Insulation and Glazing

Home Insulation and Glazing: The Full UK Guide

Heat is money. Every unit that leaves through a poorly insulated wall, an uninsulated loft or a single-glazed window is a unit a household has paid for and cannot use. The Energy Saving Trust estimates that an un-insulated dwelling loses a third of all its heat through the walls and a further quarter through the roof¹, and government analysis puts roughly 70% of heat loss from an uninsulated house down to the roof, walls and floors combined². Those are the numbers that make insulation the starting point of almost every sensible home energy plan: no heating system, tariff or battery can compensate for a building that leaks.

The good news is that the fabric of a house is fixable, in a well-understood order, and often with grant support. Loft insulation to the recommended 270 mm saves energy and money³, solid wall insulation can save £150 to £550 a year⁴, and double glazing cuts heat loss through windows by half⁵. This guide walks through where heat is lost, what each insulation and glazing measure does, what the rules require, and how it all connects to grants, Energy Performance Certificates and the wider goal of a home that demands less energy in the first place.

What insulation actually does for a home

Insulation works by slowing the movement of heat from the warm inside of a building to the cold outside. Scottish building standards state the principle directly: "Every building must be designed and constructed in such a way that an insulation envelope is provided which reduces heat loss."⁷ That envelope is the continuous layer of insulating material, glazing and draught-proofed junctions that wraps the heated space, and its quality determines how much of the heat a household pays for stays in the rooms where it is wanted.

The practical effect is twofold. First, less heat escapes, so the heating system runs for less time to hold the same temperature. Northern Ireland's direct government advice is that "installing loft and cavity wall insulation not only lowers the amount of heat escaping, but could also cut your fuel bills"⁸. Second, a better envelope holds warmth between heating cycles, so the home feels more even and comfortable, with fewer cold surfaces at the walls and windows.

It is worth being clear about what insulation does not do. It generates nothing: it does not produce heat, electricity or hot water, and it does not remove a household's dependence on a supplier for the energy it still uses. What it does is cut the amount of that energy needed, which is why insulation sits at the front of the sequence in almost every retrofit plan. A home that needs less energy is cheaper to run on any tariff, easier to heat with any system, and better placed to make use of solar panels, batteries or a heat pump later. The pages on insulation and energy independence and planning a whole-house retrofit develop this in detail.

Where the heat goes: walls, roof, floors, windows and gaps

The headline figures are consistent across official and independent sources. The Energy Saving Trust estimates that an un-insulated dwelling loses a third of all its heat through the walls and a further quarter through the roof¹. Government analysis of heat and buildings puts approximately 70% of heat loss from an uninsulated house through the roof, wall and floors². The Federation of Master Builders adds that 10% of a home's heat escapes through the floors⁶.

Windows are the other major route. Installing double glazing can cut heat loss through windows by half⁵, which tells you two things: windows matter, and even after upgrading they remain one of the weaker points in the envelope. The remaining losses come from air leakage, the draughts around doors, windows, loft hatches and service penetrations that carry warm air straight outside. Our page on airtightness and air leakage covers how these are found and measured.

Two points follow from the numbers. First, no single measure fixes a home: walls, roof, floors, glazing and draughts each carry a share of the loss, so a plan that addresses only one leaves the others untouched. Second, the order matters. The biggest losses through the fabric, the loft and the walls are usually the cheapest per unit of heat saved to remedy, which is the logic behind the fabric-first approach. A thermal imaging survey can show where a particular home is actually losing heat before any money is spent.

Choosing the right insulation for your property type

The right insulation depends on how the house was built. Most homes built after the 1920s have two walls with a cavity between them, which can usually be filled; older homes have solid walls, which need insulating on the inside or the outside; and nearly every home with a loft can take insulation laid on the floor of it.

Loft insulation is the most straightforward measure. The recommended thickness is 270 mm, and topping up an existing layer to that level saves energy and money³. In a typical semi-detached property, 270 mm of loft insulation saves around £230 a year on heating bills⁶. Our loft insulation page covers types and installation, and how thick should loft insulation be answers the common follow-up question.

