Gus Potter

Hello Pamela. That's you up and running now! Hopefully this will give you some food for thought, even if to rule things out. For all the information that is provided on a warrant drawing is particular to Scotland, but hopefully other BH members in the UK may find something of use. "Have planning and building warrant sign off for a single-story side extension (roughly 74 m2) and part remodel of existing 1950’s bungalow in West Lothian, Scotland. Next stage is deciding to either project manage or ask Architect to take this on." Yes this decision crops regularly. I imagine you have asked your Architect what the project management fee will be and what the fee will be to produce a full tender package of information. As a rough guide expect this to be at least if not more than you have already paid your designers to get planning and warrant. To get your head round this the building warrant drawings are prepared so as to satisfy the requirements of the Scottish Building regs.. they are not full construction drawings. Some warrant drawings will be more detailed than others depending on the approach the Architect/ SE has taken and what level of input and drawing detail an SE has provided. A starting point here is to look at what level of drawing information you have and if you are able to use this as a basis for a contract without exposing yourself to too much risk.. say by way of extras or the contractor swapping materials / doing something that may compromise the structure for example. Ideally, we would like to hire a main contractor to build the extension to watertight/ weathertight stage which will have an agreed start and end date. Thereafter we are content to do the internal works ourselves alongside other trades, when needed. For this part we are flexible about project finish times as we are aware that material costs are increasing and this is a way, we can offset some of this. We appreciate the pros and cons of this route. For your particular set up (we do this in the central belt of Scotland) what about having a chat with your SE. I'm reading between the lines and guessing. What can work is that you say to the SE.. look we want to do as much as we can ourselves but need to know if the founds / main structure is ok. What will you charge to update your drawings for tender.. the devil in in the SE detail and can you make say three or so visits to site to check: 1/ The ground is ok before they cast the founds 2/ Once the underbuilding is up to drop by and just have a look 3/ Come back once the main structure is up but before anything is covered up 4/ Be available should the builder just want to give you a quick call if there is something they are not sure about. 5/ Hard to ask this but once you have a rappore with the SE.. be like our "Dad" and if we get stuck give us a few free pointers. It's a halfway house but with a bit of thought and effort on your side it can work. In terms of the JCT contarcts I assume you have had a look but have posted links to the ones; homeowners with or without consultant. With consultant https://www.constructionbooks.net/jct-contracts-2016/jct-homeowner-contracts/jct-build-contract-and-consultancy-agreement-for-a-home-owneroccupier-2021-9780414098282.aspx No consultant https://www.constructionbooks.net/jct-contracts-2016/jct-homeowner-contracts/jct-building-contract-for-a-home-owneroccupier-2021-9780414098275.aspx It is our intention to produce the contract/tender paperwork and we have seen on other websites the amount of paperwork that would accompany an invitation. However, what are the basic requirements that we need and is there anywhere we can see completed templates to give an idea of what level of detail is required? Currently looking at a JCT contract. You'll be hard pushed to find this as much is intellectual property of the designers. There is some generic stuff on the web. Why not go back to your Architect / SE and say, if we pay a little can you advise. That said there is good generic info on the web. "In the above situation who would be responsible for the CDM Reg? Us or the main contractor? Depends on the contract but if you go for the homeowner with no consultant then the contractor is liable for the CDM. The link below to the HSE helps set the mood re CDM for a homeowner doing an extension with no consultant. Well worth a read. https://www.hse.gov.uk/construction/areyou/client.htm Apart from the paperwork what else is involved in a project similar to ours? Timelines and pitfalls? For example, we are aware to record any amendments/suggestions by builders that we agree to so as to evidence ‘extra’ work for contract and payment purposes but are there other things that we need to consider? With regards to timelines – how long should we be considering for the tender process itself as well as the works if the plan was to commence March/April 2022. Any guidance on this is much appreciated. Great point here. build a rappore with your builder, it's really important as they are in and working on your house.. you can even make new friends.. just like a lot of folk do through work.. but. Take loads of photographs on a daily basis if you can, record the weather and put absolutely everything in writing. This can stop you falling out in a serious way. Some good builders I know (central Scotland belt) are booked up for the next 9 months at least so 2022 sounds sensible. Also, material prices will hopefully have stabilized a bit by then. The best time to be starting founds our way (I'm in East Kilbride) seems to be May time.. had some great weather this time of year recently.

