This blog explains the main points of a talk I gave recently, titled What Makes an Ecohome? as part of Bridport Transition Town’s Open Echomes events. Judging from the comments and questions afterwards, it got people thinking, and some questions got me thinking too!
Before the talk I asked people online what the phrase “eco-home” made them think of, and these were the responses:
I agree with some of these but by no means all. Its also worth noting that some of them were seen by different people as both good and bad (hobbit houses for example). I’ll talk a bit below, about why I think a few of the things on this list do not make an ecohome.
But what is an eco-home? It should be a sustainable home, both in terms of how it’s built, and how it operates in use. The following definitions are a good gauge of whether something is sustainable.
So what does that mean, in simple terms, applied to buildings? The following are things to consider when planning a new building or a refurbishment. I’ll delve more into some of these below.
Reducing carbon emissions is essential to limit the impact of man-made climate change on our lives and on future generations. Cleaner solutions for transport and heating mostly involve greater use of electricity, so even as more energy is generated through renewable means it’s important to reduce our energy use wherever possible, to ensure there is sufficient energy available for all our needs.
People are often tempted to think first of green technology when planning an eco-home or an eco-refurbishment, particularly solar panels for generating electricity or heat-pumps for providing heat. Much more important is to first plan to reduce the amount of energy we need, regardless of the source. Insulation is key, creating buildings that maintain comfortable temperatures with minimal heating or cooling.
In addition to high levels of insulation, attention should be given to reducing heat-loss through thermal bridging (for example where the internal surface area is greater than the external area, causing greater heat-flows – window and door reveals are a major culprit – or where a less insulating material bridges an insulated layer – lintels being a common example), and through air permeability (drafts).
Use of LED or other low-energy lighting can help reduce energy consumption, especially if coupled with good design to make the most of daylight while the sun is up. Daylighting should be carefully balanced with positioning of windows and shading to avoid summer-overheating from solar gain. It’s also good to remember that even the best triple-glazed windows are many times less insulating than any well-built wall. Like so many things – it’s a balance!
Energy is also used in production and transport of building materials. Choice of materials can increase or decrease the embodied carbon of a building (the amount of carbon released during production of the materials used). It is also important to consider the effects of material choices on resource depletion and on ecology. I explore these issues in more detail here: http://sustainablebuildconsultancy.com/2017/01/19/what-makes-a-material-sustainable/
For newbuilds, location is very important. Ideally a site would enable access to as many of your needs as possible (be it work, supplies, a social life, or anything else involved in your life) with minimal energy use for transport. For example an isolated location would increase your energy use and carbon emissions if it required you to drive regularly to access your needs.
Being off-grid is often perceived as being ‘eco’, but this is rarely the case. Generally speaking, it is more energy and resource efficient to be connected to mains services wherever possible.
Is it really ‘eco’? There are always many factors to weigh up to properly answer that. But in brief, here’s the answer for three ‘green’ technologies often used by ecobuilders:
- Solar PV panels: Yes. These produce more energy in their lifetime than is used to manufacture them, if grid-connected they feed-in the amount of renewable energy generally available and can help reduce demand on fossil fuels. But – as above – reduce the amount of energy you need first.
- Rainwater harvesting: Not necessarily. This can be useful in reducing the amount of rainwater run-off from a property, helping prevent sewers becoming overloaded with rainwater and overflowing into watercourses. It can also reduce extraction from bore-holes and rivers for mains water. All systems require a pump to get the stored water into the building, and generally the energy use of these pumps is greater per litre of water than that for mains water. Some managed systems (where the pump runs only to refill a tank in the loft is when it is empty) claim to use less energy. The extra energy and resource use to manufacture the tanks and extra pipe work is another negative issue.
- Biomass: No. This is not a popular answer, and I’ve had some heated debates about it. Strictly speaking it depends on the source of biomass. For domestic properties this is generally hardwood timber. This has potentially been growing and absorbing carbon from the atmosphere for several hundred years. This carbon is released when the wood is burned and will take many decades to be reabsorbed by new tree growth. There is increasing evidence that the amount of carbon released from burning wood is actually greater than for coal, per unit of energy produced. If the wood is from fast-growing coppice wood, this may be better. But burning biomass produces particulate and other emissions that contribute to poor air quality and could add to increased incidence of asthma (a similar problem to diesel emissions). There are moves to stop the use of wood fuel in smokeless zones to tackle this growing problem. I think there’s probably a separate blog to be written about this! I’ll do that soon, and provide references to back up what I’m saying.
In summary (space efficient means not bigger than needed, not breaking more new ground than needed, as this reduces available land and biodiversity. By usable, I mean that even the most technically sustainable building is not sustainable if it doesn’t perform the function it was designed for, resulting either it being abandoned or demolished):