Low Carbon Buildings

What does it mean to create a low carbon building? It begins with improving the energy efficiency of that building (assuming you have also adopted low carbon behaviours in that building!). 

Since this is an information mini-site, and not a commercial pitch, we will not be providing advice on specific companies or products you should select in improving efficiency. That is up to you. We are only advising on the kinds of efficiency options you should consider.


Before plunging into the details, there is a simple lesson learned from past community low carbon building programs: We must stimulate demand to ensure carbon reduction targets are met, improvement costs are kept reasonable through the power of collective buying, and we all share our experiences and lessons learned - what has worked and what has not (and why). An effective program to improve the efficiency of energy use in buildings is a community effort and not just the cumulative effects of individuals acting alone. 

To see an example from Cambridge in the UK, click HERE


To begin, there are two complementary approaches to improved building efficiency. We describe these in terms of a home, but the same principles apply to other buildings such as businesses.
  1. What is around the home: This is the 'energy envelope' of the home. It is the outer skin which keeps warm air inside in winter and outside in summer. 
  2. What is in the home: These are the energy consuming goods in your home. They include your heating and cooling system as well as fridges, televisions, computers, lights and... well, you get the idea.
The improvement options described below refer to the picture to the right, taken from the Retrofit America website. They refer to the A-F options you see in the picture. The Before image shows heat escaping (red arrows) and cold air coming into the home (blue arrows). You can play the game of 'spot the differences' in the Before and Improved pictures. The aim is to significantly reduce all of those arrows.

After the descriptions of the options we provide a simple 'traffic light' assessment based on three factors using the lessons learned from our Cambridge Retrofit project:
  • Whether it is feasibly DIY (Do It Yourself) or requires hiring a professional to do the work. Red means no it is not feasible as DIY in most cases; yellow means yes you can do it, but you may need to do a bit of reading; green means full steam ahead for a weekend project.
  • The cost. Red means the cost is likely to be more than several thousand pounds; yellow means the cost will probably be somewhere between a few hundred to several thousand pounds; green means the cost will be a few hundred pounds at most.
  • The amount of energy and carbon reduction from home energy use. Red means less than 10% reduction; yellow means 10% to 25% reduction; green means more than 25% reduction.

Conduction, convection, radiation

Heat leaves or enters a home in three ways. Conduction refers to heat moving through solid materials such as the walls or ceiling. Stopping that requires insulation (increasing the R Value). Convection refers to heat or cold that is moving on air currents. Stopping that requires plugging the leaks in a home (draught proofing). Radiation refers to heat moving as radiation, primarily infrared. Stopping that requires closing curtains. 
Obviously, the 'sweet spot' is green across the board: it is a DIY project with little cost and large energy and carbon reduction. Good luck finding that! But it is possible if you are willing to do a bit of the work yourself and/or can negotiate especially good deals from suppliers by joining together with others in your community to form a buyers collective.


Draught proofing (or draft in the US): This is a great place to begin. It involves stopping convection and can refer to options A and D in the picture. It is easy to spot by just standing near each problem point: a leaky door, a window that does not close properly and so on, and sensing whether there is air coming through. Even better, find a small smoke device and blow the smoke at different points in a room, watching for swirls. Then when the points are located, plug them using whatever you can find at the DIY store (such as weather proofing strips). Or you might even consider an older solution: thick draperies over an offending door or window. Be sure to consider your outlets and light switches as well, as these often are forgotten sources of small draughts. 

Thermal bridges: These are harder to spot. Again it can refer to options A or D. A thermal bridge is anywhere in the home where conduction is carrying your heat outdoors when you want it indoors. Actually, it has a slightly more technical meaning that distinguishes it from problems involving normal insulation. A thermal bridge is a smaller area where something protrudes through the thermal envelope separating the indoor and outdoor air. Heat is a bit like water: it will move along the most readily available path. An example is a metal beam which carries the heat across the wall even when insulation is on the wall. Or it can be as simple as nails sticking through that wall insulation you just spent so much money on. To solve this, you must place insulation on the 'indoor end' of the bridge, such as the end of the beam where it enters the indoor space. 

