Energy Improvements in Flats and Apartments

Living in a flat changes what is possible. You may own your flat, but the walls, roof and ground floor belong partly to the building, and the building belongs to everyone in it. The realistic improvements are the ones inside your front door: floor insulation if you sit over cold space, internal wall insulation if your block has solid walls, better glazing and draughtproofing, and in some cases a heat pump on the wall or balcony. The ones that need the freeholder, the management company or every leaseholder to agree, such as external wall insulation across the facade or solar panels on a shared roof, are slower but not impossible.

The numbers are worth having. Floor insulation saves around £55 a year in a semi-detached property in Great Britain, and solid wall insulation around £280 a year for a semi-detached house in GB, £330 in Northern Ireland¹. A single air source heat pump is permitted on a block of flats without planning permission, provided the outdoor unit is no bigger than 0.6 cubic metres including its housing². Grants differ sharply by nation: up to £15,000 for an owner occupier in England under the Warm Homes: Local Grant, up to £7,500 in Scotland for a clean heating system³.

EPC guidance and which upgrades qualify in flats

An Energy Performance Certificate explains how energy efficient a building is and how it could be improved⁷. With each EPC comes a report that sets out the cost effective measures the owner can take to improve energy efficiency and the energy rating, such as low energy bulbs or upgrading insulation⁸. The certificate also records an estimate of the total useful floor area of the building⁹. For a flat owner, that report is the practical starting point: it lists what the assessor judged worth doing in this specific home, not a generic menu.

The rating itself carries weight. A home rated EPC C or above is generally regarded as having an adequate level of energy efficiency¹⁰. For landlords the standard is a floor, not a target: a property let with an EPC rating of F or G must be improved to a minimum of E, or an exemption registered¹¹. An EPC provides an assessment of your home's energy efficiency¹², and the improvements it names, insulation, glazing, heating controls, low energy lighting, are the measures that count for both the rating and your bills.

Two things matter for flats specifically. First, party walls: under the Home Energy Model used in the current Approved Documents, a solid party wall means no heat loss, and an unfilled cavity with effective sealing in a concrete frame building containing flats also means no heat loss, so the surfaces that matter are the ones facing outside¹³. Second, the EPC reform due in the second half of 2027 will replace the single efficiency score with four headline metrics, so a rating read today will not look the same forever. Insulation, glazing and draught reduction reduce your energy bills whatever the certificate says¹².

Floor types and their insulation options

Ground floor flats, and any flat sitting above an unheated cellar, garage or open air, lose heat straight down. The construction determines the treatment. Suspended timber floors can either be insulated from below, or from above¹⁴. Beam and block and solid concrete floors are insulated differently again, typically with a rigid board layer, and the ECO4 scheme recognises the distinction formally with separate scores for the two variants, underfloor insulation (UFI) and solid floor insulation (SFI)¹⁵.

The eligibility rule is about position, not construction. Floor insulation can only be installed to a floor that is either in contact with the ground, above an unheated space such as a cellar, or suspended and in contact with the outside air¹⁵. A first floor flat with a heated flat beneath it does not qualify, for reasons the next section sets out.

Building regulations apply once you start. The energy efficiency requirements cover the erection, extension of, and any work to or in connection with a building that is a roofed construction having walls, uses energy to condition the indoor climate, and is not in an excluded category¹⁶. In practical terms, replacing or insulating a floor or ceiling is not a free-for-all: where more than 25 per cent of a ceiling below a cold loft space or flat roof is being replaced, building regulations apply¹⁷. Insulation for walls, floors, ceilings, roofs or lofts is also one of the energy-saving materials that has enjoyed reduced VAT treatment under the long-standing legislation¹⁸, which affects what you pay.

In Scotland, floor work can come through area-based schemes: the Energy Efficient Scotland Area Based Scheme funds external wall insulation, park home insulation, internal wall insulation, cavity wall insulation, loft insulation, underfloor insulation and room-in-roof insulation¹⁹. These are delivered by local authorities, so a flat owner's route in is often through the council rather than a private contractor.

