Jeremy Harris

One major problem is that some smart meters have an anti-theft measure*** which defaults to adding export energy to import energy, unless the meter is specifically programmed to allow export energy to be separately recorded. Installers may well not be setting up smart meters properly, although this isn't a problem that is specific to smart meters, there are some standard digital meters that also have the same anti-theft measure, as there have been reports for several years now of people having increased recorded usage when PV is installed. Interestingly, practically all electricity meters installed in the past few years have the ability to measure and record export energy separately from import energy and store the value in an internal register. This can be read out via the optical meter reading port easily enough, but there is some glitch in the legislation that stops this facility being used to accurately record export energy for repayment purposes. *** The anti-theft measure is to counter one technique used by meter fiddlers, which was to make up a high current, low voltage, autotransformer, with pointed probes stuck into the meter tails from underneath. This made older mechanical meters, that weren't fitted with a wheel ratchet, run in reverse, so reducing the recorded energy. Meters have been redesigned with covers to try and prevent this now, as well as having the internal option of adding reverse energy to forward energy (accessible via the settings that can be accessed from the bidirectional optical port) as a deterrent to the fiddlers.

I'm at a loss to understand why so many vents are really needed under a beam and block floor. I've heard tales that it's to allow gas to escape, but having had to rip up the concrete floor of an old Cornish cottage nearly 30 years ago, and fit a radon sump and vent, I really cant see why more than a single vent is needed, maybe two at the most. Our radon vent was a 110mm soil pipe coming out the side of the house from the sump and running up the outside of the house, and that was deemed to provide adequate ventilation. Similarly, covered refuse tips will just have a few pipes around the same size poking up as gas release vents.

As an update to this, I've been looking at ways to retain the switched boost functionality that we have at the moment, and add energy metering for both the PV diverted energy and the grid boost energy, so that I can get a feel for just how much grid energy we use. This has been prompted by the discussion in this thread: I already had a spare 4 module DIN enclosure ( less than £7 from eBay), so I've decided to replace the time switch in my set up with a DIN rail mounted 16 A time switch, plus two single module DIN rail energy meters. I'll post photos of the set up here, as soon as I've finished it. The idea is to have one energy meter recording the diverted PV total energy to the Sunamp and the other recording the grid boost energy to the Sunamp. I'm going to retain the separate boost enable/disable switch, as the neon indicator is a useful guide to show that the system is in boost mode. The 2 module wide time switch is one like this: https://www.ebay.co.uk/itm/DIN-Rail-Digital-LCD-Power-Programmable-Timer-AC-220V-16A-Time-Switch-RelayBI117/153187211217?epid=850258809&hash=item23aaab57d1:g:9iAAAOSwSflbopYN:rk:1:pf:1 The energy meters needed a bit of thought, as the LCD ones that I've used for other energy monitoring purposes would have the disadvantage of not being able to be read when not energised, which would be the case for a fair bit of the time. Instead I've opted to use 1 module wide ones like this: https://www.ebay.co.uk/itm/AC-5-30-A-50Hz-Single-Phase-DIN-Rail-Type-Electric-Kilowatt-Hour-KWH-Meter-BI041/163042593097?epid=8019867926&hash=item25f6188949:g:YDIAAOSwCLVbvsIt:rk:1:pf:1 that have an electromechanical counter, so can be read at any time. It's a bit simplistic, and relies on my taking meter readings from time to time, but is pretty foolproof and should give a good indication as to just how much DHW energy we get from PV and how much comes from the grid. More details and photos to follow, once I've got it up and running.

The only word of caution I would add is that it's very well worth checking to make sure that the fittings are electrically safe before fitting them. If they are metal, then check that there is an adequate CPC connection (earth) and do an insulation test; it needs to be >1MΩ at a test voltage of 500 V to pass; ideally needs to be very much greater than this. >200MΩ would be fairly typical. Also check that any cables used are really copper wire with an adequate current rating. It isn't at all unusual to find that the cable used in some budget Chinese items is copper-coated steel and massively under-rated, often with poor internal insulation. Even if items need to be internally rewired to make them safe and reliable they are still very good value, as it's not much work to just add an earth connection or run in new flex.

We had this problem, a partially completed build where we needed to re-insure but we didn't need full self-build insurance and a normal buildings policy wouldn't have been possible. I went to GSI who negotiated a policy with an underwriter based on property renovation insurance and it was a great deal cheaper than Buildstore wanted to extend our self-build insurance.

That's not really an over-heating indication, as the spreadsheet doesn't account for incidental heat gains at all, so just ignore the negative numbers.

