Jeremy Harris

That's a more eloquent way of describing the risk than I could have come up with!

After our experience back then, I've deliberately been a bit nosey around building sites, and it seems pretty common for construction standards to be pretty lax. I think I know the main reason, it's to do with the amount of money some of the big builders are prepared to pay tradespeople. They expect to pay labourers rates for skilled trades, and end up with the bottom of the pile people who couldn't pass muster working for themselves or a more discerning employer. I've gone so far as to walk around a local part-complete estate nearby, that was only approved on the basis that the houses be built to the old Code For Sustainable Homes Level 4. That implies inspection of every house, unlike the usual system where only one house of a particular type is inspected and the rest are assumed to be the same. I walked around with a thermal imaging camera, on a cold evening before Christmas. The results were shocking. Every single completed house was leaking heat like a sieve, there was missing insulation evident all over the place, including one house where the entire first floor wall at the front had no wall insulation at all. Thermal bridges were all over the place, some almost certainly air leakage around door and window apertures. I discussed what I'd seen when out and about (before I walked around with the thermal camera) with our building inspector, who I'd got to know reasonably well during our build. He reckoned that probably around 60% of new homes didn't comply with Part L of the regs, and, from the tone of his voice, I got the impression that he was quite concerned about it. There's nothing that can be done by building control, whether LABC or a private company, as big builders are allowed to build the majority of their houses without any inspections at all. It seems to hit the news now and again, almost always when a newly moved in resident realises that the heating bills are way higher than they thought they should be. I saw one investigative TV programme some time ago that followed such a story, and one or two unhappy new residents have posted their thoughts around the web. However, the bottom line is that the majority of people who move into a new house just won't bother to complain about, or probably don't even notice, the poor thermal performance. As someone said to me when I was having a bit of a rant about it a couple of years ago, people buying new houses are far more influenced by the kitchen and bathroom bling than they are by the Energy Performance Certificate.

I think this thread should have a poll attached, so we can all vote for the one we like the best. Personally, @Onoff wins for me, hands down! Solidly built, really nice detailing, a fair bit of recycling and it just looks like a very nice place to escape to for a bit of peaceful and relaxing bodging. It even looks as if it may have a decent view!

Probably not! Each local authority (as Peter W mentioned) have their own list of what is included in their CIL and what is excluded. They could have chosen to exclude a public open space contribution from CIL and leave it as something that could be added via an S.106, for example. Best to check what your LA has included in their CIL and what they haven't, it should be somewhere on their website, with luck.

Terry, you are exactly right. I did look at the question from MY perspective, and that is different from the way that Martin (Sensus) looked at it, different again from the way Ian (ADIan) looked at it and definitely more aligned with the way you looked at it. Perhaps we all need to highlight where we are coming from when answering a question like this, or better still, ask the OP why they are asking the question - is it to gain a bit more understanding, or is it to satisfy building control, for example.

ST, I'm even more convinced this is probably the best solution for Crofter's needs after that. Best of all, I think, is that it's all pretty simple stuff to put together, with a performance that's likely to keep his guests happy and which has a very low maintenance overhead. I would imagine the reliability is pretty good, too. The only thing I remember watching out for, from our time spent living in Scotland, was that immersion heater elements would tend to corrode a bit, due to the slightly acidic water. I know I had to replace ours, when it was around 4 years old, as it tripped the RCD, and heard tales from around the village that it wasn't uncommon for them to have around a 5 year life up there.

