Jeremy Harris

Both the Water Supply (Water Fittings) Regulations and Scottish Water Byelaws require backflow prevention, in accordance with the risk posed. The risks are categorised in the regs, and a supply where there is only potable water on the user side doesn't require (by law) any check valve at all. The law requires a single check valve where the user side has a fluid that may have a slight taste, odour or temperature difference to the supply, a double check valve where the user side has a fluid that contains chemicals of low toxicity or health risk and an air gap where the user side may contain toxic or carcinogenic substances. However, some water companies ignore the law (both here and in Scotland) and seem to insist on double check valves even though they are not required. As water is a monopoly, and users have no choice, then all you can do is comply with the water companies demands.....................

The old "floating washer" stopcock is supposed to work as a NRV, at least when new. The design allows the part that has the washer on to move back and shut off the supply under reverse flow conditions. In practice this doesn't work well, especially when the valve has been in use for a while, as the floating piston gets stuck into the drilling in the end of the main shaft. I'm pretty sure that the water companies requirement to fit a proper, spring loaded, double check valve, as a backflow preventer, arose because the standard design of household stopcock just doesn't do a good enough job on it's own. To some extent the water companies are going a bit OTT by demanding double check valves on all properties, because the regulations don't actually require backflow prevention for domestic drinking water supplies, only for supplies where there is a risk of contamination. The only real contamination risk from a domestic supply is if there's an open tank connected without an air gap, something I've never seen. The reason that cold tanks, header tanks and cisterns use a high-level fill point, with an air gap between the water entry point and the highest level in the tank/cistern is to prevent a backflow siphon.

I can't see a problem with swapping the double NRV over with the household stop tap, all that matters is that you need to be able to turn off the supply to service the NRV if need be, and that can be done by the water company stop tap. The double NRV is a water company requirement, to positively prevent backflow from the house to the water main, as a measure to reduce the risk of contamination of the water main water if a reverse flow condition could arise (low, or non-existent, water main pressure due to it being turned off).

Yes, I have built a couple of aircraft, two cars, four boats (plus an old yacht restoration), an electric motorcycle, two electric bicycles and now a house. None were significantly cheaper than buying something ready made, but three of the boats, one of the aircraft, the electric motorcycle, one of the electric bicycles and the house were designed by me, so were projects to get something I, or we, specifically wanted, and which wasn't available to just buy. I suspect that a lot of self-builders choose self-build primarily to get the house that they want, rather than to save lots of money. If you cost in your own time spent building something, then the price will often be greater than the price of just buying something off the shelf. The hard part is assigning a value to the learning experience and the sense of achievement that you get from building something yourself.

Self-builders are not normally employers, they are clients or customers, so in general it's wrong to assume that the H&S@WA applies in the same way as it does to an employer. I managed a lot of our build, but at no time did I ever employ anyone, and at no time did I ever have any responsibilities under the H&S@WA. I did make sure that my responsibilities, where defined by contract with contractors, were fulfilled, but frankly these were minimal, and I probably went a bit OTT by providing facilities that I wasn't strictly required to provide. I've never, ever, heard of a single case where the HSE has even as much as looked at prosecuting a self-builder, which isn't surprising. The key here is to make sure that contractors are aware of their responsibilities, and that they understand that you, as a self-builder, are, by definition, not an employer. This is an important distinction, because important issues, like VAT regulations, mean that a self-builder cannot be a commercial entity, limited company, or any form of employer.

Sorry, I missed that, and was responding primarily to @Ferdinand The fact still remains that the writer is distorting the way that local authority housing need targets are defined.

I found that the calcs showed that our kitchen run (similar length to @jack 's) needed to be doubled up, but all the others were well inside the capacity for a single run. When I came to balance the system I found that the kitchen run had to be throttled right back, so that would have been fine on a single run, too.

Gerberit make a pneumatically operated remote flush button that will work up to 1.7m away from the cistern, and only needs a small bore air pipe to connect the button.

