Jeremy Harris

I have temperature sensors in the soil. beneath our house, put there out of curiosity more than anything else. They have turned out to be the most pointless temperature sensors I've installed anywhere, as both of them stay within 0.2°C of 8.7°C all year around (I suspect that about +/- 0.1°C of this may just be sensor resolution fluctuation). That suggests to me that, for a floor in contact with the ground using a typical UK soil temperature of about 8°C would make sense for floor heat loss calculations. Clearly this doesn't really apply to a suspended floor, where depending on the effectiveness of the underfloor ventilation the ∆T may well be about the same as for the walls and roof.

Which raises a valid point, in that the steady state heat loss rate doesn't automatically define the heating power requirement. There needs to be sufficient excess heating power available to be able to bring the space up to a comfortable temperature within a reasonable period of time. This depends to a significant degree on the heat capacity, and thermal conductivity, of the materials that make up the first 50 to 100mm of the internal structure (ceiling, floor, walls etc). Assuming a plasterboard ceiling, concrete floor and plastered or dot'n'dab boarded walls, then the internal fabric heat capacity could be anything from about 4 to 10 kWh for a 10°C temperature change. If the room started off 10°C cooler than desired, then significantly more heat input will be required initially in order to get the internal fabric up to temperature.

Me too, in fact I've relied on duct tape to both join and seal all our sections of rigid duct. There's a good reason that duct tape is called duct tape...

What's the floor U value? What are the door and window U values and areas? What allowance has been made for thermal bridging? What's the ventilation heat loss rate? The floor area can be considered to have a lower ∆T than the walls and roof, as the ground temperature under a floor, pretty much all year around in the UK, tends to be about 8°C. Assuming that the floor U value is also 0.2W/m².K, that there is a 1m² area window with a U value of 1.6 W/m².K and a normal pedestrian door with a U value of 1.6 W/m².K, and with a low ventilation rate, for a ∆T of 20°C between inside and out (ground temperature assumed to be 8°C, and internal to ground ∆T of 12°C) then I make the heat loss about 345 W. I've not included an allowance for thermal bridging. Also, if the doors, window and floor U values/areas are not as assumed then the heat loss will be different.

A low loss header is really just a way of making a bypass valve without needing any moving parts. It doesn't usually have enough capacity to be useful as a buffer. They work by using two hydraulic switches, in effect. The flow in and out pipes are in line, as are the return in and out pipes, so flow normally runs straight across the header, in line with the pipes. If the flow is restricted on the downstream side, then the upper hydraulic switch trips the flow downwards to the return end of the header body. They work well for dealing with the case where the flow can be restricted by a slow to operate valve, or closed thermostatic valves, as they allow a bypass in much the same way as a bypass valve. The only slight issue with them is that they partially rely on the temperature differential between flow and return to maintain a reasonable degree of separation between the two sides. With a heat pump this temperature differential may be a bit low, so separation may not be quite as good as with a boiler. There are larger LLHs made specifically for heat pumps, like this one:

Pretty much exactly my experience. The thing that convinced me to change my mind and project manage the build myself was opting for a very similar TF package as yours (minus the basement). If we'd not chosen a supplier who could also install the foundations I'm not sure I'd have made the same decision, though, as the deciding factor was really that combined foundation and frame package, as it took away a lot of risk. I opted to use a fairly tight, firm price contract for the ground works, and the ground works contractor used a QS to price everything up (and the QS gave me copies of all the costings). I may have paid slightly more for this, but having what is often the most risky bit of the build on a firm price contract meant we were pretty sure that there's be no nasty surprises. Once the frame was up and weathertight I found it pretty straightforward to either sub-contract out jobs I couldn't do, like plastering, or choose to do stuff myself. The main area for us where things went badly wrong was drilling the borehole for the water supply, but I'm inclined to think that was just bad luck, in the main. The borehole works fine now, but I now know more about drilling, hydrogeology, water treatment etc than I think I really need to...

