Jeremy Harris

AFAIK, Greg Mook's and our builds were both a fair bit before Herb J, as I think Herb came to look at our build before his started. We have the green board as the VCL, but not the bright green stuff they are using now, a darker green stuff that is some sort of coated chipboard, about 12mm thick. I have a feeling that it's Spano Durelis, or something very similar,a s it looks identical to it. I think the switch to trying just a membrane on the walls was after our build, and have a feeling that they switched back to using a vapour tight board because it was a lot quicker to fit.

I think installation is where much of the cost lies with cellulose. The machine is pretty expensive and it needs at least three people to do the job reasonably well and quickly - feeding and breaking up compressed bales into the hopper really needs two guys, if the blowing guy is working flat out. We have 300mm of cellulose in the walls and 400mm in the roof and are pleased with the outcome. Not only is the thermal insulation good, but it has a high decrement delay and it works as very effective sound insulation, too, Like @Bitpipe, our roof insulation is just blown into the space between the outer sarking boards and the inner Intello membrane.

Has anyone looked at drilling large holes though the I beam webs to reduce the thermal bridging and effectively turn them into Larsen trussses? If using blown cellulose, big holes like this would also allow an easier fill. The webs in an I beam can tolerate loads of big holes with no reduction in stiffness or strength - they are only solid because it reduces manufacturing cost.

Still gives a nasty thermal bridge though, as the beam ends will be near enough at outside air temperature. The heat loss rate around the periphery may well be high enough to cause internal condensation problems around the first floor/wall junction, inside the house.

Overhanging the joists into the cold cavity is definitely not a good idea, as they will rot out as a consequence of interstitial condensation, I suspect, which is why your building inspector won't have it. You have to keep the joist ends on the warm side, ideally hanging from the inner wall, as that is far and away the lowest risk solution.

Our house is built with a Larsen truss system. The inner studs take the structural loads, the outer ladder frames sit on the protruding under-slab insulation and provide a space for the cellulose fill to be injected, plus they add some bracing and lateral stiffness to the structure. It's essentially exactly the same as the system that John Larsen came up with, with 300mm deep trusses, but prefabricated in a factory and with slight lower thermal bridging. Mind you, John Larsen did come up with the idea back in 1981 - makes you wonder why it's taken us so many years to pick up on the idea..................

I suspect not, as it doesn't burn well and probably gives off some pretty nasty stuff when it is burned.

They look OK. The spec needs careful reading, as the very high COP being quoted is for dry air with a 35 deg C flow temperature. Increase the flow temperature to 55 deg C for hot water and the COP decreases a lot, as expected. One nice feature (if it's true!) is that the defrost system has been specifically designed for the problematic UK weather conditions around 0 deg C and just above, which is something none of the other companies seem to mention. I know, from practical testing, that that the Carrier unit I have (badged by several other manufacturers) doesn't behave well when asked to deliver a high flow temperature during the temperature/humidity conditions that are critical for ice forming on the evaporator. My guess is that they may well have increased the evaporator capacity, maybe tweaked the fan flow rates and maybe built in a bit more intelligence to the defrost cycle. That's pretty good, as defrost cycling is not included in the standard COP measurement, and does have a big impact on overall efficiency.

Governments have always been creative when it comes to generating taxes. Before we had things like cars to tax, there were taxes on things like windows, for example - the more windows you had in your house, the more tax you paid. At one time or another governments have taxed just about everything going, so I'm sure they can come up with ways to raise revenue if they start losing it from fuel taxation.

I have a Heath Robinson alternative, I stand on a step ladder and the stiff yard broom can just reach, and does a reasonable job of cleaning the fins!

I think what we need to do is de-mystify the whole low energy house building thing. I'm guilty of using science and technology here that helps some, but probably confuses and puts off others, and I'm not the only one. We've had step changes in house building many times over the centuries, from wood and mud huts, to stone houses, then, more recently the introduction of cavity walls and damp proof courses, and more recently still the incorporation of insulation in houses from new (our old house that was built in the late 70's early 80's had no insulation at all, for example). There's nothing magical about making a more energy efficient house, it's just that solving one problem tends to create a need to solve other problems that arise. This is no different to things like the introduction of cavity walls, they solved the problem of water penetration but created another problem - much higher heat loss than some thick solid walled houses. Our first cavity wall house was icy when compared to the several hundred year old stone cottages we'd lived in before, for example. We're still working through the solutions to the problems created by reducing heat loss, like needing to provide MVHR because we've improved airtightness to reduce unwanted ventilation heat loss, or needing to fit vapour control barriers on the inside of houses because we've improved the wall and roof insulation to the point where interstitial condensation can be a risk. Gradually, all these things will just naturally migrate into normal building practice, much as the fitting of central heating to houses has. I bet there were a lot of people who felt that central heating was complicated and unnecessary addition when it first came out.

