Jeremy Harris

Whilst I agree that we should be increasing the minimum size standard for homes, there is some merit in finding ways to be more space efficient, too. As a student, my bike used to be hung up on the wall in the stairwell, for example, where it was out of the way and stored in a space that was otherwise just wasted (it was above head height). Back then, a friend had a neat little portable washing machine, that sat on the draining board when in use. No idea what make it was, but it was light and easy to use, and I always wondered why it hadn't been developed into a built-in product. Until we moved into this house we had an ancient Philips tumble dryer (used to be my mothers) that was a lot smaller than a standard one. One house we lived in didn't have room for it, so I built a shelf above the cistern in the downstairs WC and sat the tumble dryer on it. That was also space that otherwise wouldn't have been used. I always thought that architects and house designers could do worse than spend a few days looking at how boats are designed. There's rarely any wasted space onboard a small boat.

The main things to monitor are CO2 concentration and humidity, as they are good indicators of how well ventilated the house is. It shouldn't make any noticeable noise if it's installed and set up properly. Set up after installation is fairly important, as the flow rates need to be balanced, the ventilation rates measured and the fan speeds set to give adequate ventilation without noise. Ours is silent in background ventilation mode, it cannot be heard at all, even in the middle of the night when the house is quiet. The fact that you can hear yours makes me suspicious that it may not have been properly commissioned, or may not have been properly installed. Often silencers are specified as being a requirement in the main duct runs to the unit; the manufacturer of our unit stipulates that these must be fitted. I didn't follow this advice initially, and there was some noise from the unit, but after fitting silencers the noise went away.

Also worth checking to ensure the filters are clean. I find that the power consumption of our MVHR rises when the filters get dirty. Filter change intervals for an MVHR depend very much on how clean the local air is, here I can just about get away with cleaning/replacing them every 6 months. I know that others have found they need to clean/replace filters more often than this, though, so probably worth checking yours, @JamesJJJ, if you haven't already.

I really like the idea of a video wall. Mine would be a view of the garden, with a night vision capability so that we can see the nocturnal wildlife as well. I'm sitting here with a pan tilt mount, a couple of 1080p video cameras (with an IR capability) and some IR floodlights, trying to work out how to arrange them so we can sit indoors watching the bats, hedgehogs and occasional visiting otter in the late evenings. Ideally I'd like to add audio too, and have just ordered an ultrasonic microphone to see if I can rig up a broadband audio system, with a frequency converter so we can hear the bats (at the moment I have to go outside with a hand held bat detector to hear them).

Doesn't sound far off for a system in a 5 bedroom house. Our (smaller) MVHR uses around 40 W or so in normal background ventilation mode and this rises to around 85 W in boost mode. It rarely stays in boost mode for long, though, as it only switches to this during showers, or if there's steam coming from cooking in the kitchen. As @PeterW mentions, there is the benefit of very much higher indoor air quality, both from the big reduction in stuff like pollen, and from the massively improved whole house ventilation, which significantly reduces the risk of condensation and stale air build up. Opening windows isn't that effective at providing proper ventilation, I found. I measured the CO2 concentration in the bedroom at our old house, and with a window open 24/7 the CO2 still rose to around 1600ppm or more in the middle of the night (a healthy level would be lower than around 800 - 1000ppm). In this house, with MVHR, I've never seen the CO2 concentration get higher than about 650ppm, and that's only when we have guests around, so there are more people breathing the stuff out. The air quality improvement alone would be enough for me to insist on fitting MVHR to any future house, and the ~£0.16 per day running cost* seems a small price to pay. * Ignores the fact that most days the PV system in the roof generates more than enough to cover the daytime running cost. The true cost is probably less than 8p/day.

Yes, I'm going to fit batteries shortly, but they don't make economic sense, yet. Part of the reason I'm fitting them is to give a backup supply, as we get a fair few power cuts here (just waiting for the power to go now, the wind's enough to take a cable or two down again).

Bit of a difference here, ~10 miles West of Salisbury. We've had a fair bit of rain this week, and right now it's blowing a hoolie, winds gusting up around 45 - 50mph.

