Jeremy Harris

Technically there's no such thing as a "self build certificate", and one shouldn't really be needed, but some people have found that the rules aren't often understood, so there are versions of a self-build chit around that can be of use in keeping contractors happy. We only had one that was funny about zero rating, and I gave him this: VAT Exemption Certificate - blank.doc

Openreach insisted that all 'phone duct was their (free issue) Duct 56. This is the grey rigid stuff, that has slip joints at the ends. They supplied all the Duct 56 needed (in fact around 50% more than was needed - I still have loads of it left over), together with hockey sticks to bring it up inside the house and outside at the base of the pole. We dug the trenches and laid the duct according to their spec, which mainly means keeping it clear from power cables (I think they need it to be around 300mm away from any power cable). I think that some have had a more flexible approach from Openreach, but they were pretty adamant that we had to use their Duct 56.

I'm not sure. A lot will depend on the wall foundation, and how that may interact with the foundation for a house wall, but there may well be a way around that. For example, you could perhaps use a cantilevered slab over the retaining wall foundation (just to decouple the two) and then build an externally insulated wall, tanked on the outside, vertically up against the retaining wall. The tapered space behind could then be filled with something free draining. The first floor could also be built on a cantilevered slab, so it could protrude back over the top of the space between the ground floor rear wall and the retaining wall, making the first floor slightly deeper than the ground floor. It'd need an open minded and creative SE, but I can't see any obvious reason why this shouldn't work well. In essence it's less difficult to design than a capped basement, and there are a couple of people here who have builds like that.

Can the BCO dictate the design like this? I'd have pushed back on this, as the BCO cannot tell you what you can and cannot build, all he/she can do is ensure that the BRs are complied with. There are lots of houses built partially, or even wholly, earth-sheltered, and they have all been able to comply with BRs OK. As you say, having one structure that performs both functions, and which frees up some useful space in the process, does seem to be a bit of a no-brainer, especially as your already a bit pushed for space in that direction. There are several well-proven ways to build a structure like this, too, especially as, in your case, it doesn't look to be more than a single storey wall that's needed. Grand Designs had one earth sheltered house that was two stories high with three walls that were effectively retaining walls, the one built in and old quarry in Cumbria.

Depends entirely on the heat capacity of the floor slab and the thermal time constant of the house. A concrete slab acts like a storage heater, with a heat output power that is proportional to the ∆T between the floor surface temperature and the room temperature. This makes it somewhat self-regulating, as if the room temperature drops the floor will deliver more heat, so bringing the room temperature up. When the room is up to temperature the floor heat output will just match the rate of heat lost. Our floor slab has an area of about 75m², so is close to that for the ground floor of a 160m² 2 storey house. That can store about 4 kWh/°C ∆T. If the slab was heated to 4°C above room temperature it would store about 16 kWh, enough to provide 1 kW of output for 16 hours*. A UFH heated slab like this is broadly the same as an electric storage heater rated at around 2.5 kWh, in terms of heat capacity, but other parts of the house also store a fair bit of heat as well. For example, our 130m² house stores about 1.6 kWh/°C in the plasterboard and skim, and that provides a useful thermal buffer store of heat that helps to regulate the internal temperature. It's probably possible to maintain a "just meets building regs" house at a comfortable temperature with maybe 70% E7 and 30% peak, using UFH. Bit of a guess, but I doubt the ratio would get lower than 50/50 even in really cold weather. With a heat pump with a COP of 3, even 50/50 peak/off peak is going to cost less than 4p/kWh of delivered heat, which is still pretty cheap. * Not strictly true, as heat output is proportional to ∆T, and Newtons law of cooling applies

This is what all the commercial, off-the-shelf, PV diverters do, and also what mine does. If the house demand rises whilst the PV system is generating, then PV diversion reduces or stops.