I agree, but it's worth looking carefully at the whole system round trip efficiency in that case, especially a system that is in use 24/7. In practice, all battery systems have a poorer round trip efficiency than the battery performance would indicate, as a lot of the losses are outside the battery chemistry itself, in inverters, chargers, battery management systems, load dumps etc. The majority of off-grid systems using renewable sources need a maximum generation capacity that is significantly greater than the average usage capacity, which means that, in practice, there will often be times where generation capability is being dumped or not being used. The energy waste from such controls may well exceed the battery round trip efficiency loss over a whole year. I'm also sure that a carefully designed cell-level, battery management system would reduce the NiFe cell round trip loss by a lot, as most of it comes from the old practice of just leaving all the cells in a pack on charge in order to balance the battery, allowing the higher terminal voltage cells to just gas off whilst the lower terminal voltage cells catch up. They tolerate this, in the same way as lead acid cells do, but it's not at all efficient, particularly given the greater cell voltage differential that occurs with NiFe battery packs. Just using a BMS like that used with lithium chemistry cells, where the charge current bypasses fully charged cells, would give a very significant round-trip efficiency improvement, and I suspect the only reason this hasn't been looked at that closely in the past is because of the history surrounding the commercial use of NiFe cells, and in particular the takeover of the original company by a large lead acid battery manufacturer (Exide) 40 odd years ago. The big advantage of NiFe cells is that they are a once in a lifetime investment, and to some degree that offsets some of the disadvantages. The only chemistry that may come close to this sort of very long life are the newer redox flow battery systems, but they haven't been around long enough to really prove themselves. The underlying chemistry of these should give a life that's comparable to that of NiFe cells, I think.

It's also glossing over some facts, to the extent of conveniently ignoring them................... Local authority housing targets are a good example. The present rules are that local authorities are required to show that they have plans for their specific 5 year housing needs. Each local authority undertakes a housing needs survey, and their local plan then reflects this in the mix of housing that they grant PP to, or at least tries to. As an example, our local authority will only approve developments of more than around half a dozen houses if the development includes a mix of house types and prices that matches local need. In general the developers are already aligned to this requirement, as they aim to build houses that will sell, which, almost by definition, are those that there is a high demand for in the local area. This development that is fairly local to us is a good example: https://www.redrow.co.uk/news/south-south-east/new-homes-in-wilton . It has a broad mix of housing, from single bedroom apartments, a care home, homes specifically designed for military veterans, plus some larger detached houses. It has this broad mix because the local authority housing need pretty much dictated what would gain PP. For that Grauniad writer to claim that any type of development satisfies a local authority housing need target is just untrue, but then I find that a fair proportion of the stuff in that particular newspaper is often just as inaccurate and poorly researched. Over the years, the Grauniad seems to have dropped to a level where it's barely better than the Daily Mail in terms of reporting accuracy.

I also decided that future-proofing the interior was a good idea, both because I have a wheelchair-using friend and because my father was a wheelchair user and I remember the hassle we had to convert the house I grew up in to accept wheelchair use. The main things I did, apart from the wheelchair ramp, turning space and entrance, was to fit wide (33") doors everywhere, with completely flush door thresholds. The extra few inches makes all the difference to a wheelchair use, and saves scraped knuckles. I also fitted hidden hard points behind the wall alongside the stairs, along with allowing extra space at the bottom of the (straight) stair run to allow a stair lift to be fitted if need be. I also arranged my study to be next to the downstairs WC, so that it could be converted to a downstairs bedroom, with an en suite alongside, if either of us was unable to use a stair lift.

Yes, I did it many years ago, no problem at all, and it flushed extremely well indeed, because of the extra head of water. What I did was fit a high-level wall mounting cistern in a small loft space (the bathroom was party room-in-roof). Instead of having the pull chain just dangling down, I fed a much longer chain inside a bit of 15mm copper water pipe, so I could feed it through two bends to get it to come out in at a convenient place. The flush pipe was similar fed down via a couple of bends (pretty sure I used 42mm waste pipe, but it's a long time ago) and fed behind a dry lined wall.

