Part L v the Code for Sustainable Homes

Coming off yesterday's piece on using kWh/m2/a as a metric (measurement) of energy efficiency, I think I have identified a major flaw in the shaping of both Part L and the Code for Sustainable Homes, and I'd appreciate some feedback.

When the Code was launched in 2006, it was much applauded for setting out a roadmap for change. The ultimate goal of zero carbon housing was to be attained in 2016, but there were two intermediate stages set out as well, being 2010 and 2013. The idea was that Part L would be used as the enforcing code to raise the base standard and, indeed, this is how the 2010 changes to Part L have been set out.

I am working from memory here so please feel free to correct me if I am wrong, but the way Part L has been chosen to work is like this. The benchmark date selected was 2002 which was the year of a Part L revision when the way of calculating energy efficiency switched from using elemental approaches to a whole house heat loss calculation. A house built to this standard is said to have a Dwelling Emission Rate (DER) of x.

The next version of Part L (in 2006) then put in place a process which called for the 2002 DER to be improved by a certain percentage, in this instance 20%. So the Target Emission Rate (TER) for 2006 was the 2002 version DER minus 20%. At this point, the Code for Sustainable Homes comes into play and with it a set of targets. Code Level 3 set an improvement of 25% on Part L 2006, and Code Level 4 an improvement of 44%.

So consequently the new version of Part L (coming into effect this October) simply attempts to put this into place. It still refers back to the 2002 model house, but asks that you now build it to a standard that is a 25% improvement on the 20% improvement requested in 2006. This tortured logic is all on display on p11 of the 2010 Part L where you can actually see the calculation set out in two stages. Essentially: "Take the 2002 DER, times (1-0.2) and then times (1-0.25)." Incredible!

Thus Part L 2010 is aligning itself with the energy standards set out in the Code, in this instance Code Level 3. And Code Level 4, which called for a 44% reduction on 2006 levels will doubtless be the basis of the next revision of Part L in 2013.

But (and it's taken me 6 paragraphs to get to the BUT) there seems to be a problem, and its revealed by yesterday's post on the Zero Carbon Hub's metrics. If you stop talking about DERs and TERs (the lingo of Part L) and instead start using kWh/m2/a as a measurement, then we run into a wall identified by the Zero Carbon Hub. You see, I don't think that kWh/m2/a space heating scores for the 2006 house are much more than 60, so a 25% improvement pulls that down to 45 kWh/m2/a for a detached house, which is already slightly below the score (46 kWh/m2/a) which the Zero Carbon Hub are calling for for 2016. And yet we still have another version of Part L to negotiate before then, one which the Code demands a 44% reduction on 2006 homes.

The challenge which the Zero Carbon Hub have identified is to do with our old friend mechanical ventilation with heat recovery (MVHR). They don't think you can build much better than the levels they have set without using MVHR, and they have stated they don't think it's a good idea to make MVHR mandatory in UK homes. Hell, I have more or less agreed with this line in the past and got it in the neck as a result.

Various random thoughts occur.

• Is there really an indoor air quality issue here? Or is it imagined?
• Is there really a point in energy efficient building process when you simply HAVE to use mechanical ventilation, and natural ventilation techniques are no longer adequate?
• If so, where is that point? Could it be expressed in the chosen metric kWh/m2/a?
• If the Part L Target Emission Rates were to be replaced with kWh/m2/a, what would the scores be for the 2002, 2006 and 2010 versions? You can do the SAP calculations easily enough, and then turn this into a kWh/m2/a score, but this calls into question just how accurate SAP is or was?

Into the Metrics

One of the things which PassivHaus has brought us is a new way of measuring energy efficiency. It's being called a performance metric and it's expressed in kilowatt-hours per square metre per annum. Or kWh/m2/a. It's a much clearer way of presenting the issues at hand but it's not without its problems - of which more in a minute.