Loft insulation: 
This is what we have all heard about over the past several decades. It has already been applied in many homes because it is such an easy problem to solve, and very cost-effective. Most council houses have this already installed, although you may need to check again to be sure the thickness is correct (installations from 20 years ago were generally too thin). It can be seen in option A if you look at the red part near the loft. Your goal is to have insulation of at least 250-300 mm. But don't go overboard. Above about 300 mm, you are spending more on the insulation but getting little additional benefit. And be sure the insulation is continuous in the loft, including covering the ceiling joists since these can act as thermal bridges. This is a suitable DIY project, although most people choose to have a professional install the insulation because the costs are reasonable and our time is precious. 

Wall insulation: 
Most of our homes in the UK have very poorly insulated walls, perhaps the worst in the EU. You can sense whether you have this problem by placing your hand on a wall inside during a cold day outside. If the wall feels cold, you have a problem with heat being conducted outdoors. This is Option A in the picture. The two solutions are interior and exterior insulation. Interior may be required if you live in a listed home or in a conservation district, since exterior insulation changes the appearance significantly (making a home look more like ones in Germany than the UK - not that this is a bad thing). However exterior insulation is easier to apply because it does not involve changing architectural features inside the home such as mouldings. And it is something installers like because costs can be kept down by bundling together a lot of homes on a street. Interior insulation is more problematic, but leaves the outside with the original look. The challenge with interior insulation is that it requires a thickness of several inches on each exterior wall to be effective. You may not want to have that amount of space lost to your room. But it can often be installed as part of a more general upgrade of your property, improving the 'look' of walls that have not aged well. When installing this kind of insulation, be sure to carry the insulation 'around the corner' onto interior walls or you run the risk of losing heat through a thermal bridge at the corners. 

Paying back your investment

When the UK introduced the now-defunct Green Deal, the aim was to provide building efficiency improvements at costs that would be paid back by the savings in energy bills. The payback might not be immediate, but the hope was that it would occur within about a decade. The reality is that for any of the options showing red in the 'traffic light' picture, the payback period can be more than a decade, and may never pay back the investment purely as savings on energy bills. In that case, the justification is either your commitment to helping solve the threat of climate change, or increased asset value (a more valuable, aesthetically pleasing and comfortable property).

As you might suspect, the payback period depends critically on the costs of materials and labour you can negotiate (either individually or by joining a 'buyers collective'), how you use the improved efficiency of your building (almost half of people use it to improve the interior temperature rather than decrease their energy use) and the future costs of energy. When people quote a payback period to you, be skeptical unless you can confirm it through a neutral, trusted source.

Floor insulation: This is the same as wall or loft insulation, but applied between the joists of a floor on the ground level. As with the wall and loft insulation, you must be careful to avoid thermal bridges created by the joists if the insulation is applied only between the joists. The challenge is getting into the space below the floor. By far the most expensive route is if you must have the floorboards removed before insulation is applied. If you can get into the space easily, then the costs are not significantly different to those of loft insulation. And it will be a possible DIY project. 

Window replacement: Windows can suffer from three problems: they may be the source of draughts, their frames can act as a thermal bridge, and they lose heat through the glazing. The solution in the first case has already been mentioned above. The solution in the second and third cases is to replace the windows with ones that have frames made of a material that does not conduct heat well (many of the modern windows already have this feature) and enhanced (double or triple pane) glazing. 

Duct and pipe insulation: This is Option B in the picture. Water pipes lose heat while passing from the water heater to the taps. Ducts lose heat while passing from the space heater (which may be the same as the water boiler). Both of these are particularly a problem if that heat is shed outside your home. The solution is to wrap all of the pipes and ducts in insulation of several inches. There is one caveat though. If that lost heat was being shed into the home air rather than outdoors, insulating pipes removes a potential heat source for the indoor air in winter (this is not true for insulating ducts, since the heat is getting to the indoor air either way). And one final caution: if your pipes or ducts are within an exterior wall, do not assume that interior wall insulation will stop the heat loss from those pipes and ducts. It will not. So you will still need to insulate those two items. 


