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Home insulation make your home energy efficient

Home insulation

Insulating your home is one of the best things you can do to reduce your energy bills.

Need-to-know information about home insulation

Insulating your home is one of the best things you can do to reduce your energy bills and it'll make your house warmer and more comfortable, while also reducing its impact on the environment in the process.

What does insulation do?

Insulation - and draught-proofing - protects your home against cold in winter and excess heat in summer, and can even reduce noise pollution (like the sound from a road or passing aircraft). What's more, some key insulation measures are 'low cost', in that they pay for themselves in less than five years.

Other than low energy lighting, these measures have the best returns of all energy efficiency investments. Furthermore, if you decide to sell or rent your home, the rating that your home receives on an Energy Performance Certificate (EPC) will be improved.

How much can you save by insulating your home?

There is no straightforward answer to this question. How much you will save depends on a variety of factors including the size of your home and the type of insulation you want installed.

The below tables should help give you an idea of how much you could save by installing various types of insulation.

All figures are taken from the Energy Saving Trust.

How much can you save with loft insulation?

Loft Insulation Detached house Semi-detached house Mid-terrace Detached bungalow
Cost (one time cost) £395 £300 £285 £265
Potential savings (each year) £250 £150 £140 £200

*These are estimates based on insulating a gas-heated home with either a totally uninsulated loft.

How much can you save with cavity wall insulation?

Building Detached Semi-detached Mid-terrace Bungalow Flat
Annual saving £250 £145 £95 £100 £75
Installation cost £870 £415 £220 £270 £146
Payback time 3 Years or less 3 Years or less 3 Years or less 3 Years or less 3 Years or less
Carbon dioxide saving per year 1040kg 600kg 395kg 410kg 325kg

*These are estimated figures based on insulating a gas-heated home. The average installed cost is unsubsidised.

How much can you save with solid wall insulation?

Building Detached Semi-detached Mid-terrace Bungalow Flat
Annual saving £460 £270 £180 £180 £150
Annual carbon dioxide saving 1040kg 600kg 395kg 410kg 325kg
Installation cost* External wall insulation: £9,000 to £25,000 Internal wall insulation: £4,500 to £15,000 External wall insulation: £9,000 to £25,000 Internal wall insulation: £4,500 to £15,000 External wall insulation: £9,000 to £25,000 Internal wall insulation: £4,500 to £15,000 External wall insulation: £9,000 to £25,000 Internal wall insulation: £4,500 to £15,000 External wall insulation: £9,000 to £25,000 Internal wall insulation: £4,500 to £15,000

*These are estimated figures based on insulating a gas-heated home and may vary greatly depending on the amount of work needed.

How much can you save with floor insulatuion?

Solid Floor Insulation Detached Semi-detached Mid-terrace Bungalow
Approximate annual saving £460 £270 £150 £180
Approximate installation cost* From £900 to £2400 From £900 to £2400 From £900 to £2400 From £900 to £2400

*These are estimated figures based on insulating a gas-heated home and may vary greatly depending on the amount of work needed.

Suspended Timber Floor Insulation Detached Semi-detached Mid-terrace Bungalow
Approximate annual saving £100 - £120 £60 - £75 £45 - £60 £75 - £95
Approximate installation cost* From £300 to £700 From £300 to £700 From £300 to £700 From £300 to £700

*These are estimated figures based on insulating a gas-heated home and may vary greatly depending on the amount of work needed.

How much can you save with energy-efficient window glazing?

Solid Floor Insulation Detached Semi-detached Mid-terrace Bungalow Flat
A rated £130 - £175 £90 - £120 £80 - £105 £60 - £80 £50 - £65
B rated £120 - £160 £80 - £110 £70 - £95 £50 - £70 £40 - £60
C rated £120 - £150 £80 - £105 £70 - £90 £50 - £65 £45 - £55

*These are estimated figures based on insulating a gas-heated home.

What is the difference in insulation between a new build and an older house?

Although new homes are now built to very good insulation standards, historically homes in the UK were insulated to a very poor standard, especially when compared to other European nations. If your house was built over twenty years ago, it's very likely that there are opportunities to 'retro-fit' insulation and improve its energy efficiency.

By contrast, some modern eco-homes are super-insulated and air-tight to the extent that they no longer need a heating system - they rely on heat from sunlight through the windows, and produced by the occupants and by electrical equipment in the home, with occasional top-ups from individual electric heating devices.

How does the heat escape from my house and the cold get in?

