Insulation is the key weapon in the fight against heat loss. By insulating walls, roof and floors, you will use less energy to keep warm. Most people will have lower heating bills as a result.  

Loft insulation

Loft insulation is generally the easiest type of insulation to deal with. It is also one of the measures that makes most difference in terms of warmth, comfort, saving on your energy bills, and reducing carbon emissions.

Building Regulations call for the equivalent of 270mm of mineral wool insulation.

An average detached property will cost anything up to £395 to install 270mm of mineral wool insulation. As a result, you will save around £250 a year in lower heating bills. 

The choice of insulating material will be dictated by a few factors; space, access and, of course, price. Mineral wool is the most common choice. 

Generally, insulation is laid horizontally between the ceiling joists and then a layer at right angles over the top. This keeps the loft space well ventilated, rather than insulating at the rafters, which is advised to avoid the roof timbers rotting and also means you are not inadvertently heating your loft space.

Cavity wall insulation

About a third of the total heat lost from a house is through the walls. The typical cavity is 50mm (2 inches) wide and 50mm of foam insulation will reduce heat loss. 

If your house was built in the 1990s or later, the cavities are probably insulated already. If you’re not sure get a reputable installer to inspect the wall for you using a borescope.  

If you are looking at installing cavity wall insulation, costs range up to about £610 for a typical gas heated, detached property. Annual savings on heating bills are around £280 per year according to the Energy Saving Trust. 

It is a quick job, taking around 2 hours to fill an average house. The installer will drill a series of holes in the walls of your house, and blow insulation into the cavity through a hose. Once done, they will fill the holes again. 

Poorly filled cavity wall insulation can result in cold spots and internal condensation and so should be carried out by a trained professional.  

Solid wall insulation

About a third of UK homes have solid walls according to the National Insulation Association. It estimates that the heat loss through the walls of these homes is 45%.  

Solid wall insulation is expensive and disruptive. It costs between £7,400 and £13,000 for a typical, semi-detached property, according to the Energy Saving Trust. Insulating internal walls tends to be cheaper than external insulation but it has a greater impact on occupants while it is being done.  

Typical savings on heating bills are £225 per year. 

Internal solid wall insulation requires the temporary removal of  radiators, electric sockets and skirting boards, and it will reduce the size of your room slightly. The good thing about internal wall insulation is that it is easy to spread the cost by doing it a room at a time.  

External solid wall insulation involves fixing an insulating layer to the outside of the house and putting a render or cladding over the top which come in a range of finishes. You may need to get planning permission for external wall insulation as it can change the appearance of the house.  External wall insulation can provide greater energy efficiency savings than internal insulation provided it is done properly, e.g. removing soil pipes and guttering and insulating behind them rather than boxing them in. 

Underfloor insulation

The heat lost through floors is smaller than through walls or roofs. However, insulating the floor can improve comfort, and the Energy Saving Trust estimates that it will save up to £75 a year on energy costs. You can save more if you fill all the gaps between the floor and skirting board. 

Costs are in the region of £520 – £1,300 depending on the size of the room, the material used, any access issues and the type of floor being insulated. 

Insulating under a suspended floor 

A suspended floor is where floorboards are laid on joists. A good way to tell whether you have a suspended floor is by looking to see if you have airbricks outside. To insulate, lift the floorboards and put insulation material between the joists.  

The insulation is usually mineral wool or loose fill insulation hung in netting. You will need to seal any gaps between boards, and between the floor and the wall. 

If you have a cellar, you can avoid lifting the floorboards by insulating from below. Upstairs rooms do not have to be insulated if they are above a heated room. 

Insulating a solid floor 

You can insulate a solid concrete floor underneath or above the concrete using rigid insulation foam. If you are insulating on top, you will lose a bit of height in the room and will have to cut the bottom off any doors. 
You must put in insulation when replacing a floor, according to Building Regulations. 

When not to insulate

Some properties, typically those built before 1940, rely on the ventilation in the cavity to stop rainwater penetrating to the inside wall. In this case you will need to either insert a vertical damp proof course or not fill the cavity. 

In any house, cavity wall insulation will reduce ventilation, preventing natural moisture build-up from being removed. So, if you have cavity wall insulation make sure you also have trickle vents, airbricks or extractor fans. 

It is also important to check that your cavity is clear of any debris before filling it with insulation, otherwise it may cause damp. 

From the blog

More information

Insulation- general

Cavity wall insulation

Loft insulation

Underfloor insulation

Solid wall insulation