Independent data on floor insulation payback

Energy Saving Trust's figures, published 3 August 2026, are the independent benchmark. Floor insulation could save around £55 a year in a semi-detached property in GB and £70 in NI. For detached homes, the savings could be £85 and £120 in NI¹. A flat sits between those cases: a mid-floor flat with heated space on every side has almost no floor to insulate, while a ground floor flat over earth or a cellar behaves much closer to the semi-detached figure.

Loft insulation is included in the same guidance for completeness: topping up from 120mm to at least 270mm saves around £17 each year on bills in GB and £20 in NI¹. That is relevant to flats only where the flat includes the roof space, a top floor maisonette or a conversion with a private loft, since a shared roof belongs to the block.

Costs are installer-quoted and depend on access. Insulating a suspended floor from below, where a cellar or underfloor void allows it, is a different job from lifting floorboards inside a furnished flat, and the quotes will reflect that. No reliable published price range for flat floor insulation exists in the sources behind this page, so treat any figure an installer gives as a quote for your floor, not a market price. The saving side is firmer: the £55 figure is for a whole semi-detached property, so a single ground floor flat should expect a proportion of it.

Why a heated room beneath blocks floor insulation

This is the rule that ends many flat insulation plans before they start. A floor cannot be treated if there is a room below it that contains a heat emitter such as a radiator¹⁵. The logic is straightforward: if the flat beneath yours is heated, your floor is already sitting on a warm surface, and insulating it saves almost nothing while adding cost and losing ceiling height.

So the test for any flat is what is underneath. A ground floor flat over the ground, over an unheated cellar, or suspended over outside air qualifies. A first floor flat over a heated living room does not, and neither does a flat over a heated communal corridor if that corridor is a conditioned space. The eligible locations are exactly the three: in contact with the ground, above an unheated space such as a cellar, or suspended and in contact with the outside air¹⁵.

There is a related constraint on thickness. Where insulation work would reduce the internal floor area of a room by more than 5%, a lesser thermal performance may be appropriate, provided the element achieves the best practicable thermal performance²⁰. The same 5% floor area reduction limit appears in the Welsh consultation version of Approved Document L²⁰. In a small flat, where every square metre counts and floor to ceiling height is often already tight, this is not a technicality: it is the difference between a compliant job and one that cannot meet the full standard.

Inside or outside: choosing solid wall insulation

Many flats, particularly pre-war conversions and blocks built before cavity walls became standard, have solid walls. A wall may be suitable to receive external wall insulation if it is of solid construction or has fully filled and insulated cavities²⁰. For a flat, the choice between internal and external is not really yours alone: external wall insulation wraps the whole block, so it is a building decision, while internal wall insulation happens inside your rooms.

Internal wall insulation has a clear advantage in planning terms: planning permission is usually not required, although both planning and listed building consent may be required in some situations¹⁴. External wall insulation on a house is treated as permitted development in many cases, but on a block of flats the facade is shared, and the freeholder or management company will need to lead. The Planning Portal's guidance on solid wall insulation notes the benefits that follow: this will help create a more even temperature in your home, help prevent condensation on the walls and ceilings and can also reduce the amount of heat building up inside your home during summer hot spells²¹.

Where a solid wall is upgraded by the installation of insulation, it must meet the minimum energy efficiency values set out in the Approved Documents. However, if such an upgrade is not technically or functionally feasible, the element should be upgraded to the best standard which can be achieved within a simple payback of no greater than 15 years²². Historic and traditional dwellings carry an extra condition: their energy efficiency should be improved only if doing so will not cause long-term deterioration of the building's fabric or fittings²³. For a flat in a listed or traditionally built block, that condition governs everything.

There are exemptions from the private rented minimum standard where wall insulation would harm the building: cavity wall insulation, external wall insulation or internal wall insulation for external walls can be discounted where written expert advice indicates the measure is not appropriate due to its potential negative impact on the fabric or structure of the property²⁴.

Warmer walls and roughly £280 saved annually

The independent figure is Energy Saving Trust's: a semi-detached house could save around £280 a year in GB and £330 in NI after installing solid wall insulation¹. A flat with fewer exposed walls saves less than a semi-detached house, because the party walls shared with neighbours are not losing heat in the first place, and in concrete frame buildings containing flats an unfilled cavity with effective sealing means no heat loss at all¹³.