My rather cynical view, heavily influenced by trying to make an NHBC warranty claim years ago, and giving up after a year of legal wrangling, is that all building warranties aren't worth the paper they are written on. Their only purpose is to satisfy lenders, who have the misguided view that a warranty somehow reduces their risk. The reality is that I'm near-certain that warranties have no significant impact on the real risk that lenders are exposed to. I wouldn't be at all surprised to find out that there is a degree of mutual back-scratching going on between lenders that insist on warranties and warranty providers.

Can only be because the valve is operating the wrong way. The ASHP energises the valve in the DHW state, and de-energises it in the heating state. This is the normal way diverter valves work, as most of the time they will be de-energised and running the heating.

Depends on several variables. First off, you need to know the heating requirement, which is derived from the house heat loss, as that determines the temperature that the floor surface needs to be in order to adequately heat the house to your particular target temperature (some like houses warmer than others, so that's another variable). The floor insulation contributes to heat loss more with UFH than with other forms of heating, so that also needs to be taken into account. Once you have a feel for the heating requirement, and hence the floor surface temperature, you can start to work out the heat loss through the floor, and this is best done by not always focussing on the percentage heat loss, as that tends to highlight the inefficiency of UFH in a low energy house in a way that can tend to cover up the fact that the actual heat loss power is pretty small, IMHO. I put together this rather simple spreadsheet to calculate floor heat loss etc that may help. Save the file and rename it, changing the .txt suffix to .xls and it should open in most spreadsheet applications OK: Floor heat loss and UFH calculator.txt

As I understand it, John Larsen was comfortable with his original external ladder frame EWI idea being adapted to the twin ladder frame structural truss system for new builds and retaining his name. Our build uses a twin stud system that is, to all intents and purposes, identical in concept, and has been widely used in North American timber framed homes for a couple of decades now. John Larsen wanted to come up with a way of better insulating existing homes with an added a non-structural outer frame as a way of making a space that could be filled with non-sheet insulation, whilst retaining the inner stud frame members as the structural components. Twin stud walls for new builds just takes John Larsen's idea and applies it to a new frame, with the outer stud being the non-structural member (as in John Larsen's add-on frames) and the inner timber being the only structural timber (just as the original timber frame timbers would be in John Larsen's add-on system). In our case the inner stud bears on the concrete slab, whilst the outer stud rests on the 200mm thick EPS upstand around the slab, so isn't load bearing. In terms of the core principal that John Larsen came up with, which was to virtually remove thermal bridging between the internal structural frame and the external weather cladding support, then there is no difference between the new build twin stud wall and a retrofit ladder frame filled with insulation to hold new cladding.

Yes, they have a couple of decades or more head start on us when it comes to using blown cellulose, both wet sprayed and pressure blown (we have the latter in our build). IIRC, they first started using blown cellulose in the 1970s, a few years before John Larsen came up with the Larsen truss as a way of adding EWI to existing timber framed houses in Canada.

The noise thing is odd, as our heat pump is extremely quiet. The only ways I can tell whether it's running or not is to look at the display, or go outside and see if I can feel air coming out the front. The slight noise of air going in the MVHR intake, high on the wall above the ASHP, is noisier than the ASHP.

Worth comparing the long term airtightness performance of tilt and turn versus casement windows. I looked into this when we were looking at windows and decided that casement windows looked a better bet. They were also a bit cheaper! The majority of our windows have two opening casements, and all those are 1200mm high and vary between 1600mm wide and 2000mm wide. All our glazing is triple glazed, with 4mm - 20mm - 4mm - 20mm - 4mm argon filled units, with an overall average Uw (the whole window U value) of around 0.7 W/m².K. They are aluminium clad timber frames, so we have the look of varnished timber inside and the maintenance-free powder coated aluminium outside. As mentioned above, access may not be as big an issue as you think. Our plot is tight for space and accessed via a single track lane, yet we managed to get a crane and lorries to the site with only some slight difficulty. There are one or two people here who have had more restricted access and have still managed to get kit frames delivered and erected OK, often using a telehandler to move the frame panels and components. One major advantage of having a kit built frame is the speed of erection, which saves money in several areas, like less scaffolding hire time, less toilet hire time, and the ability to get on with work fitting out the inside without having to worry about the weather. Our frame went up in 4 1/2 days, from having a passive slab to a weather tight house, which I'm sure saved us a fair bit of money by not having delays at that stage of the build.