Yes, extraction stops briefly whilst the flush pipe's full of water, but runs OK the rest of the time. Seems to work well, though. There;s a very definite difference between our downstairs loo, that doesn't have odour extraction, and the two upstairs that both do.

That's Ben Law's house that I mentioned and linked to earlier, I think.

Just connect it to a boost regulator. One like this: https://www.ebay.co.uk/itm/MT3608-DC-DC-Voltage-Step-Up-Adjustable-Boost-Converter-Module-2A-in-UK-FAST/163769024236?hash=item262164feec:m:mUxc03WpRU3Xg2hZo256t8A would accept the variable voltage input from the panel and could be set to give a fixed 12 V out.

As a guide to the cost of a PM, I initially looked at using one. I met a couple, either of whom I'd have happily used (our plans changed and I opted to PM myself). In terms of cost, both were about the same, 10% to 12% of the build cost for a full PM service, including 1 site visit per week. One of them suggested that he would probably be able to save the cost of his fee in the savings he'd be able to negotiate on materials, and offered to support that by passing on the contact details of previous customers for me to check.

My initial idea, when I first started thinking about self-build, was to build an earth sheltered house, and try and use the old PPG7 paragraph 55 argument. The hope was that I'd be able to find a plot suitable for an atrium style earth sheltered house, along the lines of Mole Manor ( http://www.bbc.co.uk/wiltshire/villages/nettleton_underground_house.shtml ). I still have lots of stuff written by Arthur Quarmby that was distributed by the British Earth Sheltering Association (I used to be a member, back when it was still quite active).

I mounted our inverter outside, on the North facing wall, so it stays nice and cool (most are available as an outdoor version for little or no extra cost). The hottest I've ever seen it is about 45°C, which is pretty cool for an inverter (it's not uncommon for their heat sinks to run at well over 60°C). Very roughly, every for 10°C cooler the inverter runs just about doubles the life of the commutation capacitors, which are one of the most common failure modes. The inverter is out of sight, around the back of the house, and it was easy to run the DC cables from the panels over the ridge and down the other side and out the eaves. The DC cables are run inside flexible conduit, that runs behind the slate battens and over the top of the membrane. The only cable that then has to penetrate the house is the AC cable in to the services room to the generation meter and consumer unit. This single cable comes through wall inside a bit of 25mm conduit, that's sealed up well at either end.

That's interesting, as a friend managed to get PP under the old PPG7 then PPS7 "outstanding architectural merit" route. Took him several years to get there, mind. Looking at Paragraph 79 it does seem as if it looks a bit easier, although I suspect it's still a heck of an uphill struggle:

One or two people have been able to get PP to build a house in open countryside/woodland. As already mentioned it may be easier in some parts of Wales to do something like this, based on demonstrating a certain level of sustainable living IIRC. Ben Law managed to get PP to build a house in his woodland, subject to a planning condition that it's solely for use in association with his woodland-based business, I think: https://ben-law.co.uk/ Finally, there is always the (albeit slim) chance that planners might be convinced to grant PP by using the Paragraph 79 of the NPPF approach. Far from easy, but it has been successfully argued by a few people. You can have a look at the NPPF here: https://www.gov.uk/government/publications/national-planning-policy-framework--2 , but I would suggest that it would need the experience and knowledge of a good planning consultant to make the case for a Paragraph 79 dwelling.

The snag is that the heat is mainly available when you least need it, when it's sunny and the panels are generating a lot. In winter, when you could usefully use the heat, the chances are that the panels won't be producing much power, so the inverter won't get very warm.

No seals are impacted at all by doing this. The idea is simply to ventilate the air space in the pan, and this is always directly connected to the flush pipe, and also to the air space above the water in the cistern. I suggest the BPC people need to go and take a look at how a toilet works...

Ideally you want the inverter outside the heated envelope, I'd definitely not want one sat inside a well-insulated loft space. They do give out a fair bit of heat, around 5% of the power output, and that heat has to go somewhere. If the inverter is inside the heated envelope then the heat won't have anywhere to go, so will just end up warming the space up and reducing the ability of the inverter to lose heat.

