Jeremy Harris

Apart from the dodgy way the wrong type of cable's been run, my particular worries would be these: Is there adequate earthing at the accessible outlets in the garage and summer house? (only testing can really establish this). Are the cables adequately protected against overload? Is there earth leakage/residual current protection and is it functioning within the required time and current limits?

I've seen worse, TBH, but I'd very definitely look at getting it replaced with a proper installation. Given that it's a real bodge job, my main concern would be whether or not there's adequate protection provided at the supply end of the cable. People who clearly don't know the regs, and who install bodges like this, are pretty likely to have ignored the requirement to protect that dodgy cable and the stuff that's connected to it. That may well present a significant hazard, more so than just the risk of damage to an unprotected and unsuitable run of outdoor cable.

I'll just leave this here:

Kore, Isoquick, Supergrund plus a few others, or you can DIY the thing with sheet EPS glued together to form the L shaped bits around the edge. I believe at least one person here has done a DIY passive slab, we used Kore and @PeterStarck used Isoquick I believe.

I went through a lot of detailed thermal modelling BEFORE installing a thermal store, using the data available from the manufacturer. It was an unmitigated disaster, as the manufacturers data was from a standard test method that I was unaware of, and which bore no resemblance to the way a thermal store (or hot water tank for that matter) would be used in practice. It seems that the test method used assumes that a boiler will be fired up to fill the tank shortly before hot water is needed, then hot water will be drawn off, leaving the tank relatively cool for a long time, until the boiler is fired up again. This doesn't match the way hot water storage is often used in a house where the water is heated from excess PV generation at all well. The main consequence is that the real world heat losses are massively greater than the manufacturer's data would lead you to believe. In our case, the losses were enough to push the temperature in our services room up to over 40°C, hot enough to cause damage to the door into the room. The first attempt at a solution was to add an additional layer of 50mm of PIR foam, as a well-sealed, foamed in place, extra jacket around the tank. This helped, and reduced the leat loss by about 1 kWh/day, but the loss was still way too high. The fix was to remove the thermal store and replace it with a Sunamp. The Sunamp has a really low standing loss, so low it's pretty negligible, and this both removed the overheating problem in the services room and significantly improved the overall DHW system efficiency. Our system uses excess PV generation as the primary means of heating the Sunamp, with a backup E7 boost from a time switch to ensure the Sunamp is charged first thing in the morning. This latter arrangement is only really needed in winter, when there's very little useful excess generation from our 6.25 kWp PV system, but it's a handy way of ensuring that the Sunamp always has enough charge for morning showers, even if it's been used to heat water for a bath the evening before.

After the very heavy rain over the past day or two, it seems that our SuDS solution is still working OK. I didn't bother with paying someone to design it, as it's pretty easy to just use the method in building regs to determine the capacity needed. There's no sign that our ~4,000 litre attenuation tank got close to being full, AFAICT. The main problem we have is run-off from other impermeable surfaced drives that all flow into the narrow lane alongside us and turn it into a fast flowing river during heavy rain. As we're at the bottom of the hill, this means the lane outside our drive is often under water, and gets loads of debris washed into it.

I doubt that surface frictional loss will have any detectable effect on flow rate, TBH. Bends seem to be the most significant factor, and even then all the unknown variables around the terminal and plenum end conditions, as well as turbulence around the restrictors, tends to dominate. We're using the slim semi-rigid HB+ ducting, which is only 75mm OD, 63mm ID, and the duct losses are trivial when compared to the effect of the flow restrictors that have to be fitted in order to balance the system. Balancing the system may be challenging with your proposed large duct size as it's not clear where you're going to fit the required adjustable flow restrictors for balancing. I used the rather awkward HB+ system, that uses a range of restrictor rings fitted to each radial duct inside the plenum chambers, but the more common system is to use adjustable terminals. There are pros and cons for both, but they both have a significant impact on your plan to switch between two very different flow rates. Using terminal flow rate adjustment is far and away the easiest system to adjust, as it can be done from each room very simply. The downside is that having the restrictor at the terminal may tend to slightly increase noise in the room, as the velocity is locally increased through the restricted aperture in the adjustable terminal. In practice this doesn't seem to be an particular problem, though. The general design rules for efficient (and building regs compliant) MVHR are to design to meet the boost flow rates required for the mandatory extract rates for kitchens, bathrooms, showers, WCs etc, and to generally arrange the ducting and terminals so that as little restriction balancing as possible is needed. This usually means more fresh air supply terminals than extract terminals (as extract rates have to be higher to meet building regs) and locating terminals so that there is the maximum opportunity for full diffusion between each room fresh air supply point and it's effective exit point (which will probably be under a door). The same applies in reverse for extract rooms. I arranged all our terminals so they were diagonally opposite the room extract/supply point, to try and maximise the path length, slow the velocity right down and ensure maximum diffusion. In your case, with large ducts and terminals, I think you will need to find a way to fit the required adjustable restrictors to the MVHR supply and feed side for each room, and then somehow arrange to switch these out when your system switches to the recirculating cooling mode. It can probably be done with the use of motorised valves, but might be a bit challenging in terms of maintaining access to all serviceable parts.

