Jeremy Harris

@Ed Davies has remembered the article by George Monbiot that caused a debate on the GBF years ago (I've had a quick look and can't find that discussion now, but I think it must have been back around 2011/2012). I do remember that during that discussion years ago several people (including, I think, @Ed Davies and @SteamyTea) as well as myself started digging around to see if the facts supported some of the claims being made. My view is that George Monbiot is a political activist first, and an environmental activist second. When he sticks purely to environmental stuff, and isn't trying to push his political agenda, then often he seems to be on the right track. As I mentioned originally, I agree with many of his opinions, but, as someone who prefers reporting to be accurate and supported by evidence, I find it hard to consider him to be a reliable source. As to whether he deliberately misleads, I'm inclined to the view that he probably does. He feels very strongly about his socialist principles (nothing inherently wrong with that) and I believe he lets his political views overrule supporting evidence from time to time. I strongly suspect that he may agree with this, as he's rowed back from statements he's made in the past when he's been called out. That, in my view, tends to make him unreliable as a source, although I still read what he writes from time to time.

Often airtightness and MVHR will make a more significant change to heat loss than chasing the last decimal place of fabric U values, plus decrement delay needs to be considered, as that plays a very large part in perceived comfort. If push came to shove I'd go for a construction with a slightly poorer U value if that gave a longer decrement delay, just for the comfort factor. There's a good explanation of decrement delay in this article: http://www.greenspec.co.uk/building-design/decrement-delay/ The spreadsheet is here: Heat loss calculator - Master.xls

That spreadsheet only considers heat loss, and makes no attempt to model incidental heat gains, which is it's major flaw. PHPP does a reasonable job of doing everything, but is very complex and takes a bit of time to get familiar with. I'd strongly recommend using PHPP though, as my spreadsheet was only ever intended to be a crude "what if" tool for comparing different major parts of the construction. I really put it together just to see if making, say, the window U value a bit better had a significant impact, so that cost/performance trades could be made with a bit of supporting data. I have a sub-soil temperature probe under the slab and it barely change by half a degree from it's coldest in about late February to its warmest in late September. In our case it sits at around 9°C, but 8°C seems to be a temperature that is quoted widely as being about the mean UK soil temperature. Uncontrolled infiltration in a house that's well-sealed and fitted with MVHR is negligible, as you say. The airtightness is noticeable when you open and close doors, as you can definitely feel the air being compressed or rarefied when a door is moved quickly. The pressure test isn't done at a very high pressure though, it's roughly the same as the dynamic pressure from about a 20mph wind. Mind you, a 20mph wind is pretty strong. It's a tiny fraction of atmospheric pressure, though (which is about 101,325 Pa). Your heating demand sounds about right, but will likely be a very worst case, when the house is unoccupied and has everything turned off, with zero solar gain. In reality I find that we never need much heating at all, and certainly not as much as the spreadsheet indicates. The reason is down to there being two of us in the house jointly contributing about 150 to 200 W, the base load from electrical appliances in the house that add another 200 W or so, plus a bit of solar gain, the heat released to the house from showers, baths and cooking, etc. It's not hard for the incidental gains to supply all the heating needed for much of the year, and to contribute to overheating when there's a bit of solar gain. Our house is also cut into a hillside, near the bottom of a valley, so has a surrounding microclimate that seems a fair bit warmer than the Met Office temperature data I used for this area. I've not tried to properly model solar gain, but I did have a go at roughly estimating it. I reckoned that our 9m² South facing windows (which have a fairly large overhang) could pretty easily see around 200 to 300 W/m², perhaps more on a bright, clear, day. As supplied (before I fitted the reflective film to the outside) most of this would have ended up in the house, perhaps around 70% of it, so the heat input just from the South glazing could be around 1,300 to 1,900 W, for several hours. This is way more than the house needs to stay at our preferred temperature, hence the overheating we've experienced. The worst aspect in terms of overheating seems to be the glazing on the East side. The sun rises well North of East in summer and often the early mornings are very clear here, so we have bright sun at a relatively low angle shining through the East windows for a fair time first thing in the morning. For some reason, the West facing windows don't seem anywhere near as much of a problem, due, I think, to the air tending to be more hazy here in the afternoon. Overheating seems to be a theme here for those that have built low energy homes, especially those who have incorporated large areas of glazing.