Very impressive work, Dee, it would put a fair few "professionals" to shame.

Strictly speaking, SAP doesn't penalise any fuel, all it does is reasonably accurately reflect the environmental impact of all domestic fuels. Mains gas is a pretty low emissions fuel, which is why using it usually gives a better rating, whereas oil and LPG are both significantly worse, because of the energy used to refine and transport the stuff, amongst other things. We're all-electric, as there's no mains gas here. Still managed to get an EPC of A107 though, and an EIR of 107, at -0.9 tonnes of CO2 per year.

I've had a set of LiFePO4 cells in my electric motorcycle for several years now, and am about to swap them out for new cells, as they have lost a fair bit of capacity. The problem I've found is that all lithium chemistry cells degrade with age to some degree, with the older LiFEPO4 chemistry cells losing a 2% - 3% percent or more per calendar year of useful capacity. The majority of cell development investment has been in different lithium chemistries, much of it coming from the Tesla/Panasonic partnership, I believe. The cycle life of LiFePO4 was claimed to be very good when I bought them, but it is extremely dependent on depth of discharge for each cycle. Running the cells down to 80% SOC gives around 1000 to 2000 cycles, whereas only running them down to 50% SOC increases this to well over 10,000 cycles, for example. In practice, ten years is about the maximum usable life of LiFePO4 I reckon, when combining the loss of capacity from age and the loss of capacity from cycling. The cells in my motorcycle have managed a bit over 7 years, and are now at around 60% of their original capacity. I'm not replacing them with LiFePO4, mainly because of the impact of the additional weight and size, but also because LiCoO2 cells are now safer than they were and have a longer calendar life, and it seems that calendar life is at least as significant as cycle life in this application. When managed carefully, with attention paid to maintaining SOC between about 30% and 95% all the time, then the newer LiCoO2 cells have a cycle life that is as good as LiFePO4, plus they have a calendar life that's around 50% longer. I've a set of older LiCoO2 cells in an electric bicycle that are also around 7 years old, and they are still at around 90% capacity (but they haven't been cycled that much, maybe 600 to 800 shallow cycles). NiFe cell efficiency depends very much on the usage pattern, but I used them for around 20 years or so, running high speed cameras. In practice they managed around 80% to 85% when managed properly, and that was with cells that were manufactured before I was born - they were around 30 years old when we rescued them from some old ground power units. They were still at full capacity when we stopped using them, and by then they were over 50 years old. I'm not convinced that round-trip efficiency is that big an issue for home storage, as the losses only really kick in when the cells are given a full charge to 100% SOC. If charged to 95% SOC the round trip efficiency is as good as lead acid, but charging them in this way does mean using cell-level battery management, as is the case for all lithium chemistry cells, if they are to have a long life. The main problems with NiFe is the relatively large voltage change between fully charged and fully discharged, which isn't really an issue with modern control systems, and the strong alkali electrolyte, which can be a bit unpleasant to work with.

Very true, we were still exporting over 5kW with the cooling on this afternoon....................

Bear in mind that to just meet building regs the house will have to be moderately air tight, considerably more airtight than a house built 15 or 20 years ago. This means you need to plan for a means of ventilation, one that will be effective at combatting the potential problems that @Crofter has highlighted. As you need good ventilation anyway, it makes sense to recover waste heat at the same time, both to reduce running costs and improve comfort. I'd argue that the improved level of comfort from fitting MVHR is a good enough reason to fit it; it really does make a house feel a lot nicer indoors.