Ian, I agree, but during the early stages of trying to get your head around which supplier to use, which build method, etc, it's useful to at least have some understanding as to how the basics of insulation work, before going to the extent of seeking proper values using the BS and BRE 443. As an example, when we first started planning our build we knew, in broad terms, what we could afford and what we wanted to achieve in terms of performance. I also had a basic set of drawings of the house, with no construction detail. I went around at least a dozen frame suppliers to get price and performance data, and found it very, very hard to be able to compare any of them. The final straw for me was visiting a small development being built by one supplier and seeing first hand that the specification they had quoted wasn't being followed in practice by their workers (missing insulation, no cavity closers around windows, problems even getting through the BR air test etc). It was a thoroughly demoralising time. It was then that I decided I needed to try and understand the relative importance, to us, of each element. Doing some basic research (and a lot came from the BRE) I came up with overall U values that would meet our heat loss target, but then learned about decrement delay, and the impact this has on practical comfort level. I ended up going around the whole loop again, and approached a sub-set of suppliers as a "slightly more intelligent" customer, with the intention of trying to find out, as best I could, who really understood what they were offering and who didn't. If I'm honest, I was very disappointed with the majority of the suppliers I took the time to drive fairly long distances to talk to. I ended up with two potential suppliers, both offering similar overall thermal performance in terms of heat loss, but one offering a very much higher decrement delay solution. The only way I got to that point was by a hard slog, and digging through mountains of misleading information, including some from insulation suppliers themselves (try ringing one of them up and asking for the specific heat capacity of their insulation, for example!). Only a handful of insulation manufacturers could provide specific heat capacity or decrement delay factors for their materials. In the end we chose our supplier on the basis that they met our performance spec, offered a lower risk build, by including the insulated foundation system, the fact they had a high decrement delay build system and that their price was OK. I'd be the first to admit that our requirements were just that, our requirements. Everyone doing a self-build will have differing needs, and differing priorities, so what worked for us may well not work for someone else. Finally, I'd just like to reiterate that if I offer something in the way of advice, it should be read in the context of my experience, which is designing and building ONE very low energy passive house. I'm not a professional in the building industry, I had only a DIY level of understanding when we decided to self build around 9 years ago now, and I'm entirely self-taught over that 9 year period when it comes to specific building-related stuff. The only slight advantages I had was having a lot of time to study (I've been retired for 6 years now) and having a reasonably good understanding of physics and mathematics, and I have to say that often the latter has created a bit of controversy, particularly when some suppliers don't seem to understand basic physics and quote data that is highly questionable!

Perhaps we should ask the mods/admins here to create a "sticky" post, where people can post requests and then try and sync up volunteers to carry things? Before now I've done this with people here, or arranged some half-way meeting place to hand something over, but it's always been arranged offline. A single thread just for volunteer transport would, in my view, help to kick this off. It goes without saying that I'm happy to help around the West Wiltshire/Dorset area, plus I travel to South Devon from time to time, and up to Swindon, or across to Basingstoke, occasionally.

Perhaps Peter S can give us a bit more feedback on how his performs. I agree it would be nice to see one in action, but after 20 minutes or so of web surfing I've struggled to find anything really negative about them, and generally people seem more willing to complain about something than praise it. That leads me to believe that they work OK, the old "absence of evidence to the contrary" argument, but not definitive proof!

I've been doing a bit of web searching since Peter S mentioned venturi showers, as I'd never heard of them either. This (commercial) link has some basic info, but generally they look an ideal solution for Crofter's situation, and probably something that guests would be less likely to be able to break/complain about etc: https://www.plumbingforless.co.uk/showers/venturi-showers There's also a thread on another forum about them that seems fairly well balanced: http://www.diynot.com/diy/threads/venturi-showers.33623/

I suspect that what will happen is that if you buy something from, say, Germany, post-Brexit, then it will have to be sold minus German VAT, as it's for export outside the EU. When imported to the UK VAT will be charged on the price of the item and the shipping cost and you will be able to reclaim that back from HMRC, in the same way that I reclaimed VAT charged on imported US goods. The down side is the UK could decide to charge duty on imports from the EU, and you cannot reclaim import duty. However, import duty depends on the class of goods, and is pretty low for a fair bit of stuff I've imported (generally no more that 4 to 5%, with a lot of stuff having no duty payable at all).

Just a thought, and not directly related to this thread, but probably more generally applicable, but how many of us travel around the country and could volunteer to relay items like this around? Obviously it would be slow, and rely on goodwill, but I'd happily act as a relay to help move/store something that otherwise would be difficult to transport. Sadly I don't see me driving up to the Highlands again for some time, but I wonder if we could see if there are people travelling around who would be happy to help someone out by moving something like this? Years ago, on a flying forum, I started a thread (it's still there as a "sticky" called something like "Do you have a spare seat?"). The idea there was that anyone going flying with a spare seat, and who didn't mind taking a passenger, could post there, and it evolved into a place where people, like student pilots, or just those interested in flying, could ask if anyone was flying near them, and if so could they give them a ride. It worked very well indeed, in fact I had no idea when I started the thread many years ago that it would work as well as it has. Perhaps we could think of doing something similar here, to overcome problems with moving things like a glazing unit?

Any thoughts on using a venturi hot water supply booster rather than a pump, ST? Crofter has high mains water pressure, soft water and it would seem that a venturi pressure/flow booster could well provide a pump-free solution. I know that pumps are pretty reliable, but they do have moving parts, and the idea of boosting the gravity hot water with the spare energy in the cold water flow, with no moving parts to ever go wrong, seems attractive to me.