Yes they do need to comply with the regs in terms of the max 100mm spacing between the spindles and if open treads then no gap more than 100mm. They also need to be able to carry the standard domestic loading stairs. The handrail height has to comply where there is a risk of fall from height. Landings need to comply where it is a safety issue but not for future stairlift installation. But they can be rough as you like in terms of appreance. Just you can't have nails etc sticking out of the handrail etc.. It's not to onerous. From a practical point of view.. you'll have lots of folk coming to look / admire your new home.. that last thing you need is for someone to get hurt and spoil it all.

Great info from all. All I can add is great to see raft foundations.. and the base plates need holding down bolts so the nuts protrude a bit too. In terms of drainage this can go above and below the slab. For me.. best way to make either option work is to leave yourself plenty leaway in terms of pipe position and fall. When the drains are below the slab even the best contractors get the odd pop up holes a bit off.. the pipes get a knock when concreting. Cut yourself a bit of slack on positioning and it will pay dividends later when the pressure builds, lots of trades on site and you have to make on the spot decisions. For the shower trays I would try and leave almost a partial depth generous box out in the slab, check with the SE re rebar positions. In some cases you can omit the top rebar locally but you need some extra bars and diagonal bars round the edge of the boxout to prevent the slab cracking at the corners of the box out.. very important if you are having polished concrete floors. Mention this to your SE and it's a two minute job to add these bars to the reinforcement drawings. Partial depth box outs.. the seasoned contractors / addicted self buiders etc will be quick to point out that this sounds great on paper but in practice hard to execute if not sometimes impossible on site. The easy way is to know where you want the box out with some easy reference points to measure from, jump back onto the slab 18 - 24 hours after is has been cast, cut out the depth you need with a sthill saw and gently break out the green concrete. This is the easy way especially if you have omitted the rebar. TBlew keep us posted!

Evening SillyBilly. To get you moving I would explore further cutting a pocket for the 3 x 145 lintels so they rest fully on the brick 102.5 mm. Wrap the ends of the timbers with DPC to keep them dry. I'm not sure how to interpret your plan view sketch but by the sound of it the loads the lintel are carrying are not too high.. thus you probably don't need a pad stone under these particular lintels as these bricks have a descent compressive strength and the mortar looks faily sound... the timber with the grain orientated horizontally will crush before the brick. When you get a chance just check with your designer that it is ok to do this. The two studs to the left of the doorway can come in handy and sometimes they have a structural intent...they may also be helping to restrain the masonry / carry vertical load and also as you may expect act as a sub frame for the door. You''ll probably be strapping out what was the existing outer leaf of the wall and adding a bit of insulation too. If you have transferred the vertical load to the masonry then you can maybe add studs if lateral restraint to the masonry is required and these may be able to be arranged to work around the drainage. The main thing is that by pocketing the lintel you are probably doing no harm and this will let you crack on while you check with your designer etc. Just be sensible.. clearly if you are going to knock holes in the masonry for doorways near the lintel support then it may not be enough to hold up the extension during the construction.. let common sense prevail! All the best with the project.

The ply liner has advantages.. but that is predicated on the fact that the the liner is well fixed to the inner skin.. which is supposed to be plumb assuming masonry inner leaf... and that relies in part on good workmanship. The other thing is that if the ply box is off the square you have a pile of work to do to fix the lining so the margins around the windows look sweet. On Aluminium windows the frames are slender so any out of plumb effects really show up on the finish. On a wide (masonry) cavity wall I would look to see if they can be supported off the outer leaf if the inner leaf cantilever is large..weigh up the options.. each house is different!.. let the window fitters fit, square stuff up and positively fix the frame. Then do the finishing to get an even margin around the windows. Just as an aside if you have a timber frame (TF) on the inside then this fixing to the outer leaf is a non starter in my view as the TF moves about up and down by a fair bit. In other words the window is fixed / stays still as is fixed to the outer masonry leaf.. on the inside the TF is going up and down and this will not look good when viewed from the inside!