Just tried, it seems the site just starts the sale timer as soon as you enter it. I'm struggling to see how the scam works, though. Credit card companies are pretty good at withdrawing payment facilities from dodgy sites, and if your payment hasn't been taken that suggests the payment mechanism may not be working, so how do they get any money? Could be just a way of harvesting personal data, I suppose.

No, because the storage heaters did what they are supposed to do, store heat for long periods of time. If they didn't do this they would be pretty pointless. Worth noting that all storage heaters automatically close the damper as soon as power is applied, specifically so they don't chuck out heat whilst they are charging.

Most SSRs don't switch very fast, as they are limited by the optoisolator. A few µs is probably about as good as most manage, but that's fine for mains switching. No real need to worry about isolation, as the built in optoisolator provides a high degree of safety for low voltage connected stuff. Probably a good idea to stick the mains stuff in it's own enclosure, though, and just run isolated wires across to the low voltage stuff.

What gives you the idea that storage heaters give out lots of heat when charging? Even 30+ years ago our storage heaters never over-heated the house at night, if anything they didn't really give out a lot of heat when charging at all, as with the damper shut tight most of the heat was retained in the bricks.

Why? Our first home (not far from where @SteamyTea lives) was a mid-Victorian stone cottage. it was heated solely by E7, with storage heaters. Hot water was by a tank heated using E7, too. The heating and hot water worked just fine, and kept the house nice and warm, even though it had zero insulation.

OK, assuming that the window bears on a strip that's 100mm wide at the base, then the pressure exerted by that weight and width will be ~9.35 kN/m². A bit of EPS100, for 1% compression, will take about 45 kN/m², And I doubt very much if Nudara is less than EPS100. Doesn't look as if there's any problem in just resting the window directly on the EPS to me.

Our off-peak rate is cheaper than LPG by a bit, so no real point in paying more for fuel and an additional ~£100/year in tank rental AFAICS.

What size are the 400kg windows? The weight isn't the real concern, it's the pressure exerted on the support area that determines what's needed. If the pressure's too high for the normal max working stress of the material then the area that's loaded needs to be increased to reduce that pressure. A bit of timber can do that, if need be, but best to work out the pressure to see if that's really needed. Our whole house rests on EPS - there's nothing else supporting it at all.

Just work out the compressive load on the insulation by dividing the weight of the window with the supported area under the cill. For example, if the window weighs 100kg and has a support area under the cill of 2m x 0.1m, then the compressive load is 500kgf/m² (100kg / (2m x 0.1m)). Converting that to units of force (Newtons) gives a force per unit area of about 4.9kN/m². EPS 300 (at 1% compression) is rated for 100 kN/m², so would be overkill. Even EPS 100 (rated at 45 kN/m² at 1%) is massively stronger than needed. Check what Nudara use (I doubt it's going to be less than EPS100) and then do a quick calculation to see how things look. (To convert from kg/m² to kN/m² just multiply by 0.00981)

Currently LPG costs a bit under 7p/kWh. An LPG condensing boiler will be about 85% efficient on average, so the true cost per kWh will be about 8.2p. An ASHP will run with an average COP of around 3 (a decent one will do better than this), so for every 1 kWh of electricity used ~3 kWh of heat will be generated. An ASHP running on peak rate electricity, with a unit price of 15p/kWh will deliver around 1 kWh of heat for 5p An ASHP running on off-peak rate electricity, with a unit price of 8.5p/kWh will deliver around 1 kWh of heat for 2.83p Directly comparing just the fuel cost (ignoring the standing charge/tank rental) an ASHP running from E7 off peak electricity will cost about 35% of the cost of providing the same heat from an LPG fired boiler. The standing charge needs to be accounted for, as the LPG tank rental is an additional annual cost, as the electricity standing charge will need to be paid irrespective of whether electricity is used for heating.