Cavity wall insulation fills the gap between inner and outer walls, and it is the measure most often required by official standards. Northern Ireland's Decent Homes Standard summary sets out what counts as an effective insulation package: for dwellings with gas or oil programmable heating, cavity wall insulation where there are cavity walls that can be insulated effectively, or loft insulation meeting current building regulations standards where there is loft space; for dwellings with electric storage heaters, LPG or programmable solid fuel central heating, a higher specification is required, with both cavity wall and loft insulation⁹. If you do not know which wall type your home has, cavity wall vs solid wall explains how to tell.

Solid wall insulation is the bigger job. Homes with solid walls can save £150 to £550 a year by installing it⁴, but it is more disruptive and more expensive than cavity fill, and planning rules bite harder, as covered below. The choice between internal and external systems is set out on internal vs external solid wall insulation, and older pre-1919 buildings need particular care, covered in retrofitting traditional buildings.

Floor insulation is the least discussed but still worthwhile: with 10% of a home's heat escaping through the floors, underfloor insulation can make a real difference to bills⁶. Whether a suspended timber floor can be a DIY job is answered on floor insulation DIY.

Glazing: double, triple and secondary options

Windows are a compromise between light, view, ventilation and heat retention, and the glazing chosen determines where that balance sits. Double glazing is the UK default and the measure with the clearest headline figure: installing it can cut heat loss through windows by half⁵. Triple glazing goes further, and the trade-offs are examined in double vs triple glazing. How windows are rated for energy performance is covered in window energy ratings.

Secondary glazing matters for two groups of households: those in older or protected buildings where replacing the original windows is not permitted, and those wanting to improve windows without the cost of full replacement. Official Scottish guidance on traditional buildings states that "secondary glazing can provide an effective way to reduce heat loss without altering original windows, nor significantly reducing light levels or views"⁷. On listed buildings, a local authority's heritage guidance is that "secondary glazing will be acceptable provided its framing is unobtrusive and it does not obscure internal features or interfere with the operation of shutters and windows"¹⁰. Bespoke units can be made to fit arched windows and stained glass, which is why secondary glazing is often the only glazing upgrade open to historic homes; the secondary glazing page covers the systems available.

One funding point is worth knowing: under the ECO4 scheme's measure guidance, glazing support does not include "windows with secondary glazing or external doors with double or secondary glazing, other than double glazed patio doors"¹¹. Households should not assume grant schemes will pay for glazing in the way they pay for loft or cavity insulation.

Draught proofing: the cheapest first step, and its limits

Draught proofing is where most households should start, because it costs least and because unwanted airflow undermines everything else. Sealing the gaps around doors, windows, loft hatches and pipe penetrations stops warm air being pushed out and cold air drawn in. Its importance is reflected in official scheme design: Northern Ireland's Warm Healthy Homes Fund consultation makes loft insulation, cavity wall insulation, draught proofing and ventilation mandatory for all properties unless existing insulation and ventilation meet acceptable standards¹². A scheme designed to tackle fuel poverty treats draught proofing as inseparable from the insulation measures themselves.

The ventilation limit is the crucial caveat. A house needs a controlled supply of fresh air to remove moisture and combustion products, and building regulations require adequate ventilation when loft insulation is installed³. Sealing a home without providing that ventilation trades a heating problem for a condensation and mould problem, which is why the official guidance pairs draught proofing with ventilation rather than treating it as a standalone fix. The home ventilation and draught-proofing pages set out where to seal and, just as importantly, where not to, and condensation, damp and mould covers what happens when it goes wrong.

For listed buildings there is a helpful consent route: Bristol's guidance on alterations to listed buildings notes that "low impact energy saving measures like draft proofing, loft insulation and boiler upgrades that will have minimal impact on the building but big energy saving benefit" can be covered with a Certificate of Lawfulness¹³. That gives owners of protected buildings a way to make the cheapest improvements without a full application.

What the work saves: measure by measure

The savings figures available are per measure, and they vary with house type and how much insulation is already present.

The loft figures differ because they describe different things: the £380 figure is the top of the range across households, while the £230 figure is for a specific thickness in a typical semi-detached property. Both are consistent with the same underlying reality, that the loft is the cheapest place to stop a quarter of a home's heat loss¹.

