Changing the Face of a Country for the Sake of Energy Efficiency
Whenever I come back to my adopted home country England by plane I feel elated looking down onto the beautiful country side, the lovely landscape, the fields and meadows in all shades of green, often surrounded by hedges. In between I notice all these little quaint villages made up of brick built houses; England seems to be God’s garden on earth indeed. Once landed and later on the train journey to Cambridge, I still enjoy looking out of the window while going past these neat houses in those villages. Mostly with a brick façade, they produce a very consistent appearance which is very typical for English villages, quite inviting and instilling a sensation of cosiness.
Arrived at home, however, the experience may well be a bit different. There and then one discovers that English houses tend to be a bit cold and could do with better heating systems, some kind of ventilation system that maintains humidity at a constant level, and much more insulation. This story investigates the energy saving potential on cladding brick houses with external wall insulation, as well as building new houses following modern building techniques, both resulting in a very different look of an entire country. The question then is: is it worth to change the face of a country for the sake of energy efficiency and as a contribution to mitigate climate change?
Brick & Mortar
A significant portion of energy is spent for housing; according to Residential energy expenditures and the relevance of changes in household circumstances, “In the UK, household’s residential energy consumption accounts for about 20–25% of the overall household direct and indirect CO2 emissions.“
Living Space Energy Consumption
The household energy expenditure comprises construction, operating and decommissioning of dwellings where the operational energy expenditure is mostly due to space heating (and cooling, not so much in the UK though), domestic hot water as well as running appliances of all sorts. While energy can be saved in all the latter, which is quite dependent on the occupier habits, this story focuses on space heating which is related to the construction and is, once the building is erected, more or less immutable given an internal temperature set-point, the outside weather and the thermal properties of the building.
That being said, space heating related energy expenditure is the sum of energy needed for constitution plus average heating power times life span plus the decommissioning energy. The average heating power is in turn a function of the external to internal temperature difference and overall thermal conductivity. Consequently, the balance of construction / deconstruction energy versus life span and thermal conductivity is of utmost importance. A house that consumes a lot of energy in construction (concrete, bricks and mortar) needs to have a long life span and a low thermal conductivity to keep the energy expenditure in balance and to offset its construction.
There is one laudable aspect of the UK approach to housing: people do tend to extend their dwellings rather than destroying them and build a new one from scratch in its stead. For instance, there are around 3 million 1930ies houses, all built to the same blueprint; many families add extensions to those. Even though they are constructed with a poorer build quality, extending and upgrading them may be quite energy efficient after all. It would be an interesting optimisation exercise to work out what the energy expenditure, thermal performance and life span of a new house would have to be in order to be more energy efficient over its full life span than the the old, but inefficient building house it replaces? Simon Chung from Sow Space, an Architecture & Planning outfit in Oxford, UK once said:
To quote Carl Elefante “the greenest building is the one that is already built”. We absolutely need to be using buildings to at least their designed lifespan, but we also need to be designing them to be easily deconstructed and / or retrofitted. In the UK, 80% of the buildings that will be standing in 2050 have already been built — we can’t repeat this enough (until we start getting close to 2050…). Hence the importance of retrofit, and the importance of not adding to our future retrofit problem.
Following Simon Chung’s advise to retro-fit existing houses, there are a few parameters that allow improving the energy efficiency. The outside temperature is not negotiable, the inside is, but let’s assume a constant 21 degree Celsius is desirable. From there, it is all about the overall thermal conductivity and its determinants: floor, windows, external walls and, most importantly, the roof or loft space (U-value of approximately 2.5 W/m2K for uninsulated roof space). The latter is easy to address; everybody can go up the loft and, over a weekend, put down 300mm rock wool if no or little loft insulation is in place to get a comfortable 0.1W/m2K. No need to dwell any further on that; fitting loft insulation ought to be made mandatory.
External Walls
Once the loft as the most significant thermal conductor has been addressed, next in the line are the external walls in order to reduce heat loss. In the UK, new houses are built in a traditional manner: brick façade outside, 100mm insulation, and aerated concrete blocks inside. The thermal conductivity (U-value) demands for these kind of external walls have decreased over the years and are now at a mandatory 0.2W/m2K. In older buildings the external walls may have an empty cavity or none at all and be completely solid with very poor thermal performance as shown below in comparison.
If in addition a high performance 100mm insulation is applied on the external walls, the thermal conductivity decreases significantly for the types of wall that have the poorest insulation:
Whereas external walls with cavity wall do shown some improvement, the most significant change can be observed for solid brick walls, which is more than an order of magnitude. Using data from The Greenage the gains in energy efficiency can be seen as a function of wall type.
In order to assess the total efficiency gain across the country, it is important to know the distribution of houses, e.g. taken from Schroder:
It would be an interesting exercise to calculate the convolution of the efficiency gain table and the housing completion graph. The result would be the total energy gain per house type. While I might do that at some point, once I have found the data sources, it is probably safe to assume that the most significant gain would be in adding external wall insulation to all houses without a cavity wall which may well be half of the existing housing stock. What would be the consequences of adding a warm blanket to all these houses:
- Less heating is required, obviously, the heating energy expenditure would be significantly reduced,
- No upgrade to gas or any other boiler will be needed, perhaps a heat pump powered by solar panels may be sufficient,
(UK should ban gas boiler sales by 2033, say climate advisers) - The thermal energy store is inside, and insulation is outside as it should be.
However, there is another consequence: the face of the country would change; no brick wall look any more, but rendered façades. Perhaps it is worth it for the sake of saving the planet. Brick buildings were introduced at some point in history, and could be phased out, making way for a new face of England?
Modern Alternatives
Suppose that all façades of most brick houses have now been fitted with external wall insulation and have been rendered; since the face of the country has already changed, why not go all way? The UK could adopt more modern building techniques as used in Continental Europe, e.g. my native Austria.
Building technology in Austria is often quite advanced, in particular in terms of energy efficiency; all is carried out quite well, too. Walls are usually 50cm thick, made out of high performance bricks as shown below whose thermal performance alone matches the UK building requirements. For instance, A Wienerberger Porotherm 50.20.H.i Plan brick is specified at 0.22W/m2K, or Eder Industries EDERBLOCK 50 VZ achieves 0.2W/m2K.
In addition, external isolation is usually applied together with an insulating render which brings down thermal conductivity to 0.12W/m2Km, in this case using only a 38cm Porotherm which on its own exhibits 0.28W/m2K:
Last, but not least, these modern bricks are glued; there is no mortar being used that usually constitutes a thermal bridge. After the first course is laid on the foundation, one layer after the other is glued on the previous layer. It is like building a house made of large Lego bricks; a walk in the park for qualified English bricklayers who are capable of making beautiful brick walls. By doing so, one storey is built per day as the following clip illustrates:
Conclusion
It is self evident that more insulation will help reducing energy expenditure and as a consequence the carbon footprint of housing. The government announcement of Bidding starts for £10bn whole house net zero retrofit deal is most welcome. It would also be desirable for the UK to adopt more modern building techniques to achieve better performing buildings much quicker. Both together will change the look of a whole country within a decade or two.
The reader might ask: is it worth it? Well, one could install a PV system to power a heat pump to keep an old brick building warm; it is a net zero game as all energy from the sun and the surroundings is pumped into the house to leave eventually through the walls. This might be a solution for some, in particular listed buildings. For the rest, we might get used to a new look; a similar change must have happened many centuries ago with transition to brick buildings. Then some people might have objected the change, too.
One last note: with more insulation, a heat recovery ventilation system is needed to maintain internal humidity, or simply follow a strict airing regime:
