It isn’t Zero and it isn’t Carbon

The continuing saga of the definition of zero carbon that will be used from 2016 onwards for all new housing in the UK rolls ever onwards. Next week the Zero Carbon Hub will hold a series of consultation events, a sort of X-Factor for energy geeks, where voting will take place on the proposals for the new definition.

The word zero needs to come out of the definition. It is not wise to continue to discuss zero carbon when we do not mean zero, or at least zero in a way that any consumer would understand it. A zero carbon home that achieves 14kg/CO2/m2/year will still have a large fuel bill, a substantially larger fuel bill than if the home emitted 0kg/CO2/m2/year. It is unwise to discuss the two products in the same breath. Car manufacturers could not sell two cars, one of which cost next to nothing to run, and the other which cost say £1000 per annum to run, and define them under the same standard. Housing providers shouldn’t either.
To put this in context:
The first ‘definition’ built into the Code for Sustainable Homes for Code Level 6 was that all carbon emission reductions should be carried out on-site to achieve zero emissions. In practice this turns out to be about 150% of regulated emissions because it covers appliance and other non-regulated energy. This is the first of many confusions.

The next definition was that the amount that must be achieved on-site should be 70% of regulated emissions because a lot of sites couldn’t achieve the first target. i.e. highly shaded urban sites, greenfield sites with planning restrictions, and so on.

Then we had a change of Government, or rather a change from Government to fence-sitting. The first proposal was that the Zero Carbon Hub should be scrapped because as far as our current politicians are concerned, the industry should decide what it wants to do and just get on with it, and anything that smacks of top down decision making is wrong, wrong, wrong. I think even the HBF were scratching their heads at this. Finally the ZCH was reprieved to finalise the definition before being committed to quango history. Their future is far from certain.

Next weeks consultation sets out some new issues around the definition and introduces some new thinking.
The main new idea is that the definition should be progressed in terms of kilogrammes of carbon dioxide per square meter per year to be emitted by the dwelling. This is welcome, as the process of comparing each successive improvement to the previous set of regulations was becoming tiresome. i.e. Code for Sustainable Homes Level four is now 25% improvement on Building Regs 2010, but used to be 44% improvement on Building Regs 2006. But Building Regs 2010 is 25% better than the 2006 version, so isn’t there a missing 6% there somewhere? Does anyone know where it went? Does anyone care? Probably not. Changing the thinking to independent measures is valuable and definitely welcome.

The levels of emissions that will be set will vary from building type to building type, this is similar to the Fabric Energy Efficiency Standard now set in the Building Regulations and used in the Code to award ENE2 credits. This variability takes account of the fact that improvements are easier to demonstrate in buildings with a lot of surface area than in say apartments with only one exposed wall. There is no mention of flats over garages though, which is a bit of a bug bear of mine. These are, strictly speaking, flats but from an energy perspective, they are clearly houses; they just happen to be houses one storey off the ground.

The proposed targets for apartments are from 10 to 14 Kg/CO2/m2/yr
The proposed targets for houses are from 8 to 12 Kg/CO2/m2/yr

A quick check through some of my projects shows that this equates to about a 60-65% reduction for houses and 40-56% for apartments.

For an apartment a typical specification for this would be timber framed construction achieving .11 U-values, 1.3 U-value windows, 1.5 airtightness, a gas boiler and from 7-1.3kWp pV depending on which end of the spectrum between 10 and 14 kg/CO2/m2/year one was aiming at. The same results can be achieved with much lower construction values and much higher amounts of renewables, but the ENE2 credits for Fabric Efficiency will tend to reward higher fabric performance.

What some commentatorsforget is that these will become the minimum standards in 2016. The remaining CO2 emissions i.e. the 8-14kg/m2/yr will then have to be dealt with using the yet-to-be-finalised allowable solutions. That is a whole new ball game that the ZCH will have to tackle in 2011. There will be no rule that prevents developers from building homes with an actual level of emissions of Zero. But they must meet the regulatory mimima.


The allowable solutions will set the price of carbon dioxide that the developer has to pay, to whom it has to be paid, and for how long. My money is that it will be about £100/tonne, and that it will paid to a community energy fund to cover emissions up to 2050 from the date that the dwelling is built.

So, to take that logic, an apartment of 50sqm built in 2011 to a level of 14kg/m2/year, will have to pay
(14(kgCo2) X 50(m) X 39(years) X 100(£))/1000 = £2730

The alternative is to increase the pV kWp to 5.6, an increase of 4.3kWp, or an increase of about £10k.

On that basis it will be cheaper by 8k to use the minimum level rather than achieve zero carbon onsite, so no prizes for guessing which way housebuilders will go.

If the energy companies were to devise a mechanism whereby the feed-in-tariff for renewables was to go to them for installing pV on every new dwelling, and they offered pV installations for nothing, then the picture would go the other way. To conclude, these new definitions are late, and lower than expected, but this is not a disaster.

Until the Allowable Solutions mechanism is defined and costed, it is too early to say what the final impact on the quality of new homes will be. It is by no means obvious at this point, whether these new targets will result in a future where house builders build homes with low performing fabric. It is as least as likely that they will find it financially beneficial to take their homes carbon emissions into their own hands rather than hand the problem to others through the Allowable Solutions route.



2 thoughts on “It isn’t Zero and it isn’t Carbon

  1. Pingback: Tweets that mention It isn’t Zero and it isn’t Carbon | rory bergin's blog --

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