+1 to @MJNewton ^^^^ I used to be a Notified Body, approving stuff to the LV and EMC Directives. The vast majority of stuff from China has never been anywhere near an independent test lab. CE is a complete joke, and to all intents and purposes meaningless in terms of safety or performance certification. I've posted several examples here of lethal or non-compliant CE marked stuff, from LED lights (from a UK supplier) that were CE marked, had alloy cases and no earth, through to LED power supplies that radiated so much RF that they rendered all radio devices in the house inoperable. My Chinese built lathe was absolutely lethal, 2 core mains cable and really appalling insulation; no way was it Class II. Similarly, a Chinese battery charger I bought gave me a bit of a belt. When I took it apart the L was connected to the -Ve battery terminal, and again it had a 2 core cable, and was marked as being Class II and CE compliant. There is no independent checking at all under the barking mad EU scheme, it's so bloody dangerous when compared to proper safety certification, like our old kite mark, that someone really needs to step up to the plate and kick the damned EU into touch...

The number after the "EPS" is the maximum 10% compression stress, in kN/m². So EPS300 = 300 kN/m² at 10% compression. Finding the 1% compression stress figure isn't as easy, but EPS100 has a 1% compression stress of about 45 kN/m², so that gives a reasonable guide as to what other grades will be.

It uses 2 current transformers, one on the incoming supply and one on the PV inverter output. The battery inverter is approved to not allow export to the grid, according to the paperwork, as it has an integral G100 export limiting relay.

The copper doesn't look to have been overheating, though, so my guess is that they've probably used something like 4oz board, which would be fine for the thickness of those traces and the current they are carrying. I routinely use 4oz board on the motor speed controllers I've built, and some of them work at 50 to 60 A or more without any problems. I've just done some quick and dirty sums, and for normal 2oz board for a trace carrying 12 A continuously, a 25mm long track needs to be at least 4.65mm wide. For the same with 4oz board the track only needs to be 2.35mm wide. The Sonoff, being Chinese, almost certainly uses board with very thin copper. 1oz seems commonplace for Chinese stuff, as it reduces the cost of manufacture a lot (the board is cheaper and it takes half the time to etch 1oz, rather than 2oz).

The inverter carries the appropriate approval to ensure it cannot export, though. Presumably if there is a problem with measuring the power at the incomer it does the same as the PV inverter does when that senses something like the loop impedance being above limits and just shuts down.

Not sure any isolation is needed, really, as there are no low voltage bits outside the box that can ever be touched. If I had to guess, I'd say that the contact in the connector is the cause of the overheating, not the tracks on the PCB. I think they've just been heated up from the overheating connector. Looking at the connector, I suspect that the cause of the problem is the wire termination to the socket. This looks to be a screw terminal, and Sunamp failed to comply with the requirement to always fit ferrules to stranded wires until fairly recently (our old UniQ control box didn't have ferrules on any wires, the new one does). I'd repair the board if it were me. Get a pair of new connectors, remove the plug from the board, clean everything up and solder the new one in place. Trim back the wires to the socket (to get rid of damaged/corroded bits) fit ferrules to the wires and then fit them to a new socket, making sure all the screws are properly tightened. Loose terminal screws is the number one cause of overheating - happens all the time.

Welcome. With a "massive amount of glazing on a South facing site" you will need to take very serious measures to avoid over-heating, and this may well be worse for a non-passive house (insulation works both ways, it keeps heat out in hot weather). We have a large glazed gable that faces South and have had to spend a fair bit on reducing solar gain from it. Looking back now I wish that I'd specified Sage glass, as although it's expensive it does allow large areas of glass to be used whilst keeping the solar gain under control. I also wish I'd been allowed to fit external window shutters (the planners weren't happy about fitting them) as they would have been a great help, too. One key thing to consider when looking at build methods and insulation is decrement delay. Some insulation materials can have a very short decrement delay, which means the house may respond relatively rapidly to external temperature changes, particularly when the sun is shining on a wall or roof. Others can have a long enough decrement delay that the heat doesn't have time to penetrate the wall or roof before the sun has moved away. The latter is preferable, as it leads to a more even temperature indoors, which most people find more comfortable.

