Gus Potter

Ah.. that will change the game a lot! You'll need some new threads, a hair cut and so on if you are going to be on the telly!

Good question. There is a lot of good technical comment from previous posters. MVHR is well proven technology if you design it right, build in a bit of spare capacity so you can sell the house on without copmpromising the value and live in a certain way. So in that context I'll paint you a diferent picture. Now I am a past self builder, site was in the country, like waaay out in the sticks. But round about me were other young couples that were also that were doing the same. Most wanted a house that was large enough to fill with kids. Most of us were in our 30's or a bit younger (but there was also a cohort of retiring folk who really got behind the ethos and they also wanted chickens and plenty fresh air.. like open windows and doors) and wanted to send their kids to the good local school, get chickens! And sure enough it all happend. Good teachers moved to the local school and it thrived. But it did not stop at chickens! Then there were sheep, goats, more kids, the dads got involved in the local scouts, the local pheasant shoot, (they learnt to shoot as the foxes were eating their chickens) their houses became a hive of activity.. the doors were open and shut from morning to night, the new kids got sick at first when they moved to the country so windows were open / shut .. Take a step back @Wadrian and review again! What function you want your house to perform. You are starting, it seems, to think about a bit of technical design..you'll get loads of info on BH so always review, it's Ok to change your mind as you go and learn more. If it just a house for say two of you that are in eh "later years like balding me" or a mental family with a country feel, you get to smell / topuch what is happening in the outside environment, If mental then MVHR is maybe not the best option in the first place! Personally as a designer, SE, ex building contractor with 40 years experience my personal horror is to live in a sealed box! It looks great on paper but few years down the road it makes no commercial sense to me in the self build market ( it will break down so if you can avoid installing it in the first place? ) and is probably bad for your kids.

Great comment and input from jackcowdry and Mike. Old roofs were so draughty with traditional sarking / battens that the last thing on the builders mind was to introduce more ventilation. Looking at these more modern photos I'm at a loss how they have ventilated it as the large format slates won't be helping as they are so tight. You could use traditional timber sarking with a 5.0mm gap between the boards and a breathable membrane (Tyvec Supro or similar) but again these modern slates are so tight you need to be careful. Potentially you could get eaves ventilation (50mm air gap up the roof with minimum 25mm width soffit ventilation) up behind the gutter but there is no ventilation at the ridge.. unless it's all hidden on the back side? The potential for damp at the Juliet balcony looks high. A bit spoilt by the plastic soil vent pipe. A nice bit of cast iron pipe would compliment.. if the budget stretched to that. As a rough guess it could work with a smaller slate size, a bit uneven with plenty air gaps between the slates.. but I can't promise at the moment! Food for thought though eh!

Have a quick chat with your SE. It's often missed at the Architectural design stage.. you get hung up on the thermal bridging, water penetration and so on. But masonry cavity walls can be designed as vertically or two way spanning so they resist the wind load and stay stable (not buckle sideways) when you also load up say the inner leaf with floor joists or the roof which often sits on the inner leaf that load the wall off its centroid. If you put in DPC's wily nilly you can break the vertical spanning capability of the wall which in this case it look like you might have done. You have no wall ties at lower level so that looks a bit off so this is related to the above as you have a quasi rocker bearing in the wall. I've not spent long thinking about this but I would first look at, and then test my arguement: 1/ Delete the cavity tray that runs from the bottom of the cassette vent back up into the inner leaf. What is it doing when you have vulnerable insulation below it anyway? So now we have done something good structurally too! 2/ The DPC on the inner leaf is shown at top of screed level. I would look to drop that to bottom of screed (think buildability) level and then turn it down behind the insulation against the inner leaf and stop it 20mm short of the cavity lean mix fill to stop any potential wicking effect. 3/ Get another wall tie in below the lowest one you have shown to improve the vertical spanning capability of the wall. 4/ Your cassette vents are too high so the lower insulation and cavity are not getting air. Drop them and the outer DPC so they are just over 150mm above finished ground level. Draw that out, think about the structural side and mull it over. That is what I would do in the day job and then think does what I've drawn make sense! For the sense check, yes I've talked about the SE side but let's have a look at buildability and cost. Are we making things more expensive or are there any Architectural details that prohibit say the height of the cassette vents?