The savings are only part of the value. Solid wall insulation changes how a room feels: more even temperatures, less condensation on walls and ceilings, and less heat building up during hot spells²¹. In a flat, where cross-ventilation is often poor and summer overheating is a known problem, that last benefit matters as much as the winter saving.

Costs are not settled. The figures behind this page show unresolved differences: around £12,000 for external wall insulation on a typical three-bed semi-detached home against around £7,500 for internal wall insulation²², and separate estimates of around £15,000 and around £12,000 for solid wall insulation work²³, each from independent guidance dated 2026. Because these differ, no single price can be stated with confidence, and a flat owner should get quotes for their own rooms. What can be said is that internal wall insulation is generally quoted below external for the same property, and that internal work in a flat is priced by your exposed wall area, not the block's.

On guarantees: in Northern Ireland, if you are awarded grant aid for cavity wall or solid wall insulation, the installer you employ must be able to provide a minimum 25-year guarantee for the work²⁵. That is a scheme rule, not a market guarantee, but it sets a reasonable expectation for warranty terms anywhere in the UK.

Heat pump rules for flats: 0.6 cubic metres, one unit only

A block of flats can host an air source heat pump without planning permission, but within tight limits. Permitted development rights allow for air source heat pumps to be installed on detached houses or blocks of flats without the need for a planning application²⁶. The rights cover the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage, including on a building within that curtilage²⁷.

The size limit is the headline: the volume of the air source heat pump's outdoor compressor unit, including housing, must not exceed 1.5 cubic metres on a house, but for a block of flats the limit is 0.6 cubic metres²⁷. The legislation itself says that in the case of the installation of an air source heat pump on, or within the curtilage of, a block of flats, the unit must not exceed 0.6 cubic metres². That is a small unit, and it rules out many of the larger models sold for houses.

The count limit is just as firm. Detached houses can install up to two heat pumps. A non-detached house or a block of flats can install only one unit⁵. The Welsh Government's summary of responses to its permitted development consultation confirms that under existing permitted development rights a single heat pump on a block of flats is currently permitted, and this will be retained³⁰. So one flat in a block can use the right; a second flat cannot, and a block wanting heat pumps for several flats needs planning permission for the extras.

There is one absolute bar: development is not permitted if the dwellinghouse or the block of flats is a listed building². In that case a planning application is needed regardless of size or count.

For flats, the air-to-air variant is worth knowing about. An air-to-water air source heat pump transfers heat drawn from surrounding air to water in a wet central heating system, which suits flats with radiators. Air-to-air systems blow warm (and in summer, cool) air directly, but under ECO4 rules an air-to-air system is not considered to be a renewable system, which affects grant eligibility.

Where to put a heat pump and the 42 decibel limit

Noise is the constraint that most often decides a flat heat pump. The industry standard is set by the Microgeneration Certification Scheme: a 42 decibel target external noise threshold, measured 1 metre from a neighbouring habitable room window⁶. Energy Saving Trust puts the same rule plainly: you can't normally install a heat pump unless the noise level is 42dB or less when stood one metre from a neighbouring window³¹. The scheme is designed to result in an indoor noise level of the neighbouring home of around 30 decibels, which accords with everyday expectations of a quiet room⁶.

If an installation cannot meet the MCS standard and needs planning permission instead, the bar is stricter. Central Bedfordshire's guidance states that noise levels emitted from the air source heat pump must not exceed 37 dB LAeq at any time, as measured on the boundary of the site with any neighbouring residential property²⁹. In a dense block, where the boundary may be a metre or two from the next window, siting is everything.

Practical points follow from the rules. The unit needs airflow around it, so a recess or enclosed balcony that traps air is a poor site even if it passes the noise test. Vibration through a wall bracket can matter as much as fan noise in a block of flats, and the measured threshold applies to the neighbour's window, not your own living room. Ground source heat pumps avoid the problem entirely: they are quieter and offer increased energy efficiency, though they need ground works a flat owner in a block cannot usually undertake²⁸.

Funding and costs in England, Scotland, Wales and Northern Ireland

Grant support for the measures in this page differs by nation, and the differences are large.

