Energy Improvements in Flats and Apartments

A flat is the home type where the boundary between what a household controls and what the building controls is sharpest. Inside the demise, a flat owner or occupier can usually reach the floor over an unheated space, the internal face of an external solid wall, draughtproofing, controls, lighting and the ventilation of individual rooms. Outside it, anything touching the roof, the external walls, the risers, the communal heating system or the land around the block belongs to the freeholder, the management company or the whole block acting together.

The figures that shape the decision are narrow and specific. Floor insulation in a flat is only permitted under scheme rules where the floor is in contact with the ground, sits above an unheated space such as a cellar, or is suspended in contact with outside air, and a floor cannot be treated at all if the room below contains a heat emitter such as a radiator¹. An air source heat pump serving a flat falls under permitted development only if the outdoor compressor unit, including any housing, does not exceed 0.6 cubic metres, against 1.5 cubic metres for a house, and only one unit is permitted on a block of flats². Noise is held to a 42 decibel target measured one metre from a neighbouring habitable room window⁴.

Grants exist and are sizeable. In England, the Warm Homes: Local Grant covers 100% of the cost up to £15,000 for an owner occupier or a private landlord's first property, and 50% up to £7,500 for a landlord's second and subsequent properties⁵. In Scotland, Home Energy Scotland offers up to £7,500 for energy efficiency measures such as insulation and a further amount of up to £7,500 for clean heating systems such as heat pumps⁶. What no grant supplies is consent, and in a block consent is usually the binding constraint.

What counts as an energy improvement in a flat, and what the EPC tells you

An Energy Performance Certificate provides an assessment of a home's energy efficiency and explains how efficient a building is and how it could be improved¹⁰. Each certificate comes with a report setting out cost effective measures to improve the rating, from low energy bulbs to upgrading insulation¹². That recommendation list is the practical starting point for a flat, but it is generated from a model of the dwelling and does not know what the lease says or whether the roof above is shared.

Ratings matter beyond curiosity. A home rated EPC C or above is generally regarded as having an adequate level of energy efficiency¹³. Flats tend to start from a better position than houses: in Scotland, mean energy efficiency ratings by dwelling type in 2024 were 65.6 for detached and 66.1 for semi-detached properties, against 71.6 for tenements and 69.6 for other flats¹⁴. Commons Library analysis likewise places purpose-built flats among the higher-rated property types¹⁵. Two reasons sit behind this. A mid-floor flat has less external surface per unit of floor area, and party walls in many constructions are modelled as losing no heat at all: under the Home Energy Model, a solid party wall is treated as no heat loss, as is a fully filled cavity with effective sealing, while an unfilled cavity with no effective edge sealing does lose heat¹⁶.

The practical consequence is that the remaining improvements in a flat are often the awkward ones. Where the easy wins of loft and cavity insulation are absent or belong to the block, what is left inside the demise is floor insulation where the floor is exposed, internal wall insulation on external solid walls, glazing, draughtproofing, controls and heating replacement. A useful companion read is the page on what energy improvements could improve my EPC in a flat.

Insulating the floor: suspended timber, beam and block or solid concrete

Floor insulation splits into two recognised measure types, underfloor insulation and solid floor insulation, scored separately under scheme rules¹. Which applies depends on construction. A suspended timber floor has a void beneath it, and suspended floors can be insulated either from below, where access to the void exists, or from above by lifting the boards¹⁷. Beam and block and solid concrete floors are treated as solid floor insulation, which means insulation laid over the existing slab with a new finish above, raising the floor level in the process.

In a flat, the question is not usually which method but whether the floor qualifies at all. Floor insulation can only be installed to a floor that is in contact with the ground, above an unheated space such as a cellar, or suspended and in contact with the outside air¹. That description fits a ground-floor flat over a void or an undercroft, a flat above a communal bin store or car park, and a converted basement. It does not fit a mid-floor flat over another dwelling.

