on. Let's say your build cost is 300k. A typical premium that a warranty provider may ask for is about 1.0 to 1.5% of the build cost. So take the higher end 0.015 * 300000 = 4.5K. Now lets see what profit they might make off that given that they are putting thier neck on the line for 10 years. Some providers will do 3 inspections some more. But just say they do three (ProteK I believe aim for 5) . Now an inspector can do at best 2 a day.. if the sites are close. But life is not like that where you can do 2 inspections a day week in week out. Then they need to write up the report do all the admin. Call that £400 quid a day so there goes £1200 quid. Now we are down to 4.5 - 1.2 = 3.3k. There is a bit of two and fro (I'm an SE and this post will take about an hour and a bit to write infomally, I think before I write so that counts also) so deduct another 1.0k for that two and fro. Now we are down to 2.2k. The insurer may choose to lay off some of the risk with a Lloyds syndicate so they will take their cut. The NHBC apparently have a huge pot of cash and I understand they basically self insure like local councils. I may be wrong however. For those that have interest the history of the NHBC is fascinating.. they abandoned their principles a few decades ago mind. While my figures are rough you can see that at best the warranty provider may be grossing as profit is max 2.0k and for that they have to underwrite for ten years. That is why they must shed as much liability on to folk like me, the Client and so on. The last bit is eccletcic. When I used to run a Contracting business and say we were fitting doors at £100.0 quid a pop. The apprentice was fitting the lock and destoyed the door. Working on 20% gross profit they then needed to fit another five perfectly to get to a basic recovery position. But I still need to pay for their holidays and so on. Imagine you then make a claim against the warranty provider.. there is a lot of admin at their end and they may have to pay for an inspector to come out. It may turn out they are on the hook! Do the maths for yourself, recognise how the warranty business works, be aware. Once you are aware then it's your choice to decide if that suits you or not. There was a recent thread on BH about Potten going under. The key to business is profit, that is sanity, turnover is vanity. Again, for the small profit they make you can't blame them! I'll be blunt over the last five years I've extracted well over two million quid on just two claims where I've represented Clients. They will have to write lots of permiums to recover from that.

Ok that's a great start.. good to see SE's explaining and reasoning out to Clients what they have thought about and why they are designing in a certain way and engaging with you. In terms of risk.. for all it's important to discuss with your SE this risk element and be up front about it. Some self builders are well funded and don't need to satisfy say the bank and are willing to take on more risk. To add a bit of context. The thing you won't get an SE to compromise on is safety (not fall down) but there is scope when it comes to potential movement / shrinkage that could say crack floor finishes. The Eurocodes have an element of flexibility here where as the British Standards can be more prescriptive. I could agree with you what level of risk you want to take in terms of movement, provide the movement is not too large such that it impacts on the structural safety design. If you said to me.. hey Gus I don't care if my building sways to the side by 150mm I would then say to you.. now all the loads are off centre and this will add unwanted forces to the structural frame which makes it unsafe. The warranty providers (NHBC / ProteK) may not be so "flexible" when negotiating movement / settlement say. Then in that case you have probaly got value for money. Just say your SE charged you an extra 5.0k! All he has to do is save you one week of work for 4 experienced operatives, add in some plant cost and the face is washed. Yes your slab on the face of it is thicker but it is flat, looks buildable and the drawings are probably easy to read which will avoid error on site. To finish. Go back to your SE and ask what the movement joints need to do. Is there some shear transfer. Are you going to have a tiled floor all over, you probably want to keep that level so you want to avoid on slab settling differentially. Once you get a handle on that then there are loads of joint options. All the best.

I'm assuming your SE has given you the joint locations and they should have given you a joint detail as there are about 4 different basic kinds of joint and they all behave in a different way. If not don't go out on your own as you could find yourself in very deep shit! If you go off piste your SE will not be pleased. If BC spot it .. and if you over stress part of the slab by putting the joint in the wrong place your house could move.. or more! Once you have clarified what the joint is intended to do, not just movement but also shear transfer then they are loads of proprietry joints on the internet that you can get at a reasonable price. Sometimes when we have a L or a funny shape it's more cost effective to put in a movement joint. But if you go off and do your own thing..imagine if we put a movement joint under a big sensitive set of glass doors or glazing! It sounds so wrong and is, but that is why design must be coordinated and you need to run it by your SE. That works on smaller slabs at times. The ring beam ties stuff together.