The Warm Homes: Local Grant covers a wide list of improvements relevant to flats: cavity wall insulation, external wall insulation, internal wall insulation, loft insulation, room in roof insulation, flat roof insulation, under floor insulation, draughtproofing, hot water cylinder insulation, low energy lighting, heating controls, solar PV, battery storage, double or triple glazing (only recommended in rare cases) and energy efficient doors (only recommended in rare cases)⁴. Note the caution on glazing: it is funded, but only in rare cases, because replacement windows are rarely the most cost effective measure.

In Scotland, the Area Based Scheme route adds locally delivered insulation work¹⁹. In Northern Ireland, the Decent Homes Standard consultation sets out the insulation packages expected for different heating types: a dwelling with gas or oil programmable heating needs cavity wall insulation where cavities can be insulated effectively, or loft insulation meeting current NI Building Regulations standards where there is loft space, and a dwelling with electric storage heaters, LPG or programmable solid fuel central heating requires a higher specification of insulation³³.

Heat pump costs themselves are not settled: independent estimates differ, with figures of £7,000 to £13,000 for a typical installation³⁴ against around £14,000 according to Energy Saving Trust estimates³⁵, and separate estimates of £7,000 to £10,000³⁶. Because these differ, no single figure can be given, and a flat's smaller heat demand may sit at the lower end of any range. Treat any number as a quote for your flat, not a market price.

Changes a leaseholder may make without permission

The dividing line is ownership and consent. Inside the flat, an owner can usually act: internal wall insulation usually needs no planning permission¹⁴, floor insulation within the eligible locations is internal work, and draughtproofing, low energy lighting and heating controls are squarely the leaseholder's own. Anything touching the structure or the facade, external wall insulation, the roof, communal heating, the block's walls, needs the freeholder or management company, and the rules are set out in detail on leasehold consent for energy work.

Floor insulation is one of the improvements a flat or leasehold home may still be able to benefit from, and it comes in two forms: underfloor insulation (UFI) for homes with a suspended floor, and solid floor insulation (SFI) where the floor is solid. It sits in the highest indicative capital cost tier, at under £7,500, so it is rarely a small job, but improving floor insulation also supports a better Energy Performance Certificate (EPC) rating, which is beneficial for compliance. More on this is on asking a landlord for energy improvements.

Cost and evidence are what a landlord or freeholder will ask about first. Floor insulation falls in the highest indicative capital cost tier, at under £7,500, and there are separate scores for both variants, underfloor insulation (UFI) and solid floor insulation (SFI), so the right one depends on the construction of the floor. Because improving floor insulation also supports a better Energy Performance Certificate (EPC) rating, it is a measure that helps a property towards compliance rather than away from it, which matters when consent is being negotiated in a leasehold block.

Where a landlord has made all the relevant energy efficiency improvements, or there are none that can be made, and the property remains below EPC E, an exemption can be registered²⁴. Improving floor insulation also supports a better Energy Performance Certificate (EPC) rating, beneficial for compliance, and it exists in two variants, underfloor insulation (UFI) and solid floor insulation (SFI), with separate scores for each. In Northern Ireland, private landlords on the Affordable Warmth Scheme must pay 50% of the total cost of the energy efficiency measures to improve their property³².

How far a flat can go on its own energy

A flat can reduce its dependence on imported heat, but not its dependence on the building. Floor insulation, internal wall insulation, glazing upgrades and draughtproofing all cut the gas or electricity needed to hold a temperature, and every kilowatt-hour saved is energy the flat no longer buys. A heat pump shifts the flat off gas entirely, and most current models work fine down to about -25°C, while some advanced cold-climate heat pumps work in temperatures as low as -35°C³¹, so cold snaps do not create the fallback problem that boiler breakdowns do.

The dependence that remains is structural. The facade, the roof, the communal heating system and the ground under the block all belong to others, and the one-unit permitted development rule means a block of flats gets a single heat pump as of right, no more⁵. Solar panels on a shared flat roof are a block decision, not a flat decision. Even the EPC that governs the legal minimums is being reformed, with four headline metrics replacing the single score from the second half of 2027.

So the honest position is this: a flat owner can act alone on the surfaces inside the front door, can act with neighbours on the building, and cannot act at all on some things. The measures in this page, taken in the order the EPC report suggests, are the ones that deliver. For the wider picture of what renters and flat households can control, see energy independence when you rent or live in a flat, and for the building safety rules that apply to work in taller blocks, energy work in high-rise flats.