andyscotland

@JSHarris @Sensus I'm not an architect, and my physics could charitably be described as "hazy". But reading this it sounds like it might be one of those where you're both right, but @JSHarris is more right in practical terms? In my head an analogy might be if you wanted to stabilise the pressure in a pipe. You could connect a sealed air-filled expansion vessel. Or you could attach a water-filled reservoir. There are clearly measurable differences in the mass, density and compressibility of the air and the water (and, therefore, the amount of potential energy each vessel stores). But in practical terms, the size of the pipes to/from the vessels would also have a significant effect on the pressure-stabilisation characteristics of the system. A huge head of water up a narrow pipe would work less well than a small volume of air on a big pipe. I think? So it seems to me like the concept of "thermal mass" may be similar. Concrete may well be able to store a larger quantity of energy than timber. But (as I think @JSHarris is saying), the way the materials work to stabilise temperature gain and loss in a building is much more to do with how, and how fast, the materials absorb and release that energy than about their storage potential. And therefore the difference between timber frame and masonry may not be as significant as you'd imagine if you only consider their storage characteristics. If my cod physics has opened an unrelated can of worms feel free to ignore it ?

Don't know for sure, but certainly when I spoke to ProWarm tech support last year about their 18mm dry screed boards they said I'd need a floating chipboard floor between the insulation and the panel, as the insulation alone wouldn't be firm enough.

@zoothorn I feel a sense of déja-vu coming over me... The wall thickness depends on the u-value, and the u-value on the wall thickness. So even though you don't need to show the u-value or provide it to the council in advance, you most certainly do need the precise u-value info in order to get the wall thickness right. You cannot tell the builder what the wall thickness should be, he needs to tell you what it is (after he has done his u-value calculations). You therefore also cannot tell the builder any of the critical dimensions that depend on the wall thickness. In terms of actually drawing it, there are many many ways including various free or cheap drawing and CAD software packages (the latter being able to draw to scale and calculate / mark dimensions from the drawing). However I think it will take you a fair while to find one, install it and learn how to use it. And if you use it incorrectly you will introduce (costly) errors into your plans. My advice is still therefore the same as it was - draw it by hand and take extreme care that you are not accidentally specifying something that the builder should be deciding for you.

I've learned the hard way that claiming/proving anything based on professional negligence is enormously difficult (and therefore expensive). You have to prove the architect/whoever made a mistake that was totally unreasonable to make (defence: get another architect to say they could imagine making the same mistake). You also have to prove it directly caused the loss (defence: the loss was as much caused by the poor workmanship so it should really be the contractor in the dock). When I tried to use my home insurance legal cover to raise a negligence claim against a surveyor last year they reviewed the case and declined : the insurer's lawyer told me although the policy covers negligence in theory, in practice they almost never go beyond the case review as it's so rare that a case meets the threshold for prospect of success. She said they'd really only help with "surgeon left a pair of scissors in me" and similarly cut-and-dried cases. However in terms of value it seems to me that it depends what you want to achieve. If you're buying off plan / using a main contractor then I suspect a warranty more likely than a PCC to actually pay out, at least for the most extreme cases. If you're going DIY or competently project managing, are pretty confident everything is being built right, are happy to "self-insure" for any defects and just want a bit of paper for the mortgage a PCC may be a much cheaper way of doing it. Equally if primarily just want a bit of reassurance at key stages that you've got everything right a PCC (or other paid-for inspections without a warranty) might give you more control over exactly what's checked and when and the level of advice you're able to get, again at lower cost. I agree that my impression is the warranties are somewhat mis-sold. As you say, seem only really designed to cover cases where the house falls down, so if you just want protection for a leaking gutter or drafty window you'd probably be as well sticking the money in the bank.

Hmm good point. I wonder how significant this will be. Looks like with the tubes I'd need to drill a hole for each one, and drill a 50mm X 2mm countersink/rebate for the head (according to one supplier it would otherwise be visible through the GRP). That's quite a lot of work for each fixing. And there's still a partial thickness bridge from the screw through the bottom 40ish mm of the insulation. My u-value calc for the roof includes an allowance for nails or screws through the insulation, tempted to think the time and effort for the tubes wouldn't be entirely justifiable?

If you're taking it in buckets anyway you could tip into another dumpy bag to keep it all together but that'll be tedious to tip into from a barrow. If barrowing I'd just spread a large tarpaulin (or a dumpy bag cut and "flatpacked" and tip into that. Use some spare [anything] to turn up three sides of the tarp a bit to stop the pile sliding away. Not the end of the world if you collect a few tiny bits of dirt for a job like this, but not too much. And you don't want to lose too much of the sand either, so best to keep it separated from the ground.