I design stuff like this as an SE. Sometimes it works out that a thick slab is the most economic. Sometimes it's just more buildable to keep an even slab thickness as you avoid funny rebar, shutering and so on. Labour and shuttering is expensive so you have to balance that by just making the lsab the same thickness. Just ask your SE why they think this is the most economic solution and why. They should be able to tell you. They may also give you some extra tips if you offer to pay a little more, chip in for the staff Xmas fund they will often refuse. The builder gets a drawing with the slab and rebar. A good SE will make this buildable and easy to understand, a key requirement. What you don't see is that in the SE office a huge amount of thought often goes into this. A raft slab is a complex animal and it takes a lot of time to learn how to design them well and buildable. For all when I design raft slabs for the self build market I add some notes on my drawings like this: The last bit of paragraph one explains why I'm asking the builder to do what I want and the reason for doing it. If you don't let the concrete harden then it won't bond to the rebar properly. Let the concrete harden, then dry it out so the shrinkage loads are transfered to the rebar.

Pasquill have a bit of history for me. Years ago, about 30-35 years, I dabbled (when I was a builder before I reinvented mysefl as an SE) in roof truss manufacture, posi joists were not on the market then. Pasquill used to be a "competitor" as a local Scottish business. Both of us held the Mitek software licence. The owner of Pasquill sold on a great business with a lot of good staff. I met him on and off and was a straight up guy, bloody hard nosed mind.. like Yorkshire folk. Pasquill at the time were straight up folk, they had one or two fantastic timber engineers, .. it's ok to be a good Engineer but if you can't pay your way then your long term job prospects are not so good. Great to see they have kept the founder's ethos and stepped up to the plate on this one. Nice bit of nostagia for me.

What a belter of a statement.. heretic I say! That said, what John is presenting is based on sound arguement, although some may not want to hear it. Here is a bit of background. If we have a large industrial building that is to be heated to say an office (domestic) environment temperature then the first thing we look at is the ground. We ask..what is the ground.. I'll pick clay as it is the best performing. Next.. is it pretty impermeable clay that has negligeable ground water cross flow movement? Any significant ground water cross flow will take any stored heat away. If the water flow can be neglected then we have what we call a "dumpling" in the middle of the building that we can heat and then later recover that. To get your head around this.. think of Adobe clay bricks.. the clay has insulating properties, normally associated with hot climates but the same principle applies as the clay does not know from which direction the heat is coming from. Now we know heat can leak out the sides of the floor.. and if we heat the dumpling heat we need to know how much heat will leak out the sides, call that a thermal bridge.. we now have PSI values say that look at this effect in detail. But on a large building the perimeter / floor area ratio is small so much less heat loss out the sides. On a small extension much more heat gets lost out the sides in relative terms. If you know a bit about large industrial floor design then often you'll just see the edges of the floor insulated. I've been dabbling in this for a long time as has @saveasteading. A lot of the modern raft slabs, passive ones also are based on techniques we were using since the 1980's, maybe before. Now on a smaller floor area we can adapt large building floor slab design by for example insulating the perimeter walls down to the founds and capture the heat in a clay dumpling. This basic understanding can be invaluable when upgrading old buildings. Great comment John!

All the best... but prepare for bad news. On the upside at least you caught it now before anyone got hurt. Keep us posted.

Pretty much to say the least. Sometimes you can get away with notching the bottom flange and stiffen it properly.. but not that much!

Have done it this way many times in the past using the overcladding solution. On the face of it it seems like double work but at the end of the day you often find it's the most cost effective method.

Yes you'll struggle to find bespoke details like this. Let's say we kind of want to follow the ethos of the building regulations, introduce some practicality and so on. The regs often require a minimum vertical upstand on a flashing of 150mm. You want to be able to keep the roof clean and get your hand in under the edge of the roof sheet to clear leaves and keep any ventilation clear.. Say measured vertically we need 75mm for getting your hand in to clean. Now we have a vertical measurement of 150mm + 75 mm = 225 mm. That translates to a slope length measured up the 45 degree roof slope of 1.41 x 225 = say 320mm and that is where your first batten will be from the EPDM when measured up the slope. As the box profile does not go all the way down to the EPDM the length of box profile cantilever is 150 x 1.41 = 212 mm not a lot for say a Steadmans 32mm box profile. I could calculate it out but I think you'll be fine under normal conditions to have a cantilever of 300mm. Provided no one stands on it at the leading edge of the cantilever. The weak spot is maybe at the roof edges where you get high wind suction. One belt and braces way is just to put an one extra fixing at the bottom of any gable verge cover flashing to prevent the very edge of the roof sheet pealing off.