Raising the floor level inside a flat has knock-on effects that rarely appear in a savings figure: door heights, thresholds, skirtings, pipe runs and the head height of a room that may already be modest. Where insulation is fitted from above in an occupied flat, the room has to be cleared. Where it is fitted from below in a shared undercroft, the work is in common parts and the freeholder's position becomes relevant before any installer sets foot there.

Related building control triggers sit nearby. Where more than 25 per cent of a ceiling below a cold loft space or a flat roof is being replaced, building regulations are triggered¹⁸. Top-floor flats with a flat roof above should treat that threshold as live, because ceiling work that looks cosmetic can cross it.

Floor insulation costs and savings: what the independent figures show

Published savings for floor insulation are modest and are quoted by house type rather than flat type. The Energy Saving Trust puts the saving at around £55 a year in a semi-detached property in Great Britain and £70 in Northern Ireland, rising to £85 for detached homes in Great Britain and £120 in Northern Ireland¹⁹. Those are August 2026 figures. The Northern Ireland numbers run higher throughout, reflecting different fuel costs and stock.

All four rows are Energy Saving Trust estimates published on 3 August 2026¹⁹.

A flat's exposed floor area is smaller than a detached house's, so a flat should expect to sit at or below the lower end of these ranges rather than above them. The honest reading is that floor insulation in a flat is a comfort measure first and a bill measure second: it removes the cold surface and the draught through the boards, and the cash return follows some way behind. Prices for the work itself are installer-quoted and vary with access, so no published range is given here.

Materials themselves carry a defined VAT treatment: insulation for walls, floors, ceilings, roofs or lofts, or for water tanks, pipes or other plumbing fittings, is listed among energy-saving materials in the relevant schedule²⁰. That status applies to supply and installation as set out in that legislation, not to a householder buying boards alone for a DIY job.

The rule that stops floor insulation: a heated room below

The single clearest constraint on insulating a flat's floor is stated plainly in the ECO4 delivery guidance.

The logic is that insulating between two heated spaces does not reduce heat loss from the building: it only transfers warmth between neighbours, and in a block that means one household paying to keep another household's heat out. For the great majority of flats above the ground floor, this rule ends the conversation about floor insulation entirely. It also means that a mid-floor flat's realistic fabric work is confined to the external wall, the glazing and the seals.

Two further limits from the building regulations bear on what can be done inside a flat. Where meeting the full standard for an insulated wall would reduce the internal floor area of the bounded room by more than 5%, a lesser thermal performance may be appropriate provided the wall achieves the best practicable thermal performance¹⁶. In a small flat, where a 100mm internal insulation board across two external walls can eat a measurable share of a bedroom, that clause is not theoretical.

The energy efficiency requirements apply to 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 category²². Flats fall squarely within that. One practical exception worth noting for anyone with a glazed addition: the exemption for a conservatory or porch depends on the heating system of the dwelling not being extended into it²³.

Solid wall insulation: internal boards or external treatment

Where a flat's external walls have no cavity, two routes exist. Guidance for Northern Ireland describes them as a decorative, weatherproof insulating treatment on the outside of the walls, or ready made insulation boards added internally²⁴. A wall may be suitable to receive external wall insulation if it is of solid construction or has fully filled and insulated cavities²¹.

For a flat, the division is decisive. External wall insulation changes the appearance of the whole building and is applied to a surface a leaseholder almost never owns. It is a block-level project, requiring the freeholder, the other leaseholders and usually a section of the service charge. Internal wall insulation stays inside the demise. Planning permission is usually not required for internal insulation, although both planning and listed building consent may be required in some situations¹⁷. Separately, in planning terms the installation of solid wall insulation constitutes an improvement rather than an enlargement or extension to the house²⁵.

Where the work is done, the standard is not optional. 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; if such an upgrade is not technically or functionally feasible, the element should be upgraded to the best standard achievable within a simple payback of no greater than 15 years²⁶. And where a wall measure is genuinely inappropriate for a property, exemption guidance recognises that cavity, external or internal wall insulation is not a relevant measure where written expert advice indicates it would have a potential negative impact on the fabric or structure of the property²⁷.