Hi Mike2020. @Roundtuit needs credit for this one.. the ten years. In terms of you 50 hours a week I can from experience advise that you may want to consider breaking this down. I have discovered from my own project that; 1/ I'm not 30 years old any more with endless physical energy. 2/ Best to break the day down into physical work and thinking time.. 3/ Have a large lunch and a sleep after, lets the brain work on solutions for the afternoon. Each to their own I suppose, the main thing is to set yourself up so you get a dail (at best) or weekly burst of reward for your efforts and this keeps you motivated for the long haul.

Hi Temp. Just to take a step back. When you are doing the panel drawings for a joiner to work to for a timber frame you look at what off cuts you are going to generate. Now a standard length of timber is 4.8m and you can end up with say a few handy offcuts that you can use. Now although you may have a 3 ply 150 "lintel" on paper it may be that it is not carrying any significant load. If you you are using 145mm studs for the walls then this is an easy way of using the offcuts to build out the thickness of the wall over a doorway / window. The actual width of a C16 timber is 45mm so 3*45 gives 135mm, often the OSB board on the kit is 9.0 or 11.0mm so the joiner just needs to put a ripping on the inside of the lintel and this allows the plaster board to plane through with the 145mm studs ( we cut ourselves a bit of slack on 1.0mm). It's the simple stupid approach but economic practical design. If the 3 ply lintel is carrying some load then rather than trying to find a hanger then you can often support the end of the lintel using a couple of vertical studs and these you fix to the wall. Have a look to see what your 3 ply timbers are doing and look for the simple easy options?

Quick question.. For domestic houses do we not look at the number of bedrooms first.. then jump to the British Waterways flows and loads guidance and this gives us the flows.. and we use this to design the drains and the water usage. Now I could have a bathroom with two baths, maybe three all in the same room.. but the flows are based on the number of folk that could be in the house and this is dictated by the "normal occupancy" for domestic purpose and this is derived from the number of bedrooms? To be pedantic.. you fit a new kitchen with and island unit. In the island you have a tiny sink for tipping out the gin you can't finish, you have another sink for day to day stuff then in the corner you have one of these massive deep 1960's 700mm deep sinks with a mangle over as you still like to do all you washing by hand and that sink holds the same amount of water as this baby bath. Now the folk that wrote the regs know / hope that it is uncommon that you may be.. so drunk to the extent that you are chucking out your night cap / washing the dishes / and doing a last hand wash all at the same time before you hit the sack. Dan F .. hope this helps.

Yes, but you still need a carrier for the plaster. The surveyor is correct, it's just they may have assumed that you know that the lime plaster needs something solid to "stick / bond to"

Hi Mike2020. Your project sounds great. On these jobs it's easy to get carried away and do stuff that at the time on an ad hoc basis.. fire fighting!. For example you have moved in, have kids, a day job and need to do things that just have to be done in the interests of family harmony... that is life when you don't have a money / time tree growing in the back garden. Taking pictures is really important. Sometimes on these big old houses (DIY) projects your head goes down and you feel you are not making any progress. At that point you can sit down.. look at the photos of when you started and say.. hey look.. we have done quite a lot and this can lift the spirits and spur you on. Before you buy your dehimidifiers then reflect on where you are.. do you really need them.. have you checked you gutters, down pipes, cut back vegitation next to the outside walls, opened the windows during the day. It's a different mind set.. imagine you are a custodian of the building! You'll often find that once you get a handle on your house you can really appreciate what you have bought. learn to live with it and adapt.. that is the joy of owning a 17th centuary house..