We have an MVHR unit that includes an air-to-air heat pump, so can heat and cool. We never use it for heating, but as I'm sitting here typing this, with an outside air temperature of 25.6 deg C, the MVHR outlets are feeding nice cool air at around 12 deg C into the house. It isn't powerful enough to cool the house down if it has been allowed to get too hot, but is quite effective at maintaining a comfortable temperature. The most effective way of cooling the house is the under floor cooling system, run from the ASHP that can also heat the floor in winter. That's not running right now, as it's set to come on if the house gets above 22.5 deg C, but when it does, we find that cooling the floor is more powerful at reducing the house temperature than the MVHR. Summer bypass is not very effective during the day here, but does provide cooling at night, when the outside temperature drops below room temperature. However, we are in a sheltered location, with the house set in a cutting in a south-facing slope, and that does mean we have higher than average outside air temperatures. BTW, there is no problem with condensation in the ducts, as they will always be well above dew point. There is a lot of condensation in the MVHR unit when the cooling is on, with a constant trickle of condensate running out of the drain pipe.

I agree, I'd not worry now about the PD rights being removed, the chances are that you will stand a better chance of getting them re-instated later, I suspect. Our original recommendation from the planning officer included removing PD rights, for several good reasons, including being opposite a listed building, being within an AONB etc. Between the recommendation and the decision notice I managed to persuade him to not include the condition revoking PD, but this was mainly because we ended up with no objections (there had been loads of objections to previous applications on the same plot). I'm convinced that the planning officer only changed his mind because all the previous objections had disappeared. In terms of neighbours, I think they'll probably come around in the end. All our neighbours had objected to the previous applications, some of them pretty vociferously. Now we get on well with all of them.

Given the large areas of glazing, I think MVHR will be essential, just to get an acceptable energy performance to get through building regs. It also improves the indoor air quality a fair bit, and that alone would be a good reason to fit it..

I think the problem with a single cell unit (as mentioned earlier) might be the heat exchanger capacity. The cells are in parallel in the Sunamp PV, which gives a maximum power output that's around the same as many combi boilers. A single cell would be half the maximum power as well as half the capacity, I think. I also suspect that the cells aren't where a lot of the money is within the unit.

I'd agree with older people being more at risk. I think the main reason is just complacence, as we get older and gain experience we probably tend to focus more on getting the job done, rather than on how to do it safely. When you've been up and down ladders hundreds of times in your life you're probably less likely to be focussed on the bit you've done many times, i.e. putting up the ladder properly, and more likely to be focussed on whatever it is you have to do when you're up there. I remember years ago seeing some statistics of aircraft accidents that someone had compiled, that plotted out experience versus accident rate. Newly trained pilots tended to have minor incidents, through lack of experience. Then the accident rate dropped for a few years, probably as a consequence of experience gained. After a few more years the accident rate increased again, as complacency set in. IIRC, the person that compiled the data had accounted for age, and the pattern was much the same no matter what age the pilot was first granted a licence. I strongly suspect the same is true for accidents at work, too. I don't think we ever did any detailed analysis, but my recollection is that the few major workplace accidents I knew of were all older people, with many years experience.

Good idea. Blown bonded beads might be good enough, and are pretty cheap. I'm pretty sure they are blown with a coating of PVA, and it may well be possible to increase the amount of PVA, so that they bond securely to the OSB skins. The bond strength doesn't need to be massive, as the loads on the foam are very low, it's only stopping the OSB sheets from crippling under the compressive load.

£1700 + VAT, I think.

The problem is judging the expansion rate, I think. I've used two-pack PU foam to fill cavities (boat floatation chambers) and it expands with a great deal of pressure, enough to bow out pretty robust panels if you get it wrong, it also tends to shrink back after it's cured, causing the panels to then bow inwards. I have a feeling that the EPS SIPS panels are made using OSB glued either side of accurately sliced EPS sheets. I'm sure I've seen a video on the web somewhere of the process. I reckon that it could be a DIY proposition, using something like a slow cure PU adhesive. The key would be finding an easy way to apply even pressure to the OSB - EPS - OSB sandwich, as the glue was curing. Whether it would be cost effective or not I don't know, but it might be.