Just had to face reading one then ?

If you're on your own (even if not) you will be pushed for time and energy to get the material down, straight into mixer, mixed, barrowed and poured all in a single operation. If you bring the material down to the mixer first it may mean a little extra effort (picking it up twice, everything else you'd have had to do anyway). But the advantage a) it gives you a chance to measure what you're using so you can have confidence you'll have enough for the second pillar and b) more importantly, shifting the material initially is not under any time pressure so you can stop as often as you need. Then once it's done you can take a proper break and get your breath back before you start the mixer and enter the flat-out-non-stop stage of the process That trade-off, for me, would always be well worth it.

@zoothorn easiest option is probably to just crack on with the first pillar. Bring down plenty more ballast / cement than you think you'll need for one pillar (but less than you think you'll need for two) and drop it by the mixer. Count how many buckets you brought. Then start mixing concrete and pouring until the first pillar is full. Count how many buckets you used - easiest to have a bit of card taped to the mixer and a pen on a string and keep a tally as you will be busy! You will now know how many buckets you have left by the mixer, and how many more you need for the second pillar. That's probably a good point to clean the mixer and take a break. You can then bring down enough material for the other pillar - you have time then to order/collect more ballast if you need it. If you need loads get a bulk bag and keep it for the extension, if you need a little bit pop to the diy shop. No point getting too precise with the quantities in advance. Ballast will settle slightly differently depending on the exact ratio of sand/aggregate and how well you compact it. You will also drop some on the way down the hill, and you'll spill some concrete when you pour it into the tube. For the actual mix, most ratios are done by volume so just measure full buckets of each material in the right proportion. If a full bucket is too heavy to lift, find a smaller container and use that (again full). Water volume is trickier, most cements will give an indication of how many litres per bag of cement however this includes any moisture already in the ballast. Kinda have to do it by eye. Use a separate measuring bucket with a scale marked on it, pour it in a bit at a time and stop well before the recommended amount. Let it mix a minute or two then if it looks dry add a little bit more and repeat as necessary. Never spray from the hose direct to the mixer, it's impossible to gauge how much you're putting in. Sometimes it looks dry but just needs another minute of mixing rather than any more water. Ideally once it's in the tube you'd use a vibrating poker to get air bubbles out and make sure each pour mixes with / bonds to the one below. For this job probably not crucial, if you have a power sander you could put on the outside of the tube for a minute or two that would help, and/or just stir the two layers together a bit with a big stick each time you pour a new barrow in. I wouldn't worry too much about being bang on with levels. You can always pack up the beam with slate / mortar / brick / timber / whatever to deal with any small variation. In fact that will probably be easier than trying to level the pillars perfectly to each other as you pour so I'd work on the assumption they'll be slightly out and design on that basis.

So it is, didn't spot that. Yes I believe it's 1:4 for mixed ballast to equate to a 1:2:3

According to https://source4me.co.uk/calculate_concrete_mix.php for 0.28 cubic metres you need 90 kg (4 bags) of cement and 0.47 tonnes of mixed ballast.

For the overall volume, start with the area of the circle forming the cylinder - π X (radius squared). Then multiply by the height. To get from the overall volume to the ballast qty depends on the concrete mix you're doing.

@Mr Punter thanks. They're T&G boards, long side perpendicular to joist and staggered rows. Only butt joints are on diagonal lines of the roof hips but those joists are tripled so plenty to hit. I've deliberately held off doing the VCL and ceiling battens underneath so I'll be able to see from below that all the fixings have made it into the timber. Also considering making up a wee guide block to start the screw at perfect right angle to the deck.

Yikes. So what would you use? Long screws, fancy "warm deck" nails, or something else?

Thanks, hoping that would be less of an issue in this case as only the top 18mm and bottom 60mm will be in timber, the centre section should turn fairly easily in the PIR? Or is the torque just a function of the distance between tip and drive head?

Yeah that was my concern about a purely adhesive fix. We're not cliff-top, but we are relatively exposed for an urban site (on top of a hill) so would rather be sure it's solidly fixed down.

Yes - with a warm roof (insulation above the structure) there's no requirement to ventilate. You make a "sealed parcel" of insulation, top deck and waterproofing sitting on top of the structural roof. At least, that's what I understood from advice from insulation and GRP manufacturers (and put on my building warrant drawing) so hope it's correct!

