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Energy saving at home

Energy saving at home

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Domestic energy saving measures are vital if we are to achieve the goal of a zero carbon future. Reducing the UK’s energy demand will make it much easier to meet the remaining energy need with renewable energy.

Some energy saving measures are very cheap, and in some homes these could make a big difference to your bills and carbon emissions. If you rent your home, many of these simple measures are still possible. However, getting your home ‘zero carbon ready’ would need more planning and investment, and the involvement of the landlord.

The energy we use in all our homes leads to about a quarter of the UK’s carbon emissions. In an average home, space heating will be about two-thirds of your total energy use. Of the remaining third, about half will be for water heating and half for everything else (lighting and appliances).

Reducing heating demand

Reducing the amount of energy needed for heating is the key to an energy-efficient and low or zero carbon home. It’s more important to achieve this than to generate your own renewable energy. From the very earliest days of CAT, people here focused on renovating and building to high levels of insulation and draught-proofing.

You need to combine insulation measures with careful attention to draught-proofing (or airtightness) and also provide appropriate ventilation. When done properly these energy saving measures should also address damp and condensation problems. This means that as well as reducing bills they make your home more comfortable and healthy.

Joining a local energy group is often a good way to get some practical advice and feedback. Or you may have a local energy agency that can help with a basic home survey.


Draughts occur around window & door frames, through letterboxes & cat flaps, down chimneys, at skirting boards, between floorboards, and where services enter. Even very small draughts can make a room uncomfortable in cold weather and have a big impact on heating bills.

There are many low-cost DIY measures that both homeowners and tenants can take to reduce draughts. See the related questions below for more.

It’s important to avoid blocking any intentional vents. These include wall vents where he room has a fire or stove, trickle vents on windows, and underfloor airbricks.

For a higher level whole house eco-retrofit to a zero carbon ready standard, a much more careful approach to airtightness and ventilation will be needed.


In many cases loft insulation will be a DIY job. The savings on your bills should repay the cost within a couple of years. For insulation in a pitched roof or flat roof you’re likely to need professional help. Adding or topping up to about 300mm of standard woolly types of insulation meets current standards, but you could add more. Certain types of plastic foam insulation are thinner but have a higher environmental impact.

For homes with cavity walls, blowing in insulation should take less than a day and cause little disruption. This will cost a few hundred pounds and you’ll save this on bills within 3 or 4 years. However, if your home is exposed to wind driven rain you may need to be more cautious about insulating cavity walls. See the related question below for details.

If your home has solid walls, insulating these is more expensive and disruptive. To get to zero carbon we will need to insulate most of these older homes, and support is available in some cases. For lots more advice see our pages on external and internal wall insulation.

In suspended ground floors, aim for about 200mm of insulation. You can add this between the floor joists either by access from the underfloor space or by lifting the floorboards. For solid floors you may need less insulation but it’s usually more work. You can either dig out the existing floor, or raise the floor level (and reduce door sizes).

See the related questions for more on the details involved with all these insulation measures. In addition to these, wrap hot water pipes in insulating foam sleeves and ensure your hot water cylinder has a cosy jacket.

Natural insulation batt
Natural insulation batt

Windows and doors

If you need to replace windows, the most efficient units are argon-filled with low emissivity (low-E) glass. Using argon gas between the panes improves performance, because argon does not conduct heat as well as air. Low-E glass has a coating inside the gap that reflects heat back into your house. Existing windows that are in good condition could be improved with secondary glazing. This can be anything from a clear plastic film to a second window fitted inside the original. See our page on windows for more advice.

New outer doors are usually insulated to meet the current minimum standards. It’s important for a new door to be well-fitted, and the existing frame to be draught-proofed. If you have a conservatory you’ll need an external grade door between this and the main house. You must leave a conservatory unheated and close it off in cold weather. See the related question below for more on making best use of a conservatory.