Interesting. I've been working and advising a Client that has been wading their way through the ProteK procedures, their fine print, how they are looking to offset their risk to produce, I assume, a competetive 10 year warranty quote. In the last couple of days this seems to be resolved and a deal has been done. I can say it's been a journey and I feel for the Client but they are now able to move on. I can't expand much more on the detail as much is confidential. From my experience so far with ProteK it may be worth letting the public liability slide for now. My reasoning is as follows: As an SE / Architectural designer my Professional indemnity insurance premium is quite a lot. There are two primary reasons for this. First is that if I cock up as an SE injury or worse could occur and that would result in a high level of claim. If you want to be an SE then a high premium comes with the terratory and we maintain that cover normally for 3 to 5 years unless otherwise agreed. Second. with my Architectural hat on if I miss something like daylight requirement, breach the building regs there will be a potential claim. ProteK, as you'll find out may or may not ask you for a plans check / the insurance the Architect or you carry if have drawn the plans yourself carry against a breach of the building regs. Again cover is for 3 to 5 years unless agreed otherwise. ProteK have "now" got the jist of the above. Now the above coupled with your (Contractor's site insurance) adds up to a fair sum, but all of the above cover most aspects of risk and what you are left with is the public liability (PL) insurance which is cheep in comparison. I think ProteK bundle everything up and that is why they don't want the hassle of separating out the PL as it's a small element. There are "commisions" and so on. To provide a bit of context my PL cover is less than 5% of my PI cover. This is where the premium could vary a lot, concentrate on this bigger ticket item rather than the PL. Check your fine print for contaminated land clauses and the statement of facts you made. They may have updated their documentation but note, SE's need to be insured, but by omission in their statement of fact questions an Architect or Architectural Technician maybe does not require insurance and thus this could infer that you can do your own drawings for BC as a self builder. Have a look at their PD (CDM) requirements and with that comes the need for a health and safety file at the end of the build. I'm sure you'll get it sorted out but you probably need to get a hold of a senior person at ProteK. ProteK as I understand (having sat down with one of their inspectors) sub contract (sort of) out their site inspections to independent surveyors. The inspector that came to meet me in my office was highly competent and appeared a dilligent individual which was reassuring I felt. In the round I got the feeling that ProteK are doing a good job, have quality surveyors, yes they might be strict but that is what you want surely.. to get your house right? Where I think they may fall down is on admin and the computer says no!

But you should be interested in how they go about making their money; their procedure, inspection regime, plans check, how they offset their risk by passing it onto your other professional designers. If you can get a feel for that then it will inform you more when choosing a warranty provider. Check with your designers and see what they are offering in terms of their PI cover. It's common for example for SE's Architects to offer 3 or 5 years cover. If ProteK turn round and say well we want ten out your Architect then you need to discuss that with them now and not wait until later. Your drainage field may well come under the warranty as not least it will need to be mentioned in the Health and Safety File that ProteK ask for so they can issue the insurance certificate, that your lender also needs.. The best advice I can give you is to nail this as soon as you can as if not it could cause you a lot of stress later. But it's also your business!

If well known then it should be no problem for him to provide the evidence that what has been installed it not detrimental to the underlying structure. If you suspect deviancy then post here as there are lots of legal and hard nosed contractors on BH that will review.

I have read some of your posts re this and you have my support. I come across this when arguing with warranty providers, it's one expert against another and often about workmanship which can be an abstract subject.. What I would do is to turn the table, look under the bonnet and see if you can skin this cat in a different way. This is a tactic I use against warranty providers when they deny / delay / defend. In your case of the zinc roof I would ask them / him to demonstrate that the method of installation does not compromise the structural intergrity of the building. It's a simple question but if that is not answered then the zinc workmanship becomes a moot point. If they can't show the structure is protected then it likely has to come off and be replaced to ensure the safety of the structure. Let's say they go to court and say.. our workmanship is we think ok because we are "boys".. the judge says but you @Mulberry Vieware protected under the consumer protection act (domestic client which attracts extra protection cf a commercial client), any work they do should not be to the detriment of the underllying structure, it must comply with the HSE 1974 act, current CDM regulations and Building regulations.. but you xyz zinc "boys" have not demonstrated that the roof you installed is compliant with the statutory regulations so until you do your argument about the actual zinc workmanship is not going to be considered. So your next step is to write to them / him in this case and ask him to demonstrate that what he has done does not compromise the underlying structure. This is a fair and reasonable question. If he fails to answer this then he is on a sticky wickett.

Ah but as an SE I can bring you back to life, train you in maths and all will be ok! You'll also be a good cook so you can make us all on BH good... pick your dialect.. England.. dinner, Scotland.. scran.. Wales..grass fed lamb stew.

No I'm not and I speak from experience, that said, you are right Nick and I had not included that in my previous post. . Say you are a young couple that has bought their first house and are skint. They suspect that something is wrong, they contact the warranty provider, they might send and inspector after many emails and then do the delay.. they work their way around to inferring that the young folk need to spend cash to investigate further which they often don't have. So I get a phone call, I listen, try and give advice and then say I need to be paid if they want to go full monty. It breaks my heart at times. I know the warranty provider are taking the piss while at the same time being very pleasant about it and personable.. But the KEY here is that as an insurer you can hear off half the claims straight away so folk never get round to making a formal claim. For all this is a numbers game. I know this as I sometimes do this as a day job! In my earlier post I explain the finances of the warranty system. I don't think they do make that much in the self build market, which is risky. There are a pile of self builders that have no clue what they are doing. There are also some devious self builders that try their hand as a one off.. not all self builders are honest to god! A few have cropped up on BH from time to time. In the volume build market you have loads of professionals involved and that reduces risk. It's not venting. It is an adult discussion. BH is one of the few forums where you can be open and honest.

This is a good approach, often you can be safe and protect others at no extra cost, all you often need to do is a bvit of thinking! Being safe often does noit add cost. Being unsafe and cutting corners can be very expensive if you get caught. If anyone gets hurt then the HSE will be down on you, you could go to jail!

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.