Given that it's only my view of the man, and that the article in question was written about 5 or 6 years ago, I fail to see why I'm under any obligation to spend a few hours going back over research I did back then. My view was set when I found that he'd been economical with the truth, and that's not going to change. Your views are your own, I don't expect you to justify or explain them, any more than you should expect me to spend hours going back over some inconsequential stuff written by a journalist I now consider to be unreliable. The pity is that I both admired Monbiot and shared many of his views, right up until I was pushed to cross check some stuff he'd written by a couple of sceptics.

Simple. He quoted "facts" that turned out not to be facts at all, and which didn't stand up to detailed scrutiny. The pity is that I agree with his general opinions. The bottom line is that he now seems to seek out "evidence" selectively, and often only publishes that which supports his own views, and often fails to provide balance. As a reporter I expect more from him, as he now seems to come across as a political activist than a journalist. Perhaps this is just the way the media works now, which is a pity, as the Guardian, despite the emphasis it puts on being an independently funded source of information, has suffered (IMHO) as a consequence of a reduction in the robustness and balance with which it reports stories. Twenty years ago I'd have said that the only significant issue with the reporting in the Guardian was it's notoriously poor spelling, but it seems to be following the lead of every other newspaper, in that it's become a self-licking lollipop, that only publishes stories that it's established readers accept without question.

I've no idea. Once I'd found that he'd been very economical with the truth when trying to support a particular view I decided he was untrustworthy as a source, so I've just not bothered to take any notice of anything he's written. If he could deliberate mislead once, then in my view there is a good chance that he may mislead again. After all, he makes a living from selling stories to those who agree with his political views (which isn't to say that I don't, but I prefer facts over unsupported rhetoric)

The last time I went looking for peer reviewed evidence of something he'd written was about climate change and the use of biomass as fuel. IIRC, there was a debate on the GBF about the specific article, probably around 5 or 6 years ago (before the nutter that runs the GBF threw me off because he's a wood burning stove fanatic and animal rights extremist, whose wife then spammed me with extreme animal rights stuff for weeks). Whatever may be left on the GBF will have been edited by the site owner, as he has a penchant for editing posts that he personally disagrees with, something one or two of us spotted and called him out on.

Welcome. We built a passive house, timber clad with larch, that is effectively a "negative energy, negative CO2" house (it generates more energy than it uses over the course of a year, and has total CO2 "emissions" of -0.9 tonnes CO2/year). We're not a million miles away from you, about 10 miles west of Salisbury, and you're welcome to drop in if you're on the mainland at any time.

