As we strive for more energy efficient new homes, there is a strong argument that reducing heat losses and improving the energy efficiency of the building fabric is the most cost-effective, reliable and robust method of improving the energy efficiency of a building. Getting the fabric right, ie the components and materials that the building itself is made of, such as the walls, floors, roof, windows and doors, will save energy throughout the life-span of the house.
Fabric Efficiency standards are now part of the latest Building Regulations to ensure that building fabric is improved and to discourage the use of excessive and inappropriate low carbon or renewable trade-offs.
Read our checklist below for ideas on how to reduce heat loss from the building fabric, as well as insights into different factors to consider when implementing energy saving measures.
Energy Performance in buildings
Heating is by far the biggest consumer of energy in our homes so cutting the amount of energy used for heating is key if we are going to significantly reduce energy consumption and carbon emissions. Whilst we can make our homes more energy efficient by installing more efficient heating systems, reducing heat losses and improving the energy efficiency of the building fabric is often considered more important.
A ‘Fabric First’ approach can be more cost effective, save more energy and also reduce the need for maintenance during the building’s life.
The focus therefore needs to be on the parts of the building where most heat escapes from first, ie: walls, roof, floors, draughts and windows.
Where heat is lost from homes
Ensuring our homes are not losing heat is one of the most cost-effective ways to reduce energy use and therefore reduce carbon emissions and energy bills. Some of the options include:
Homes with loft insulation of 10cm or less should top it up to at least 27cm – the current minimum requirement for new build properties. Doing so can save 1 tonne of CO₂ per year and reduce heating bills by a fifth.
The image below shows the difference in the amount of heat typically lost from different parts of the building for an insulated versus an uninsulated house.
House A – Uninsulated
House B – Insulated, estimated saving 57%
Cavity Wall Insulation
Most homes built in or after the 1930s have cavity walls (an inner and outer wall with a gap in between). For homes with cavity walls, making sure the cavity is full of insulating material can lead to huge energy savings for a fairly small initial outlay and it is a quick job that causes minimal disruption. Holes are drilled in the building’s external wall and insulation material is injected into the cavity.
Solid Wall Insulation
Around a third of the UK’s homes were built before 1930 and have solid rather than cavity walls. Insulating this kind of wall, whilst more costly and labour intensive, will be the most effective step homeowners can take to reduce their home’s carbon footprint. Solid wall insulation can be applied on the inside or the outside of the walls.
Some homes lose as much heat to the ground as they do through the windows. For houses with wooden floors on the ground level insulating is simple: some boards can temporarily be taken up and the insulation rolled between the joists. If you have solid floors, sheets of insulating material can be placed on the underlying concrete with chipboard and a finishing layer on top.
Doors and windows
Single-glazed windows, or even old and broken double-glazing, can be a significant source of heat loss, especially in homes that have lots of windows and doors.
Double and Triple Glazing
Whilst double or triple glazed windows are another form of insulation, they are not generally as efficient as wall and roof insulation. However, replacing a single-glazed window with a quality double-glazed unit can more than halve heat loss.
The Energy Saving Trust estimates savings of around £165 a year by replacing single glazed windows with B-rated double glazing. Other benefits include outside noise reduction and less condensation.
With only about 10% of the total heat loss from a house through the windows, it is not advisable to install expensive double-glazed windows in uninsulated walls and it’s only worth investing in triple glazed windows if you have super-insulated your property beforehand.
Standard windows have air in the gaps between the panes of glass. Higher performing windows usually have argon or other gases between them. They will also have a low emissivity coating which allows the heat from the sun into a building whilst at the same time reducing the amount that escapes.
UPVC are a low maintenance option. However, their production is energy intensive, and they are very environmentally unfriendly when it comes to their manufacture and disposal.
Alternatives include wood, aluminium and composites which have wood on the inside and aluminium on the outside. New double glazing is now required to feature trickle vents in the frames because modern windows are more air-tight than older ones. A trickle vent is a very small opening which allows air to pass through to provide natural ventilation when windows and doors are closed.
Whilst all new buildings must now be fitted with double glazing, not all old properties can be upgraded. If you are in a conservation area or live in a listed building, planning rules can prevent you from installing double glazing. This leaves three possible alternative solutions to reduce heat loss (and increase warmth): secondary glazing, thick curtains and draught proofing doors.
This is an additional pane of glass fitted over the window internally. How sophisticated it is will depend on whether or not you want to open the window (you can get glazing that slides open) or not. The Energy Saving Trust estimates a reduction in heating bills of £100 per year by using secondary glazing.
Hanging heavy curtains can reduce heat loss through traditional sash windows by 41% according to research by English Heritage. Curtains ideally need to be hung flush against the wall (not on a pole that leaves gaps) and there should be a pelmet to help trap the cold air that comes in through the window behind the curtain.
You can improve the energy efficiency of existing doors by draught proofing so that they seal better, and by using brush draft excluders. It’s also a good idea to draught proof the letterbox. When buying a new door, uPVC doors tend to be most energy efficient. However, as mentioned above, they also use more energy in manufacture and lead to more pollution.
Draughts and ventilation
Draughts are the cause of considerable heat loss which can lead to discomfort, cold and higher heating bills. The good news is that there is something you can do about it.
In a typical UK house draughts will account for at least 10% of the total heat loss. However, if there is an unused open fireplace that figure will rise to over 50%!
Draughts are easy and cheap to fix – it’s just a matter of blocking up any holes which allow warm air out, and hot air in. There are all the obvious places to seal – gaps around windows and under doors, floor to wall joints, ceiling to wall joints, gaps between floorboards – but the real culprits tend to be where pipes and cables are laid through walls or floors.
Draught proofing is a cheap, effective and easy DIY measure to install. Add weather strips to windows, external doors and loft hatches and use products for sealing round windows and doors, and gaps between floorboards such as mastic, caulk or sealant.
Chimney flues can be bricked up or there is a balloon-type invention that will do the job. It is important to seal the top as well as the bottom to prevent rainwater getting in. Sealing the bottom will still allow rainwater into the top, with consequent damp problems now that the flow of air that used to dry it has been blocked.
Beware of air bricks! These are special bricks that are made with holes in them to allow the circulation of air under the floor of a building. So make sure you don’t fill in the gaps! Also avoid blocking trickle vents in windows and extractor fans – controlled ventilation prevents damp, rot and mould.
Openings for windows and doors are vulnerable to heat loss through thermal bridging so if you are building a new home, it is really important to pay close attention to the performance of structural elements such as lintels which are installed in these junctions.
Ventilation is the ‘controlled’ entry of fresh air into a building.
Most modern window frames have these small vents which you can open and close at will to allow air to pass through.
Generally found in bathrooms and kitchens, they can operate automatically when a certain level of humidity is reached, or come on with a light, or be controlled manually.
In super-insulated buildings, such as Passivhaus buildings, mechanical ventilation with heat recovery is used to extract warm, humid air from rooms such as the bathroom and kitchen via a heat exchanger. Fresh air is drawn from outside, warmed in the heat exchanger and delivered to cooler rooms such as the lounge and bedrooms.
How to air a room in winter
Top tip from the Home Energy Handbook: If you don’t have good ventilation in a room, it is better to turn off the heating and open the window for a five minute burst of air, than to leave the heating on and the window half open for a long time.