My knickers are just fine thanks. If I had any concerns about knicker torsion then an old remedy is a Jock Strap use by many famous sportsmen. My day rate varies but had provided you with an indicative industry figure that you might aim for as a self builder. A graduate Engineer for say a mid sized consulatancy, is, under competetive conditions charged out at around £85.00 upwards and hour, senior engineers more. The devil is in the detailing and thought that goes into buildability. The way people design is important as self builders often don't have the same buying power and range of contractors to chose from. I think you do! Ok let's put is all down to a miss understanding and move on. BH is a great place to share knowledge, I learn loads here and in return try and give a bit back. Seriously though all the best with the project. If you have any SE type queries then feel free to post and if I can give you a few pointers or help out I'll be happy to do so.

Looks good but get your SE to check this at you have two roof spans loading only two cripple studs at ground floor level. The higher roof bears onto the upper steel which bears onto the lower steel. That load looks like it goes down a double cripple stud.. all probably fine until you get to the DPC level where the sole plate timber is now loaded perpendicular to the grain. If you work this out yourself and follow the loads you'll probably see why I'm asking the question. Once I see something like this.. which could be a basic SE failure it make me lose confidence in the rest of the design. I'm only looking at a photo but there is enough for me to ask.. is that OK? It's up to you whether you take my advice or not but if it was my house better to ask a silly question! You internal wall heights are significant, few nogging for stiffness.. what you have is outwith normal TF design parameters.. hope you have a good SE that has taken into account internal wind pressures and wall flexibility!

I would comment as an SE but I kind of feel that you are taking advantage of the BH ethos where things are not monetised. I'm definitly not going to give up my time as an SE ( call that £400.00 a day) if when you get into bother when I know you are back ending it. I won't be following you on U tube! Buildhub in my view was never set up with that intention.

Nick. As you know In used to be a contractor, went off to uni to reinvent myself as an SE at the age of 40, I got my bus pass this year. Now some of my mates say.. was it worth it financially?.. some said you'll never get through uni. In terms of pure money probably not. To get to uni I shut my business, flogged the house I had self built, dog died and wife departed.. I was lonely! I used to take home say 40 -50k a year 20 years ago. I got entry to Uni in second year as I had got an HND when I was a teenager. In the round I recon on the face of it my uni adventure cost me about £ 250k. However what uni did for me was to give me the tools to teach myself. I saw uni as a way to start a consultancy and fly a desk most of the time.. Deep down I knew that the years working on the tools were going to take a toll on my body.. need new hips in the future.. so now that £250k is not so bad and anyway it's an abstract concept as I would have still needed to work my arse off when instead I spent 4 years enjoying lectures and doing research. I used to employ about 6- 8 full time staff and then subbies.. lots of mouths to feed.. the stress can be hard at times.Now when I went to uni I thought once I get to learn about this SE malarky it will take me about another 5 years to build some kind of business that I can make a living from. It's actually taken me about 7 years where now I get lots of repeat business, have got a list of builders that I work with and get whacky jobs all over the UK.. the great fun part coming in. Now in that time I have landed for example a couple of Clients that are big business folk in and around Glasgow.. they have large industrial holdings, big retail business, own parcels of land and so on and they do self builds for themselves and importantly for family members. In summary they are quite happy to employ the likes of me and small builders to stick build some of their multi million pound houses! as they are in now rush and by not being in a rush they save a pile of cash.. and that is maybe why they are mutli millionairs! Bide your time Nick.. you work hard and funnily folk that work hard often get lucky! But one last word of warning.. work on 30 days payment, if in doubt proforma many genuine good customers will appreciate your good deal and pay on the nail. I have one Client at the moment that pays the same day! and in return I try to reciprocate in recognition. But Nick that is where you can make hay. You have the experience, the contacts. What I've noticed about you is that your range of knowledge is exceptional, play to your strenghts and play of a straight bat.

Do my simple sums make sense? A good self employed trades person costs taken on the UK average, if you do a deal say £250 - £300 a day. They need to run a van, replace their tools, maybe set aside to invest in their business, have some insurance and need holidays so they need to earn enough so they can take time off. As a basic rate tax payer you need to earn say 23% more so that equates to 1.23 * say average £275 a day * 1.2 = £330.00 to pay the trades person. Now just say you take twice as long to do the same quality of job, you'll make some mistakes.. cut timber wrong say at your own expense, so every day you work is a net gain of £165.00. But the more work you do the beter you will get at it and make less mistakes. Now if you put in one weekends work as a novice that is probaly worth having. Then you get the enjoyment of having done it yourself and that is hard to put a value on. If you scale that up to a self build you'll find that as per my previous post it equates to about a 15% saving.

