Denby Dale PassivHaus revisited

Seven months on from my previous visit, I take a day out to travel up to Denby Dale in Yorkshire to have another look at the now nearly completed PassivHaus, the home of Geoff and Kate Tunstall, and to meet the builder, Bill Butcher (pictured left). The three hours in their company passed very quickly, much of it spent over a delicious lunch. What did I learn?

• Passivhaus is a very technical subject. Every time I dip into it, I learn a little more and realise that there is also a lot more I don’t know and/or don’t understand. The basic tenet - to reduce space heating requirements to a minimum - is common sense, but getting there requires a fair bit of discipline and a fair bit of science. Things like where in the wall you should place the windows, how you stop wind washing over and around insulation, and just how big a hole you are allowed in a Passivhaus to get that airtightness down below 0.6. (in fact Denby Dale came in much lower, at around 0.3).

• One of the big delights of the Denby Dale Passivhaus is that it’s a cavity wall construction, with most of the heavyside materials coming from the local builder’s merchant. Some sceptics said it couldn’t be done as a cavity wall construction, but here’s the living proof. It is probably the only one like this in the world (though there may be something similar in Northern Germany where cavity walls are also used). Bill had to design a number of details to get it to work, most notably the insulated aluminium cappings on the outside of the windows.

• Since the Denby Dale house has received a lot of publicity, the Green Building Store has been approached by a number of people who would like to “build a Passive House” but already have plans drawn up and agreed. You can’t realistically do that, because once you put the plans through the PassivHaus Planning Package, there are almost certainly big changes going to happen. The advice is to start out with the aspiration to build a PassivHaus, and to have the initial design work put through PHPP at the outset. PassivHaus is integral, not a bolt-on.

In fact, the suggestion was that if you are really interested in building a PassivHaus, you could do much worse than go on a one day course run by the PassivHaus trust, and take your architect along with you.

• Cost and certification. The cost of "going Passiv" consists of two parts. One is the extra cost of using specialised materials, triple glazing, added insulation, etc. The other is the added consultancy fees. These can vary enormously depending on how the scheme has been conceived and who is driving the design. If the architect is already up to speed on PassivHaus, it's probably no more than five days extra work to make the design sing, but if the client or their chosen designer already have strong ideas of what they want and the result has to be Passified, it will be a much longer process. Experience suggest it could take 15 - 20 days, and the cost could easily be £5,000 to £10,000 extra. The final step, certification by the PassivHaus Institute, costs around £1500.

As you can see, it's not easy to say exactly how much it costs to build a PassivHaus, or how much extra it might cost over and above building to conventional standards. Yes, it’s expensive. But what we are really talking about here is quality control. If you don’t certify, then how do you really know you are getting a PassivHaus? If you do, you get a plaque like this.

•MVHR systems. I discovered that they need pre-heaters as well as post-heaters. The pre-heaters are there as frost protection because when the incoming air falls below -4°C, you start to get problems with frost in the heat exchangers. In Germany, a lot of incoming air is put through earth pipes which act as pre-heaters, but this can be much easier to do with a basement, something usually absent from British homes. It was felt at Denby Dale, this was not a practical or cost effective solution, so a small electric pre-heater has been fitted, controlled by a frost stat.

• Wood stoves? Passivhaus are not homes without heating, but they are efficient enough to be able to rely on small post-heaters placed in the MVHR system - effectively turning the MVHR system into a warm air heating system. So you don’t need a wood stove. However, many people want a focal point fire, and we had all seen examples of Passiv Houses in Germany and Austria that had wood chip or pellet boilers with flues. Just how you manage to incorporate such a beast within a Passivhaus and still get the required air tightness test is something that remains a bit of a mystery.

Bill suggested that alcohol stoves might be a way around this issue. I’d never heard of alcohol stoves before: if you google alcohol stoves, you get links to camping gear, but apparently in Germany you can buy alcohol-fired indoor stoves which don’t require any flue.

• PassivHaus probably works best with contemporary-styled homes. Think clean lines, hard surfaces, minimalism. Wood stoves? probably not. Cat flaps? I don’t think so. Letter boxes? Mounted on the outside wall please. You need to learn to drive a PassivHaus. Know when to open windows, know when to boost the ventilation system, know when to change filters. It’s not difficult, certainly no more difficult than getting your head around a car’s climate control system. But you do perhaps have to start thinking of your home as a machine for living in. You can’t just start knocking it about, adding new bits here and there. This may in fact be one of the major criticisms of PassivHaus - it’s not readily adaptable. Even things like running a cable through for a satellite dish, or a new phone line, are frowned upon. Sure, you can do what you want to your PassivHaus but it will cease to be a PassivHaus if you mess it around. Just like it will cease to act as a PassivHaus if you sleep with the windows open.