Anything that runs on mains gas can usually be converted to run on LPG OK. Of all fuels available, LPG is probably the most expensive. I did this fuel cost comparison for our (admittedly very low heating requirement) house a while ago:

Just an "off the wall" thought, from someone who's built in a very similar situation (close to a high retaining wall that tended to restrict space). How about making the retaining wall the rear wall of the house? Not hard to do, really much the same as part of a basement. This would give you back some width, which would free up some of the design constraints, and may well not add any additional cost, as you're paying for the retaining wall anyway. We have a corridor ~1.8m wide between the rear wall of the house and the retaining wall, and it's really lost space. I've put our ASHP in there, plus the water treatment plant shed (which isn't something most would have) but other than that the space is really wasted. I've often wondered why I didn't think to just make the retaining wall the rear wall of the house. For whatever reason it just didn't occur to me to do this when I was struggling with getting enough width to build the house.

My immersion diverter uses a 25 A Crydom SSR, switched directly from a microcontroller pin (5 V at ~8 mA, well within the ~20 mA capability for a PIC pin). The SSR I used was a panel mount D2425, which has an input range of 3 - 32 VDC, so will just about work OK from a 3.3 V logic output (it needs ~6 to 7 mA to turn on). The SSR is just bolted to the back of a small diecast box; that seems fine as a heatsink. The dissipation when turned on is about 15 W maximum, according to the datasheet, but in practice it seems to be less than this, as the box barely gets warm to the touch. It's been working continuously for a few years now, with no glitches or problems.

The main differences will be that most of the cheap Chinese units won't have inverter control (this makes a big difference to both performance and noise level) and getting any sort of warranty or spares support for a Chinese unit is likely to be a bit of a challenge. There's also a significant risk that some of the Chinese units may not be as safe as they could be. Faking approval marks is completely normal at the cheaper end of the market, and no one here in the UK checks that these things are actually safe. Missing earth connections, inadequate wire sizes and poor electrical insulation are pretty much to be expected. Not really a problem if you're aware of the potential problems and are prepared to inspect and check any unit, fixing any inadequacies as you find them. Sometimes you can buy reasonably OK stuff from China, sometimes you can buy stuff that's fine and sometimes you can buy something and find it's lethal. It's pretty much pot luck, in my experience. Having said that, I have a Chinese made lathe that's now OK, but I did have to replace the wiring, motor and control electronics, all of which were near-lethal. I reckon it was good value, as even with the work I've done on it to bring it up to a reasonable standard it was still cheap.

My flood risk assessment was just a few pages: Flood risk assessment - redacted.pdf The scanned hard copy flood plan was obtained from the EA following a phone call from me, they printed it off and popped it in the post. For SuDS I just said I'd comply - didn't give any details.

I bought a new, but surplus stock, inverter controlled ASHP from eBay. Turned out to be fine, a brand name unit, complete with controller and manual. The reason it was for sale was because the heating company concerned had pulled out of the heat pump market (I strongly suspect they had burned their fingers installing heat pumps as if they were boilers). As @SteamyTea says, this is technology that's well over 100 years old. About the only things that have changed since Willis Carrier first came up with the idea are inverter controlled compressors and electrically actuated 4 way valves. Everything else is essentially 100 year old technology.

Looks very much like a fairly generic Chinese import. Might be OK, but it doesn't seem to be inverter controlled (giveaway is the big motor start capacitor), so will be an "all or nothing" machine, much like units from a decade or so ago. I suspect a look around somewhere like Alibaba would find the exact same unit available direct from China.

The "MH" on the plan will be for a manhole, I suspect. If the intention was to connect to mains drainage as soon as it was available then it may well have been a cess pit, and the original owners may have just put up with having it regularly emptied for the time that it was in use. Should make it easier to find, too, as the chances are what's marked as a manhole may be the access to the cess pit.

Our neighbours foul drain pipe is visible. It's a clay pipe that can be seen where it crosses the stream bed. Not sure when it was put in, probably 50 years or so ago when mains drainage came to the village. I doubt it complied with any regulations, even when it was first laid.