Solid wall insulation savings: around £280 a year, and warmer surfaces

For a semi-detached house, the Energy Saving Trust estimates solid wall insulation saves around £280 a year in Great Britain and £330 in Northern Ireland¹⁹. A flat with fewer exposed walls will save less in absolute terms, and a corner or top-floor flat with two or three exposed elevations more than a mid-terrace equivalent. There is no separately published per-flat figure.

The non-financial effects are set out by the Planning Portal: solid wall insulation helps create a more even temperature in the home, helps prevent condensation on the walls and ceilings, and can also reduce the amount of heat building up inside during summer hot spells²⁸. The condensation point is the one that matters most in flats, where cold external wall surfaces behind furniture are a standard site for mould growth. Warming the internal surface removes the condition; it does not remove the moisture, which still needs a working extract path. That relationship is set out in detail on ventilation in flats and apartments.

Guarantee terms give a sense of expected life. Under the Northern Ireland Affordable Warmth Scheme, where grant aid is awarded for cavity or solid wall insulation the installer employed must be able to provide a minimum 25-year guarantee for the work⁹.

Air source heat pumps in a block: the 0.6 cubic metre limit and the one-unit rule

Permitted development rights cover the installation, alteration or replacement of an air source heat pump on a house or block of flats, or within the curtilage of either, including on a building within that curtilage². The size limit is where flats and houses part company. The outdoor compressor unit, including any housing, must not exceed 1.5 cubic metres on a house or 0.6 cubic metres for a block of flats². The 0.6 cubic metre figure for a block of flats is set out in the legislation itself²⁹.

Permitted development does not apply where the dwellinghouse or the block of flats is a listed building²⁹. Councils put the position bluntly: permitted development rules for air source heat pumps are more restricted for flats and shared buildings, and planning permission is more likely to be required³⁰. Welsh consultation material confirms that under existing permitted development rights a single heat pump on a block of flats is currently permitted and that this will be retained, while the external volume for other cases is proposed to increase from 1 cubic metre to 1.5 cubic metres³¹.

The implication for a household is stark. A block of twenty flats cannot give each flat its own permitted-development heat pump. One unit is the whole block's allowance, which pushes individual retrofit either towards a planning application, towards a block-wide communal scheme, or towards an alternative such as an air-to-air system or direct electric heating. Note that an air-to-water system transfers heat drawn from surrounding air to water in a wet central heating system, while an air-to-air system is not considered to be a renewable system in ECO4³², which affects funding eligibility. The trade-offs are compared on electric boiler vs heat pump for flats and the wider rules on permitted development by home type.

Cold weather performance is rarely the deciding factor. Most current models are reported to work down to about minus 25 degrees Celsius, while some advanced cold-climate heat pumps work in temperatures as low as minus 35 degrees Celsius⁸.

Noise, siting and the 42 decibel threshold

Noise levels for an air source heat pump on its own must stay at or below 42 decibels measured one metre away from any habitable room⁴. Certification material describes the same figure as a 42 decibel target external noise threshold measured one metre from a neighbouring habitable room window, designed to result in an indoor noise level in the neighbouring home of around 30 decibels³³. Independent guidance states the condition as a practical bar: a heat pump cannot normally be installed unless the noise level is 42dB or less when stood one metre from a neighbouring window⁸. One council states it as a UK legal noise limit of 42 decibels³⁴.

Where a unit exceeds the certification standards and planning permission is therefore required, a stricter condition may be applied: noise emitted from the air source heat pump not exceeding 37 dB LAeq at any time, measured on the boundary of the site with any neighbouring residential property³⁵. Ground source heat pumps are described as quieter and as offering increased energy efficiency³⁶, though they are seldom feasible for a single flat.

In a block, the assessment is unusually demanding because habitable room windows are close on several sides, sometimes above and below the proposed unit as well as beside it. A courtyard or a light well reflects sound. A balcony mounting places the unit within a metre or two of the flat's own bedroom window and the neighbour's. This, more than capacity or cost, is what defeats many individual flat heat pump proposals.