Choosing and controlling heating

Good quality controls are vital for maximising the efficiency of your central heating. Having control gives you heat where and when you need it, and avoids over-heating. With a standard boiler you will usually need a room thermostat, timer/programmer, boiler & cylinder thermostats and thermostatic radiator valves (TRVs).

If your boiler is very old, then rather than upgrading to a new boiler it should be worth looking at a heat pump as a much lower carbon alternative. Or for a old house in a rural spot, with insulation options restricted, perhaps modern biomass heating could be appropriate.

Direct electric heating, such as electric wall heaters or an electric boiler, will not usually be a good choice. This is because direct electric options give only one unit of heat for each unit of electricity consumed. Whereas a heat pump can give three or four units of heat for each unit of electricity it uses. Therefore, the running costs of electric heating will be 3 or 4 times as much. In addition, the widespread use of direct electric heating would put a very high load onto the electricity grid.

There’s currently a fair amount of promotion of ‘hydrogen-ready’ boilers, which seems to be led by the fossil fuel industry. However, to make hydrogen from electricity is even less efficient than direct electric heating. One unit of electricity will give only 0.6 units of heat if hydrogen generation is 70% efficient and the boiler 90% efficient. Overall, a heat pump would then be 5 or 6 times as efficient as the hydrogen boiler. The main industry proposal is to make hydrogen from fossil fuel (natural gas) and use some not yet proven way of capturing and storing the emitted carbon. There are big questions about how this will be achieved and how much the hydrogen will then cost.

Related Questions

What draught-proofing measures should I take?

For basic measures, checking around the house on a windy day is a good way to locate draughts. You must not block intentional vents such as wall vents (especially for rooms with a fire or stove), trickle vents on windows, and underfloor airbricks.

Wiper and compression seals are readily available for use on opening windows, external door frames and loft hatch. Foam types are cheaper but tend to wear out more quickly. Draught-proofing strips come in many types and thicknesses – so to choose the right one you need good measurements of the gaps you need to fill.

At the bottom of external doors you could add a batten along the bottom with a rubber flange or a strip of brushing. Internal doors to unheated rooms could have the same – or just use a draught-excluder.

Sash windows can be tricky – a brush seal may work, but some sort of secondary glazing will be better. See our page on windows for more.

Thick, well-fitting curtains will greatly reduce night-time heat loss from windows. Make sure curtains finish on a shelf above a radiator rather than hanging in front.

For letterboxes and old-fashioned keyholes you can buy special cover. Either board up and insulate an unused fireplace, or add a ‘chimney balloon’ if you’re planning to use the chimney in future.

For the gaps at skirting boards, between floorboards and around service ducts you can use a filler or sealant. Check that the type of filler (e.g. mastic or caulk) is suitable for the surfaces.

For big gaps you could wedge in wooden beading or round dowels. You can trim this to shape (using a surform or other tool) and tap into position using a dab of wood glue. The added wood could be stained to match surrounding timber.

A more in-depth approach to air-tightness would involve a full test with blower door equipment. As well as measuring heat loss more precisely, this helps identify the less obvious draughts through the building fabric.

Is cavity wall insulation a good idea?

If you have cavity walls and they haven’t been insulated, up to a third of the heat produced in your home could be escaping. Insulation should reduce your heating costs and carbon emissions from your home significantly. The insulation itself needs to be suitable for the conditions inside a masonry cavity, and so choices are limited to three options: blown mineral wool, plastic beads or plastic foam.

Cavity wall insulation should cost only a few hundred pounds and recoup this installation cost within 3 or 4 years. With gas-fired heating, you’ll reduce annual carbon emissions by almost half a tonne per year. This makes it several times better than installing a solar PV roof in terms of both carbon savings per pound spent and payback time. Both costs and savings will be higher for a detached house.

The installation process must include an assessment to ensure that the construction is of a suitable type. Installers should work through an accredited scheme and guarantee the installation for 25 years. It may take about 3 hours to inject the insulating material into the cavity. For installers, see the Cavity Insulation Guarantee Agency (CIGA), National Insulation Association, or British Board of Agrément.