It's not that hard to get under 0.6 ACH, our build came in at 0.49 ACH on the first air test, and I've since gone around and adjusted a couple of small leaks at the doors. We also have a Genvex Premium 1L MVHR, but we don't use it for heating as we don't much like the dry air we seem to get with it, so instead use UFH on the ground floor for both heating and cooling. The MVHR does provide a modest amount of cooling, but wouldn't be enough on it's own. We have about 9m² of south facing glazing (with a large roof overhang), 5.5m² of east facing glazing and 7.5m² of west facing glazing. The house is 130m² and meets or exceeds the PH standard (roof 0.1 W/m².K, walls 0.12 W/m².K, floor 0.1 W/m².K and doors and windows about 0.7 W/m².K). We run the MVHR at around 0.4 ACH, except when it's cooling where we have to boost it to about 1 ACH. We had severe overheating initially, and added solar reflective film to the south glazing and also to the east. That's significantly reduced solar gain, but it is still an issue in Spring and Autumn, when the sun is low. We run the ASHP in reverse to cool the floor which makes a very significant difference, far more so than running the Genvex in cooling mode (and the Genvex is over-sized for our house, really). I found that both my own thermal modelling and that in PHPP was seriously in error. The heating demand is slightly lower than predicted (our peak heating requirement in really cold weather rarely gets above 1 kW in practice) and the cooling requirement is massively greater than predicted, in part because we've found that the house feels uncomfortable if it's warmer than about 23°C (unlike our old house where 24° to 25°C seemed OK). Our house is all-electric, and electricity and telephone are the only services we have (borehole for water plus a treatment plant for sewage). We have 25 PV panels built in to the roof, and they provide a great deal of our energy needs in summer (including charging my car), but we are reliant on the grid between about October and March, when PV output pretty much falls off a cliff. Our annual electricity bill (on E7, with about 55% to 60% at the off-peak rate) is around £350 a year or so. Heating is really sod-all, as the house rarely needs much heat, and the 6 kW to 7 kW peak output ASHP we have is a massive overkill and far too large for the heating/cooling demand. It was the smallest unit I could find at a reasonable price, though. If doing this again then I would not bother fitting the Genvex and would go for a cheaper non-active MVHR. The Genvex cost around £3.5k or so, and we could have bought a basic MVHR for less than 1/3rd of that. I would definitely have fitted split air-to-air aircon units, though, perhaps one at the top of the hall and maybe one or two in the bedrooms. They would have been cheaper than the Genvex and given far greater cooling capacity. It's really hard to get effective cooling at the sort of low air flow rates that an MVHR system works at, and having to boost the MVHR to try and improve cooling is a nuisance. The other thing I'd definitely do if ever building another passive house would be to build in external shutters or blinds, to reduce solar gain. The reflective film works, but is really a bodge and it does tint the windows a bit. Alternatively I think I'd seriously look at SageGlass, as it apparently works very well at reducing solar gain, and even at ~£1000/m² it's probably not that much more expensive than other solutions, and has the advantage of being variable.

George Monbiot seems a bit like the Curate's Egg to me; he has sparks of common sense, let down by a failure to check facts from time to time, which in my view makes him unreliable as a source (I really can't be bothered to do any more fact-checking on stuff he writes). Not sure about dodging inheritance tax, as it's now a year since my mother died and the sale of the farm and associated taxes that are payable is still being dragged out. As far as I can see there isn't any obvious way to avoid inheritance tax, although there is a means to allow farms to pass on to children to continue to be run, just as there always has been. I don't see this as being a particularly bad thing, as if children don't want to take on a family run farm then it will be sold to someone who does want to run it. Not an easy life being a farmer, anyway, and fewer people seem interested in becoming farmers now. It's not easy to bring about just land reform, as has been demonstrated many times in history. A look at what's been going on in countries that have tried radical land reform shows that, whilst the principle of taking land away from the wealthy, and giving it to the less wealthy, may seem reasonable in the eyes of some, in practice it seems that those who take on such land often fail to work it efficiently.

We have four 6 W LED panels over the island, 14 W/metre LED strips under the wall units (to light the work surfaces) and eight 3 W panel LEDs in the rest of the ceiling. It works well, but I did end up dividing it into two sections, so we can dim the lighting down without the faff of dimmers.

Welcome!

Adding 50mm of PIR to the inside EPS (or better still the outside, if possible) and reducing the internal service void down to 25mm (just to mitigate the wall build up thickness) would bring the U value down to around 0.15 W/m², which is getting there, and certainly a lot better than the original build up. There's a chance that the specific type of high density EPS used in Nudura may have a slightly better λ than the figure of 0.034 W/m.K that I've used in these calculations. Might be worth digging around in their specifications to see if they list it.

Why EPS and not PIR? Switching to PIR would make a useful difference, as it has a λ of around 0.022 W/m.K, versus a λ of around 0.034 W/m.K for high density EPS. Two 65mm layers of PIR on their own would give a U value of about 0.165 W/m².K, or your wall build up with PIR in place of EPS would give about 0.16 W/m².K, which is heading towards a sensible design target (although still not great). The notional fabric values in Part L1A aren't a bad aiming point, and they quote a wall U value for design of 0.13 W/m².K, which seems pretty sensible.

