Gus Potter

Yes, treat all this with a big pinch of salt, check their fine print. You must look at their technical spec, the range of moisture content, expansion edge gaps and so on and make sure that the way you want to live fits. In other words, say you bail out to Spain in the winter and turn the heating low.. or rent it out and folk dry their washing!

I'll try here to give a bit more info. I can see why you may think I'm being a bit rough, but with 40 years experience in the construction industry I've seen stuff, not all good. But some designs are very elegant, clever and you'll often see these cropping up on Build Hub first. What makes a bad designer is someone who thinks they know it all. I don't and one great learning resource for me is Buildhub. As a member of BH you really have access to a lot of clever folk who are innovative. I'll try add some detail. Remember though you can ask ten different designers and you'll get ten different answers. Your job is to work out what best suits you. My own view in design is to provide Clients with information so they can make an informed judgement. If they don't take my advise then that does not mean the job is going to be a disaster! Call this differential settlement. To avoid one big crack we design the building with movement joints in the external walls and try to position these so we get more cracks but smaller ones. Then we need to make sure our internal walls are not introducing stiff points that stop the external walls from moving about. In doing so we have to consider the Architectural constraints as SE's. Then just as we feel we are getting somewhere in the design we have underfloor heating that often needs to be zoned. There is a heirarchy in the design process. We are mixing up all sorts of different materials that repsond in different ways and then asking a builder to execute all of that at a reasonable price while taking cognisance of air tighness and ensuring the cold bridges are built as the design. Now all that is a big ask! This can be achieve but along the way you always find you have to make compromises. There is no "perfect design" in practice. That is one reason I ecourage more loops as it lets us introduce more movement joints in the floor if we need to. This is a really good question and observation. Here is a basic explanation about concrete with some numbers. When designing say a concrete slab, could be a first floor slab or a ground bearing slab. The first thing we want to ensure is that it does not fall down or in the case of a ground floor slab suddenly fail. Call this designing for safety. The next thing is that we want to know how concrete shrinks. There are two main types of shrinkage. When you first pour it we get what's called plastic shrinkage. This is the phase where all the chemical components in the concrete are reacting to "make" the concrete. Now your UFH pipes are in the slab so the plastic shrinkage can start to introduce tensile stress in the UFH pipes at this stage. Next we have drying shrinkage. The concrete dries out and this causes it to shrink more. Again more tensile stress. But in all cases the shrinkage causes "micro cracks" and all these induce tensile stress in the UFH pipes. They can cope with this. Now we know about the above so as concrete designers, even for screeds we ask ourselves.. can we put a number on that.. and yes we can. The starting point is to say lets design our concrete so no cracks exceed 0.3 mm. For say an ICF basement wall where the ground water is at ground level our starting point is 0.2mm. Now for UFH design we can do a big slab / screed with lots of rebar / fibres, to control this shrinkage, or smaller, movement jointed slabs with no reinforcement. This is more practical and achievable given my earlier point. It also means we can use self levelling scredd and so on. To sumarise. Yes you are correct to say that UFH pipes can tolerate shrinkage but they are absolutely not able to tolerate potentially 5 - 15mm of stretching over a localised area. Ok. The surveyor turns up, values the house on the basis that the heating works, they make this clear. You move in and say on day two you find the house is not warm enough. You call someone like @Nickfromwales who really knows his stuff. He crawls over it, provides an evidenced report that says... it does not work, and never will work well enough to comply with the building regs. So as a consumer you have been sold a pup. Nick then says in his report. Ah, to fix this you have a number of options.. none are going to be cheep. You can open up stuff and put in some supplementary radators, but that will mean opening up walls and possibly floors. Then you need to reinstate, make good, alter the boiler plumbing, add more components and find space for the radiators. Or you can start digging up floors to try and find the problem. Now that is going to be expensive! But UFH is becoming more main stream. At some point the RICS and insurers are going to say to their members.. look we really need to be taking this risk into account as we are supposed to be giving professional advice that keeps up with the times. We can't just keep saying to folks and thier lenders.. you have 7 days to report a problem with the heating. I'll stand by my point.. if your heating does not work as sold then expect at least a 5% write down. You counter my points well. Yes, there is more conjestion at the manifolds. As I said earleir there is not perfect solution. But I always come back to this. What buried in the floor is "forever". Once you get the pipes out the floor you can change the controls and boiler mechanics to suit the technology as it develops, or you can just stick with simple stupid. Ok so say you want to run your pipes in cooling mode. In the UK the weather can change rapidly. The thing about the UK is that the sun can be full on, but go 50 miles up the road its a dull day. Your weather compensation is not going to help you here. The solar gain can be rapid, thus you need ability to cool rapidly. This supports my approach towards redundancy. Ok I've had a go at responding to some of your points. Main thing is to have fun at this stage and enjoy the design process. One main reason is that when you have finished you can look back and say quietly to yourself. I made a bloody good job of that!

