Insulating your home is a great way to reduce your energy use.

The Energy Saving Trust estimates that around a quarter of the heat in your home can be lost through the roof if it’s not insulated. So adding insulation to your loft or attic can be a quick win – quite a cheap and easy way to save you energy and money.

Man wearing a safety mask rolling out a large roll of mineral wool insulation over the joists in a loft

What is loft insulation and how does it work?

Loft insulation is like a blanket for your house.

The most common type of loft insulation comes in rolls of glass or mineral wool. It’s unrolled like a rug across your loft floor between and over the joists (the horizontal beams in the loft floor). This blanket of material helps to keep the warmth in your home and reduce heat loss through your roof.

You’ll use less energy to heat your home. And saving energy means saving money.

How much could I save with loft insulation?

The Energy Saving Trust estimates that you could save up to £250 a year by adding loft insulation.

If you consider that loft insulation can last for at least 40 years, those savings could really add up.

The estimated cost of insulating your roof and potential savings you could make depend on the size and type of home you live in. Here are the estimated costs and savings if you add the recommended 270mm of mineral wool loft insulation to a loft with no insulation in a gas-heated home:

Detached house Semi-detached house Mid-terrace house Detached bungalow
Savings on fuel bill (per year) £250 £150 £135 £210
Average cost of unsubsidised professional installation £395 £300 £285 £375

Figures are based on fuel prices as of April 2019. Source: Energy Saving Trust

For more details on the costs and benefits of loft and roof insulation, visit the Energy Saving Trust.

Diagram showing a layer of insulation laid on the floor in a cold loft, and insulation applied to the under surface of the roof in warm loft

Will my loft be very cold with loft insulation?

You can choose to have a cold loft or a warm loft:

  • Cold loft: You lay insulation on the floor of your loft so no heat from your home passes into the roof area – the easiest and most common type of installation.
  • Warm loft: You insulate immediately under your sloping roof so your loft space is kept warm – the best option if you’ll use your roof as living space.
Diagram of a cold loft with a layer of insulation laid on the floor of a loft

Can I lay loft insulation myself?

The easiest and cheapest loft insulation is a cold loft installation – rolling out insulating material onto your loft floor between and over the joists.

It’s a fairly easy job to do yourself if:

  • You have a sloping roof (flat roofs are usually insulated from the outside).
  • You can get into your loft easily and safely.
  • The joists in your loft are a regular distance apart.
  • Your loft has no serious damp or condensation.

You should make sure your skin is covered and wear a mask to prevent inhalation because mineral wool can cause irritation.

If you’re not sure about your roof or you’re not a confident DIYer, you should get a professional installer to help.

How thick does loft insulation need to be?

The recommended depth for glass or mineral wool blanket-style insulation is 270mm.

If you already have some insulation in your loft, check how thick it is. If it’s less than 270mm, you can top it up to that level with new insulation. But if you prefer, you can put the old material in bags and dispose of it at your local household waste centre.

Insulation made of other materials, like sheep’s wool or recycled plastic, will have different recommended thicknesses. Consult the manufacturer for advice.

Can I still use my loft to store things with loft insulation?

What if you fit the recommended 270mm of insulation and want to store things in your loft?

If you lay floorboards across the joists, you’ll probably end up squashing the insulation down and it won’t work properly.

There are two common solutions:

  • You can add wood to the joists so that you can fit 270mm of insulation under any floorboards that you lay. If you’re not a dab hand at carpentry, you may need a joiner to help.
  • You can roll out a layer of mineral wool insulation and fit solid insulation boards on the joists with floorboards on top.

Will I have to lag water pipes, tanks and electrical cables in a cold loft?

Your loft will be a lot colder after it’s insulated. So if you have water pipes or a tank in your roof, you should make sure the pipes are lagged and the water tank properly insulated to stop them freezing in winter.

Electrical cables have the opposite problem. It’s best to leave them uncovered if you can so that they don’t get too hot. If you have old wiring or junction boxes that are in bad condition, you should ask an electrician for advice.

Don’t forget to include these extra jobs in your quote if you’re having your insulation installed professionally or under a grant.

More energy saving tips

Loft insulation is not the only way to cut your energy bills. Find out more about energy saving at home, including cavity wall insulation, solid wall insulation, draught proofing and exclusion, and hot water tank insulation.