I've just checked, and with only 130mm of EPS in total you aren't going to have very good wall insulation really. Ignoring the concrete, 130mm of EPS on it's own is only going to be about 0.25 W/m².K, which is a bit grim really. Running the calculations by hand for a build up that's (from inside to out): 12.5mm plasterboard - 50mm service void - 65mm EPS - 150mm concrete - 65mm EPS - 15mm cement render I get 0.23 W/m².K Double checking with this online calculator : http://www.changeplan.co.uk/u_value_calculator.php gives a significantly worse U value of 0.27 W/m².K, mainly because the default values of λ for the EPS and the concrete seem to be a bit worse than the values I selected.

The limiting fabric values aren't really that significant in Part L1A now, as a lot of the time the house may need to exceed those values in order to get a "pass" in SAP, I believe. Those values in the spreadsheet are only there for reference, they aren't used in any calculations and could be just deleted easily enough. I'll check the calcs. What's outside the outer layer of EPS?

Not really, I just think of psychedelic patterns and things moving when they shouldn't...

Phew, that's a relief! You don't need any password unless you want to modify any of the locked cells. I locked them just to prevent accidental finger trouble deleting the formulae in them, so only cells that need to have values changed are unlocked and can be edited as needed.

That's what should be in the spreadsheet, at least that's what's showing on the master copy, 0.13 W/m².K for floor and roof, 0.18 W/m².K for the walls and 1.4 W/m².K for the doors and windows.

Technically you can DIY an installation that needs a Part P building regs approval (in England and Wales) without using an electrician that belongs to one of the Part P cartels. All you do is make a normal building regs application and they are supposed to send out someone to inspect and test the installation. Recently I ran into a case locally where someone had done exactly this, and pushed back at the reticence of building control to do the inspection and test. What normally happens here is the building control will say that they have no one accredited to do a third party installation inspection and test, and they will request that you get the work done by someone with a Part P ticket. This chap pushed it, though, pointing out that building control had a legal obligation to do this work. What happened was that building control sent an inspector around, who didn't do any inspection and test work, but who witnessed the DIY'er (who's a retired electrician) do a few tests, then they signed the job off (it was a conservatory, with a lighting circuit, plus a few outlets and an air con unit). Makes me wish I'd pushed harder when building control were extremely reluctant to inspect and test our electrical installation.

I've knocked up a simple spreadsheet for calculating U value, and included some typical material λ values, and a simple calculator for working out the λ for an air gap. The calculator adds the thermal resistance of the internal and external surfaces and includes provision for walls. floors etc with up to 6 layers of different materials. It's a bit rough and ready, but seems to work OK. To help prevent accidental deletion of calculation and fixed data cells I've locked the worksheet, but if anyone wants to unlock it the password is BuildHub If anyone finds any bugs let me know and I'll try and fix them. Simple U value calculator.xls

It's not hard to calculate U values using basic principles. You need to calculate the R value (from the material λ values for each layer material and thickness), add the surface R values for either side (typically 0.13 m².K/W internally and 0.04 m².K/W externally) and then just add all the R values together. Take the reciprocal and you have the U value. For example, for a simple wall with 12mm OSB both sides, no thermal bridging and a core of 200mm of EPS, then the R values are calculated like this: External resistance = 0.13 12mm OSB, λ = 0.13 W/m.K, R = 0.092 200mm EPS, λ = 0.034 W/m.K, R = 5.405 12mm OSB, λ = 0.13 W/m.K, R = 0.092 Internal resistance = 0.04 Total R = 5.759 m².K/W U value = 1/5.759 = 0.174 W/m².K

You need about 1.55 times the thickness of EPS for the same U value as if using PIR. It's the ratio of the relative λ values that matters, so EPS with a λ of about 0.034 W/m.K and PIR with a λ of about 0.022 W/m.K gives a ratio of 0.034 / 0.022 = 1.55

The US use °F·ft2·h/BTU for R values, whereas we use K·m2/W .

Bear in mind that video is from the USA, so the R value is in US units, not metric. The U value is definitely not 0.05 W/m².K, it's more like 0.24 W/m².K.