Ok it looks like we are still in love but just disagree on some points. That is the great thing about BH. Ah, but as an SE's we design for around 25mm settlement, often differential settlement over a 50 year period. This is a common value for most UK house builders. I design raft ( semi passive) slabs for intitial plastic and drying shrinkage, on a standard smallish house this can be 10 - 15mm. Unless you really know how your SE has designed the slab / foundation then your UFH pipes are vulnerable. You can't have you cake and eat it! To expand. The concrete found / slab moves so it is a "bigger issue". What it means is that you need to know and understand what you are putting your UFH on and account for that. Unless you want to pay a lot more for your underbuilding.. which is nuts. I love the challenge.. design and who is availble to build it. I can design lots of stuff but if the Client can't find someone to build it at a reasonable cost then it's a waste of time. Funnily enough it's not that hard if you look and understand how the structure acts as a whole.. but the big problem in the market is that every designer is acting in isolation. Often they are conservative which drives up the cost of the build. But if they work together then the cost should go down! It's mostly to idiot proof it! The UFH design look great on paper but life on site and a bit of rain makes for potential problems. If you are willing to stand over the Contracotr on site, then yes you may realise the design. No it's actually really high as unless you have put in the pipes yourself, contractors don't give a shit. If they kink the pipe they will just straighten it out so it looks good. You won't see it. That is why you see lots of regular and experienced members saying their UFH works well, as they are aware of the pitfalls and have supervised it the right way. I can tell you I also work with UFH that has been put in by developers and the pipes, radius bend are a complete disaster. But you can't design for low and slow when you then put rugs on the floor! This means you need to up the flow temperature which technically can breach the design values for the rest of the floor finishes, say engineered timber. Do you know how much a large sofa insulates UFH? It's a lot but no one on BH has acounted for this. Ok to complete, see if you get a joint leaking in the middle of the floor.. that is going to cause complete havoc! You can't easliy fix this! As a designer I design from the ground up, I have my SE hat on, my cost hat on and my Architectural hat on. I look at all the variables, how folk want to use the house. You have to have a deep understanding of how all the components fit together, the materials and so on. But as self builders you ain't going to be doing this as your day job. But it is well within you remit to think.. see this stuff I'm installing.. will if still be ok in 15 -50 years time ot more and if not is some surveyor going to come round and knock value off my house. No, as you have to run pipes to it. One of the great things about UFH is that it frees up wall space. So retro fitting a rad can be much harder than you think. Also rads tend to run at a higher temperature.. how are you going to make that work? From my end on the face of it your quick retort sounds good but practically.. just how are you going to execute that? and how much do you think that will cost? Why not just follow my advice and put in an extra loop, redundancey. My gut feeling is I'll never convince you... but hey ho, it's your money, not mine!

This is brilliant, great explanation of the fundamentals.

Good post. Hope my comment help rather than hinder. The law in Scotland is differs from the rest of the UK. Your starting point is to check that the existing tank has been registered with SEPA, your Solicitor should check this, you can also do this yourself. It's worth doing your own due dilligence. Now it gets a bit more complicated / political. The tail pipe seems to extend onto land you don't own and yes this is likely too short for a soak away. Also if you extend then you'll maybe need to discharge more. So putting my crusty Scottish hat on, like Yorkshire farmers, I think, do I smell a rat? Has the seller fallen out with the farmer / owner next door or is it just benign? Why have they not shown how the soakaway works and the location of the drainage field. I suspect that once you delve down you may find that you are exposed risk wise. Push your solicitor to get the the bottom of this. Now some folk may just buy this, maybe get stung. But also look to see if you can do a soakaway in your own land. Make no mistake, when it comes to farmers / rural Scottish sellers most are well clued up and if they can pass the buck to you they will. One way is to think, can I do my own soakaway in my own land and negotiate a discount on the price.

Apologise for being a bit rough. Had not recognised your previous posts. That's good, the contract will have a contingency? Maybe let this one slide in the interests of goodwill, but record. If it becomes a pattern where the goodwill is only one way street then post and you get some ideas. All the best and hope it keeps, from the sound of it, going well.