I think that, at the moment at least, they are probably really more ISO (DIN) than BS, given the subsidiary ranking BS have within our current rule-making arrangements!

You're right, Dave, but I'm pretty sure the 15% here is the assumption made in the BS method if psi isn't calculated. It's rather like the ventilation rate assumption if an air test isn't performed in SAP. Calculation of psi is easy enough, but time consuming if you have a complex structure, unless you use a thermal modelling application that will do the analysis for you. Even then there are limitations. For example, some models use 2D flow approximations to true 3D flow, to ease the time taken to run the model. This is reasonable for a typical form of construction, but falls over a bit when looking at methods where any thermal bridging is by long and relatively slender members surrounded with insulation. Some time ago I did take the time to do a proper 3D model of a 1m² square in the centre of a 300mm Larsen truss type wall, with two noggins included. I spent a lot of time doing it for no useful purpose, as the heat transmitted through the noggins and the thinner insulation between the twin studs was so small that it was lower than the inaccuracies in some of the other assumptions made in the standard method. Rightly or wrongly I took the view that when you were dealing with 1% to 2% variations it wasn't worth the disproportionate effort of calculation involved. I don't think this is unreasonable, as it's similar to the way BS ISO 6946 works; that also makes some assumptions and gives approximate calculation methods that are simplified to the point where the absolute errors they introduce are down in the noise.

If you read the disclaimer I wrote yesterday morning, before you posted in this thread, you will see that I clearly said that thermal bridging needed to be accounted for in a conventional frame, long before your first post here! I actually wrote that it could increase the U value by around 15%. I think the issue here is that I knew, some hours before you first posted, that I'd made thinks transparently clear in the link I gave for the OP. Every other post by me after that was assuming that everyone had read that, and frankly I don't think some did, as if they had then they would see there was no obfuscation going on by me at all. EDITED TO ADD: As it seems that the disclaimer and statement of limitations that I posted in good faith yesterday morning has been overlooked by some, I've just taken the spreadsheet down, added a similar disclaimer highlighting the limitations in a row at the top of the spreadsheet and re-posted it in the same place. Can I suggest that anyone who has already downloaded it please delete their copy and download the version with the disclaimer in, as I really don't want this topic to pop up again because someone has the older copy without the limitations explained. I should add that I wrote the thing for my own benefit a few years ago, and never for one moment thought that it'd be argued over like this. Perhaps if I'd thought to take the time to do this yesterday morning some of the unpleasantness here could have been avoided - I apologise for that like of foresight on my part, I really didn't envision this thread going the way it did, nor do I understand at all why it has.

We imported our MVHR/A2AHP from Denmark and saved over 40%, plus we reclaimed the 25% Danish VAT from HMRC OK, so you can do it. The problems are really around any taxes or duties that may apply, the fee payable to clear customs and the transport cost, but there are still savings to be made. I also bought some of the borehole stuff from the USA, as it was a fraction of the price there, and even with shipping and duty/tax it was still cheaper. Again I could reclaim the VAT in the same way, but not the import duty. I think a few here have bought from places like Germany, where it seems that things like kitchen and bathroom stuff can be a fair bit cheaper, and I know of one person who hired a van to drive over and buy a few thousand pounds worth of stuff in Germany and bring it back here, as that was cheaper than shipping, plus he got to see what he was buying before purchase.

I'm pretty sure that electric showers are really designed for mains pressure, so probably don't like anything less than about 1 bar or more. There's no such limitation on a power-modulating IWH, like the one we have though. The only potential problem is that all the single phase IWHs I've seen only have 15mm pipe work, so they could be a bit restrictive on a gravity system. I think Nick would be the best to advise on this, as my instinctive feeling is that the pressure/head loss in an IWH when run from a gravity system is likely to be a bit too high.