The area by the back door (which is where this intake would end up) is pretty sheltered by the retaining wall that is still around 1.5m high at that corner, so the intake itself and the air around it is in near permanent shade. A bit higher up the wall (say from above about a metre above ground level) and the duct would catch the early morning sun, as that tends to be around the level of the lower edge of the window in the top half of the back door. Good idea, I reckon around a metre off the ground might be about right, not only for access, but also for neatness. I can tuck it down the edge of the rear wall without getting too close to the rear of the ASHP if I do that. Unmanaged woodland has it about right. A tree that falls and decays naturally releases CO2 at a rate that's pretty close to the uptake rate of the living trees around it. Making things like houses out of wood is even better, as they will last many decades, locking up the CO2 for a lot longer.

I have external finned vents and the intake one regularly clogs with cobwebs and fluffy seeds. The "old man's beard" fluff seem the worst of the fluffy seeds, as there is loads of it in the hedges around here and I'm forever having to get up a ladder and brush the intake grille clear. Being able to do this from ground level would be a lot easier.

To be fair, it was an apolitical bit of daft policy on the environment that caused the driver for this in the first place. Years ago the "green" movement kept stating (completely without any basis in fact) that burning wood was "CO2 neutral". They were very wrong, as the idiots failed to understand the time factor in the atmospheric CO2 equation, they were so dim that they assumed that plants and trees absorbed CO2 at the same rate that fires burn it (I really can't understand people who fail to see the obvious like this). It takes decades for plants and trees to absorb atmospheric CO2, but only hours to burn the wood and put it back into the atmosphere. Sadly, the idiots in the "green" movement had a fair bit of input into government (of any flavour) energy policy, so we ended up with ludicrous decisions like converting Drax to burn wood and giving subsidies to home owners to burn wood. What's worse is that there is a massive inertia associated with changes like this. It took decades for the idiots in the "green" lobby to get government policies to include some of their views and it will take decades to have those policies changed now we know just how barking mad they were. One of the sad things about government (any government) is that they very rarely take any heed of their scientific advice. In fact they often play down the scientific advice they receive, change it's emphasis, or even reverse it's meaning, when it suits. There are some classic examples of this, ranging from all the advice that showed that limited badger culls were not going to achieve any useful aim (they haven't) through to the way they ignored epidemiological advice during both the BSE and foot and mouth outbreaks.

You're OK here - I still have a few contacts that should let me know if the helos are on the way to you............

Thanks, that's useful to know and makes me even more encouraged to try it. I have some lengths of 150mm rigid PVC duct left over, plus some bends and clips, so it wouldn't be hard to just jury rig something up to see if it makes a difference. If it works, I could look at boxing the duct in with some of the spare larch boards I kept, and that are getting in the way a bit (they are too good to throw out!).

I have no evidence, other than seeing two new nicely built covered wood stores being built by houses in the village, but I do strongly suspect that the RHI may well have encouraged some here to buy wood stoves, and that may well have led to the recent problem. In the previous three years I've only once had to turn the MVHR off because of smoke, and that was a neighbour having a bonfire. Now I've had three days in a week when the MVHR has had to be turned off, because the valley is full of woodsmoke. Something has changed, and I suspect its a few people fitting wood stoves. One reason may be that most houses in the village have (or had) oil fired central heating and the oil price makes this expensive to run. Perhaps they've been enticed by the grant to fit a wood burner, to save on heating oil.