"Seemed to" is entirely your personal misinterpretation. This is what I wrote, have a go at reading it again: The point I was making was that there had been a lot of cases of mass built houses suffering from mortar failure, as a consequence of corners being cut to save money. The last sentence I wrote is the key one.

I misunderstood, and read it s being 90l/s for the cooling air flow rate, hence my observation that our experience suggests that this might be a bit low for cooling. The main issue with ducted cooling at high flow rates is sizing the ducts to keep the air flow velocity below 2.5m/s. If the velocity exceeds that then flow noise may well be high enough to cause a noise nuisance.

90l/s is about 0.9 ACH for our house, and is about the flow rate that our MVHR runs at in cooling mode. I can say for sure that this is not enough airflow to cool our house, with a cooled air temperature of between 10°C and 12°C.. I'd estimate that we could do with about three times this airflow rate to be effective, and our house is a fair bit smaller than yours, at 130m².

Without a shadow of doubt. Even out here in the sticks I only need to walk a few hundred yards later this evening to be sure of seeing someone totally off their face.

I think the dilution of mortar strength and the involvement of NHBC was a result of mass housebuilders cutting corners/costs by reducing the cement ratio in their on-site batch plants. One consequence was that several new builds have suffered from premature mortar failure, with the stuff just crumbling away after a few years. https://www.bbc.co.uk/news/business-46454844 My guess is that NHBC may have picked up the tab for this and so have tried to mitigate it whilst still allowing a weaker mix to be used in some areas, in order to keep the hand that feeds them happy. It's completely bonkers for any self-builder to agree to reduced strength mortar, IMHO. The cost saving is trivial in the overall scheme of things.

I was ignoring the PV system, as that doesn't heat the house, but just offsets the overall energy use over a year. The bottom line is that the house heating demand for only a modest worsening of the insulation (the values I quoted are still better than building regs limiting fabric values), and reverting to airtightness which is twice as good as building regs require, results in a pretty massive increase in heating cost.

Here's some absolute numbers for our build. If I changed the U values to 0.13 W/m².K for the floor and roof, 0.18 W/m².K for the walls and 1.4 W/m².K for the doors and windows, and change the airtightness to 5m³(h.m²) at 50 PA, with no MVHR, then the heating fuel consumption increases by 239%.

It's beyond me, too. I saw a report on the BBC earlier by a woman that nearly died from liver failure, because she was in the habit of drinking large quantities of wine every day. She didn't seem to think she was at fault, and wanted the law changed so that the amount of alcohol in a bottle of wine was clearer (what could be clearer that the ABV that's already on the label I don't really know). The really big problem with having maintained a ban on cannabis for so long is that it's stimulated the development of very strong strains. If it had been made legal 40 odd years ago I doubt this would have happened, as it could have been regulated and taxed like alcohol and tobacco.

So much depends on individual details, including the size, shape, surface area and volume of the house, that it's near-impossible to make a generalisation that a particular set of U values and air tightness will save a specific sum of money. Even the choice of fuel could give about a 3:1 range of cost variation (maybe more). If a house is larger than average, but is a simple square shape, then wall, roof and floor U values become less significant and airtightness becomes more significant. Conversely, if the house is smaller than average, and has a more complex shape, then wall, floor and roof U values will become more significant and airtightness less so. It's a variation of the elephant and mouse metabolic rate analogy.

Mortar is reasonably good at keeping water out, which is why cement rendering works as a weatherproofing layer.

The most I've paid recently is £220/day, and that was for a chap that works like a demon and does a cracking good job. His rate's gone up from £200/day in the past year or so, and we're down South where everything is supposedly more expensive.