I really wish you'd not come across as so intent on creating an argument, rather than a more reasonable debate. To summarise, the OP asked how to calculate the U value of a structure, I gave the simplistic way of doing it JUST FOR THE INSULATION AND SKIN MATERIALS. The conversation continued and I offered to upload a simple U value calculator to my website and give a link, which I did, and with that link I wrote this text disclaimer, for the OP in this thread and anyone else reading it: From my point of view, early in this thread (some four hours before your first contribution) I had explained the limitations and why I'd not bothered to include thermal bridging in the "quick and dirty" spreadsheet. Many of the online U value calculators from the insulation suppliers take the same approach, but for different reasons, they almost certainly want to show the best U value their products can achieve and they also have no way of knowing how the customer will use the product. The thread then deviated, as threads do, to Daves build and his thermal bridge mitigation strategy, which is, I believe,. a separate issue. I don't disagree with what you've written above at all, BUT, you decided to take a rather argumentative approach and I don't think you actually followed what had happened some hours before you posted here. Did you read the disclaimer and warning of the limitations I wrote on the link I gave yesterday morning? Finally, our Larsen truss type timber frame has thermal bridges that are so tiny as to be down in the noise when it comes to all the other approximations that are made in BS ISO 6946. And, FWIW, one of the timber frame houses we looked at, built by the same frame company we used, had zero thermal bridging, and I really mean zero. It's not a system they use now, because it took longer to build and so was not as cost effective as using the modified Larsen truss method, but others have used the same technique of EWI on a structural frame for the same reason. Personally I accepted the minuscule additional loss through the noggins in return for a lower price and quicker frame erection time.

That's a good point about continuing to expand, but you can usually mitigate it by spraying water in first. I think that the reason the cure continues for so long in a sealed space is that single pack PUs are moisture curing, and so cure from the outside face inwards, with atmospheric moisture as the effective curing agent. If you spray water into the cavity first, you provide the moisture needed to achieve a full cure in the centre far more quickly, and so reduce, or eliminate, the on-going expansion problem. A bit of water sprayed in also helps with adhesion to some materials, I've noticed. Another thing I found out with some PU foams (the two part, fast cure stuff) is that they tend to shrink back a bit after they've cured. I've had this happen when filling large voids, but not seen it with the single pack can foam, so I'm guessing the different cure method doesn't cause post-cure shrinkage. ST probably knows more about this, as I think he worked with foams professionally at one time.

This sounds like a great solution if you don't live in a hard water area, and where Crofter is the water is soft to the point of being below neutral pH, I think. It's not something I'd heard of, but it makes perfect sense if you have reasonably good cold water pressure, as it saves the bother of fitting a pump, plus there aren't any moving parts. I made a venturi aerator to draw ozone into our water supply at the feed from the borehole, and was surprised at how effective it was. Even my home-made venturi matched the differential pressures predicted by Bernoulli around 280 odd years ago - I reckon he was a pretty clever chap for his time!

I should have been a bit more specific, as I was thinking of our old vented thermal store, and that's probably not typical, as we had to use a combination one, due to a lack of room to fit a separate header tank, and for some reason I had it fixed in my mind that Crofter had limited height, too. If not, then the difference between a UVC and a vented cylinder fed from a header would be a lot smaller, just a bit of extra pipe heat loss from the pipe from the header, which shouldn't get too hot as it goes in at the bottom. I'm inclined to think that a standard gravity fed tank with a pump, as ST has suggested, has a lot going for it. DIY install is fine, no need for special safety inspections on the plumbing, plenty of water flow and pretty easy to reduce the heat losses. It may well even be cheaper to install that one or more decent IWHs. Our 9.6 kW Stiebel Eltron was around £230, IIRC, and realistically that would only give a shower that's around 4 to 5 litres/minute, and anyone used to a more standard shower flow rate (the average is around 10 litres/minute, the big ones can go well over 20 litres/minute!) would probably complain a bit. I lived with a 10 kW electric shower and it's 4 to 5 litres/minute flow rate for around 8 years, and sort of got used to it, but boy was there a difference when we put in a 10 litre/minute mixer shower!

I agree, it's what I dug through from the BRE around 4 years or so ago when doing the calcs (and looking for the "proper" way the building industry looks at things!). It falls over a bit with Larsen truss type walls and roof construction, because the inner and outer timber frames are only connected with small section timber noggins (38mm x 89mm). In our case there are only three of these noggins per wall truss and the trusses are on 400mm centres. Additionally, in common with all Larsen truss type construction, the thermal path through the noggins is long, 300mm, and so the thermal bridging is actually extremely small, so small as to not be worth including in the calcs, because the other assumptions, like those on the surface emissivity and other surface effect losses, massively outweigh the tiny effect of these long and relatively small section noggins. Terry's given the numbers for his house, which uses the same construction method as ours, at 3%. For our house it was under half this, just because our design is different and our walls are a fair bit lower. Ian, thanks for using the same terminology I used when describing Dave's construction! Mitigation is indeed the approach his design takes. Our systems a bit different, in that the idea was to effectively remove the thermal bridges, by making the heat path through them so long, and their cross section so small, that other assumptions in the standard methods were in error to a greater extent than the thermal bridging calcs. A good example is the method in BS ISO 6946 for calculation of the thermal conductivity of sealed air gaps. It's an approximation, that's good enough for building regs purposes, but has significant errors as the width of the void increases, as it doesn't take into account internal convection. This matters not one jot in practice, for a normal form of construction, but it does introduce errors when dealing with a low U value construction method, especially when that construction method has negligible thermal bridging. All these calculations are flawed, and at best approximations, but OK as long as common sense is applied and they are not assumed to be absolutes. Edited to add: Sorry Terry, I was just hitting post on the above when the notification of your post saying much the same about Larsen truss type construction was posted.

