What is a 'Sustainable Building'

A Guide to Energy Efficient Construction

By John Cave, Sustainable Products Manager

There is a lot of attention in the media at the moment on the reduction of our CO2 emmissions and the environmental impact of human activity. Another strand running alongside this is the fact that we have reached a peak in our extraction of fossil fuels and they are now starting to decline.

The Energy Issue
In the UK we have long depended on the rich reserves of Gas in the North Sea but not only has demand for energy increased, North Sea gas is now on the decline. We are now nett importers of gas and as a result we have seen a spike in fuel prices that is set to continue. The picture with oil is much the same. The graph below shows oil prices over the last 10 years:

The sharp drop was the impact of the global recession, but you will notice the climb has started again. In 2009 the energy watchdog issued a warning that domestic energy prices could rise by up to 60% in the next 7 years. We have seen a steep climb in energy costs over the last 10 years and that is likely to continue for the forseeable future.

Sustainable Buildings
Around 50% of CO2 emmissions in the UK are from the construction and use of buildings, by far the largest contributer to emmissions. More than 40% of the energy that is generated in this country is also used in buildings, mainly in space heating and cooling, lighting and other equipment (computers, washing machines etc.)

A lot has been written about lowering the consumption of electricity in equipment, but can the building itself be more efficient? Of course the answer is a resounding yes.

Heating and Cooling
We have become reliant on being able to crank the thermostat up a few notches when we are cold or (not so relevant in the UK) switch on the air conditioning when it is too hot. It is easy and up until recently we wouldn't really think twice about what it costs.

But what if the building could do most of the work for us? What if the temperature could be regulated by the walls and the energy used in heating and cooling could be minimised?

It may surprise you to learn that the Germans, Scandinavians and Canadians have been doing this for decades....

Energy Efficient Buildings
I'll try to keep this simple, as the basics are actually very easy to understand. There are three main things to think about:

1. Insulation
2. Air Tightness
3. Thermal Properties

I'll tackle these in that order.

Insulation
We all know that insulation acts as a barrier to heat escaping a building and you may be aware that the average house in the UK is nowhere near the level of insulation that it could be. I won't go into great depth in this article, but there are a number of different ways to insulate buildings.

In the domestic sector cavity wall insulation is gaining in popularity. A word of caution. The cavity is there for a reason and filling it with insulation may not be the best idea. Cavities are designed to stop driving rain penetrating the external skin of the building and causing problems with damp internally. When these cavities are filled with insulation, the moisture can sometimes penetrate the outer layer and become trapped in the insulation layer.

It is important to note that when designed from new, cavity insulation is perfectly OK as it will be fitted in the form of rigid batts which are either weatherproof themselves or they have a protective membrane. The problems can occur when 'retro-fitting' cavity wall insulation by blowing the insulation into the cavity.

Other more straightforward forms of insulation include loft insulation, pipe lagging, floor insulation and solid wall insulation. The Energy Saving Trust estimates that for buildings with solid walls, properly applied insulation can lead to energy savings of around £400 a year!

Airtightness

Research shows that up to half of all heat loss in buildings can be due to unintended air leakage and uncontrolled ventilation. Insulation levels have increased substantially over the last few decades, but heated air is still escaping and can be pinpointed as a major source of energy loss. The climate of the UK does not expose us to extremes in temperatures but we are exposed to extremes in wind pressure, especially in coastal areas. While insulation is central to low energy construction, air and windtightness must also be central to an energy efficient design strategy to reduce unnecessary heat loss.

Is an Airtight Building Stuffy?

This is a common misunderstanding when thinking of airtight construction. We need ventilation, but unmanaged ventilation wastes vast amounts of energy. The current UK building regulations allow for a hole the size of a 20p in every square metre of the building fabric - this leads to all sorts of problems.

Heat that escapes from buildings carries a significant amount of moisture. This moisture can cause damage to the building fabric as it travells through and may have a severe effect of living conditions and the air quality of the living space. Common problems such as damp, mildew, rot and condensation are caused by the moisture becoming trapped inside the wall. Some of these can lead to structural problems, while others can lead to poor air quality and poor performance of insulation.

So in summary, it is exactly the opposite. If we manage the ventilation of our buildings effectively we can virtually eliminate these problems.

Will installing for airtightness save energy and reduce heating bills?

Research shows that we can lose as much as half of all the energy used to heat our buildings through unwanted draughts, inefficient and poor ventilation. We now generally insulate new houses very well but the proportion of energy lost to draughts has increased and in some cases around half of all heat losses are due to air leakage across the building fabric.

Now this might get a little technical.... Insulation is measured in a term called a 'U-value.' The lower the U-value the more effective the insulation is.

If a vapour check (a membrane that covers the insulation) has as little as a 1mm tear within a square metre area, the U value can reduce by a factor of 4.8 or 480%!(see diagram on right) This means that the U value is not achieved if the structure is not airtight and hence you need a lot more energy to heat the house.

Airtightness does not generally increase U values, but ensures the calculated U value is achieved.

Measurements were taken at an air temperature difference of +20ºC (69ºF) indoors and -10ºC (14ºF) outdoors, a pressure difference of 20 Pa (equivalent to wind force 2-3) using conventional, fibrous insulating material.

U-value with airtight vapour barrier = 0.30 W/m²

U-value with 1mm gap in vapour barrier = 1.44 W/m²

A gap as small as 1mm in the vapour barrier can reduce the U-value by a factor of 4.8

What does this mean?
In simple terms, if you are out hillwalking in the winter and all you are wearing is a big fluffy woolly jumper, you will still get cold as the air can penetrate the wooly layer. It is the same with insulation. If air is flowing across insulation it carries the heat through the insulation.

If you are out on the hills with a nice woolly jumper and a windproof jacket, you will remain warm - that is the principle of airtightness.

Thermal Performance

This can get a bit technical as well, but I'll try and keep it readable! The aforementioned U-values are part of the thermal performance of a wall, but there are other things to consider.

If the right materials are used it is possible to even out the extremes of temperature of the external environment through a combination of high thermal mass, low thermal conductivity and high thermal inertia. The graph below shows how the peaks of the highs and lows are evened out to a more constant internal temperature

About EH Smith:
EH Smith are one of the largest independent building materials distrubuters in the UK. We have spent the last 2 years researching the field of energy efficient construction and now work with many of the UK's leading Architects, Contractors and Housebuilders. We also work with self builders to help them achieve an energy efficient and/or low carbon home. Our website www.sustainablebuildingmaterials.co.uk details some of the products that we stock that can address these issues.

EH Smith have depots in Leicester, Cannock, Birmingham, Solihull, Stourbridge, Sutton Coldfield, Witham (Essex) and Hemel Hempstead and has been trading since 1923.

If you have any queries on any aspect of sustainable construction please contact us on sustainableproducts@ehsmith.co.uk