@scottishjohn a few reasons for not using SIPS. Main one is most of the roof is existing garage joists in unusual fan-out shape, had to optimise position of several rooflight openings and lightwells on site and then set out trimmers/doubles etc to suit. So easier to build up a layer at a time in situ. Also no heavy plant on site (and no access for it). I've already fixed the bottom layer of OSB. There's a polythene VCL to go on top before the PIR so was concerned adhesive fix might not be sufficient. The Forge Fast construction screws work out about 95p a screw...! Would you definitely recommend them over "normal" ones? Yes, the OSB deck is T&G roofing OSB and aware of the need for it to be dry. The boards and the PIR have been stored outside (well covered and with no visible sign of leaks). I was considering laying the deck and covering with properly lapped / battened breather membrane (I have a good bit spare) for a day or two to make certain any dampness has a chance to migrate out before I GRP. Then uncover and laminate in a single day.

(hopefully) quick question. I need to get fixings for the upper deck of my warm flat roof. I have 18mm OSB (nailed down) then 130mm PIR, then 18mm OSB. My engineer specified the nails for the bottom deck but there's nothing mentioned for the top one. The GRP manufacturer says I need 40mm penetration into the joist - so 206mm min overall length. I've seen various fancy "warm roof deck fixings" - helical nails, plastic tubes with a screw at the bottom etc. All fairly expensive, coming in about 50p per fixing. Can I just use very long ordinary woodscrews? E.g. these self-drilling countersunk 6 X 240 which work out about 25p each online. Or am I missing something and I need a fancy specialist fixing for some technical reason? As well as the cost, I'm thinking it'll be easier to keep a screw vertical into the joist below where a long nail might drift and miss it?

This is very true. But also why all the other cupboards get full so the carefully ventilated, beautifully spacious, future-proofed data centre ends up with wet mops leaning against the router, and boxes of stationery rammed up against the vents. Both causes of fried gear I've been to over the years. You could of course fit a lock and control what gets put in there, but I know how that would go down in my house. Better to design out the argument I reckon ?

@zoothorn it may seem pendantic, but there is a very important difference between "common" and "standard". Yes, 100/50/140-150 is common. It is often the most cost effective way to balance the various constraints in the most common conditions. But that does not make it standard. Standard implies it will always be valid, and there are many, many situations in which it is not. This is where it gets particularly dangerous. If you do a neat careful drawing of a common construction detail, it is very easy for the builder to assume someone has checked it is valid for your situation. And because it is common, they won't question it. Which then leaves you high and dry if in fact you needed something less common to suit the constraints on your build. In my experience, in problems often boil down to one of two causes: * A client who was vague when they should have been specific. e.g. "make it roughly 4 feet wide". Builder uses a full sheet as that's easiest for him and the client doesn't seem to mind. Later turns out it needed to be exactly 1.1 metres, and it's too big. But the builder made what he was asked to make. * A client who was specific when they should have been vague. E.g. "make it 140mm thick". The number is plausible, and builder assumes the client has done the calculations to get the specific value. Later turns out the client meant "make it have a u-value of 0.18", and there's not enough insulation depth. But the builder made what he was asked to make. I have seen this happen again and again, not just in construction-related fields but also in software development (my current trade) and elsewhere. Or, think of it another way. Imagine for a moment you do hire an architectural technician to do your building plans. Would you prepare them a drawing showing what you wanted? No, of course not. You'd give them the planning drawings and tell them to draw up construction details and come back to you with any questions. When you pay a technician to draw construction drawings, you're not really paying them to draw - anyone can do that. You're paying them to do the calculations and make the decisions required to know what should be built. The drawing is just the way they communicate those calculations to the builder. In your situation, you are not paying someone for drawings. But you are paying the builder to do the calculations and make the decisions that a technician would have done. The builder may do some drawings (e.g. for a panel supplier) or he may do it all in his head. Regardless of how he chooses to communicate with his team, he has taken on the role of the technician. If in the midst of that there are drawings floating around that you've done based on what you think is "standard" there will be conflicting information. And conflicting information always, always means trouble. The more carefully you draw, the more it looks like you've put a lot of thought (and knowledge) into what you're drawing. And the less likely it is that someone will query it. People don't like to think unless they have to. If there is no drawing at all, the builder will have no option but to think about everything. If there is a rough sketch, it will still be obvious nobody is meant to actually work from it. You need to insist the builder does all the thinking you're paying him to do. This is the only way to ensure you and he are on exactly the same page about who is responsible for what. If his role is as you've described it to us, he should be able and happy to work from the planning drawings.