The subject is dealt with at some length in the document produced by the Zero Carbon Hub late last year. It looked at using another metric, kg/co2/m2/a, but rejected it because of the confusion relating to the different carbon factors in various fuels - i.e. if you selected to heat with biomass, you could virtually ignore energy efficiency. It also looked at using the so-called Heat Loss Parameter which is a sort of amalgamation of all the U values surrounding the building, but felt it was too little understood and no one outside the UK has ever heard of it. And it alighted on kWh/m2/a because it was the one pushed by the PassivHaus standard and it has some sort of meaning for ordinary mortals. If you can just figure out how many bloody square metres there are that you are trying to heat, then it gives a good indication of what the fuel usage will be.

Now the Zero Carbon Hub has come in for a fair bit of stick from darker greens than me for setting a target which doesn't look so very hard to beat, compared with the Passivhaus standard. These comparable metrics look like this:

• PassivHaus standard: no more than 15 kWh/m2/a
• Zero Carbon Hub suggestion: no more than 39 kWh/m2/a for flats and mid terraces, no more than 46 kWh/m2/a for detached houses, semis and end terraces.

By way of comparison, the last time I carried out this exercise was in producing the 2008 edition of the Housebuilders Bible, when I put my benchmark house through its paces. I configured the house in different times and the performance metrics looked like this:

• 1975 (pre-insulation) standard: 270 kWh/m2/a
• 2006 (as built) standard: 60 kWh/m2/a

Interesting that the 2006 standard really isn't that far short of what the Zero Carbon Hub are suggesting for 2016. Which, I guess, is why they have come in for so much flack. But, to their credit, they have chosen a metric which makes it much easier to compare one standard with another. Would that Part L would do this as well, instead of creating maximum confusion with its over-complex DER and TER calculations.

And what of the problems? Well none of these metrics is perfect and a metric based on kWh/m2/a can be abused. You might think that a kWh is a kWh, but are we talking about heating demand or consumption? The definition clearly states that it is demand that is being measured, so the efficiency of the delivery method shouldn't be taken into account. Nevertheless, expect one of two heat pump suppliers to misuse the metric to suggest that they can heat draughty old piles for much less than the Zero Carbon standard.

Another old chestnut is playing around with the footprint that you are measuring. We still don't have a standardised way of measuring floor areas, so there are advantages in exaggerating the floor area. This factor was graphically illustrated on the PassivHaus study tour to Hanover that I went on with the BRE in 2007, where Carsten Grobe, the architect/selfbuilder we visited, admitted that he had chosen to include his basement within the heated envelope because it made the floor area grow by 30%, and therefore made the task of meeting the 15kWh/m2/a metric that much easier.

There will be confusion, also, about what's included in the kWh measurements. Does it include provision for hot water? No. It's too dependent on other factors and has nothing to do with the built fabric. Does it include anything for cooling? Sort of. As far as I can see, it only takes the cooling effects of thermal mass and natural ventilation into account, and assumes that no active cooling gets used. Lighting? No. Ventilation? No. That's because they are not insisting on mechanical ventilation for the 2016 standard. Really, it's just space heating.

Finally, there may be a danger that consumers will take the metric as a guarantee, and we may find that if they use more energy than this, they start complaining. Heaven help us! The idea of the metric is that this amount of energy will be capable of keeping the building warm and comfortable throughout the year, but the actual performance is still very much dependent on how the house is lived in, and experience of Passive Houses to date reveals that the best performing homes use about a quarter of the energy of the worst, and that the metric score lies somewhere in the middle. It can in reality be very hard to distinguish space heating demand from hot water, and so it's far from straightforward to tell just how successful a scheme has been just by analysing fuel bills.

Heat Pumps: troubling times

If you were to sit down and look for business ideas where there seems to be explosive growth potential, I reckon that heat pumps would pretty quickly bubble up towards the top of most peoples' lists. It's not exactly a new technology, having been around in one form or another since the 1950s, and in some territories (I'm thinking Sweden here, and maybe Switzerland) it's established as the No 1 method of providing home heating. But in the UK, it has been and remains distinctly fringe.

Now this is all set to change with the introduction of the Renewable Heat Incentive (RHI), about which I have blogged several times. The RHI promises to throw large dollops of money at people who choose to install heat pumps. Large dollops. Like enough to pay for the entire heat pump, and a good chunk of the running costs as well. Whether the RHI is a good thing or a bad thing I won't go into here, but what is indisputable is the RHI has the power to turn the home heating market upside down and make heat pumps No 1 here in the UK in a very short space of time. Which is its intention.