There are five ways that heat can escape:

  1. Conduction - that's heat moving through solids like metal or brick.

  2. Radiation - this is the heat you directly feel when you stand near a heat source. It is in fact infra-red radiation, and just another form of 'electromagnetic radiation' like radio waves, visible light, ultra-violet and x-rays - which all travel at the speed of light. If you take infra-red photos of your house on a cold, still night you can help see where heat is being lost.

  3. Convection - this is the natural tendency of warm air or water or other gases and liquids to rise, while cold air or water falls. This often results in circulation of air and is the main principle behind central heating radiators.

  4. Air movement - draughts are a common form of heat loss, taking warm air from within the home and letting it out into the outside (and typically replacing it with cold air coming in). Another example is a wind blowing past a house, which will generally have a cooling effect on it. Water movement has the same effect, but there are no known UK examples of systems to recover heat from water before it is put into the drains.

  5. Evaporation - not a process that we naturally associate with heat loss, but if it rains on a hot summer day, after the rain stops, some of it may evaporate from the roof and walls, and this will cool the home considerably.

How do these methods apply to heat loss in my home?

In practice a lot of heat loss from your home will include a number of paths, each involving a combination of these methods. For example, in a bedroom, warm air can convect to the ceiling, the warmth will then be conducted through the ceiling, radiated or convected through the loft to the pitched roof, conducted through the roof tiles and then radiated or convected into the atmosphere.

On another path, heat from a radiator may radiate through the windows, while on a third, warm air might also be carried in draughts through gaps in the window frame and around the skirting boards. A fourth path could involve heat going through the inner 'leaf' of the cavity wall, being convected or radiated across the un-insulated cavity, conducted through the outer 'leaf' and then radiated, convected and conducted out into the atmosphere.

Where do I need to insulate in my home to protect myself from heat loss?

On a cold day, heat can escape from your home in all directions - up, down and sideways. So you should think about insulating the whole 'envelope':

  • the roof,

  • the walls,

  • the floor,

  • windows and doors.

Many people make the mistake of assuming that heat only goes up - but only one form of heat transfer (convection) primarily moves up. In reality heat travels in all directions.

If you adjoin another home, either through shared walls or through a floor that is in effect another household's ceiling, or vice versa, you are fortunate as you will not suffer from heat loss, assuming the other side is heated as well. However, you will still need to heat your home, as you won't have heat gain either. The general rule is that the bigger the temperature difference, the greater the flow of heat. So, the colder it is outside, the greater the heat loss from your home.

Can I completely eradicate heat loss?

You cannot completely eradicate heat loss through any one part of your home's envelope. Beware of assuming that just because heat loss through, say, your roof will account for 25% of your heat losses, that you will completely eradicate that loss and reduce your bills by 25%. You can save a substantial chunk of that, but there will still be some loss through that 'face' of your home.

How much heat is being lost from different parts of my home?

This depends on the type of house you live in, whether it's detached or semi-detached, or if it's a terrace property, and if so, if it is mid or end terrace. If you live in a flat, the losses will be different again, and will depend on whether your flat is in the middle, at the top or at ground floor level.

For a typical house the walls will lose most heat, around 30% and up to 40%. The roof will be next at around 25%, probably followed by windows and doors at around 20%, and the floor (of your lowest storey, at around 10%). Quite a large loss will occur because of draughts, excess ventilation and lack of air-tightness. Of course, draughts can also be attributed to floors, doors and windows, the walls or roof.

Do I need planning permission for insulation work?

In most cases, insulation work does not require planning permission from your local council. The exceptions may include external wall insulation and, in areas where there are conservation schemes, glazing.

Even if you don't need planning permission, building regulations could apply, so check with your local council's building control department.

What about the environmental impact of insulation products?

'Embodied energy' is the energy used in the manufacture and shipping of a product. Sensible insulation measures will prevent the future need for energy, which will reduce overall energy needs, and reduce overall environmental damage, as such the initial 'cost' in terms of embodied energy is outweighed by their positive impact.

Some insulation materials have a lower environmental impact than others, such as those made from sheep's wool, wood, hemp, and recycled paper, glass or plastic bottles. And some insulation measures retain existing facilities, such as secondary double glazing.

Broadly speaking, if you eventually save money by investing in insulation, you are probably also reducing your overall environmental impact. Furthermore, processes proven to be particularly environmentally damaging are in any case generally banned or controlled.