Some homes may be classified as ‘hard to fill’ cavities – perhaps too narrow or uneven to fill easily. Insulation may then be more expensive to install (perhaps 2 to 3 times as much), or it may not be feasible – external or internal insulation may then be better.

A Which? Magazine survey in 2011 found that some installers were not undertaking adequate assessments. According to industry guidelines, they should inspect all external walls thoroughly to check for cracks/defects, check all internal walls to check for any existing damp, and do a cavity check (with a drill hole) on all walls. A proper survey like this is likely to take an hour. Do ask a few companies around to give quotes.

Cavity wall insulation should not cause problems of dampness, but a proper assessment of the property is needed to ensure it would be suitable. If your home is towards the west coast of the UK, more prone to wind-driven rain, then it might be unsuitable for cavity insulation if it’s in a very exposed, unsheltered position and there are cracks in the external wall. For those few homes in this position, measures could taken to prevent damp risks – for example by putting extra protection in the form of boards or tiles on the exposed walls. There will be a cost to this of course, and it should be compared with quotes for options such as internal or external wall insulation.

BRE (Building Research Establishment) research in the 1990s showed that cavity wall insulation when assessed & installed properly does not lead to an increased risk of damp. The study found that the structural condition of the walls was the most important factor in damp problems – for example, badly filled mortar joints or ‘dirty cavities’ (where, during construction, mortar has dropped down inside the cavity – i.e. if too much is used). Over time, this can cause problems with damp-proofing.

How could I insulate a pitched (sloping) roof?

A ‘cold loft’ roof, with the insulation at ceiling level (laid flat in the floor of the loft) is generally the most economical, and easy to install. However, if you want to insulate in the slope of a roof in order to make use of the space, then here are some tips.

The most economical way of achieving a good thickness of insulation in the roof slope is to have two layers of timber, one supporting the roof finish and another supporting the insulation and ceiling finish. To reduce cold-bridging, timber I-Beams can be used in new constructions. In an existing roof (with rafters supported on roof beams), the second layer of timbers (ceiling joists) can be hung off the rafters using hardboard, ply or timber ‘hangers’, or nailed crosswise to them, or they can span between the roof beams. This technique can also be used with flat roofs.

An air space of 50mm must be left between the insulation and the tiling felt, unless the felt is of a low-vapour resistance type. If using a breathable membrane, with insulation up against it, then above the membrane you would put counter battens (top to bottom) as well as the standard battens (side to side), for adequate ventilation beneath the tiles. Sometimes, a breathable membrane is used with only standard battens, with the membrane slightly draped between rafters to allow ventilation – in this case an air gap of about 25 mm would be needed between membrane and insulation.

Pitched roof insulation
Pitched roof insulation

Thin wood-fibre boards (22 or 35mm thick) can be used as an alternative to a membrane under tiles. When re-roofing, the fibre-board is laid over the rafters, and then counter battens (in line with rafters), and then standard battens to fix the tiles/slates to. Thicker wood fibre boards can also be used, to give more insulation and achieve a lower U-value (to minimise heat loss).

A ‘warm roof’ will have waterproof insulation on the outside of the structure (so the main timbers are on the warm side of the insulation). It’s a useful way of upgrading an existing roof when internal room height is at a premium. On a sloping roof, the tiling battens are supported by rigid insulation and fixed through to the rafters by special screwnail fixings. The insulation must be waterproof, such as cork, foamed glass or closed-cell plastic foam board – these will tend to be more expensive than the standard insulation materials for internal use.

There are many different types of insulation material to choose from. Please do contact us if you need to find suppliers of natural & renewable insulation.

You can also read more at the webpage of the Energy Saving Trust, on Greenspec’s pages about ventilated and unventilated roof insulation options, and in a guide from Historic England.

How could I insulate a suspended timber ground floor?

If you can access the floor from below via an unheated cellar or basement it will be easier, otherwise you’ll have to lift the floorboards (which requires care to avoid damaging them).

