Energy Efficiency
If you want to keep your energy bills low and reduce your carbon emissions, installing insulation is one of the most effective things you can do — keeping the heat in your home and the cold out. Here is where the heat goes, what each job costs and what it saves.
Where the heat goes
One third
Of all the heat lost in an uninsulated home escapes through the walls.
Up to 25%
Of a home's heat can be lost through an uninsulated roof.
£15
The cost of a hot water cylinder jacket — the cheapest job on the list.
Insulating walls
Usually identifiable by an even brick pattern, with all the bricks laid lengthways. A professional injects insulation material into the cavity — the space between the two skins of the wall — by drilling holes in the outside wall, filling the void and sealing the holes with mortar.
The bricks follow an alternating pattern, with some laid across the wall so you see the smaller ends from outside. Solid walls can be insulated from the inside or the outside, and both routes cost considerably more than filling a cavity.
Where the outside wall is covered with render you cannot read the brick pattern. The age of the house and the thickness of the walls are the usual clues, and a surveyor can confirm the construction before you commit to any work.
Rigid insulation boards are fitted to the wall, or a stud wall is built and filled with insulation material. It is the cheaper of the two options, but it takes a little room off the floor area and means redecorating.
A layer of insulation material is fixed to the outside of the wall and then covered with render or cladding. It costs more, but it leaves internal rooms untouched and refreshes the appearance of the building.
Costs, savings and installation
Cost: Around £7,000
Saving: Around £225 a year
Based on an average semi-detached house. Costs and savings vary with wall type and house size, and the work should come with a 25-year guarantee.
Cost: Around £10,000
Saving: Around £225 a year
Likely to be more expensive than the internal route on an average semi-detached house, but it avoids losing internal floor area.
Cost: Around £300
Saving: Around £150 a year
For an average semi-detached house, and it cuts your carbon footprint by more than 600kg a year. One of the strongest returns of any insulation job.
Cost: Varies by floor type
Saving: Around £40 a year
Stops heat escaping through the ground. Sealing gaps between floorboards and skirting boards is a low-cost job you can do yourself.
Cost: From £15
Saving: Around £90 a year
Adding up to 80mm of insulation to an uninsulated hot water tank in a gas-heated average semi-detached house. A cylinder jacket is simple to fit yourself.
All figures sourced from Energy Saving Trust 2021 and quoted for an average semi-detached house. Costs and savings vary by property, construction and installer, and energy tariffs move frequently — price any work against current rates.
Insulating roofs
Use rolls of insulation and lay the first layer between the joists — the horizontal beams that make up the floor of the loft. A second layer is then laid at right angles across the joists to build the insulation up to the required depth, typically 270mm.
Costs and savings vary with the level of insulation and the size of the home. In an average semi-detached house, installing up to 270mm at a cost of around £300 could save roughly £150 a year on energy bills and cut your carbon footprint by more than 600kg a year.
Adding insulation makes the loft colder above the layer, so airflow matters. Maintaining ventilation to the roof space prevents condensation forming on the underside of the covering and on timbers.
Insulating floors
Common in newer homes, and insulated by adding rigid insulation boards on top of the existing slab. Worth planning around door thresholds and floor levels before work starts.
More likely in older homes. The floorboards are lifted and insulation is laid down, supported by netting between the joists. Insulating under the floorboards could save around £40 a year.
Sealing the gaps between floors and skirting boards with a sealant is a job most owners can do themselves. Rugs and carpets make floors feel warmer underfoot, which often means reaching for the thermostat less often.
Insulating pipes and tanks
Around £15 and straightforward to fit by following the manufacturer's instructions. In a gas-heated average semi-detached house, adding up to 80mm of insulation to an uninsulated tank could save around £90 a year.
Relatively cheap and as simple as choosing the correct size and slipping it around the hot water pipes. It keeps heat in the water rather than losing it to unheated spaces on the way to the tap.
Fixed behind radiators to reflect heat back into the room instead of letting it pass out through an external wall. A good low-cost option where radiators sit on external walls.
Before the work starts
Cavity or solid, and whether render is hiding the answer. Getting this right determines which insulation route is even available to you and what it will realistically cost.
Insulation added to a property with an existing damp or condensation problem can make matters worse. We identify moisture issues and ventilation shortfalls so they are dealt with in the right order.
On a purchase, we look at what is already there — loft depth, cavity fill, retrofitted external systems — and whether it has been installed and detailed properly.
Common questions
Start where the heat is going. Around one third of the heat lost in an uninsulated home escapes through the walls and up to 25% through the roof, so walls and loft are usually the priority. Floors, pipes and the hot water tank cost far less and are worth doing alongside.
Look at the brick pattern. Cavity walls usually show an even pattern with all bricks laid lengthways; solid walls show an alternating pattern with the smaller ends of some bricks visible. If the wall is rendered, the age of the property and the thickness of the walls are the usual indicators.
Internal solid wall insulation for an average semi-detached house costs around £7,000 and could save roughly £225 a year on energy bills. External insulation is likely to be more expensive at around £10,000 for the same property. The work should come with a 25-year guarantee.
It is one of the best-value jobs available. Installing up to 270mm of insulation in an average semi-detached house costs around £300, could save around £150 a year and reduces your carbon footprint by more than 600kg a year.
If the loft is easy to access and free of dampness or condensation, it is a job many owners take on. Lay the first layer of rolls between the joists, then a second layer at right angles across them to reach the required depth — and keep the roof space well ventilated to prevent condensation.
Fix the damp first. Insulating a loft or wall that already has moisture or condensation problems can trap the issue and accelerate damage. A survey establishes the condition of the fabric so the work is sequenced correctly.
Know the building first
We assess construction, existing insulation, damp and ventilation, so you know which jobs will actually pay back and which problems need solving first. Useful whether you are improving the home you own or buying one.
Keep reading
Energy efficiency
Installation costs, realistic generation, export rates and the payback period on a domestic array.
Read MoreMaintaining your property
Permitted development limits and Building Regulations for conservatories across the UK's three regimes.
Read MoreMaintaining your property
What an extension or conversion adds, what it costs, and the site factors that decide whether it works.
Read More