Costs and funding across the four nations

Funding is national and household-specific rather than flat-specific. The table sets out the headline amounts.

The Scottish maximum of £7,500 for energy efficiency measures is confirmed in the 2025 progress report³⁸, and the Commons Library describes the combination as up to £7,500 for energy-efficiency improvements such as insulation and up to £7,500 for clean heating systems such as heat pumps³⁹.

What the English scheme will fund is broad and includes measures that apply directly 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, and double or triple glazing and energy efficient doors, the last two only recommended in rare cases⁵. Local delivery lists also name air source heat pumps and high retention storage heaters among the low carbon heating options, alongside solar PV, solar thermal and battery storage⁴⁰. In Scotland, area-based schemes fund external wall insulation, internal wall insulation, cavity wall insulation, loft insulation, underfloor insulation and room-in-roof insulation⁴¹.

Two gaps deserve naming. First, grant lists include solar PV, but a flat's roof is almost never within the leaseholder's demise, so the measure that is funded may not be one the household can consent to. Second, funding does not cover the professional fees, structural surveys or freeholder's costs a block-level project generates.

What a flat owner can and cannot change alone

Inside the demise, the realistic solo measures are internal wall insulation on external walls, floor insulation where the floor qualifies, draughtproofing, glazing where the lease permits, lighting, controls and in-flat heating appliances. Outside it, roofs, external walls, communal heating plant, risers, meters and the ground around the block are shared. For traditional and historic buildings there is an additional constraint: energy efficiency should be improved only if doing so will not cause long-term deterioration of the building's fabric or fittings²³.

Tenants sit under a further layer. In England and Wales, properties let with an EPC rating of F or G must be improved to a minimum rating of E, or an exemption registered where applicable⁴². A landlord will never be made to spend more than £3,500 on the improvements⁴³, and a recommended measure is only a relevant energy efficiency improvement where third-party funding covers the full cost, or the cost is £3,500 or less inclusive of VAT, or a combination of landlord self-funding and third-party funding totals £3,500 or less inclusive of VAT⁴⁴. Landlords must not unreasonably refuse tenant requests for energy efficiency improvements funded at no cost to the landlord, for example through grants or third-party funding⁴⁴. An exemption applies where a landlord has made all the relevant energy efficiency improvements for the property, or there are none that can be made, and the property remains below EPC E²⁷.

Consent cuts both ways. A landlord may claim an exemption where, within the preceding five years, they have been unable to raise the property's energy performance indicator to the minimum level because a tenant refused consent, or because third party consent was refused or granted subject to a condition with which the landlord cannot reasonably comply⁴⁵. In a block, that third party is typically the freeholder. Government has consulted on increasing the number of exemptions available and amending current ones⁴⁶. More detail sits on asking a landlord for energy improvements and renting and home energy.

In Scotland, work on tenements is expected to be phased: at phase 1, individual flats within tenement buildings would be required to meet new energy efficiency standards where feasible and cost-effective, alongside the rest of the housing stock, with some tenement types not initially asked to replace fossil fuel systems until more suitable options are offered⁴⁷. Scottish permitted development also separately covers the installation, alteration or replacement of a flue forming part of a combined heat and power system on a dwellinghouse or building containing a flat⁴⁸, which is relevant where a block runs communal plant.

What this means for a flat's energy independence

A flat that completes every measure available inside its own walls remains connected to more than a house does. It stays on the grid, and usually on a supplier's tariff, because a flat rarely has roof rights for solar PV or space for storage that the freeholder will accept. It stays dependent on the block for anything structural, for the external wall, and for the single permitted heat pump that twenty households cannot each have. Where there is communal heating, the household depends on the block's plant, its operator and its charging method, not on a boiler it owns.

What a flat can genuinely win is a warmer, tighter, better-ventilated envelope with lower demand, and control over its own heating appliance and its own timing. That is a real reduction in exposure to price, and it is achievable without anyone's permission in many cases. It is not self-supply. The realistic ambition is set out further on energy independence when you rent or live in a flat and across the guide to home energy by home type and household.