Good comment John. Actually in Scotland we were at the forefront of bringing TF to the UK market. We are still at the forefront of insulation values I have to say. I work all over the UK but I'm just making a point that us Jocks know a bit about TF design! Main reason as always.. is money and that was backed up by us having some great family timber type merchants that got into TF design..they could be trusted to keep your money safe..up to a point.. no massive deposits up front in the early days. to cut a long story short. When I started in this business some 40 years ago as a builder (before I became an SE / Designer), I used to stick build the TF walls, maybe on site or in a farmer's shed and buy in roof trusses.. there was a saving and importantly there still is. The old rule of thumb and still applies it that if you split lots of things into small work packages then you'll build a house for about 15% less. @nod is a massively hard working and dedicated self builder and can achieve greater savings.. but let's say this is your first self build so expect a 15% saving. Now when I was a builder I obtained a Mitek licence to manufacture our own roof trusses. Here is what I learnt! There is very little money in manufacturing unless you are doing huge volume, the profits lie in what you can sell off the back of that. That might be say insulation.. or hidden things like inflating the fire stopping cost. What can you sell in terms of air tightness, the service you provide, smooth the way with say BC. The reality is that if you go to any TF outfit there is negligeable milage in it for them just selling you the timber nailed together.. it's the add ons where their profit lies. And once you add all that up it makes you ask why don't you just buy a new house off the shelf! But you'll still think you are a self builder. As an SE that knows a bit about insulated raft design. I'm sceptical as to whether some of these turn key TF packages actually offer best value.. In summary I would encourage folk to back to basics.. like real self builders.. expecting that you are going to make any significant saving by spliting a build into a few main work packages is like shopping at M & S.. it tastes good at the time but in the long run.. you be adding the oncost onto your mortgage. To make any reasonable comparison you need to look a simple stupid stick build cost and that will let you see if all the others are ripping you off or not! To be blunt thye all know how each other price.. but is the spread of prices actually reasonable. I can tell you that this is not always the case. I often work for Clients who build some high end houses, well insulated.. we find the right contractor and stick build it. Now here is a bit of a rub.. it's to do with the "art of the financial deal" and method of payment that can be more "flexible" than say dealing with MBC et al. @Nickfromwales catch my drift?

Pick a different tray. If you muck with the joist then to get an SE will set you back say £ 600.00 quid.. they will add a bit for your stupidity. If you don't pay for an SE and get caught.. you are in bother.. or you floor may fall down! Get a tray with the hole positioned to avoid the joist. Spend your saving on something you see and get enjoyment out of, towel rail, tiles, higher quality sanitary ware.

It is massively hard to get your head around this. I've been dabbling in UFH and stuff for 40 years and the learning curve is hard to keep up with. John makes a valid point about how much it costs (£75.00) to run a circulation pump. Now pumps give out heat. If they are inside the insulation envelope then it is fair game to count that heat in the calculation. To be pedantic.. say gas is 1/3 the price of electricity. Now your £75 quid is more like £50 quid nett, one problem is though.. you don't live in the boiler cupboard... I hope. @LnP earlier and on another thread put forward a proposal that certain publications were using flawed data to argue against climate change. Now what we are doing on BH is building our own houses and extending say. Over my adult life I've come to recognise that the political landscape changes a lot, at the moment with Reform UK this has the potential to be quite dramatic. Govenment policy could change a lot. No matter where you sit on the polical spectrum things won't stay the same as they are now. Research funds etc get directed to deliver certain outcomes. This landscape changes more frequently than the lifespan of the house and probably a mortgage. As a designer I would encourage Clients to think about energy policy and costs and recognise that they will change for good.. or bad and try and design for the long term. Design for durability, ease of part replacement and mitigate servicing cost. This is one key aspect that underpins sustainable and environmental design.

Quick pratical question. If you put your hot water cylinder in a modest cupboard with slatted shelves over the top to keep your linen dry and to get that "crispy warm towel effect" does it help prevent heat loss from the cylinder enough to make the excercise worthwhile? If you fancy a go at a fag packet heat loss calculation for a bit of fun! The cylinder and cupboard insulation coupled with the air gap effect in the cupboard changes the numbers as they work in series. Easier to do a fag packet calc as there is little cold bridging that you get with say repeating timbers in a stud wall. Yes I know you will get convection effects occurring in the cupboard, and so on, but to give you a flavour and to anticipate this question here is a copy of the table from BS.. 6946. The cylinder insulation, air gap, and enclosure all work in series. The question is how often do you open the cupboard, at what time and how many towels do you have? Seriously though. If you are tight for cylinder space then it's worth an ecclectic look. If you look at the table ( developed really for double glazing / secondary glazing) you can see that the horizontal resistance become constant once you exceed a gap of ~25mm. Or... if you are designer and have eh.. designed below the margin.. this might be a way of getting yourself out of trouble! When drowning you will grasp any straw!