Yes. If I've not articulated well that then the fault lies at my end. I've copied your post below in plain text and comment in line. I'll have a go at the good points you make. Main thing is that BH is a place where you can discuss without having to watch every P and Q. To quote you: You've said stuff like this a few times and everytime I try to understand what you are getting at but I'm afriad I'm not really getting your point. In case it doesn't come across in the way I indend, the below is not having a go, just trying to understand your argument. Gus: You're welcome to question me, I don't see it as you "having a go" rather just entering into a conversation, a design discussion. If we agreed all the time then that does not bode well in terms of good design. It's OK to disagree! BH is a place where you can explore ideas and sometimes these can be very different view points. Without the mods on BH this wouldn't happen so thanks to them. The pipes buried in concrete (at least in low energy houses) are going to be able to cope with almost anything thrown at them and will last a very very long time.* Agree with the first bit. I did my first UFH system about 30 years ago and from what I hear the pipes have maintained their integrity. I also look after another self build (circa 30 years) house with a similar system and have not observed pipe material degredation, say like Upvc that can deteriorate under UV light. The second part.. you need to be careful as if you don't have good filters / competent maintenance then you can introduce "gunk" i.e bits of rust, a flake off a cast pump that can just put a spanner in the works. And that is why you'll often see me arguing for more loops. If one gets totally buggered then you still have a fall back. A lot of what we discuss here is how to get the maximum efficiency out of a system and the theme here to achieve that is minimum controls, low water temperature, system on most of the time with weather compensation (a technology that has been standard in all heating systems in other countries for literally decades). Agree with the headline points you make. Your first point.. maximum efficiency, I agree.. but efficiency has to be measured over say 50 years. You have to recognise that over time that can drop off a bit. Yes low flow temperatures, this encourages boilers to work in condensation mode. Minimum controls.. totally agree.. but you have to have a flexible loops in the floor which can, as you best guess cope with controls that migh be developed in the future. Weather compensation. Yes that has been around for a while, but I see fundamental problem with this. The first is the cost of updating the software, much is now an app on your phone! The second is that young folk with busy lives don't have the time to fanny about with it. We live in the UK! Our weather can change rapidly , four seasons in one day..where in many other countries it is often more predictable. The response time of UFH makes weather compensation less reliable. Now you may live in a benign part of the UK but there a lots of folk that don't. Even if you add lots of fancy controls on top of the basic system, the fundamentals of the system are such that you should be able to remove those controls and still get a very functional system. Agree. This is the point I've been putting forward, but I've maybe not made it that well. To to reiterate. Build in redundancy in the UFH pipes in the floor and that gives you flexibility as technology changes in the future.. it's called future proofing. Similarly, if the heat demand of the house increases then worst case you need to up the flow temperature in the pipes to compensate. Again, most of the designs talked about here for new builds are based on very low temperature heating. If you can output sufficient heat with the water in the pipes flowing at less than 30oC then if some cataclysimic climate change happened and suddenly we were all living in -20C then upping the temperature in the pipes to 40-45C should still be able to adequately heat the house. You are talking sense here! Yes I have experience of this in the past. The average outside temperature was about minus 20 deg for three days in a row, that was preceeded by a week or so of below zero so things got well cold. Solution was to bump up the flow temprature as you say. Now some may say.. oh it will cuase havoc with our timber floor finishes. I doesn't as generaly in the autumn the moisture content drops! In the summer often you have the heating turned off. Obviously if people want to extend the house then any extension would need work, but thats no real difference to any other system. If you have a low and slow design the system shouldn't care too much where the walls are if they needed to be moved. I do think that any 'smart' stuff added to a house should always be removable while maintaining the basic function of the house. Maybe you lose convenience or a little efficiency, but things should still work. Again, in the vast majority of cases, the systems discussed here are of the type that could be removed without significantly reducing the basic function of the house. Therefore, it is easy to offer any future buyer of the property the option to have all smart systems removed before they complete any purchase. So these shouldn't have a negative impact on the price of the property. More sense! Smaret sytems. I have two zones in my own house. One zone is radiators, the other UFH. I control these with the Hive sytem.. I think most folk can cope with that. What they can't cope with is lots of home automation. * Plastic pipes don't corrode and UFH systems should have much less metal in them overall reducing corrosion of other parts and build up of gunk. They can be flushed if there is a problem. Even in the unlikely event of the pipes developing a problem, retro fitting radiators or even electric heating to affected rooms would be unlikely to dramatically change the sale price of the house. Ah.. if you have to retro fit rads that is going to be expensive.. My own house is designed with areas of glass. there is not that much room to retro fit rads.. that is the beaty of UFH as it keeps the wall clear. Also retro fiting rads can be very expensive.. how to you get the pipes to the rads? I do see a concern about whether rafts can be relied on to last as long as traditional foundations, but this has nothing to do with UFH. This is an interesting question. The first thing I would say is that common to popular belief SE's / insulated raft specialist that do this kind of design in the evolving self build market don't rush out to pick faults in others designs, or claim to be the best. A good example is Advanced Foundation Technology (AFD) and Tanners in Ireland. I have been deisgning rafts for a long time, decades, so kind of know what I'm doing. In summary though there is a time and a place for a raft foundation. Sometimes the ground moves and the last thing you want is a strip foundation. A well desinged raft can perofrm just as well as a strip foundation if noit better. The big and evolving challenge for me as a raft designer is to deal with the thermal bridging, how and where you set up the UFH. Do you integrate in the "raft" or put it in say the screed. Each site is often different so you need to try and sort that while making the raft structurally ok. Much of the time it comes down to the way self builders are set up and the sequence of works. This actually often drives the desing cost wise. To finish. Hope the above helps, if not keep asking.