What makes a good insulator?

home insulation

Good insulators include many products that typically have a structure similar to wool. In effect a good insulator will trap tiny pockets of air within a material which itself is also a good insulator. These include the very common mineral and glass wools, which come on rolls in blanket form, or in a somewhat denser form as batts or slabs.

Sheep's wool is of course a great insulator, as are other natural fabrics like hemp and cotton - so curtains are good insulation products. Some mineral and glass wool style products are 'higher density' and therefore have greater insulation effect, typically about 25% greater.

Most wood and wood based products, for example, MDF, plywood, and hardboard, are also fairly good insulators - so wooden doors and wooden loft boards help keep warmth in the home.

Not surprisingly, paper is another a good insulator, including recycled paper, and cellulose from other sources such as crop wastes. Although flammable in its untreated form, it is treated to make it fire resistant for use as insulation. This is supplied in sealed sacks, but once opened is in loose form, which makes it suitable for installing in circumstances where blankets or batts won't fit.

Polystyrene and similar products are generally good insulators. Polystyrene is sometimes referred to as EPS (expanded or extruded polystyrene slab) form. These products are also usually fire resistant, and much denser and heavier than the sort of polystyrene that is used for packaging. EPS is typically 50% more effective, for the same depth, as standard mineral or glass wool products.

Closely related are spray foam solutions, which are typically polyurethane based. The foam forms on the mixing of two chemicals and it hardens, trapping tiny pockets of air. Because the foam fills crevices and gaps, it can also eliminate draughts and provide strengthening to existing building structures, for example roof tiles. Other foam solutions include adhesive strips for insulating around windows, doors, or loft hatches.

Some 'insulators' work by stopping the flow of air (draughts) through cracks and gaps, such as sealants (mastics). One of the cheapest sealants is papier-mache, which you can make yourself from torn-up paper and wallpaper glue.

Another method of insulation is reflection. There are now multi-foil products, which are generally a sandwich of metal foils and plastic style insulators. These can be used to reflect radiated heat (infra red) and are designed to insulate where there isn't the space for wool, batt and EPS type products. Some polystyrene and other products are also coated with foils.

Good insulation material doesn't just slow the process of heat loss, depending on its specific use, there are other properties that are important too, such as physical strength, fire resistance, resistance to mould, and non-toxicity; cost is another important consideration too.

What about bad insulators?

Unfortunately, many materials with physical strength and which are therefore used in building construction, including metals (such as copper, steel, and aluminium), stone, brick, tiles, and concrete, are bad insulators . However, some more modern versions of these materials have been designed to have construction strength but lower heat transmission than in the past, for example, modern breeze blocks.

Water is also a bad insulator, which means that anything that soaks up moisture will usually conduct heat away quite quickly. Moving air also takes heat away quickly even though air that is prevented from moving, generally when trapped in tiny pockets, makes a good insulator.

How do I know if the material I'm buying is a good insulator?

The rate of heat flow through a material is dependent upon the temperature difference on each side, the thickness of the material, the surface area, and the 'thermal conductivity' of the material, that is, it's ability to conduct heat, or 'k' as it is called in physics. However, when you are investigating insulating materials, you are more likely to come across R-values and U-values as these are usually quoted on packaging and in catalogues.

The R-value is quoted taking account of the depth of material as sold, for example, 100 mm of mineral wool will have an R value of about 2.25, while 170 mm depth product will have an R value of about 3.8.

You can then add R-values together if you are using layers of different materials, to get an overall R-value; an overall R-value of greater than 6.0 is recommended for lofts.

R-values (and U-values) for products also take account of the effect of surface resistances - the texture and reflectivity as well as the other properties of the surface of a product also affects heat transmission.

U-values measure how well different aspects of a building, such as the walls, the roof or windows, allow heat to flow out of it. The lower the U-value, the better, as this equates to lower heat loss. Some parts of buildings have naturally lower U-values -a well-insulated wall will generally have a lower U-value than a window, even if it is double-glazed. You may come into contact with U-values if you have to deal with planning matters, for example, if you build an extension or make a major change to your home such as putting in a loft room.

Are there limits to the effects of insulation?

In short, yes there are. Piling up layers of insulation becomes decreasingly cost-effective. If you have some insulation in place, and then double the thickness of it, the original heat flow will be halved. But to halve the heat flow again, and therefore reduce it to one quarter of the original, you will need four times the original insulation depth, and for one eighth the heat flow, you will need eight times the original insulation!

You can see how the cost savings relative to the initial outlay could quickly diminish, not to mention how impractical it would be.

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