Thursday, 28 October 2010

The planning saga

These two posts were written before we received planning permission. It would be so tempting to write a rant about the few, mean-spirited people whose intemperate and ill-informed objections made the whole process so stressful and who, by forcing a redesign and delaying the approval process, added thousands to the project's costs. But I won't. Here are two posts written before approval came through.

18 July
Our property is one of a row of three different units running north-south, within an estate with quite a strong, distinctive architectural style. The roof ridge on all three properties runs north-south. In our original design, we had wanted to rotate our roof to create a 35° south facing roof, optimised for solar hot water and photovoltaic panels and minimising shading in our garden (the house sits on the southern edge of the 550m2 site with a garden that wraps around east, north, west). Although it is not in a conservation area or listed, the planners wanted a design that conforms very closely to the shape of one of the neighbouring properties: this has translated into retention of the north-south ridge line. We will now have a 23° east-west facing roof, matching the current pitch. The change means that the 4kWp solar PV array we are planning will generate 500kWh a year less than it would have done: equivalent to 12.5MWh less over 25 years. It is annoying for us, as it means £21 a month less Feed-in-Tariff income but it is also extraordinary that one arm of the state prioritises subjective aesthetics while another is rightly concerned with replacing our ageing fossil fuel based electricity generating capacity with non-fossil fuel based alternatives. Given that we are losing an unprecedented proportion of our existing generating capacity (30+%) over a decade and that a portion of the rest is based on gas, which has significant security of supply issues, you'd think that all public policy would reflect this imperative.

27 September

I write tonight on what I believe and hope to be the eve of a positive decision to approve our revised plans. The planning process has been horrible. We took a big chance by doing so much design work at risk. This being our first Passivhaus project and a refurb, made it very hard for us to do otherwise. The planning system needs urgently to be redesigned to:
  • make local decision-making less arbitrary - decisions need to be governed by policy and much less by subjective matters of aesthetics
  • for smaller householder scale projects, which according to Wikipedia make up 60% of all planning applications, the public should be restricted to a form online and on paper where objections can only be made based on specific issues: loss of light, privacy or other amenity; or on other issues that relate to the local planning policy. The "any other comments" box should be small! Our application generated a huge number of words that took time and resources to read, analyse and read.
  • There needs to be an explicit warning to the public on the comments form that comments or attacks of a personal nature are not acceptable and will count against any point the commenter wishes to make.
  • The planning process needs to be integrated with the building control process.
  • Conservation issues seem to hold sway over sustainability issues - this imbalance needs to be addressed urgently

28 October

Well, it's now a month later and we have this week finally got our planning permission. I feel relieved but battle weary. It has been very scary having committed so much resource to the project, knowing that I could not be certain that it would actually go ahead.

We hope we have all our ducks in a row now and can get started very soon.

Thursday, 14 October 2010

What shape of building works best

At this year's AECB conference two weeks ago, Peter Warm gave an informative talk on the Passivhaus certification process. One of his PowerPoint slides showed the impact of a building's form on the wall U-values needed to get to the 15kWh/m2.a target.

By dividing the total "heat loss" area by the "treated floor area", you get a ratio which describes how compact the building form is. The "heat loss" in most cases is, essentially, the sum of the areas of the building footprint (ground floor), roof and external walls; all measurements taken externally. The "treated floor area" or TFA is the usable internal floor area; calculated according to the convention used in Germany (as you would expect, given that the Passivhaus standard originates there). The higher the form factor ratio, the lower the U-values need to be to reach the target.

Non-compact detached houses, particularly bungalows, score the worst, sometimes with a ratio as high as 5. They need walls with a very low U-value of around 0.05 to get to the 15kWh target. Blocks of flats typically have a ratio of 2 and they only need wall U-values of around 0.15 to reach the Passivhaus target.

Semi-detached and terraces are somewhere in-between.

Form factor ratio Typical wall U-value
4 < 5 0.05
3 < 4 0.10
2 < 3 0.15

This means that, if you want to build a Passivhaus with reasonably sensibly sized walls (i.e. less than 500mm thick) or using natural materials or at a sensible cost, you really are going to have to pay attention to the shape of your thermal envelope; the building itself can be any shape you want but the "warm" space (contained by the thermal envelope) needs to be compact.

In our project, our form factor ratio is 2.53 - so I'm feeling quite pleased with myself, even though this was partly by luck.

In Passivhaus refurbs I think that building form is as least as important as orientation and solar gain, if not more so.

Interesting post on Green Living Blog at

There is a lot of talk about the importance of using low embodied energy materials in construction. In our project, there is an element of new build, as well as the refurbishment of the existing house. As I have noted previously, we found that it was impractical in this project to use natural, low embodied materials exclusively. In particular, constraints of the existing structure have meant that we are using a lot of Phenolic foam to insulate the floor (on top of the concrete slab) and externally on the walls. In the new build element we are mainly using wood-based structural and insulative materials.

There is an interesting post on the Guardian's Green Living Blog about this. In a study in Scotland, a two bedroomed cottage takes 80 tonnes of CO2e to build, using standard building techniques and materials. If built to building regs energy efficiency levels, this is the equivalent of six years' energy consumption/CO2e emissions living in the cottage. If that cottage were a Passivhaus, and assuming the energy needed to build it was similar to the standard build, it would take 60 years to 'payback' the energy/CO2e. This gives some support to the argument used by natural material proponents that, if you build a very low energy house, the embodied energy in construction becomes proportionately more important in determining the building's lifetime energy consumption. In the post, they have concluded that refurbishing is the best option (compared with either new build or do nothing) because a refurb of the same sized property is only emits 8 tonnes of CO2e.

Here is a quote from the article. The link to the original is here.
"80 tonnes is a lot – equivalent to five brand-new family cars, about six years of living for the average Brit or 24 economy-class trips to Hong Kong from London. But a house may last for a century or more, so the annual carbon cost is much less – and for all the new-build options, the up-front emissions from construction work were paid back by savings from better energy efficiency in 15–20 years.
However, the winning option was to refurbish the old house, because the carbon investment of doing this was just 8 tonnes CO2e, and even the highest-specification newbuild could not catch up this advantage over the 100-year period. Once cost was taken into account, refurbishment became dramatically the most practical and attractive option, too."