Hi Mike2020. I may have pick up your post wrongly.. Have you been told that you can fit the wool boards between the beams and then plaster the ceiling? If so I would avoid. Maybe a starting point is to look at a new house. You have the ceiling beams, below is attached plaster board which acts as a carrier for say a skim coat of gypsum based plaster. On an old house you have the ceiling beams, timber laths (carrier) with a gap between. They used a plaster with horse hair and a bit of stuff from the barber shop. The base coat of plaster (lime based) was forced up between the spaces in the laths.. this gives the key. each lathe carries a bit of the weigh of the plaster and each lathe is nailed to the underside of the ceiling beam. Then the finish coats (lime based) were applied. If you want to use a lime plaster then you need to relicate an old lathe and plaster ceiling either by lathes or by using an expanded metal mesh. The insulation is just intended to keep the place warm.. not to carry the weight of the plaster. This is (lime based plaster on ceilings is expensive) hence my previous post about understanding your house. Hope this helps.

Hello Mike2020. Sounds like a cracking project. Have you taken plenty photos so you can look back on your efforts once you have finished? Before you make a decision on how to tackle the ceiling start right at the top of the house.. look to see what you have and write it down. This excercise often crystalizes your thoughts.. imagine you have to expain to someone how your house works. Start with the roof covering.. work down. Ask youself.. how is the roof kept water tight and ventilated.. how does the water vapour get out / in? get a handle on this (if you have not already done so) and this will help drive how you plaster your ceiling. If you don't know the answers then fine.. but now you know what you don't know. It seems pedantic but it forces you to look at the structure holistically.. can be a lot of fun too! This holistic approach is essential when dealing with "old houses" You want to spend your money carefully and target your spend to get the best out of your endevours. If you feel able, post your findings on BH and you'll get loads of ideas and suggestions.. for free!

I wish you all the best with your windows. For all. One great thing about BH is that if you give a bit you'll get lots of ideas. Some may not suit (some you may think are .. ? ) you but good design often involves looking at other's designs critically and how they interface with your own home / wall construction... often ruling things out is a great way of reaching an informed decision. Once you get into the 3g (triple glazed) world of windows and aluminium frames with wide wall cavities you have two basic choices. Do we try and transfer the weight of the window to the inner skin or do we look to see if we can use the outer skin to support the weight of the window. Now if you have a wide cavity and aim to use the inner skin to support the window then we need say brackets / a box type liner that are going to resist the cantilevering effect. We need to look very carefully at the fixings and how they will perform long term. In general anything that is cantilevered tends to move a bit more. Windows over time need adjusted / maintained as the glass moves about in the frames and the seals slacken over time. Couple this with cantillevered brackets and you have introduced more potential movement.. and these windows are expensive! If we use the outer skin then we also have potential rotational forces as the outside of the frame only has potentially / commonly a 15.0 - 20.0 mm rest on the outer leaf and.. we have issues about not breaching the water seal on the cill below as you need to fix the cill to the base of the window frame. We need for example to make sure we keep the drain channel at the bottom of the glass clear.. to prevent the sealed units from resting in standing water etc. But if you have a wide cavity then in some cases you can use the outer skin to support the window, you can remove a lot of the cold bridging effects and rotational / cantilever effects.. much will depend on your wall construction but it's worth exploring to see if it suits you or if you can get some mileage out of it. You can see on BH much discussion about bifiold doors and the options regarding top and bottom supported doors.. imagine your window is a bit the same.. do we bottom support it or try and support it up the sides / bottom with some cantilevered structure? To finish.. BH is also about having a home / extension / DIY project that no one else has! Not just on the outside but also under the bonnet.. the guts of the structure. Don't be afraid to post up a sketch, just draw it on A4 paper, take a photo and post it.. you are not entering a drawing competition. No one here will judge you on your drawing skills. Have fun exploring..

Any chance of a sketch showing the wall construction, frame thickness and cill detail, will help clarify the 90%? Just draw it on a bit of paper, take a photo and post it?

Hello Sillybilly. If you can post a sketch drawing and maybe a photo you may get some good pointers.