A good "woodsperson.. woke" woodsman will always choose an axe head made from a steel that can be made reasonably sharp but also be durable. While they may not get the edge perfectly sharp and keen it will still out perfom a steel that can take a good edge but is not durable in the long run. There is little point in installing complex systems which on the face of it will work for a few years and then become difficult to service, suffer from a large drop off in performace or need replacement. Take a step back and use your common sense.

It would be a good idea to get an SE in to have a look at this. One thing that you need to look out for is when you muck about with the roof you can change the load paths on the floors below / any old beams and so on. This can become an issue. As a domestic Client you have a good bit of protection under the consumer protection act, the building regulations, CDM regulations and the HSE act 1974. Write to Oso and say that in the interests of fairness it would be appropriate to get a independent opinion. Say you are seriously concerned about the safety of the structure and give them 48 hours to respond. Point out that you have observed excessive deflections. Do this right away, don't delay! I agree with the other posters.. It does not look rosy as things stand and seeing the standard of workmanship gives me concern in terms of safety. You need to take the long view. At some point you will want to sell the house so best to get all your ducks in a row.

Hiya. If you click on the drawing that @Russdl has posted yesterday it takes you to his thread. There is a fair bit going on in the slab. Here is a bit of detail that works for a reasonable lightweight structure like this even with solid single story masonry walls above, which add a line load to the edge of the slab. Your pod will be pretty light but hopefully the below may give you some ideas as to how you can use Foamglass in other ways. If you are close to trees then you'll maybe have some swelling / shrinkage of the soil, thus you'll have some element of excavation to navigate around that. Rather than filling the excavation back up with say type one it sometimes works if you back fill with an insulating materail such as Geocell Foamglass. Below is a screen shot from a data sheet. On the odd ocasion if you have ground with a very poor bearing capacity you can make some headway by digging out the soil and replacing it with a lighter material. Just say the soil you dig out is 1800 kg/ m^3 and the Geocell Foamglass is 150 kg/m^3. Now stick a raft slab on top of that and you basically get some "free load". The excess load is then used in the settlement and bearing calculation.. you need to mindful of the water table for example as this can put a spanner in the works at times. On the drawing posted you'll notice that the slab is 150mm thick.. but it has an A252 mesh which has an 8.0mm bar size spaced at 200mm centres in both directions. It's not uncommon to use a thinner mesh, say A142, for a lightly loaded ground bearing floor slab, which has a 6.0mm thick bar. So why the A252? Using the thicker A252 mesh allows you to qualify the slab as a reinforced concrete slab. And now the mesh serves two purposes: 1/ It allows you to have less movement joints in the slab, within reason, depending on the slab size and it controls the drying shrinkage of the concrete more. 2/ The nuance is that if / when the wall loads induce too much bearing stress on the foamglass under the edge of the slab the A252 mesh starts to work by transferring some of the load back into the slab. This is a common technique used when we design raft founds for houses. You'll see that the mesh is bent down on site. This anchors the mesh which will be in tension. It's ok to bend this kind of low risk mesh on site provided you only bend it once (so as not to work harden the steel) and you must not have too tight a bend radius. In this case the bend radius is roughly twice the bar diameter. You can bend this mesh easily with a bit of steel 22 mm gas pipe offcut while applying some common sense. @mjc55 have fun exploring the pods design.

I think this is a great idea as it will give you a feel for the material. I've designed with foamglass before for an insulated raft slab. The foam glass is different to work with when you compact it. Basically you need to give it a bit of a "shoogle / shake about" and it needs careful surface preparation so as not to damage any DPM on top, all doable. It drains well. But roughly for it to work as intended the ground water needs to be below the foam glass or the water will just bypass the insulating effect. Now if you want to use it for your house then we need to know a lot about the ground water levels and what loads the superstructure are putting on say a raft slab for example. Foamglass can deliver a big advantage in that it is able to carry high compressive load with negligeable movement (settlement) and for a house seeking to achieve a good insulated slab this can be a card in your deck you can play, or at least look at as an SE and this can be the key for overall build cost. There are times when it can be a fabulous cost effective solution.. there is a time and place for it.. the stars need to align.

No I'm not! The building trade is not an exact science, ground conditions, setting out, making errors in detailing, fabrication and following the drawings. We are all human, mistakes happen. Mistakes happen.. it's a fact of life! It's often easier to navigate an implement a solution if you have local folk round about to help solve on site issues. Maybe you got very lucky and things went according to plan.