Generally the air doesn't get much cleaner than the downs South of Salisbury Plain - we're miles from any industry and well South of the busy A303 trunk route, and well North of the slightly less busy A31/A35 route along the coast, and the prevailing wind means we have pretty low levels of air pollution most of the time. The problem is specific to the nature of small population centres here, and over wide areas of the UK. Settlements tend to be built down in valleys, not on the top of hills. If the valley happens to have a number of houses where there are open fires or wood burning stoves, then there are likely to be times when these valleys will fill with smoke. Where our old house was located was far worse. That was in what amounted to a "blind valley", where there was almost no wind flow at all, even on extremely windy days. During periods of cold weather, usually prolonged high pressure associated with very low wind speeds, not only would that valley get cold, but it would fill with smoke for days on end. In the end a serious car accident, caused in part by the very poor visibility along the road at the bottom of the valley, caused the local environmental health people to start taking action over bonfires, and they are now in the process of checking excessive smoke from fires and stoves. As you probably know, plot hunting is a challenge, and finding a plot in a general area where you want to live is pretty damned hard. Finding one that is perfect, in all respects, is near-impossible, unless you happen to be very wealthy. I spent well over two years full time plot hunting (as in out and about every day of the week for two years looking around at plots). Eventually I found our plot, and it wasn't perfect, but was affordable, in a quiet rural location and oriented so that a passive house was an easier proposition. It wasn't an easy plot to build on, and, until the past week we've not had a problem with smoke. I strongly suspect that some people in the village have recently had stoves installed, as I've noticed wood stores that have been erected in the past few months.

Funnily enough, but I was just re-reading this and had the same thought, move the MVHR intake down towards ground level. Practically this isn't that hard for me, as the intake is out of sight, high up around the back of the house, so I could add some external ducting to bring the intake around the corner of the house (which then fix the other issue I have, of having the intake at right angles to the exhaust) so that it is on the East facing wall, lower down, by the back door. This would also make it less susceptible to drawings in any smells that come with the wind, that tends to tunnel along the gap between the North wall and the retaining wall, especially in a strong Westerly wind. Other advantages would be that the length of duct down the Eastern wall would warm up in the early morning sun (useful in winter for pre-heating the MVHR intake) and having the intake grill lower down would make it easier to clean out all the cobwebs and fluffy seeds that tend to clog it up. It's an interesting idea, and one that I'll definitely give some further thought to.

It's a good idea, but living in a sheltered valley means the whole valley tends to fill with smoke, from the inversion layer** at the top of the valley downwards. This means that over a period of hours the smoke descends from the inversion layer down to the base of the valley. This pattern is only disturbed if either the inversion layer dissipates or the wind speed and direction increase/change so that the valley is blown clear of smoke. The photos of Launceston, Tasmania, that head one of the papers I cited earlier shows this effect: You can see the line of the inversion layer in the right hand photo, with relatively clear air above it (you can see the distant mountains) and also see that the smoke initially rises, hits the inversion layer, starts to cool and then sinks to gradually fill the valley from the top down. Any upwards pointing snorkel arrangement would initially make things worse, and to be effective would need to poke out above the top of the inversion layer, several hundred feet up, perhaps. As another illustration of an inversion layer over the UK, here's a photo I took when flying back to Dover from a trip to France, where you can see the "dirty" faintly yellow, air trapped by the inversion over London in the far distance (around 80 or so miles away from where I was over the Channel when taking this photo). London sits in a bowl-shaped depression, so tends to be prone to having local inversion layers over the top of it, one thing that contributed to the very bad smogs of the 1950's : ** An inversion layer forms when a layer of warmer air overlies a region of colder air. In the specific case of hollows in the ground, like valleys, what tends to happen is that the ground in the valley radiates heat to a clear sky overnight, so the ground temperature, and surrounding air, get very cold (the "frost hollow" effect). Meanwhile, the air above stays warmer, often because there will be a gentle flow of warm air above the inversion, in the UK often as a consequence of Oceanic air movement coming from the West. Normally, air gets colder as you go higher, according to a rule called the adiabatic lapse rate. In rough terms, the dry adiabatic lapse rate here tends to be around 2 deg C per 1000ft, which means that normally warm smoke will continue to rise, even though it is cooling down. The rate of cooling of the smoke only needs to be slightly lower that the adiabatic lapse rate to ensure that it carries on rising. As soon as warm smoke hits warmer air above it stops rising, and continues to cool, so starts to sink towards the ground, where it cools faster as it encounters cooler air lower down for the second time.

Just tongue in cheek - should have put a smiley in there. Apologies to any non-wood burning stove owning Conservatives........