These improvement options are all about the efficiency of the things we own, rather than the integrity of the energy envelope. Modern appliances, lights etc are increasingly efficient, so there is no excuse for sticking with low efficiency devices when it is time to replace them.

Boiler replacement: This is option C in the picture. Modern boilers are more than 90% efficient. In fact, you would just about need to go out of your way to find a low efficiency boiler. Whether boiler replacement is a solution to reducing energy use and carbon emissions depends entirely on the boiler you have now. Good boilers at reasonable prices will have an efficiency of 92 to 95%, with a few models reaching 98%. Just keep in mind the Duct and Pipe Insulation discussion above.

Zone temperature control: This is a good point at which to discuss an issue not shown in the picture, that of zone control of heating and cooling. People older than 60 years will remember the days when only a few rooms in the home had any heating. And those older around 40 will remember the days before central heating, days when you turned radiators on and off in rooms as you came in and out. We need to return to those latter days using modern control systems that ensure heat is only being applied where and when it is needed for comfort. Be very careful about installing these new highly energy efficient zonal heaters, though. Our experience has been that they are often undersized, so much so that they fail to keep a room properly warm (much less toasty). This is especially true if you have not yet greatly improved the thermal envelope of your building. You will need a very competent and technically savvy person to select and install such systems. And if they are electric systems, be prepared for sticker shock when your first winter power bill arrives!

LED lighting: 
Lights have made remarkable advances over the past decade. There is no excuse for using incandescent bulbs anymore, unless you want to heat your home incredibly inefficiently with such bulbs. Gone are the days when LEDs had a harsh or unpleasant light. And they are now manufactured to fit almost any light fixture without rewiring. For the same number of lumens (the correct way to measure light, rather than watts), the LED uses about a sixth the energy of an incandescent bulb. Compact Fluorescent Lights (CFLs) are in second place, although some CFLs are now approaching the energy use of LEDs. By the way, this option is not even shown in the picture, for a reason that eludes us given the importance of lighting energy use.

Appliance replacement: On to item E in the picture. This is probably the most expensive path you will take if you want to replace outdated white goods, televisions, computers etc with more efficient modern versions. But energy requirements for each item can vary widely depending on the manufacturer and model. Just read the information on the sticker, and keep in mind our earlier behavioural issue of using lifetime cost rather than initial (purchase) cost when making comparisons. Fortunately the EU - and through them, the UK for at least the moment (you know what we mean) - has set increasingly stringent energy efficiency requirements on all goods. 

If you must focus on only one of these three 'in the home' options, which should you choose? First, some crucial information. In a typical Cambridgeshire home, electricity use for lighting and natural gas use for heating contribute about the same amount to your carbon footprint. So they are equally important as a retrofit option. Plug load, or the electricity used by appliances, is in third place with about half the emissions caused by either lighting or heating. 

Therefore, if your current boiler has an efficiency above 80%, we recommend replacing light bulbs with LEDs first. If it is below 80%, replace the boiler with a new one with at least 92% efficiency. But then move quickly to LED replacement because that replacement will pay back your investment within the year.  And over the next 5 years, replace any inefficient appliances with new efficient ones.

Did you notice that items C and F in the picture have not been discussed? That is because they are the Third Priority and so not included here. Low carbon energy is still important, but it is not the kinds of energy efficiency improvements we are considering on this page. And if the national grid becomes almost completely decarbonised (it will never be completely so for various technical reasons, including the energy used and carbon  released when solar panels and wind turbines are manufactured), then we will electrify all aspects of our homes and run them off the grid.  


Do you still need to consider behavioural change? Go to the Low Carbon Behaviour part of the CCR site.

And if you are considering an energy project, go to the Low Carbon Energy part of the CCR site.