Depends entirely on the load that's going to be applied. I estimated that our house weighs something like 40 tonnes (didn't write it down anywhere, so this is just from memory). The load bearing area of the EPS (which is the total slab area) is about 85m². The load on the EPS is therefore about 4.62 kN/m², well within the capability of pretty much any grade of EPS I'm aware of. To stay within the load region where creep may be an issue the max allowable bearing stress needs to be kept below the 1% compression figure.

We have 10mm glass panels on our stairs, with a simple oak handrail above. I find the handrail essential, and out of preference would like it to be on the side of my dominant hand when descending the stairs. When coming down stairs half-asleep in the morning I very much rely on the handrail to make sure I don't fall if I miss a step. It's happened a few times now, enough to convince me that a handrail is essential.

What he described in that podcast was a phenomenon that was recognised in major military projects years ago. We gave it the name "optimism bias". There's even a formula used when looking at project costings for military projects that works out how much needs to be added in order to come up with a reasonable project cost. I strongly suspect that self-builders are very prone to "optimism bias", for a few reasons. Few self-builders have much experience of the way that houses are built, and a lack of knowledge can add a lot of cost. Similarly, few self-builders have experience of quantity surveying, so most probably leave out some elements (by oversight) and assign optimistic costs to other elements. Finally, I suspect that "mission creep" happens a fair bit, where the spec gets enhanced during the build, with a corresponding increase in the cost. Looking around here, it's noticeable that those with previous building experience tend to have come in at significantly lower costs per metre² then those that have little experience. Although the sample size is small, I suspect this holds true in general.

I'm not entirely convinced, either! It is the approved way of dealing with unventilated cavities in walls, though, I believe.

It measures import/export power at the incomer, and ramps the inverter power down so that it never exports.

Sometimes, it depends on the local network. I asked for the maximum the DNO would allow under G59 (as it was then) and they told me that I could go up to 10 kWp on our single phase supply. We've got 6.25 kWp, as that was as much as I could fit on to the roof. It's useful, though, as the spare capacity we have in our authorisation means that fitting a 3.6 kWp battery system stays within the existing approval (it's bizarre, but for some reason DNOs seem to assume that battery systems will export to the grid, even if they physically cannot).

The snag is that most of your domestic loads will probably be on a single phase, as it would be unusual for a house to need more than the ~23 kVA that a single phase supply can deliver. Ideally you want your PV to be connected to the same phase as the household loads, so that any PV generation offsets normal use. If PV is on 3 phase, then only around 1/3rd of the generated PV energy will be offset against the house domestic loads.

Yes, there's an approved method for approximating the λ for horizontal heat flow in a non-ventilated cavity in BS EN ISO 6946, λ = 0.00858 + 5.518 x d W/m·K, where d is the gap thickness in metres. If anyone wants to determine the basic U value for any given thickness of something (ignoring surface thermal resistance) then just work out the thermal resistance, R, from thickness in m / λ, then U value = 1 / R

Brilliant! Didn't know it had a name. Reading that, I'd guess that whoever set up the task on our course knew all about it, although it was pre-internet, and hence pre-Wikipedia, so they must have heard of it from somewhere else.

160mm of PIR roughly equates to about 250mm of EPS. I'd be inclined to consider that a sensible minimum if fitting UFH, and there's some merit in going up to 300mm of EPS. We have 300mm of EPS and our UFH still loses about 8% or so of the heat input to the underlying ground.

I agree about the bifolds being an airtightness liability. Few seal very well when new, and all get more leaky with time, just because of the inherent inability of the seals to be kept properly compressed, because of the geometry of the closing mechanism. Pretty much everyone I know that's had bifolds has mentioned that they never actually open them up fully, so although the idea sounds nice, and they look good in magazines, I'm inclined to think that the poor performance probably isn't worth putting up with for the very occasional time when they might be fully opened. We have French windows and very rarely open up both, in fact I don't think we ever have, apart from checking to see they worked OK when they were installed. There are some pretty good lift and slide options that are much more airtight, and will retain that airtightness for years, or their is the option of having a couple of fixed panes either side with French eindows in the centre, as they also seal well and the sealing stays reliable over time.