No, because we genuinely, hand-on-heart want to help you avoid problems. Based on problems that we have seen happen to other people (or that have happened to us). And because, as we've repeatedly tried to explain (and I spent quite some time trying to give examples to help you see the complexity of what you were asking when you wouldn't just take our word for it) it's not a standard dimension from build to build. Yes, some sizes are more common than others. And yes, your builder probably does know off the top of his head which of the common sizes he'll build. He knows your project, he knows your site, he probably has a fair idea of your existing house (which affects u-value targets for the extension) etc, etc. We don't. By way of example, I am converting my garage and building a 2 metre by 2 metre utility on the front. It is a ludicrously simple project, really - a 30 square metre L-shaped building with two rooms. My walls are 183mm, 244mm, 262.5mm, 275.5mm and 270.5mm. There are very good reasons why each of them is different. And why I have 5 thicknesses of wall when on a simple outline drawing my room only has 4 walls : one changes thickness part way along. So you see, it's not even a standard dimension from wall to wall on a single build with a single designer, never mind from build to build. I'm glad that you were able to speak to your builder and that he was able to answer your questions. Hope that has reduced your stress.

OK - am now clearer that you're not actually trying to specify any of these things. In that case, my very strong advice would be to tell the builder that he has the planning drawings (which presumably show e.g. the fixed outer corner point and the position of the door), that those are the only drawings that exist, and that your understanding is he will entirely take responsibility for getting from that to a completed building. The problem with providing neat drawings that contain information that is "of no consequence" is that sooner or later someone along the way misunderstands the status of the drawing. And orders materials / sets out a corner / etc based on a detail or dimension that looked like it was of critical importance even though in your head it isn't. If you are not experienced in producing construction drawings, there's a fair chance you will draw or label something that you think is just diagrammatic without realising the implications of where you just put your pencil. And that will make it your problem, and your cost, to solve. In my experience, it's much better if drawings don't exist (or at most look like a fag packet sketch) than if they exist but are not accurate. Drawings that don't exist prompt people to ask questions and discuss answers. If you're determined to produce a build plan, draw the accurate lines (from your planning drawing) neatly with a scale ruler. Then draw the internal walls freehand, roughly 300mm away for an external wall, 150mm for internal, and roughly shade the gap so it looks more like an estate agent's floorplan than the architect drawings he's given you as an example. Do not attempt to draw the different material layers etc. Calculate and mark all your dimensions by reference to the external walls. This will encourage anyone looking at the plans to realise that they're looking at a sketch, not a drawing. Alternatively, you could print off the planning drawings and mark up - freehand - rather than trying to redraw them.

Ok, one last attempt. Common timber frame thicknesses are 90, 100, 125, 140 and 150mm. Some of those, on their own, will not fit enough insulation to meet the u value requirements. Depending of course on the type of block and the type of insulation. They may therefore need an extra layer of rigid insulation between the timber and the plasterboard, or outside the blocks. Some of those are only strong enough to carry their own weight, others will be able to carry the roof, others will be able to withstand wind loading. Some will need a rigid sheathing board, commonly 18mm but varies (and sometimes not required). Off-site prefabricated panels have a different range of sizes again. It's simply not possible for us to tell you what thickness the wall will be. Nor is it possible for you to tell the builder the thickness and then "HE builds the walls to satisfy BCO: HE decides the membrane & C'tex "U factor" etc etc.." The wall thickness depends on those decisions. So if the builder is making them, only he can tell you how thick the wall will be. Your planning drawings should already show the outline sizes, door size and position etc - all the info the builder needs for you to "pass the buck to him". Hence why we're struggling to understand what additional detail you're now trying to draw and why, if he's doing the construction design, he needs it.

To boil it down. A Build Notice doesn't need Full Plans, but someone, somewhere still has to make all the decisions that would have had to be made to produce a set of full plans. All of these decisions have a circular relationship with (they affect, and are affected by) the internal and external dimensions of the spaces. Every dimension and material affects every other dimension and material. There are basically two possibilities: Your builder is going to be responsible for making these decisions. In that case, he needs to produce the build plans himself (or use his experience and the simplicity of the project to do them in his head / on his fag packet as he's building). You give him the planning drawings you already have and he builds something that looks as close to that as possible while meeting the building regulations. If there are things on the planning drawing that aren't clear enough for him to work from, he asks you specific questions about what you want to achieve, and advises you on the implications of your answers. You are responsible for making these decisions, and your builder is just going to build what you tell him. In that case you need professional support.