225mm of a renewable or mineral fibre type of insulation is a decent amount. Make sure you keep good ventilation to the underfloor space beneath the insulation – with vents at either side for air flow.

Renewable insulation will need to be protected by a breathable membrane to protect it – if the floorboards are not well sealed. See the website of the supplier of insulation you’re using (or call their advice line) for advice on the type of membrane that would be needed.

Loose fill insulation can be carried between the joists on a membrane or netting nailed to floor joists or on a low-vapour resistance board (for example softboard, a fibreboard bonded by heat rather than glues – this is good for Warmcel insulation made from recycled newspaper).

For other insulation materials (e.g. standard mineral fibre types) it will also be worth looking up the website of the manufacturer (e.g. Rockwool or Knauf) as they’ll usually have guidance sheets on how the material should be installed and what limitations there may be.

You can also see some information and examples on the Energy Saving Trust and Historic England websites.

How could I insulate a solid floor?

Traditionally, solid floors were laid directly onto soil. This relies on the ground underneath being kept dry, usually by it being higher than the ground outside the building, and by having adequate drainage.

The most common method now used is to have a thick concrete slab laid on a damp-proof course (e.g. a polythene membrane). A layer of polystyrene insulation is then finished with sand/cement screed and tiles or board.

For a low-impact alternative to the above you could look into using recycled aggregate in the concrete (rather then newly quarried material), and perhaps using stabilised earth as the screed. You could also consider using recycled polythene or bitumen for the damp-proof course.

A solid floor of stabilised earth or limecrete should have a solid insulation material below it, such as cork, perlite or foamed glass, with recycled polythene vapour check and damp-proof membrane (DPM) below this.

Try to achieve at least 150mm of insulation for a solid floor. Insulation should be placed around the edge of the floor, and the floor finish supported on some sort of rigid insulation. Possible materials include cork, perlite (volcanic glass), lightweight expanded clay aggregate (‘Leca’), foamed glass (slabs or granules), fibreboard, mineral wool boards, or plastic foam of some sort. A vapour check layer will normally be required to prevent condensation occurring within the insulation layer.

Another possibility is a hemp & lime (or ‘hempcrete’) floor. Lime has a much lower environmental impact than cement, so if you can use it place of cement in mortars or concrete you will be reducing the ’embodied energy’ of the floor and the carbon emissions from construction. The hemp provides the insulation. See for example the details of how we insulated the WISE building at CAT.

If you are redoing a floor, then you may have the chance to consider underfloor heating. Because it runs at a much lower temperature than standard radiators, wet underfloor heating is more efficient and provides a more comfortable type of heat. It’s particularly appropriate for use with heat pumps, as these need to supply low-temperature water to run efficiently.

You can also see some information and examples on the Energy Saving Trust and Historic England websites.

How could I insulate a flat roof?

The first two of the following four methods involve adding insulation to the outside of the roof, so will be suitable if there is little headroom underneath, or if access is difficult. The second two involve adding insulation underneath the roof. If insulating on top of a flat roof, make sure that it still drains well so that water does not pool on top.

Upside Down or Inverted Roof

An ‘upside down’ roof uses waterproof insulation on the outside of the building structure. The insulation is laid over the existing waterproof membrane and held down with something – which could be pebbles, turf (for a green roof), paving slabs, etc. Suitable insulation materials will tend to be a bit more expensive, and include cork, foamed glass and closed-cell plastic foam. You’ll need to check that the structure can bear the weight of the insulation and finish. This option keeps the existing membrane, but there is a risk that water will percolate through the insulation and so cool down the roof deck – causing condensation.

Warm Roof

A warm roof will have the insulation laid over a vapour control layer (itself over the roof deck), with a membrane laid over the insulation and suitable finish on top. You’ll need to check that the structure can bear the weight of the insulation and finish. If you are replacing the roof membrane anyway, then this will be a better solution than the ‘upside down’ roof (above), as it will keep water above the insulation and so keep the roof decking warm. You could still keep the existing membrane underneath the insulation if it would be difficult to remove.

