20 Sep 2007

Code for Sustainable Homes: cracks appearing

Just got back from a two-day symposium run by Nottingham University’s School of the Built Environment. There were a number of very interesting and cogent presentations given mostly by academics, architects and materials suppliers, and unusually for an event such as this, an overall theme emerged which could perhaps be best summarised as Code for Sustainable Homes — Whoaaahh, steady on, not quite so fast.

Many experienced voices expressed disquiet about the turn of events over the past twelve months, ever since the government published the Code and announced that it intended to move all new housebuilding to zero carbon by 2016. In particular the Code’s almost wholesale adoption of the PassivHaus standard came in for questioning: its apparent insistence on mechanical ventilation with heat recovery came in for a lot of flack, as was its insistence on heavy and expensive triple glazing and almost excessive zeal in which it promoted airtight construction. There was a feeling that this represented a degree of over-engineering for houses in a relatively mild (and getting milder) climate, where many people still routinely sleep with their windows open. The event saw the launch of a set of different proposals for low energy housing in Mediterranean climates, but the question of whether these were more applicable to the UK than the German PassivHaus standard was left for another day.

There was also a healthy debate about how best to power these post-2016 homes. The Code explicitly calls for the homes to generate renewable energy to cover their own energy requirements, but it remains unclear just where or how it can be produced. The preferred solution would seem to be onsite, but everyone agrees that many homes will be completely unsuitable for onsite production. But once you accept that the energy harvesting can move offsite, you run into all manner of problems of definition. District heating systems? Shares in windfarms? Or just buying power from a green energy supplier? All are possible, but they are either technically challenging (CHP) or are just another version of carbon offsetting (widely derided).

There was also a good deal of discussion about the water saving proposals contained in the code. The idea is that we should aim to be reducing our water use from around 150lts/day each down to just 80 lts/day at Code Level 6, the 2016 standard. That is surprisingly challenging: even if you fit every water saving device, ultra low flush toilet and lo-flow shower, you still struggle to get below a notional 100lts/day. To get right down below 80lts/day requires on site water harvesting or recycling which again was felt to be fine in principle but the thought of rolling this out into 250,000 new homes a year appears to be fanciful at best. But this is what the code demands after 2016.


  1. It seems pretty clear that a lot of the decisions on CSH have been politically driven without giving much thought to how the requirements are going to be met in practice - or whether the measures are appropriate in a UK climate, as you point out. The water requirements are a good example. The danger is that by setting the goals so high they almost guarantee that house builders won't meet them - putting us back at square one. More modest targets might result in greater benefits overall.

    What was the Mediterranean standard that you mentioned in the post? Have you got any more info on that?

  2. Passivhaus is not a standard. It's a design concept. If the climate here is very mild, that means it's easier to do and gives all the more reason to adopt it.

  3. Martin ClarkeSeptember 21, 2007

    interesting report but I detect no rowing back from the commitment by CLG at this time despite on-site generation looking like a dead end. I hope Nottingham Univ post the papers on their website. Did you see the demonstration houses ?

  4. Some details are available at www.passive-on.org/en/index.php

    f - Passivhaus is most definitely a standard, not a concept.

    It's early days