But right now, heat pump suppliers are having a very difficult time, because the RHI remains a consultation document and since it was launched earlier this year there has been a change of government and the new government has been very quiet (OK — completely silent) about its fate. At a time when new cuts are being announced on a daily basis, there is concern in the industry that the RHI won't see the light of day, even though the funding for it was due to be taken from our gas bills, rather than directly from the Treasury. The RHI consultation document signalled that the new subsidies would come into effect in April 2011, and that people purchasing heat pumps now would be be able to receive the payments as and when they become available. But it was only a consultation document......

So what has happened is entirely predictable. Heat pump suppliers now have interest in the product racing ahead at record levels, but no one is actually placing any orders because they are all waiting to see if the RHI is going ahead or not. So, far from booming, business is going backwards rather fast. It's nail biting time.

And against this difficult background, I keep hearing reports of unsatisfactory heat pump installations where either the heat pump fails to provide adequate levels of heating, or the electricity bills turn out to be way higher than was anticipated. Some manufacturers are getting mired in disputes with unhappy customers, and the nascent industry risks getting dragged down by adverse publicity before it's got off the ground.

It's not that the heat pumps themselves don't work. The failures seem to stem from two areas: one is that the houses in question are not nearly as energy efficient as they were designed to be, the other is that the collecting fields on ground source heat pumps are often too small, or that the ground conditions are too dry for the ground loops to work well. The first error is the fault of the builder, whilst the second is the fault of the heat pump installer, so you can guess how the blame is attributed when a dispute arises. It's messy.

When a plumber installs a conventional gas or oil fired heating system, they build in a huge margin of error. Because the additional capital costs of a larger boiler and larger radiators are not that great, it's no great cost to the plumber, and its worth it to prevent any potential disputes with unsatisfied clients. But heat pumps, especially ground source heat pumps, are expensive beasts (typical installation costs are upwards of £12,000) so there is a temptation to engineer their output far more closely to the designed demand, hence a much greater likelihood of the finished installation failing to deliver on expectations.

To avoid these problems, my suggestions would be:

• Make sure you are comparing like with like when looking at the quotations you get. Look at the heat output side of things. Don't just accept the supplier's word that their designed output will be adequate. Ask to see the calculations and ask what the margin of error is.

• Get a soil sample analysis carried out if you are going for a ground source heat pump. Tim Pullen tells me that the seasonal difference in heat draw between a dry, sandy soil and a wet, clay soil is huge - like 10w/m2 v 40w/m2. Some suppliers take this into account, many don't.

Part L and the Fuel Factors

If you want a good example of how contentious and how political the building regs have become, then the fuel factors are a great example.

The aim of Part L is to make our buildings more energy efficient. And the aim of energy efficiency is to reduce carbon emissions. But they are not quite one and the same thing, because one of the big imponderables about energy efficiency is the choice of fuel you use for heating. Each available fuel has a known carbon intensity, conventionally expressed as kilograms of carbon dioxide released for every kilowatt-hour burned. Or kg Co2/kWh, if you like abbreviations.

Now if carbon reduction was your sole aim, you could simply switch to a very low carbon fuel — we are talking biomass here, wood chips, pellets or logs — and not give two hoots about all this energy efficiency malarky. But that sort of seems a little illogical, doesn't it? Just because you chose to burn wood somehow shouldn't mean you can forget about double glazing and insulation. So Part L fuel factors take this into account and assume that no fuel can score better than mains gas.

But what of the alternative fuels? What if you are a rural selfbuilder and you are away from gas mains? Logically, you would think that your building plans would have to take the carbon intensity of your chosen fuel into account. And Part L does just that, via it's fuel factor table. If you want to heat with oil, you have to build to a higher standard. And if you want an electric heat pump, you need to build to a higher standard still. It's all explained in Table 1 of the new Part L, the Fuel Factor Table.