Cold Roof

The insulation is put between the roof joists. A ventilated gap needs to be retained between the top of the insulation and the roof decking, to avoid condensation build-up. It can be difficult to get adequate ventilation, so this method is often not recommended.

Internal Insulation

A method similar to dry-lining of walls can be used, with a plasterboard/insulation board added to the underside of the internal roof, below the joists.

How do I choose between insulation materials?

There are basically three different types of insulation material:

  1. Organic – those derived from natural vegetation or similar renewable sources, which tend to require a low energy use in manufacture (a low ‘embodied energy’). Examples are sheep’s wool, cellulose, cork, wood fibre, and hemp.
  2. Inorganic – derived from naturally occurring minerals which are non-renewable but plentiful at source. Likely to have a higher embodied energy than organic materials. Examples are mineral/glass fibre, perlite and vermiculite (from volcanic rock) and rigid foamed glass.
  3. Fossil organic – derived by chemical processes from fossilised vegetation (oil) – a finite resource. Fossil organic insulation materials such as expanded polystyrene and polyisocyanurate or phenolic foam are highly processed, resulting in a high embodied energy.

Which is best?

If possible it is better to choose insulation materials that have not been heavily processed as this will reduce the carbon footprint and environmental impact of your home. But it is far better to install cheaper inorganic or fossil organic materials with the right physical properties and a low thermal conductivity than to install nothing at all.

In many cases, organic insulation material can be applied instead of inorganic or fossil organic, but there are exceptions. For example, there is not an organic insulation material suitable for cavity wall insulation.

Think also about the ease of installation. Loose fill insulation is quick to put in in lofts, but cannot be DIY installed in anything other than a flat place. Rigid boards and batts will come in certain sizes, but need to be cut to shape if you have some unusual spaces. Some materials can be cut with a knife, but a few will need a saw. Some mineral wool now comes in a thin foil or plastic wrap, to protect from the fibres. You should still wear a face mask when installing any type of installation, as small fibres of any kind are best not inhaled.

Can a conservatory make my home more energy efficient?

A conservatory can be a great way to use solar power. And as well as saving energy, it will provide a pleasant extra room. The big thing to remember is that a conservatory should never be heated – or all the benefits will be lost!

A conservatory is a ‘buffer’ against the outside weather – the temperature will stay a few degrees warmer than it is outside. For much of the year a conservatory is a very nice place to be. However, you’ll need blinds or shutters to prevent overheating in high summer. Growing seasonal vines or creepers across the roof is also a great way to get summer shading. A south-east facing conservatory is best, as it gains from the morning sun but will be slightly shaded from the westerly sun at the warmest time of day.

A conservatory can also act as a lobby for coming and going from the house, so reducing draughts and heat loss. Fresh air coming in to the house via the conservatory will be warmed on its way through. This is good, because lots of the heat loss from a well-insulated house is through ventilation.

A danger with conservatories is that they come to be relied upon as an extra living space in the home. As the coldest months come around, a few degrees above outdoor temperatures is still quite chilly. This leads to the temptation of putting a heater or radiator in, a move that would make your home an energy guzzler! It is impossible to insulate such a highly glazed room sufficiently,so if you want to maintain energy and monetary savings, you’ll need to resist temptation and keep it unheated.

Shutting the conservatory off from the main part of the house with solid doors, or glass doors with thick curtains, will stop heat escaping at the coldest times of the year. Plenty of ‘thermal mass’ within the conservatory will store the heat gained for longer. So if it is being added to an existing brick wall, much of this could be kept for this purpose. Alternatively, a solid stone or brick floor will soak up and then slowly release heat as the evening cools down.

For a sunny but heated space in your home, consider instead a sun-room. This would have double glazing throughout with an insulated solid roof and well-insulated curtains or blinds. An insulated, heated sunroom would need to meet Building Regulations, so the balance of windows and insulated roof or walls would need to be designed carefully.