I wish BH had a spell checker. I just can't be arsed checking my dyslexia bit and spelling when I'm writing about stuff as a hobby. For all, my grammer and spelling may be a bit off when I'm off duty.. but neglect what I'm saying at your peril.

Hi all. The party is over indeed. I'm going to lay this on thick as it's time. I've picked UFH first but will turn to PV in another post. But to wet your aptetite! I've argued on this forum for a long time that underfloor heating is the bees knees. I've done this and worn the tee shirt. Long before most of you were in short pants. So if any of you can tell me how you installed and designed an UFH 22 years ago on a self build then I'm all ears! I would love to hear from you how we all flew by the seat of our pants at that time. I do hope that there may be one person. Many think they have invented the UFH wheel.. well you have not! The Scandinavians were at long time before the Brits.. I've made the case for simplicity and the need for UFH (the pipes in the slabs) to last the lifetime of the building, the cost of maintenance, reacting to how technology will evolve in terms of boilers etc. BUT what is in the concrete floor is a FIXED ASSET! Just like the walls and the roof! I also happen to be an SE who has actually been designing these slabs, insulated rafts to work with UFH for decades. So If there are any on BH that want to have a serious structural discussion with me then I would welcome that. You can ponce about with your weather compensation as much as you like, the flow rates.. your controls and buffering.. but see.. your heating has to work for 50 years so until you can make that arguement fdor life time performance, then I'll write down the value of your house if the pipes in the floor are not designed to adapt. SO GET A GRIP! I can and estate agents will also take a dim viw on a house value! Now some may just want to have a house that is a hobby, that is fine and I'm ok with that. But actually that may also make your house unsellable! Seriously.. you need to WAKE UP and smell the coffee, surveyors et al are clocking this so your hobby might come at an unexpected expense! Don't trust me. maybe ask a valuer? What I'm not OK with- if your house gets a loss of value as you have played with (and it is playing) home automation / complex UFH controls then that is a price you pay. But if you try and sell your house to some unexpecting young couple.. you can f... off., and I'm going to go hard on you! You are not going to sell your house to my kids! Advance Foundation technolgy have grasped some of it, Tanners in Ireland are competant SE's but no one has actually put all the bits together! The thing for me is that I want to design and build stuff that lasts, that delivers profit for self builders and that encourages young folk to enter the market, that benefits society. It's not a big ask? But as a designer with lots of real life experience I want to help young folk see the wood for the trees. I want them to get on the self build ladder on the self build ladder, I did it on a shoe string and that is why I keep pushing the simple stupid... as that means you can get a wider coice of Contractors.. which drives cost down. That is why I often push against the UFH complex thing and other stuff. It's also basically bonkers, but a lot of tecky folk on BH can'r see beyond 5 years.. So in summary I would like to see a lot of experienced folk on BH saying.. this works and if you are young folk embarking on a self build, on a limited budget this can work for you to. OK this is not going to go down well. But the life and future of BH is in the young folk, that are strapped for cash.. This for me and is why I'm still here.. I want to help and this is my hobby. To enthuse young folk, we need to solve problems, use our experience to say this can be not as hard as you think, if you take our advice, but at the same time give a bit of tough love if need be. PV is following much the same cycle..

Nick. I made my last post as I got a feeling that something was not right, it smells bad to me. I think why did NCX.. come on BH in the first place with some random generated name? Yes, we have not seen the drawings, the steelwork may be a small element. So here is a thing. Say we can save NCX five grand or potentially a lot more. and then say.. you got lots of help on BH so make a donation of 20%..