But the increased build standards don't fully reflect the carbon intensity of the various fuels and here is a natty graph to show you what the situation actually is. The true carbon intensity of each fuel relative to mains gas (as defined in SAP 2009) is in blue; the way they are each treated in Part L is in red.


The one that leaps out is electricity which is two and a half times more carbon intensive than mains gas but only gets penalised by 47% in Part L. That's still a penalty, for sure, but looked at another way, it represents (yet another?) subsidy for electric heat pumps.

Now some might argue that what is at issue here is not so much the current carbon intensity of electricity, but the future intensity. If the government's targets are met, then in a decade or so, the grid will be considerably greener than today and the carbon intensity of electricity will fall. So maybe it is justifiable to treat electricity so lightly in 2010.

But — make no mistake — the fuel factor tables don't represent the true carbon intensity of the fuels in question. They come with a very large slice of political meddling.

Conservatories and Part L

I am still trying to get my head around the next version of Part L (the energy efficiency regs) which comes into effect in England & Wales in October this year. One of the things that looks to me to be contentious is the status of conservatories and porches.

In the last version of Part L (2006), the guidance was clear enough. It stated that if you built a conservatory outside the heated envelope, you could effectively ignore it, as far as energy efficiency measures went, as long as the thermal separation between dwelling and conservatory was constructed to a standard comparable to the rest of the external envelope of the dwelling.

This time around it’s changed. The guidance for new dwellings states this: Where conservatories and porches are installed at the same time as the construction of a new dwelling, the guidance in this document applies. The sense of this doesn’t exactly leap out at you, but you have to presume that what it is hinting at is that the whole building, including conservatories and porches, has to be treated as if it was within the thermal envelope, and that the SAP calculations have to include the conservatory (and the porch - no mention of porches in 2006). There is just one additional sentence here: For conservatories and porches added as extensions to a dwelling, see guidance in Approved Document L1B.

For those of you getting confused by these designations, Part L is split into four sections. L1A deals with new dwellings, L1B with extensions and alterations to existing dwellings, whilst L2A and L2B cover non-domestics with a simliar distinction between new and old.

So what is this guidance in L1B?

It suggests that most conservatories added as extensions will still be exempt from Part L compliance.
The exemption (from having to comply with Part L) applies only for conservatories or porches:
␣␣ which are at ground level;
␣␣ where the floor area is less than 30 m2;
␣␣ where the existing walls, doors and windows in the part of the dwelling which separates the conservatory are retained or, if removed, replaced by walls, windows and doors which meet the energy efficiency requirements; and
␣␣ where the heating system of the dwelling is not extended into the conservatory or porch.

I think that will cover 99% of conservatories and porches. So it looks as though Part L is choosing to make a distinction between how conservatories are treated in new builds as opposed to as extensions to existing homes. A new build conservatory will have to use glazing that meets WER rating of C or better, or have a U value of no more than 1.6. That means expensive double glazing at the very least, and essentially a very different beast to the basic single-glazed box you can pick up at Wickes for a few hundred quid.

So - presuming I have got this right - the question is why the difference? Surely what will happen is that people won’t build conservatories into new builds, but will wait for the house to be finalled and then go out and get what they want later. Which will result in much poorer building standards.

There is also a wider question here about who should decide where the boundaries of the thermal envelope should be. If you want an unheated room - be it conservatory, sunspace. workshop, larder or whatever you choose - why shouldn’t you be able to build one? Shouldn’t the client or their designer be able to choose just which parts of the home should be heated, and which shouldn’t?

Wood burning issues

Greg Taylor, my contact at Stovax, has highlighted a problem for those wanting to heat near-airtight houses with wood burning stoves. As things stand, they are not compatible.

How come? It's to do with air supply to the wood burners. In common with many people, I had been assuming that this was a problem easily addressed by having a room-sealed stove, just like a gas fire or boiler with a balanced flue. But this is not how a wood burner works because it needs re-fueling and, everytime you open the door to re-fuel, you upset the airflow balance and the smoke will tend to come out into the room, rather than go up the flue. It's referred to as spillage. So whilst you can have an external air supply ducted towards the wood burner, there are as yet no off-the-shelf wood burners which can operate in a way that is genuinely room-sealed.