300 a day is quite a big ask on a DIY build. I would go for around the 250 a day. Then factor in the recent weather! Yes the blocks may be laid out for them but do they have a good working space for the mixer? / is it a premixed mortar? If hand batching on site then where and how you store the sand can impact on productivity. If you have let the sand get soaking wet this slows things down, also, if in bulk bags that have not been covered from the rain and sat on a pallet.. then as you work your way down the bag each batch of sand gets wetter.. each batch has to be carfefully monitored.. takes time. Before you take a view then have a look at the quality of their work. Have they kept say the cavities clean, are any solum / cassette vents all protruding the right amount, are they plumb / level. Have they got their wall ties clean, are the right amount inserted, every course around openings etc. Are the ties embedded properly into each leaf say or neatly nailed to a timber frame. Do and cavity trays you can see look neat and water tight. Are the dpcs looking nice and straight. Do the mortar beds look level and of a consistent thickness, are the walls plumb? Good workmanship takes time to execute. Speed an quality are often not good bedfellows.

Try a softer broom. Chase the water to the low point. Rope in a helper with a dust pan, hand brush and pail.. scoop water into pail. Dry the last bit with an old towel. Check your damp proof membrane positions. Now you will have a nice clean surface to lay your cellotex on?

Great informative thread this as have a particular interest in this type of construction, solid stone walls. It's remarkable how the body / tacit knowledge has built up over the last 30 years and how we are introducing modern materials. and " More curveballs please"... "The analogy fails though if I say I may come back to that one..." For say steading conversions in Scotland a common roof build as a starting point up may be 50 - 60mm of insulated plasterboard (with integral vapour barrier) fixed to underside of rafters, another vapour barrier as a second line of defense (my personal preferance which accounts for perhaps reduced standard of workmanship here and there). Then full fill between the rafters which are normally 18" centres on a typical steading. On top of the rafters you have the timber sarking boards, then a breathable membrane, then the slates. You may need to reslate so may well need to stick with a 1/2 in sarking board to plane though with the existing... and this chucks up all sorts of issues, the slate nail penetration being one. If re slating large area then go for a thicker board (19mm) as this takes the bounce out of the sarking. This makes it easier for the slater to get the roof tight but also easy to maintain in the long term... provided you have not double nailed the head of each slate.. slate the way the slaters do in your area, you can void the guarentee on the slates (if buying new) to a certain extent but at least you can make an informed decision considering ongoing maintenance. Practically if you look at an old roof the nails don't pull out as they often have some corrosion on the underside which binds the nail. If you have PIR with shiny foil tight up to the underside of the sarking the foil gets a regular punching.. not sure if this makes much of a difference. The point is that there is a fair bit to mull over. OSB is a bit vapour permeable but not much and not enough to let a full fill roof breathe in the Scottish climate. However timber sarking is much more forgiving. The 2.0mm gap is a figure that crops up. Some of the design codes are based on past experience and observation rather than pure calculation. One way to demonstrate this is to look at the suite of Eurocodes, many of the codes have a national annex.. which reflects the environmental conditions in the UK. If you look at an old steading roof you'll see that the sarking boards have shrunk, gaps can be 5- 10- 14! mm. Also the boards have warped which encourages air flow under the breathable membrane. Normally the sarking boards that get delivered to site in Scotland are pretty wet. I have fitted them tight before.. no gap, give them a month or two and you'll see that even a board 100mm wide has shrunk to give the 2.0mm gap, once you put some heat in the place the gaps widen further. Certain parts of Scotland can get pretty cold -18 to -24 deg for several days. Putting a good thickness of insulated plasterboard on the underside of the rafter can reduce the risk of "ghosting" .. where you get some local surface condensation which shows up as darker lines on the ceiling. If in a kitchen then cooking fats can condense more easily here. Although the ceiling may not be "wet" these marks don't go away.