Our house had the electric shower because the old boiler was a system one with just a low head from the loft tank. There was nowhere near enough hot water pressure for a shower, and all the cold feeds came from the mains, so were around 4 bar.................. When we first bought it it had an 8 kW electric shower, and when that packed in I had it replaced and rewired with a 10 kW, but to be frank the 10 kW one wasn't noticeably better. We also found that even the very best electric shower would only last three years, if we were lucky, before they failed, almost certainly because of our hard water (not a problem where you are!). The key thing is really that there's a finite limit on the power you can draw for an instant water heater. IIRC, the biggest single phase ones I found were around 12 kW. With cold incoming mains water, 12 kW isn't going to be able to deliver much flow at shower temperature, say 40 deg C. Our 9.6 kW IWI can raise the water temperature by about 13 deg C at 10 litres/ minute, so if you had cold water coming in at, say, 6 deg C, then the DHW would be at 19 deg C at 10 litres/minute, which is barely warm. If the flow rate is halved, to 5 litres/minute, then the thing will increase the temperature by around 26 deg C, so gets a 6 deg C incoming cold supply up to about 32 deg C, which is a bit luke warm and not really hot enough for a shower. I did some tests with our existing thermostatic mixer shower, that's fed off the combi at mains pressure. The lowest comfortable temperature for me was around 38 deg C, and that for my other half around 42 deg C. The combi can chuck around 28 kW into the water, though, so is massively more powerful than an electric shower. I'd be inclined to explore ST's ideas above. Yes, a DHW UVC does need an inspection, but (and I'm sure Nick will correct me if I'm wrong) I'm pretty sure the annual check is just a visual inspection, with no testing required. I'm not sure what you have to do with a self-catering holiday let, do the same rules apply that apply to guest houses? If you want to get around the UVC annual test problem you could look at using a vented thermal store. The heat losses are higher, but that may not matter too much if you can get a decent off peak tariff and manage the thing reasonably well. The heat losses in winter aren't really losses, either, as they go towards heating the place.

The main issue with electric IWHs is that they are of limited power, and with cold water coming in they struggle to raise the temperature enough for a decent shower, although that depends on your definition of decent. We used to have a 10 kW electric shower, before we put a gas combi boiler in a few years ago. It was sort of OK, but the flow rate used to drop to a very low rate in winter, when the incoming cold water was around 4 deg C. In summer it was just about OK, but even then it wouldn't deliver over around 5 litres/minute, and a lot of people would consider that a bit low for a shower. When we installed the combi, the biggest difference (apart from the BIG reduction in our energy bill!) was that we could have a hot shower at around 10 litres/minute (I re-plumbed the bathroom at the same time that we changed the boiler and got rid of the electric shower). So, I guess a lot depends on your target market for guests. Personally, I quite enjoy staying in unusual, out of the way, places and will happily accept a few minor niggles, like less than perfect showers. My other half is, unfortunately, the opposite! You're right that it's better to heat water to just the right temperature for the purpose, and only heat it when you need it, unless you can get an E7 or similar tariff, where the off-peak price is so much lower that it makes a lot of sense to have a well-insulated store of hotter water. UVCs can be pretty low loss, and I believe there's still an option in your neck of the woods to have a very good off-peak tariff (I can't recall what it's called, but Dave mentioned it a while ago). I think your best bet might be to look at the relative cost of running either a few IWIs (accepting that the flow rate will never be more than around 5 or 6 litres/minute) and that of using an off-peak tariff and a decent UVC. The latter would have a higher capital cost, and take up space, but would definitely give a better "customer experience" and could be cheaper to run, IF you can get a decent tariff. BTW, you can put an immersion on a timer, or just pop in and turn it off, when you have no guests booked in, which gets around the standing loss wastage when not in use problem.