Now our building regs (Part J) recognise this problem and in their next iteration (due to come into effect in October 2010) the problem of reconciling airtightness and flue efficiency is covered. In the previous version (2002), Part J only called for open vents on appliances rated at 5kW or more. But the new regs now take all sizes of wood burner into account and, for the first time, relate it all to the overall airtightness score of the house.

Look at row 4 of Table 1 in p29. It covers the minimum air supply required to keep stoves burning safely and efficiently and it states that for:


Appliances, such as a stoves, cookers or boilers, with no flue draught stabiliser, you must have permanently open vents:

• Option 1 (the leaky house) - If design air permeability >5.0m3/(h.m2) then 550mm2/kW of appliance rated output above 5kW

• Option 2 (the airtight house) - If design air permeability <5.0m3/(h.m2) then 550mm2 per kW of appliance rated output.

So let's take the second option, the house with a good airtightness score, and a wood stove with a 4kW output, typical of what might be required for a low energy house. Part J is intimating that you would need a 4 x 550mm2 hole in order to satisfy the air requirements for the stove. That's 2200mm2, which is 47x47mm, 2 inches by 2 inches. You'd end up having to fit a product like this in your wall. A hole, permanently open, in your elaborately constructed airtight structure. Doesn't that upset you just a little? And won't it make the room cold when the stove isn't in use. ANSWER: yes.

At the moment, there appears to be no solution. A mechanical ventilation system isn't acceptable as an air supply (it might breakdown); even a hit or miss vent isn't OK (it might be set to miss). It has to be a permanently open vent. Not that this is really safe in operation because there is a very high chance that (cold) people will take matters into their own hands and simply block off the vent.

There may well be a techno-fix for this problem; for instance a valve that closes off when the stove door is opened, or something of that ilk. It's being worked on across Europe, and when it becomes clear that the issue can be resolved, then Part J and its attendant BS 8303 may/will be re-written. In the meantime, it's a conundrum that I don't think people have fully got their heads around.

On Garden Grabbing

If you naively thought that the new Coalition government would put an end to spin, you may be in for a shock. Take garden grabbing. The very phrase is pure spin. Despite this blog now being five years old, you won’t find any mention of this phrase before now. That’s because, until recently, it didn’t exist. We spoke instead of infill plots, because that is what they are. Or were. According to this DCLG news story, they will probably be no more.

So where does this phrase garden grabbing come from? A large finger of suspicion is pointing at Greg Clark, the new Decentralisation Minister (pictured). You couldn’t make this up, could you? Just as we are preparing for a round of public spending cuts, they go and invent a new ministry. Clark features in the short video on this site looking rather pleased with himself, as if he has not only named a new curse, but provided a cure at the same time.

Now the selfbuild community is up in arms because back gardens have provided a rich vein of plots over the past twenty years or so, as the supply of conventional plots has all but dried up. For every “block of flats” crammed into back gardens, there are several individually-crafted homes nestled away where you would barely be aware of their existence. Clark’s anti garden grabbing measures look set to stop virtually all development in gardens, not just inappropriate cramming.

Back to the spin. Let’s look at this video a little more closely.

It starts with a printed statement: Over the last five years 180,000 homes have been built on gardens.

Followed by: Roughly one every 15 minutes.

Now how’s that for a warm up? You could just as well state that there are something like 10 million gardens in the UK, and at the current rate of progress it will take 300 years before they are all built on, but that wouldn’t sound quite as frightening, would it? And I have grave doubts about this figure of 180,000, in any event. What the DCLG statistics say is that:

the number of new houses being built on previously residential land such as people's back gardens - up from one in ten to one in four between 1997 and 2008.

Work back five years from 2009 and you’ll find that there were around 750,000 homes built during that time. So, very roughly, 25% of these would equate to 180,000, which is doubtless where they have derived this figure from. But previously residential land isn’t just gardens, not by a long chalk.

Take the 40 sheltered flats just completed next to where I live — see last blog post on Nichols Court. They replaced a few bungalows that were demolished to make way for the new development. This is development on previously residential land but no way can you construe this as garden grabbing — unless of course you are Greg Clark wanting to make a point.