Onoff.. You are a star! .. what lovely hands. Are they yours? and the flints look great by the way. My view is that cement is not an option. All cements shrink.. flints have a very smooth impermeable surface and you won't get a flexible bond if you use a mix with any cement content. Plenty info about lime mortars from other poster already. One great thing is that if you use non hydraulic lime you can do a foot or so every few days.. just have fun! Just put a cover over it to keep the rain off. You may build say a foot every few days, but if it's not looking right you can take it off, clean the flints and have another go. Harder to do if using a cement based mortar. I real life you just need to get on with it, stand back and see how you go! even if you have a template once you get a foot or so up it will all go to pot.

The vulnerable points are where the drain cock is, drafts under where you may have a bit of suspended floor. Please don't fill it (UF) with antifreeze as at some point when you service the heating this will end up in the ground / sewer or local stream. If it gets that cold your other water pipes will burst long before the UF pipes which are insulated by screed?

Craig.. thanks for your post.. every day is a school day re first floor windows. Being Scottish based most of the burglers are too incapacitated to reach the first floor! it's the Buckfast effect. For all Uk wide just make sure you have covered the regs regarding fire escape, it's easy to get caught out here in the excitement of you new home.

For all the above all sounds a bit technical but if you are a self builder and want to get your head round the structure start with a card board box. Tape up all the sides and tape onto the top the sloping sides or your flat roof. Stick the box to the top of the table just like it is sitting on you foundations. Next push it from side to side and put a bit of weight on the roof. Observe.. get the kids involved. Now start to cut out your windows and repeat. Observe.. Then cut out say dormers or add a floor.. it's like say that game Jenga! You can then start to understand what is going to happen to your house. This will then let you communicate with the Architect and SE and enable you to ask some searching questions! It is then up to them to respond.. you have captured the high ground from the start! Make them expain! Spot on Tony with your appreciation that unless you resolve all the forces things will move. In a structure all the forces need to be in balance. George the ridge beam... I chucked that bit in at the end of my long rambling post for the very keen and as a bit of "last resort stuff" in the spirit of BH and.. I was on a roll.. typing away like mad you see...technically feasible but to prove it calculation wise you need several sheets of paper a lot of pencil lead! @saveasteading Having read some of your posts you know a fair bit about industrial building design and building say B&Q sheds. You'll know (as a contractor) that the wriggly tin roofs provide diaphragm action.. so they don't deflect at the wall head as much as the SE says they will from their basic model in the office... same applies on a smaller scale with a steading roof with timber sarking. @saveasteading save points out rightly that sarking has series of boards with gaps between to ventilate the roof. OSB does too! just the gaps are further apart...OSB needs a 3.0mm gap that is why the size of the sheet delivered (1197mm ) on say the nominal width is not 1200mm metric size. With a fair wind (very fair wind) you can make this fly.. if you have a long rafter and not daft holes for velux. That is one reason (one other is that they are heavy and thick) why these old steading roofs are still sound and the walls are not spreading after 100 years plus. Also, the old nails had a bit more poke to them, near the sea.. story for another day. For all. The above all sounds a bit technical but if you are a self builder and want to get a feel for things structural wise then start with a cardboard box (also could be your ICF basement). Tape up all the sides and tape onto the top the sloping sides or your flat roof. Stick the box to the top of the table just like it is sitting on you foundations. Next push it from side to side and put a bit of weight on the roof. Observe.. get the kids involved. Now start to cut out your windows and repeat. Observe.. Then cut out say dormers or add a floor.. it's like say that game Jenga! You can then start to understand what is going to happen to your house. This will them let / help you communicate with the Architect and SE and ask them to explain what you have observed playing about.. I may not sound too convincing here but the cardboard box thing is a great way of learning by observation. We actually use this concept to train SE's about more complex theory for example shear centre behavoir.. we make a cee section beam (as opposed to an I shaped beam) out of cardboard load it up and watch what happens.. then we learn the mathematics behind what we have observed. @saveasteading Don't give up on the solid timber sarking just yet to restrain your old stone wall heads !