So building a PassivHaus is a lot of trouble to go to if you don't respect it's integrity. However, the one really big plus for PassivHaus is that it works, and has been shown to work over a large number of buildings. Whereas it is beginning to look fairly simple to build to a performance metric of around 45kWh/m2/a, to get right down to 15kWh/m2/a requires discipline in the design, attention to detail in the building and co-operative, willing residents.

Feed-in-Tariffs: the Sums and the Risks

There’s been a lot of discussion recently about the financial attractiveness of FiTs and, in particular, whether any of these deals which offer you free electricity in exchange for your roofspace are a good deal. I thought I’d run my calculator over the FiT offer and proffer some thoughts.

Firstly, what is the offer? It’s complicated. The place to find detailed information is the Energy Savings Trust website. There are four different technologies covered by the scheme, being Solar PV, Wind, Hydroelectric and Micro CHP. For most people in most properties, hydro and wind are not going to be options; micro CHP might be, but the one I am looking at is the one where most of the action is and will be, which is roof mounted solar PV.

The offer on existing buildings is this (it slightly less for newbuilds):
• You have to bear all the installations costs yourself. Both the kit and the installer must be MCS certified.
• The output is metered and you are paid for every kilowatt hour of electricity you produce at a rate of 41.3p per kWh
• Further to this you are paid an additional 3p per kWh for electricity that you export, rather than consume at home.
• These payments are inflation-indexed, tax free and will last for 25 years
• In addition, you will be spared paying for the electricity that you would have purchased from the Grid had you not been using your home-made electricity.

So is it worth it?

You have to estimate how much it will cost you, how much electricity your plant will generate, and what income/savings you will receive.

As a rule of thumb, it seems that most people are opting for a 1.5kW system, and it’s costing around £10,000 to install. It’s a good benchmark to start from. A 1.5kW system is quite large - it will probably involve 10 or 12m2 of PV on the roof.

How much power will this produce? Let’s assume it’s around 1,250kWh/annum. Maybe that’s a little generous - it rather depends on where you live - but we’ll leave it here. It means that the PV arrays operate at an average of around 20% of peak power in daylight hours.

And let’s assume that around half of the power you generate is consumed at home, and the other half is exported. What is the financial value of these 1,250kWh?

• The value of the generation tariff is 41.3p x 1250kWh = £516
• The value of the export tariff (remember we are exporting 50% of what we produce) is 3p x 625kWh = £18.75
• The value of what we save is 625kWh x 10p/kWh = £62.50

In total, that’s £597.50. Let’s call that £600. Or 6% of what we paid upfront to install the system. This more or less tallies with what DECC set out in their Consultation Document.

Tariff levels have been set to provide an expected rate of return, in real terms, of approximately 5-8% for well sited installations, taking into account the risks associated with deploying the different technologies and the likely effect those risks would have on investors’ willingness to invest. As the tariffs are linked to inflation, in nominal terms this rate of return could then be considered to be approximately 7-10%.

Is that an unbeatable return? I don’t think so. It’s OK, but hardly outstanding. Especially when you take into account that the capital outlay has to be written off. The actual return is also very difficult to predict. It depends on a number of assumptions.

• The installation cost: I’ve pencilled in a fairly conservative figure of around £7,000 per peak kWh installation costs. You might get it for less, but would it be any good?
• The longevity of the PV system - just how long will it last? No one can say for sure. They might be good for 50 years, or they might be useless after 10 and need replacing. What happens in case of a major malfunction? Or theft? Or, in accountancy terms, how quickly should the value of the PV array be written down to zero?
• The efficiency of the system - are they going to continue producing the same amount of electricity, or are they going to tail off after a while?
• Will there be maintenance costs? How long will the inverters last?
• How long you will stay in the house? And if you think you'll move on before the 25 years is up, what effect does adding PV to a roof have on resale values? Apocryphal evidence suggests that it adds only marginal value, certainly nothing like the capital costs incurred.
• Future inflation rates? And future electricity prices? And will the electricity price outstrip the overall inflation rate? I think most people signing up for FiTs think this will happen, but it’s pretty much unknowable.
• The legislative risk. The assumption is that the feed-in tariffs are as safe as gilts, and that if the government promises to pay them for 25 years, then they will have to stand by that promise. But 25 years is a long time.....