So what is the true proportion of development taken from gardens? I suspect no one can tell, because I doubt the statistics are good enough to distinguish, but common sense suggests that it will be far lower than this 180,000 figure bandied about by Clark.

It gets worse.

Clark states that the only reason that garden grabbing has been allowed is that “gardens were classified as brownfield sites.” This is simply not true. Gardens have always enjoyed potential development status: they were included within the original development zones because no one ever thought to exclude them. The framework boundaries were drawn around settlements in the 1950s and 60s, and it was only at this point that any land was ever excluded from development. Garden land was usually included within the development zones because the planners were trying to stop development spilling over into the surrounding countryside, not to stop it happening at all. The original idea was that parcels of land within the development zones — and that included back gardens — should be available for building on, if the owners wished to do so. The greenfield v brownfield distinction is relatively recent – a product of the 1990s – and gardens were never even considered as part of this debate.

The reasons why back gardens have proved so popular for development is two-fold. Firstly, there are almost no small building plots available in some areas, except for garden plots. Secondly, building land is incredibly valuable and the sale of a garden as a plot is a very nice little tax-free earner for the householder.

Back to this pesky video. At 1:15 into the video, up pops Bromley councillor Alexa Michael to give us her take on the horror that is garden grabbing. What she says is revealing. For a start, she says “local” five times in 15 seconds. At 2:23 she pipes up “with the new legislation restoring back gardens as greenfield sites, it will make it much easier to refuse unwanted development on domestic back gardens, so that they can be preserved as open recreational space.” This is pure tosh. Back gardens have never been regarded as greenfield sites, so there is no “restoration” going on here. And there is no way a back garden is “open recreational space.” They are not public parks, they are gardens!

Then up pops Clark again, this time with his ministerial red box, telling us that he is excited by his first decision to change the designation of gardens so that they are “no longer brownfield sites.” Bollocks. What he is actually doing is tightening the development control zones to include gardens for the first time ever. Shout it from the hilltops — he is rolling out the power of the state to include land never previously controlled by either central or local government.

He goes on (at 3:01): “that means local communities will once again get the chance to decide whether they want to keep a particular garden or whether they think it’s better that it should be built on”. What sticks in the craw is the insertion of that little phrase “once again” which suggests that this is somehow returning to a pre-Labour policy that existed in some golden past.

Now we are all wondering what happens next. The pronouncements thus far are ambiguous. On the one hand, Clark is saying that back gardens will be zoned as greenfield sites. That’s planning code for No Building At All. On the other hand, he says that local councils will have the chance to decide whether garden development is appropriate, which is in fact exactly what happens now. You can’t have it both ways.

At the moment, we have some bizarre policies in place in some local authorities where people applying to develop garden land are instructed on what and how much they can build, sometimes being told to build several houses when they only want to build one. But it’s less bizarre than prohibiting garden development completely.

A more sensible policy would be to allow appropriate garden land development, but to raise tax on the windfall profit.

PPG3 is now for the Birds

Barely 250m from where I live is a brand new development called Nichols Court, an extra care living facility to be run by the Sanctuary Group. It's not going to win any architectural awards. With its mixture of buff facing bricks, regulation cedar cladding and odd bits of pink rendering, it looks like countless other (very boring) contemporary designs. And I wouldn't mention it at all in my dispatches except for this feature which caught my eye — the triple bird box.

Now I know that the Code gives points for enhancing site ecology, and nesting boxes are going to tick that particular box. But triple ones? Since when did PPG3 density requirements get applied to blue tits?

PS I understand that house sparrows like to nest communally, but other common garden species don't. But I reckon these holes are too small for a sparrow. The only tit you are likely to see here is the architect responsible.

Housing for Dummies

Spotted last week at the housing hell that is King's Warren in Red Lodge, Suffolk. It was the dummy window that caught my eye, but on closer inspection it reveals a dummy chimney (the brickwork is a different colour) and fake flintwork. Not to mention dummy sash windows as well. Just about the only authentic things here are the railings.

If Poundbury was the father of PPG3, then this is its bastard child.