For the flow and return pipes, plus cables, for the ASHP, then it's best, IMHO, to put them in underground if you can, as it makes for a neater installation. Might be an idea to just run pre-insulated pipes in now, as pulling insulated pipes through ducts isn't that easy. The PV connections depends very much on the layout and where your consumer unit and PV panels are in relation to each other. If possible it's best to have the inverter outside the heated envelope, ideally somewhere cool, as you don't want the heat from the inverter inside the house when it's running at full power. Also, the cooler the inverter the more reliable it will be. If the power cable is your own, running from an external meter cabinet isolator to the internal consumer unit, then you can use whatever duct you like. If it's the DNO's cable then they usually insist on the duct being black (but not always). I ran our three core 25mm² SWA in through a length of 63mm flexible duct. It needs gentle bends, as the cable is fairly stiff. 110mm soil pipe seems to be overkill for this size of cable to me, plus it will look like a foul drain, rather than an electrical duct. Remember to put warning tape above the buried duct in the trench.

When we had a big wasp nest treated at the old house the chap doing the job told us that he'd heard of a case where someone had sealed up the entrance to a wasp nest in a loft and the wasps had chewed through a plasterboard ceiling, and filled the bedroom below. If true, then I'd guess a bit of foam wouldn't be too much of a challenge for them at all.

Tape or plastic bags taped over the ducts will temporarily seal them. Once cables, pipes etc are in the ducts they can be sealed with a ball of chicken wire, fitted with a length of fencing wire as a pull, push down the duct and then filled with spray foam, leaving the pull wire accessible through the foam if you ever need to get the plug out. The chicken wire embedded in the foam will act as a rodent barrier (rodents can very easily chew through spray foam).

Just gets a bit soggy... When I was flying in fast jets, I used to have to cover my beard with vaseline, in order to get the oxygen mask to seal (there's a mask pressure test as a part of pre-flight checks). It was a real bugger trying to wash the vaseline out of my beard afterwards.

I have a genuine 3M one and an (accidentally bought) Chinese knock-off. Do not be tempted to buy the cheaper knock-off masks, as they may be made of a really nasty, smelly, rubber-like material. The 3M one is fine, well-made, easy to get different cartridges for different classes of protection, and works OK with my glasses. The only snag, which I think applies to many decent masks, is that they get a bit sweaty inside, when worn for an hour or two. This can end up leaving a sort of nasty dust slurry around the places where the mask seats on your face.

I made up a laminated oak board from leftovers from the skirting, drew up a design and had a chap CNC machine it on both sides:

FWIW, our Carrier ASHP is also really sensitive to flow rate. The water pump on ours is a three speed one, so it can be adjusted as one way to try and stop it tripping out on low flow, but the thing that finally fixed the low flow error trips was fitting an adjustable pressure bypass valve. This opens a "short circuit" between flow and return if the pressure in the flow pipe is momentarily too high (the ASHP seems to sense flow rate indirectly by measuring pressure) and by opening it lowers the flow pressure and stops the ASHP tripping out. It needed a bit of fiddling about to get it to work, though. The cause in our case was that the ASHP is running UFH, and the actuators take a fair time to open when the system is turned on, so the ASHP is initially working against a heavy flow restriction. I changed the main actuator valve to a Salus temperature controlled servo operated one, that helps, as it only takes about 30 seconds or so to open, but that's still a bit marginal, as the ASHP seems to trip out after about 20 seconds or so, as far as I can tell.

I remember staying in a place in Germany years ago that had a 3 phase supply, from what I can gather this is normal practice there. The phases seemed to be randomly distributed within the board, with no consumer unit as we'd have, just a load of rail mounted MCBs (all 2 pole, IIRC) all neatly wired up with individual L and N wires on both sides. Didn't look to me as if there was any logic as to what was fed from each phase, and everything looked to be wired as radials as far as I could tell (I was just being nosey and was curious to see how things were wired).