Now if I was a financial advisor suggesting income streams for my wealthy clients, I am not sure I would go a bundle on the Feed-in Tariff. You can purchase index-linked gilts with inflation-proofed yields above 2% and your capital is both safe and instantly retrievable. Or you can buy Vodafone or Glaxo with yields above 5%, both with less risk involved than putting PV on your roof, and with a better chance that your initial capital would still be worth something after 25 years.

And If I was a businessman borrowing money at anything over 4%, I’d steer well clear, because the upside depends on everything working well, and the cashflow is negative for many years (until the capital is paid off). If inflation kicks in, then the investment begins to look clever, but then inflation has a habit of making all borrowing look clever.

As it stands, the Feed-in-Tariff is a bit like buy-to-let, only with a wasting asset. Which is why I am surprised we are seeing companies setting up to harvest this subsidy. Despite the Guardian describing FiTs as “super lucrative,” I reckon they are anything but. Have these guys really done their sums? Or do they know something we don’t?

More thoughts on housing demand

Some really interesting comments on my last post, deserving of a new post. A well-briefed and articulate "Anonymous" lays into my argument, basically buying the Barker/NHPAU/New Labour line that we should be building 3 million new homes by 2020.

He/she writes I'd say there are some clear signs that some people need more housing in the UK - high housing costs relative to incomes, instances of overcrowding, street homelessness and sofa surfing...

• The high cost of private housing is/was caused by easy credit and favourable tax status. Sometime in the 1970s, housing became "an investment opportunity." The truth of this is demonstrated by the Irish property bubble which saw a phenomenal increase in housebuilding activity, accompanied by a huge surge in prices. People were building homes there because there was money to be made, not because there was a shortage of houses. It's all come crashing down now and there are apparently estates of empty new homes in the Irish Midlands with not a buyer in sight.

• Overcrowding. Relative to what? Sure there is overcrowding but it's nothing compared to our Victorian forebears, or to many third world countries today. And there are many more examples of undercrowding (is that even a word?): single older people living in large family homes that they have paid for and don't have to move on from. Both are bad uses of resources. Think of the number of empty bedrooms in this country which are lucky if they get slept in more than once a year. How many? My guess is many millions.

• Street homelesness. This surely is a litmus test of housing demand. These are people with nowhere to live at all. But if government stats are to be believed, the number of homeless people has fallen dramatically in the past few years. Hardly evidence of an undersupply of housing.

So my beef is this. There is actually no way of telling whether we have too much or too little housing, anymore than we can know if we have too many or too few roads. What we have is a housing stock of around 23 million homes, and some rather poor ways of allocating them across a population of around 65 million. Obviously, if we increase the stock to 25 or 26 million homes, there will be more room for everyone (unless of course the population increases by five or ten million), but this isn't necessarily a good use of scarce resources when so much of our existing stock is in a poor state of repair and/or is under occupied.

There are also sustainability issues here as well. However close to zero carbon these new homes might be, they are still going to add to the carbon output of the UK. In today's Times (paywalled, so I won't give a link) Conservative peer Simon Wolfson continues to trot out the usual pro-development line without so much as a word about the environmental impact all these new homes will have. His idea is to compulsorarily purchase bits of dull farmland and hand them over to "independent bodies made up of leading property developers who would be given a free hand to build the best they can." He's obviously been watching The Normans. He goes on "At a time of economic woe this type of project would create wealth, jobs and growth — not to mention new income streams for a Government that could do with the revenue."

But this is precisely the sort of lazy thinking that created the credit crunch in the first place. It's Labours eco towns, only stripped of the eco. It sounds just like the Irish Bubble Mk 2. The dumbest of dumb growth. And all in the name of "an insatiable demand for new housing."

If targets don't work, maybe bribes will

Grant Shapps is this very morning doing the media rounds, chirrupping about one of his pet initiatives, which is offering councils money for allowing new homes to be built within their boundaries. This is not new money. Rather it’s taken from “existing revenue grants” - i.e. money that central government already pays to local government. So there is a downside here as well. Councils taking on less than average amounts of new housebuilding will, in effect, be getting penalised.