When the powers that be find a way of getting a revenue stream from those burning wood. It's dead easy to slap another tax or charge on motorists, even though they are a tiny part of the problem, but it's very much harder to come up with a way of taxing wood and those who burn it. For a start, many people burn wood in cities and towns as a "fashion statement", rather than because they have too. I can have a guess that a lot of city wood burners are Conservative voters, too.............. The other point is that many of those who still have open fireplaces or stoves that burn wood are relatively poor, living in areas where there isn't ready access to gas and who don't have the capital needed to change their way of heating. Politically, trying to reduce wood burning is a real poisoned chalice, that I doubt that any political party would tackle, even if it is 79% of the particulate pollution. Motorists are, as always, an easy target.

Yes. Burning with a deficit of oxygen creates a cocktail of toxic volatiles, like creosotes and tars, plus it produces many times more particulates. It's why rocket stoves are generally a better idea if you really have to burn wood, although they create a different problem, which in some ways is almost as nasty. They burn with excess oxygen, so the temperature is high and pretty much all the volatile products of combustion are burned further down the flue. This reduces the emissions of particulates a bit, too. The down side is that like a lean burn car engine, they generate nitrogen oxides, as there is an excess of nitrogen in the feed air that can be oxidised at the high burn temperature. Generally this is the lesser of two evils, though, as in terms of health risk it's primarily the organic volatiles and smaller particulates (the PM10s and PM2.5s) that are probably the greatest health risk. To put this in perspective, some of the data from Australia seems to have been reasonably well validated, and there are some health risk factors that do seem to generally fit with the observed data, accepting that the study samples have not been very large, or conducted over long periods of time, so they are broadly indicative, rather than definitive. A three month winter average reduction in particulate emissions, just from wood burning stoves, of 40% resulted in the following observations: For men, deaths from all causes over the next 6 years reduced by 11.4%, deaths from cardiovascular disease reduced by 17.9% and deaths from respiratory disease reduced by 22.8% Results for just the winter months, for both men and women, over the same period, showed that deaths from cardiovascular disease reduced by 20% and deaths from respiratory disease reduced by 28%. These were benchmarked against deaths from an earlier 7 year period immediately before the restriction on burning wood came into force. Politics here is clearly getting in the way of science and the facts. By our governments own data, 79% of harmful emissions in the air that the government is trying to reduce are coming from burning wood, yet who are they targeting? The 14% of emissions that come from vehicles. The reason is plain to see, they can tax and legislate "dirty vehicles", but they simply do not want to tackle the enforcement of the Clean Air Act..............

You could almost certainly use some form of water trap/filter, but it would need a fair bit of power to drive it. The suction on the intake side of an MVHR is very small, not enough to bubble air through water by a long way. A water spray mist curtain might well wash out much of the stuff, but again would need a lot of power, create a lot of waste water and increase the humidity of the incoming air. Ideally, some sort of activated carbon filter might work best, although again there would be the major problem of regenerating the carbon at regular intervals. Ozone would reactivate a carbon filter pretty quickly, I think, so some sort of reciprocating arrangement, or perhaps a rotary arrangement as you have in commercial air handling system heat exchangers, might work. The idea would be to have one filter in use, and periodically have it change over with another filter that was "backwashed" out with air and ozone (air to blow out the particulates, ozone to oxidise out all the volatile smelly stuff). Filter regeneration probably wouldn't take more than a few minutes, and it should be possible to blow the trapped particulates down into a water tank, where they could be trapped. The water tank would have to be cleaned and drained periodically, but it could probably be made to work. If you weren't too bothered by the severe health risk from the woodsmoke particulates, but just wanted to get rid of the smell of from the volatiles being sucked in, then some way of detecting them and injecting a very low dose of ozone, as required, would almost certainly remove any smell. This sort of system is very effective. For the past few years we've had a small, battery operated, ozone generator in the fridge. It periodically releases a very tiny amount of ozone, barely enough to detect, yet is extremely good at keeping the odours from things like smelly cheese undetectable (as long as it stays in the fridge). Similarly, when I was playing around making the ozone generator for our water system, I tried one inside the house. Even modest amounts of ozone blown into the house made it unbearable to stay in for more than a few seconds, but was extremely effective at removing all lingering odours. It works by being an extremely powerful oxidant, that preferentially oxidises volatile organic compounds that we detect as bad smells, It does this at concentrations that are very low, in terms of health risk, and also far lower than the sort of concentration needed to bleach things (ozone is a much more powerful oxidising agent than chlorine).

It is, but perhaps of more relevance here is this UK paper: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/579200/Emissions_airpollutants_statisticalrelease_2016_final.pdf This quote from it, regarding PM10s and PM2.5s is worth noting: Note the final sentence that I have highlighted...................