A conservatory may seem cheaper to build than a proper extension, but this is not always the case – they can be more costly per square metre than the rest of the house. And if it ends up as a heated room then the less obvious heating costs will not be at all cheap!

How can I reduce condensation in my house?

Condensation is due to excessive moisture, cold conditions, cold surfaces or inadequate ventilation. It can cause mould, heat loss and building damage. To address these issues, the room should be properly insulated and adequately heated (to keep the surfaces warm).

So do take all feasible insulation and draught-proofing options, and look into improving single glazing with either replacement glazing or with secondary glazing (a cheaper option).

Condensation may still occur on replacement windows, as they’ll still be the coolest surface. New windows will be more airtight than old ones, so warm moist air will be no longer be escaping through cracks in the frame and around the seals. This means that existing damp issues may become more pronounced. Many windows will include trickle vents in the frame, to allow a small amount of ventilation, but to keep the house warm and dry you may need to take a few other measures to avoid producing lots of moist air.

Drying clothes indoors can easily cause problems of damp and condensation, leading perhaps to mould, etc. So if you need to dry indoors, it should be in a room that can be shut off and ventilated (perhaps with heat recovery, as mentioned below).

The bathroom and kitchen in particular should be able to be ventilated in a controllable way, to stop moist air circulating into the rest of the house. For example, after a shower or bath, leave the bathroom door shut and the window open for a while until moist air & condensation on the window/mirror has cleared. Do the same when cooking if you can; if your home has an open plan layout at least stop the moist air circulation where possible (e.g. to the upstairs rooms).

To avoid heat loss from a room like a kitchen or bathroom, where lots of moist air is regularly produced, you could consider a heat recovery extractor fan. It may be worth getting a slightly bigger heat-recovery fan unit than you need, as they can be a bit noisy if they are operating on full power. This may be fine if are just switching it on for a short while to clear the bathroom, but it could be obtrusive in the kitchen. If a fan unit is not supplied with more solid covers over the plastic slatting, it could be worth fitting something if you live in a house that is a bit exposed to the wind (as they could let in draughts when not in use). An openable wooden casing could be fitted quite easily.

If drying clothes indoors is not an issue, and you’re already careful about venting away moisture from bathroom & kitchen, then excessive condensation may be from some other cause, such as a water leak somewhere (e.g. from a pipe under the floor or in the loft), or water penetrating the structure from outside (such as rainwater coming in cracks in masonry, or if gutters are broken). If problems persist, it would be worth investigating these issues, as over time they’ll cause damage to the building.

What is a U-value, and what is thermal conductivity?

The U-value is a measure of how many watts (representing the rate of flow of energy) pass through one square metre (m²) of a construction detail (such as a wall) for every degree difference in temperature between the inside and the outside. Temperature is measured in kelvin, and 1K = 1°C (degree centigrade).

As an example, a U-value of 6.0W/m²K for a single glazed window means that six watts will be escaping through each square metre of glass when the temperature difference is one degree. If it is 20°C in the house and 0°C outside, then the heat loss is 20 x 6 = 120 watts per square metre.

U-values are generally used to describe the thermal performance (heat loss) for a section of construction that involves several materials – such as a wall made up of timber, insulation, board & render.

Thermal conductivity

For individual materials, such as a type of insulation, you’ll come across the term ‘thermal conductivity’, also known as a k-value or λ-value (lambda). This is the rate at which heat flows through a particular material, and good insulation will have a low thermal conductivity. It is measured in watts (heat flow) per metre (depth of material) per degree difference (inside to outside), so the unit is W/mK.

Most natural insulation materials (hemp, wool, recycled paper or textile) will have a thermal conductivity of about 0.035 to 0.040 W/mK, which is similar to the performance of conventional mineral wool insulation. Foil-backed plastic foam insulation boards are slightly better, with thermal conductivity about 0.023 W/mK. So about 100mm of the plastic foam board will give equivalent insulation value to about 150mm of the various woolly types.

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