FWIW I don't think there is a particular problem with rendered EWI on one or two storey houses, as long as there are fire resistant barriers above every opening, to prevent molten EPS from dripping down over what might be a fire escape route. I'm not sure I'd rely on the render for that barrier, but it should be easy enough to fix a bit of cement board above every opening as a barrier and render over that.

The ASHP will modulate down, then turn on and off as required to maintain the flow temperature at 40 deg C. In practice this isn't a problem at all, as there is hysteresis on the ASHP flow sensor, so it won't turn back on again until the flow temperature has dropped a bit. I don't have any controls on mine - if the UFH is calling for heat the heat pump is just switched on and runs at 40 deg C, modulating or turning itself on and off as required to maintain that flow temperature. It's no different to a combi boiler, they control temperature in a heating circuit the same way. If the room stat calls for heat the boiler turns on and heats to the set flow temperature, then modulates down to try and hold that as the heating demand drops, then turns off until the flow has cooled a bit before turning back on again.

A search of Youtube with the term "facade fire" will show a few videos of EPS burning quite happily behind rendered walls. I posted a video showing this earlier in this thread. The video of birds nesting in a German building's EPS EWI, having pecked a hole in the render, is interesting, too:

FWIW, our timber frame has barely moved in the five years it's been up. Any movement should be visible around the top of the two storey high gable window, which is resting on the slab and has an aluminium outer frame. When I was up a ladder inside cleaning the windows a few weeks ago I could see a hairline crack around the frame and the plastered walls internally (which are screwed directly to the frame). If I had to guess, I'd say the movement was at most around 1mm over a height of over 5m. The sealant around the windows can easily cope with movement that's a fair bit greater than this, I think.

There are two ways of controlling DHW temp with these units, either use dry contact controls and use a tank stat to both deselect DHW mode and also turn off the ASHP, or just let the ASHP flow temp control the DHW tank temp. Either will work OK. In my setup I have a tank stat set midway up the buffer (which in my case is used just to preheat DHW) and I use that to control relays to operate the dry contact inputs. I have my controls set so that the DHW buffer heating takes priority over floor heating or cooling, and I don't use the valve control output of the ASHP to switch the buffer in and out of circuit, but do that with a separate 12 V motorised valve. If opting to use dry contact control (which I think is the simplest way) then you can just follow the Kingspan wiring diagram, as that allows DHW to have priority.

Welcome Patrick, and thanks for the kind words about our blog - I must get around to updating it soon! You're not far away from us, either, if you wanted to visit and have a look around.

I decided to do a bit of digging around to see if I could find some reasonably well documented evidence to support the view that blown cellulose insulation was reasonably fire resistant when used in a timber frame structure. This video is old, but seems to show that it is significantly more fire resistant than rockwool/fibreglass, something I found a bit surprising:

Yes, you can wet spray cellulose to open panels fairly easily. Doesn't seem to have caught on here, but it's used elsewhere: I've used DIY spray PU foam to help a friend insulate the inside of a steel boat hull years ago. Not that difficult, but it does require a fair bit of practice to judge the expansion level. It's pretty temperature sensitive we found, so that when we were getting to the end of the job, when the interior had warmed up a fair bit, the foam started to expand a bit more and we needed to speed up the application rate. Even then we had to cut off loads of excess foam, we had dozens of sackfuls of trimmings where we'd cut the foam back to get it level with the battens that the lining was screwed to.

Yes, but as above I'd have concerns with using blown cellulose, as that can hold moisture well and will probably sustain fungal growth. Rockwool, EPS, XPS etc are all fine when bridging the DPC, AFAIK.

It's treated with borax to be fire retardant, but some of its resistance to fire comes from it being packed in tightly to a sealed cavity, so air can't get in at a fast enough rate to allow it to sustain combustion. I tested some with a blow torch and found that when compressed into a tight ball it tended to char and burn whilst the flame was playing on it, but self-extinguished when the flame was removed. If spread out on a surface it would sometimes try to burn slowly once ignited, but still wasn't easy to ignite. My concern with using it as EWI would be damp penetration. Unlike rockwool, blown cellulose will support fungal growth, even when treated with borax, I believe.

Birds have made holes through the render and nested inside the EPS in some places, and there's been at least one case where a bin was set on fire which then managed to set fire to the EWI - not sure if a hole was made first.

With the Larsen Truss EWI option you normally use rockwool, so the fire break issue is reduced in importance, as only the external timber ladder frame supports are flammable, and if well-sealed with render board fitted externally air won't be able to get in easily. All openings would be surrounded by the render board (MgO2 or similar) so that should constitute an adequate level of fire resistance and resistance to the spread of fire.