All the old shibboleths are being wheeled out.
• "Homebuilding is good for the economy and good for communities." If so, why is it so unpopular? And why would councils need all this encouragement?
• "Housebuilding is at its lowest level since 1924 - we can’t go on like this.”
• "The council house waiting list stands at 4.5 million in England alone — it doubled under Labour.”

Again and again, policy is being set within these very narrow terms of debate. The reason the council house waiting lists have expanded so dramatically is because private housing has become so damned expensive (it's a tax haven, after all) and private rented housing is so damned insecure. In contrast social housing, now being built to higher standards than private housing, and where rents are subsidised and tenure is for life, has become an aspiration. The wonder is that there are not far more people on the waiting lists. Building a few more social houses each year isn't going to have any effect on this state of affairs whatsoever.

And just what is the "correct" level of housebuilding anyway? How can Shapps boast that he has dismantled Labour's target approach, and yet at the same time have the nerve to say that we are not building enough houses. Isn't that just like being told that there is still a target in place but we won't tell you what it is (Hint - it's more than were built in 1924). Is there a national population target? No. Is there an occupant density standard? No. So how the hell can anyone say there are not enough homes being built?

In the absence of any credible yardsticks against which a target can be set, the debate keeps coming back to this waiting list for council houses. "It's 4.5 million and rising." This is the lynchpin of the not enough homes argument. But, of course, it's nothing of the sort. Rather it's a sad reflection of the fact that the ownership of private housing is now out of reach to many millions. They accept that the best option for them now is social housing and so they join the queue. All quite logical. But unless private housing becomes a whole lot cheaper (which probably means some politically inexpedient taxes on property ownership), the social housing queue will stay at much the same length however many social houses we build. It's not really a problem we can build our way out of.

What would be nice is to have some adult debate about this, rather than the constant repetition of these circular arguments about the "need" for new homes.

The Mackay Calculator

Well, we now know what Prof David Mackay has been up to at DECC. Rather than fiendishly devising infuriating incentives, he has been beavering away on a spreadsheet the size of Hyde Park, attempting to put some maths into the carbon reduction targets. It’s called the 2050 Calculator and it’s here. It’s open source and Mackay asks for interested parties to download it and play with it, and even tinker with the source code to try and improve it. Whether it will be the sort of thing that attracts the Linux set, I have my doubts, but there’s no harm in asking.

The Guardian launched its own carbon calculator back in April. It makes an interesting compare and contrast. The Guardian’s version is far simpler, and the graphics are much better. It works on a series of sliders which give instant feedback on the effects of your choices. In contrast, the DECC calculator is clunky: instead of slider controls, you get multiple choice boxes. Click on one of these and the graphic changes, but not instantly, and usually the change is so small that you can’t actually take in the effect your action has had. Maybe this is deliberate, maybe it isn’t, but it’s disconcerting at best.

The briefs are different too. The Guardian’s calculator is altogether a darker shade of green, looking at issues like low carbon diets and consumer consumption. The DECC calculator is more complex, giving a total of 134 choices, but they are more narrowly focused on pure energy issues.

The depth of the work going into this calculator is revealed in a supporting document called 2050 Pathways Analysis, a 246 page epic which takes off from where Sustainability Without Hot Air left off. Here you can read the assumptions that Mackay has made, and in many ways this is more interesting than simply playing with the calculator (which pales very rapidly - I doubt it will keep many people interested for more than a few minutes).

What stands out is that some actions have huge consequences - a massive switch to nuclear power, carbon capture and storage - whilst most have very limited impact, second-order effects at best. Our great debates about heat pumps, biomass and the rights and wrongs of the Code for Sustainable Homes look pretty trivial in the face of all this.

And there are assumptions in this Calculator which presumably have to be taken as political givens, when in fact they should also be questioned. For instance, Mackay seems to be happy to accept that over the 40 year period the population grows by 25%, the number of households by 50% and GDP by almost 200%. I’ve always felt that these growth assumptions are ludicrous in the face of the problems we are up against, and that we should be aiming for a stable population, a stable number of households and a commitment to smart (i.e. low carbon) growth. Ok, it’s just my opinion, but why shouldn’t they be presented as options for limiting energy demand? Why are they off limits?

What would be nice to see is a simple executive summary which explains what all the assumptions are, and then ranks the importance of the actions we can take. I know its complicated. Everything is interconnected. Nothing is quite that straightforward. But it doesn’t get easier to understand by presenting it as a Calculator.


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