Each to their own Russell. Pesonally it looks like you have gone well over the score. Never mind so long as it works.. that is the main thing.

Ah, I'm going to take wide view on this, a bit brutal at times but I've put my claims hat on and explore if you have grounds for pushing back. I'm going to make some assumptions, but these you can explore yourself / mull over. First thing is I'm assuming you are a domestic Client, you have an element of protection under the consumer protection act. If your builder has worded their contract unfairly then they can be a bit stuffed as the law in the UK is more supportive than not. Next. Did your drawings show an opening with some steel? As you are a domestic Client and probably don't have; detailed drawings, a QS, probably not a recognised building contract then you still have a bit of protection as again.. your are a domestic Client. There is an argument in law that says.. as a domestic Client you can reasonably expect that a competant builder should be able to account for all the work even if it's not shown on the drawings. I do this as a day job (SE / designer and while we can be nice we don't take pish from folk when they step over the mark) and that includes a clause that says.. not every bit of (down to the last nails etc) the design is shown in detail. But even if that clause is not there you still have protection! OK that's the legal kind of bit. But how to you go about ascertaining if the builder has charged you too much? The steel cost may vary a bit but the big costs lies in how you tie the steels back to the building and any foundations below.. these bits can be very labour intensive and that is where the real cost lies. This cost can far outweigh an increase in steel weight. To dispute this you need to be able to look at these ancilliary bits and compare with what it would be a reasonable expectation from a competant builder. I'm just letting you know what has worked for me in the past when representing Clients when questioning builders costs. Now that is a lot of money when you look at the way it's presented! For all DIY folk.. the amount of money is relative in my book, I started out in life a bit skint so every pound was a prisoner. So I wonder is ( £28k + 10k ) plus vat in the grand scheme of things something you can live with or is it really going to hurt you? Do you feel you are getting ripped off? or do you feel that your builder in general has done a good job.. there is good will on all sides and it might not be worth not rocking the boat? Now is the time to maybe say to your builder.. and tie them down to their guarantee for the work. There are a number of ways of skinning this cat! If you feel you are getting ripped off then the first thing is to ask.. how much by and how do you go about getting a reduction in the invoice? Well, you have to be brutal if you can. Get them to finish as much as they can, for the least payment, then argue about the final payment. There are no friends in the desert!

A good number to get a feel for things for how much, at what rate you can discharge from your site, is mentioned in the SUDS manual CIRIA publication C753, when considering Vortex flow control (attenuation) for example is 2.0 litres per second. But what does that mean qualitatively. A discharge of 2 litres per second = 2 * 3600 seconds in an hour = 7.2 cubic metres per hour. So calculate how many mm of rain that is over one hectare in an hour. One hectare = 10,000 square metres. Thus 7.2 / 10000 *1000 (to convert it into mm of rain) = 0.72 mm of rain in an hour that you can discharge. Some of C753 also mentions 5.0 litres per second for example. The concept of SUDS is to make sure that what you build does not result in an increase in run off rate. Ok what does 5% look like say if you get 25 mm of rain in an hour? 0.05 * 25 = 1.25mm which is more than the 0.72 rate I calculated above. Now say you get a heavy down pour! So if we look at what @saveasteading is saying the rough sums kind of prove his point?

You have to start from somewhere, so try an Architect first if inclined to do so. Let us know how you get on, you have got some tips / hints so far on BH so that should aid your discussion. As always, try and enjoy the design process, it's not a competition! Keep us posted.

Have a look at the building regs. On upgrades I often have to have a discussion with BC in terms of what is "reasonably prcticable" In your case as you don't seem to be increasing the building foot print or the volume then this supports the "in so far as reasonably practicable" approach. The key to this is as you have clocked it is to maintain good ventilation, the more insulation the more ventilation you need, that's a rule of thumb. The other key is to tightly fit the insulation and use tapes to stop convection currents bypassing your hard work installing the insulation. Last is to install a good vapour barrier on the warm side to stop water gas getting into the insulation layer in the first place. Moist air does liittle harm.. the harm arises when the gas temperature lowers and you get water condensing out, we call this the dew point. The best way to get increased performance is to use insulating plasterboard on the underside but this may reduce the ceiling height. This works as you don't have the repeating bridging effect of the joists. Below is a link to Kingspan. You can play about to see the difference between insulated plasterboard and insulation between the joists. https://u-valuecalculator.com/gb Hope this helps and you have a bit of fun playing about with it.