This as "reasonably practicable" crops up from time to time and is mentioned in the Scottish regs for conversions. A few decades ago we just used to line out these steadings in Scotland with 50 x 50 timber with brackets back to the stone walls, a bit of 50mm cellotex between and off we went. Now I suppose I'm a bit more cautious. The insulation requirements are more onerous, we have less drafts and now we worry about dew points and so on as we are insulating these places to death. These days I want to know bit more before hanging my coat on a peg. I have mentioned Scotland as the climate is much different and challenging for a designer. Saveasteading has posted some photos of a cracking old steading that could be frankly stunning. Hopefully more to come. Looks like there could be the odd structural issue but nothing drastic. For me steading conversions in 2021 are a different animal from the ones I did 30 years ago.. @saveasteading maybe this is the time for a review of what you have. There comes a time in a project on say a steading conversion when you need to make some decisions on how you approach the design in detail, you start getting bogged down in the regulations, insulation for example.. as far as reasonably practicable...maybe it's time for a wholesale review of where you are at. You invest so much time on just getting the plot that for a while you can take your eye off the ball. To make your case for "as far as reasonably practicable" I would start with the founds and the ground under. You almost have to tell a story.. just like I'm doing here in some ways. The soil and water table. Is the soil say clay, that can transmit moisture or is it gravel. Say you have gravel /sand soils. Is the gravel / sand igneous, if so the porosity of each particle will be very low. In other words. I could have a pail of glass marbles. Each marble is water tight. Put water in the bottom of the pail and it won't get to the top. But add to the marbles some clays, silts, organic material and the water can rise a little. This is called permability. Describe the soil, behavoir and work up. Say you have demonstrated that ground water / significant moisture can't get near the floor level and that you have a gravel soil that does not promote frost (ice) crystal grouth. That solves the damp proofing and frost protection issue. For all..yes you can have a foundation formation level less than 450mm below finished ground level. The next thing to would be to ask.. how do we heat the place? Are we going for underfloor heating? We need to comply with the regs. To do so we are having a slab with perimeter insulation?, it is all air tight?. Now we have a stone wall just behind the insulation above the floor level envelop that is freezing cold. You invite trouble in the long term as it's an often unventilated space and is right in the cold spot? That leads to water vapour that can't get out and manifests as condensation..often called "rising damp" I have chucked a spanner in the works here to demonstrate a point. It's all about understanding how an old structure works, what happens when you insulate it, understand how modern approaches of say insulated slabs for underfloor heating work. Appreciate where too much insulation could actually cause a problem. Once you get a handle on this and get your head around it you'll probably find that BC just love you! and you'll just not sail through the warrant process but also know you really understand what you are doing. Take a step back here, work from the ground up and be sure of your ground (excuse the pun) Understand the consequences of where you place insulation and why you are doing so. Do this and you will be able to satisfy the "as far as reasonable practicable" requirement. That in actual fact should be the least of your worries. You need to satisfy yourself that you are right! In summary I would want to review / look at what you have. Take a holistic view, yes you can often only do this if you have time on your side. Barn conversions suffer from the lack of width, a few extra inches can make a world of difference.

Can you post a sketch cross section? Try and show where you think the ground water level is. Don't skimp on the detail if you want good feedback.

Good points Adsibob about attaching too much responsibility / control over materials and workmanship to the BCO. I think that a lot of folk on BH place too much reliance on the BCO's. It's not that they don't have competance.. it's just not their job to look after your self build (hold your hand) and the day to nuances. @Adsibob"I can also say that even the best professionals make mistakes, and good teams consist of members that will spot other’s mistakes. My SE is good, occasionally a bit slow/lazy but on the whole has helped us do things I didn’t think were possible. He did however make a mistake in one of the beam designs. Luckily, my builder is very experienced and spotted the mistake before he ordered all of the beams. Who is going to spot your SE’s mistakes? Who is going to spot your mistakes? If you think it’s the BCO, then you are, to an extent, elevating your BCO to that of a project manager or site foreman, with a level of expertise that I don’t think they have. " I'll leave it at that as cannot add anything further of value to your well articulated post.