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25 February 2021

Loft insulation costs and savings

Weigh up the costs and savings of installing loft insulation
Installing loft insulation 450367
WhichEditorial team

Our research has found that installing loft insulation could reduce your energy bills by up to £215 per year, depending on your home.

We’ve worked out how much you can save on your energy bills and how long loft insulation will take to pay for itself. 

The payback time is very quick if you start from having no loft insulation at all. But we've found that even homes with existing loft insulation can save money by increasing the amount there is.

Scroll down for more on loft insulation prices and savings, or head to types of loft insulation or the best free and cheap insulation deals.

How much does loft insulation cost?

We've worked with the Royal Institution of Chartered Surveyors* (RICS), which publishes average building work and repair costs, to bring you the average cost for loft insulation. 

We've also split these so you can look at the average costs for a terraced, semi-detached and detached house. Do bear in mind that costs will vary, depending on where you live in the country. 

Only logged-in Which? members can view our recommendations in the table below. If you're not yet a member, join Which? to get instant access.

House type Price from Price to
Table notes: Glass mineral wool insulation quilt laid over and between the joists, 270mm thick.

Loft insulation savings

Professionally installed loft insulation for a typical three-bedroom, semi-detached house with gas central heating costs around £400. It will take around two years to pay for itself through the savings you’ll make on your heating bills if you go from no insulation to the recommended amount.

The recommended thickness for loft insulation is 270mm. 

First, check whether you have any insulation at all in your loft and, if you do, how much. 

If you do already have some insulation in your loft but it falls short of the recommended 270mm, then you could make further savings on your energy bills by topping it up.

The tables below show how much it's likely to cost to install loft insulation, how much you'll save per year in money and CO2, and how quickly you’ll make your cash back in bill savings.

They are separated according to whether you’re insulating from scratch or just topping up.  

Of course, it’s cheaper to buy the insulation and fit it yourself. Loft insulation typically costs around £20 for a 100mm-thick roll, designed to cover 8.3sq m.

Some energy suppliers still offer free insulation to householders who fit certain criteria (such as being a member of a vulnerable group or those who receive certain benefits). 

Find out whether any offers are available for you in our guide to free insulation.

Loft or roof insulation?

Lofts are usually cheaper and easier to insulate than roofs. But if your loft has been converted into living space, you'll have to insulate the roof itself. 

See the options available in our guide to roof insulation.

Fitting loft insulation

One reason some people don’t insulate their loft is because they want to use it for storage and the required 270mm of insulation material over the joists would make it impossible to lay boards on top. 

But there is a way around this, so you can have 270mm of insulation and still use your loft for storage:

  • Insulate between the joists with mineral wool and then lay rigid insulation boards on top, with wooden floor boarding on top of that. You can buy insulation board that's been pre-bonded to floor boarding to make the job easier.
  • Alternatively, raise the level of the floor so you can fit enough mineral wool beneath the new floor level. 

Either way, make sure you don’t squash the mineral wool when you fit the boards on top. If you do, this will reduce its insulation properties. 

Improve your home's energy-efficiency rating

The energy performance certificate (EPC) you get when you buy a home shows an overall energy-efficiency rating for your home. This ranges from A (the most energy efficient) to G (the worst). It also gives advice on how to cut carbon emissions and fuel bills by making home improvements.

If you’re selling a property in England or Wales, you must get an EPC. You’ll also need one if you’re a landlord marketing a property for rent. Like buyers, prospective tenants can ask to view it before they sign a rental contract.

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Fitting insulation is an effective way of raising your home’s energy-efficiency rating. If your home isn’t insulated, the EPC will recommend the type and level of insulation required for maximum efficiency.

If you do have loft insulation but it’s deemed to be old, inadequate or inefficient, the EPC may also recommend necessary improvements.

A quick way to cut your energy bills is to use our independent switching site, Which? Switch, to check you're on the cheapest energy deal.

RICS cost calculations

*To arrive at the average prices above, RICS uses cost data from its Building Cost Information Service (BCIS) database, where costs are collated from a variety of sources and analysed. 

Materials costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average. Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. Data copyright RICS 2020, reproduced with permission. Data is current as of October 2020. 

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