Many years ago, when I did the Airworthiness for Military Aircraft course at Cranwell, we spent a long time going through the "read across" principles, and what could and could not be read across from an older approved component to a newer, seemingly identical component. One key principle was that we should seek to apply the current airworthiness approval standard, even to a new model of an older aircraft, unless this was proved to be wholly impractical. I think the most public example of this principle being adhered to by a colleague at the time was the refusal to grant airworthiness approval to the Chinook Mk3s that were originally purchased for the Special Forces. The cockpit systems included software that didn't meet any of the UK safety approval requirements, so the new aircraft were grounded as soon as they got here. I faced a similar issue when I was the programme manager for Future Lynx (now Lynx Wildcat) in that the Honeywell/Rolls Royce FADEC system had code written in C, and compiled with a non-certified compiler, so it simply wasn't going to get a UK airworthiness approval as it stood. Boeing seem to have just stretched the "grandfather" rights of the 737 way beyond what was reasonable, even for the much more lax certification requirements that prevail in the US.

Given that the cladding on Grenfell Tower had a BBA certification as being resistant to the spread of fire, then I'd have to say that it's probably not worth the paper it's written on for some products.

Yes, it's measured during the air test that's done as a part of building regs compliance usually. A reasonable target is to aim for an airtightness that's a fair bit better than building regs require, especially if you want to get an EPC rating that's up around 85. Having good airtightness is only a benefit if you also fit MVHR, though, as much of the benefit comes from the heat recovery provided by that system. A wall U value of 0.15 W/m².K might be OK, but it very much depends on the totality of all the parts of the building, so the insulation values of the walls, floor and roof, the elimination of thermal bridges in the structure (as these can easily undermine otherwise good insulation levels) and the airtightness level and MVHR efficiency.

I think you've hit the nail on the head, @jack. My reason for wishing I'd opted to install a split aircon system for cooling was largely driven by the fact that the MVHR just cannot ever shift very much air through the heat exchanger and always runs at a serious disadvantage, in hot weather, by drawing in hot air to cool down. Because an aircon unit just recirculates air, as well as having a very much greater air flow rate, it is both far more effective and more efficient to run. If retrofitting a split aircon wasn't such a PITA I'd already have done it. I dearly wish I'd made provision to get the pipes and cables in where needed, right up near the apex of our entrance hall. Being able to cool the air ~6m up, in the centre of the house, would make a very useful difference to comfort in hot weather, and the slight noise from an aircon unit up there wouldn't really be a nuisance.

Those with long memories, and who were on Ebuild about 11 or 12 years ago, may remember that my very first post there mentioned that I wanted to build an earth sheltered house. Part of me still wishes we'd chosen to build one, but, as often seems to be the case, the plot tends to determine what can and cannot be built. Our plot had too high a water table, and too small an available build area, to allow a practical earth sheltered house, really.

I read this and wondered whether they would succeed in such a case if it were brought here in the UK. I suspect they wouldn't, as all three manufacturers could claim that they "acted in good faith" by having their products accredited as either meeting the required regulations or by meeting the Class O requirements. The key issue seems to be that none of these products actually met the regulatory requirements in practice, and that the manufacturers of the cladding and insulation may have exploited the flaws in the accreditation system when they were given their Class O accreditation. The question then is whether it's the manufacturers that are wholly to blame or the accreditation scheme. My view is that it's the latter, in the main, as we've been diluting the stringency with which regulations are applied for decades, first as a consequence of Thatcher's obsession with deregulation, privatisation and self-certification, and more recently as a consequence of financial pressures that have led to corners being cut (another thread here recently made the point that inspectors couldn't be bothered, or didn't have the time, to come out to do mandatory inspections, for example). If we want stringent regulation to help preserve life, then we have to make sure it's rigorously enforced, and that means proper, mandatory, inspection and test, not some meaningless desk accreditation process by analogy (which is what seems to have been the case here).

Me too. At the moment we use the grid as a seasonal storage battery, as we generate more electricity over a year than we use, but generation in winter is pretty poor, so we're reliant on the grid then. The next stage in my plan to reduce grid consumption is to fit a battery storage system. It won't be a Tesla, because of the lack of control that Tesla have over when their product charges and discharges (it's impossible to override the Tesla algorithm). I want to be able to charge the battery only from excess PV generation and off-peak electricity, with the aim of reducing our peak rate electricity consumption to near zero. I believe that doing this will probably have a disproportionately large impact on our grid electricity CO2 footprint, as the big and dirty power stations seem to get most use during peak rate periods.