Glossary · Controls, energy efficiency and insulation
What is loft insulation?
Loft insulation is a layer of insulating material in the roof space that slows the heat rising out of a home through the ceiling. With less heat lost, the heating needs to work less hard to keep the rooms warm. It is one of the measures government energy-saving schemes pay for.
Key points
- Loft insulation slows heat loss through the roof, so the same heating keeps the rooms warm with less energy.
- In a government evaluation, homes with gas central heating that fitted loft insulation used on average 1.4 kWh a day less gas, a 4.2% reduction.
- Building Regulations guidance sets a target U-value of 0.16 W/(m2.K) when a roof in an existing home is upgraded, with exceptions where headroom or condensation is a problem.
- Insulation may be free or part-funded through the Energy Company Obligation, which closes on 31 December 2026, or the Warm Homes: Local Grant.
How loft insulation works
Heat rises. In a house with an unheated loft, warm air from the rooms below reaches the ceiling, and heat passes through it into the roof space unless something slows it down. Loft insulation is that something. It is a layer of insulating material in the roof space that reduces the rate at which heat escapes.
The result is that the heating has less heat to replace. Government research on the Green Homes Grant looked at homes with gas central heating. It found loft insulation correlated with an average reduction of 1.4 kWh a day in gas use, a 4.2% reduction. Modelled national estimates for loft insulation were lower, at 2.6%.[1]Department for Business, Energy and Industrial Strategy, Evaluation of the Green Homes Grant Voucher Scheme (GHGV): Final outcome and economic evaluation report Real savings depend on how much insulation the loft already has, the size of the roof and how the home is heated.
Where the insulation goes
Building Regulations guidance describes two ways of insulating a roof.[2]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
| Approach | Where the insulation sits | Typical home |
|---|---|---|
| Ceiling level | On the loft floor, above the bedroom ceilings | A house with a cold, unused loft |
| Rafter level | Between or under the rafters, following the slope of the roof | A room in the roof, or a loft that is used |
At ceiling level, the guidance says insulation at the eaves should extend past the wall insulation without losing thickness because of the slope of the roof. It also says loft hatches should be designed so they do not leak air.[2]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
The guidance covers new homes and existing homes. For an existing home, when a roof is being renovated its U-value should be no worse than before and should meet the improved target of 0.16 W/(m2.K), where the threshold is 0.35.[2]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments A lower U-value means less heat lost. If meeting the target would limit headroom, a lesser standard may be appropriate. The guidance also says a lesser standard may be acceptable where the work complies with Part C of the Building Regulations on condensation.[2]Ministry of Housing, Communities and Local Government, Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments
The Warm Homes Plan makes a related point: insulation is described as a cornerstone of energy efficiency when installed with appropriate ventilation.[5]Department for Energy Security and Net Zero, Warm Homes Plan (HTML)
Help paying for it
Two schemes may help. The Energy Company Obligation can help with the cost of insulation work such as loft or cavity wall insulation. It covers owners with an EPC rating of D to G and private tenants with E to G, if they receive certain benefits. The scheme is closing on 31 December 2026.[3]GOV.UK, Help from your energy supplier: the Energy Company Obligation
The Warm Homes: Local Grant is run through local councils in England. The home must be privately owned and have an EPC of D, E, F or G, and the household income must usually be £36,000 a year or less. Councils may suggest improvements such as wall, loft and underfloor insulation.[4]GOV.UK, Apply for the Warm Homes: Local Grant to improve a home Our page on boiler grants has more on current support.
Example
Hannah owns a 1960s semi in Leeds. Her energy performance certificate says the loft has only a thin layer of insulation. She claims one of the qualifying benefits and her home is rated D, so she asks her council about the Warm Homes: Local Grant. The council arranges a survey and fits extra loft insulation at no cost to her. She orders a new EPC so the improvement is on record.
What people get wrong
The most common mistake is to assume more insulation is always the answer, whatever the loft looks like. Insulation is only part of a roof that needs ventilation and care over condensation. Government guidance allows a lesser standard where the full U-value target would cause a condensation problem or reduce headroom.
The second mistake is expecting a guaranteed saving. The evaluation found a 4.2% reduction in gas use on average from loft insulation, while modelled estimates were lower. Treat any promise of a fixed saving with caution, and ask a registered installer to inspect the loft first.
The bottom line
Loft insulation is a layer in the roof space that slows heat loss, so the heating works less hard. Building Regulations guidance sets a target of 0.16 W/(m2.K) for upgraded roofs, with sensible exceptions. Help may be available through the Energy Company Obligation until 31 December 2026 and through the Warm Homes: Local Grant. If you are replacing a boiler at the same time, ask your installer about the central heating side too.
Common questions
How much does loft insulation save?
A government evaluation of the Green Homes Grant found gas-heated homes that installed loft insulation used 1.4 kWh a day less gas on average, a 4.2% reduction. Modelled national estimates were lower, at 2.6%, so savings vary by home.
Can I get loft insulation free?
Possibly. Help with insulation work such as loft insulation is available through the Energy Company Obligation, which closes on 31 December 2026, and the Warm Homes: Local Grant. Both depend on your benefits, income and the home's EPC rating.
What U-value should a loft meet?
When a roof in an existing home is renovated, Approved Document L sets an improved target of 0.16 W/(m2.K). A lesser standard may be acceptable where headroom or condensation risk makes the target impractical.
Does loft insulation affect my EPC rating?
Loft insulation is one of the improvements government schemes pay for, and your EPC may recommend it. Order a new EPC afterwards so the improvement is recorded.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- Department for Business, Energy and Industrial Strategy. Evaluation of the Green Homes Grant Voucher Scheme (GHGV): Final outcome and economic evaluation report. Checked 11 November 2026. ↩
- Ministry of Housing, Communities and Local Government. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments. Checked 11 November 2026. ↩
- GOV.UK. Help from your energy supplier: the Energy Company Obligation. Checked 11 November 2026. ↩
- GOV.UK. Apply for the Warm Homes: Local Grant to improve a home. Checked 11 November 2026. ↩
- Department for Energy Security and Net Zero. Warm Homes Plan (HTML). Checked 11 November 2026. ↩