Solid wall insulation's wide range, £150 to £550 a year⁴, reflects the variety of solid-walled homes: a small mid-terrace and a large detached stone house have very different wall areas and starting heat losses. The cost side of the equation, and payback periods, are covered in detail on insulation and glazing costs and insulation savings and payback.

Two caveats belong alongside any saving figure. First, savings depend on the heating pattern: a home heated barely at all saves less from insulation than one kept warm, because there is less heat being lost to save. Second, savings shrink if the fabric work is done piecemeal, because heat finds the next weakest route. That is the argument for the fabric-first sequence rather than a single measure.

Funding support and tax breaks

Insulation attracts more public support than almost any other home improvement, though the schemes differ across the four nations.

In England, the ECO scheme funds insulation, for example loft, roofs, and walls, for eligible households¹⁴, with local authorities able to refer households under ECO4 Flex¹⁴. In Northern Ireland, households may qualify for financial support towards the cost of loft and cavity wall insulation³. The Northern Ireland Sustainable Energy Programme's scheme list for 2026-27 includes a Help to Insulate scheme offering a grant of 40% towards the cost of cavity wall insulation and/or loft insulation, up to £650 maximum grant per insulation measure and up to £1,000 maximum grant for cavity wall insulation extraction and refill, with a fully funded hot water tank jacket as an additional measure¹⁵. The same programme's Whole House Warmer Homes NI scheme covers solid wall insulation, cavity wall insulation where required, loft insulation, and a new gas or oil central heating system or high heat retention electric storage heaters¹⁵.

VAT relief applies across Great Britain to the installation of energy-saving materials. Insulation on walls, floors, ceilings and lofts qualifies for the lower rate, as does draught stripping, for example insulation fixed around windows and doors to reduce draughts¹⁶. HMRC's manual defines insulation as "materials that are designed and installed because of their insulating qualities", covering walls, floors, ceilings, roofs or lofts, and water tanks, pipes or other plumbing fittings¹⁷. The relief works on the total supply: in HMRC's worked example, an installer charged £400 excluding VAT for insulation material, and the reduced rate of 5% applied to the whole £1,000 job, giving £50 of VAT¹⁸. Grant-funded heating equipment work, including the installation of heating appliances and central heating systems, is also covered¹⁶.

Nation-specific routes are covered in full on insulation grants in England, Scotland, Wales and Northern Ireland, and closed schemes such as the Green Deal are covered separately.

Planning permission and building regulations

The default position is permissive. Planning permission is not normally required for fitting insulation where there is no change in external appearance¹⁹. Internal wall insulation usually needs no planning permission, although both planning and listed building consent may be required in some situations⁷.

External wall insulation is where the rules tighten. Permission may be required if the work impacts the external appearance of the building, and is likely not required if the materials are of a similar appearance to those used in the house's construction²¹. In Wales, the rule is explicit: if the home is in a Conservation Area, a National Park, an Area of Outstanding Natural Beauty or a World Heritage Site, planning permission is required, while outside these areas cladding may be carried out without permission provided the materials are of a similar appearance to those used in the construction of the house²². Cotswold District Council's permitted development checklist records the same split: planning permission not required for a dwelling outside protected areas, and required for a dwelling in an Area of Outstanding Natural Beauty or a conservation area²³. Independent trade guidance adds that if the installation significantly alters the building's external appearance, the property is in a conservation area, or is a listed building, permission may be needed⁶.

Building regulations are a separate question from planning. Floor insulation may need Building Regulation Approval²⁴. Insulating at rafter level changes the picture again: planning permission is required if there is any change to the external appearance or dimensions of the roof²⁴. Loft insulation triggers a ventilation requirement, and householders are advised to check with their local building control office³. The detailed requirements are covered in Building Regulations Part L, Part F ventilation and planning permission for insulation and windows.

EPCs: what the certificate says about your insulation

An Energy Performance Certificate provides an assessment of a home's energy efficiency²⁵. Buildings are rated on a scale from A to G, with A the most efficient²⁶, and each certificate comes with a report setting out cost-effective measures to improve energy efficiency and rating, such as low energy bulbs or upgrading insulation²⁷. The report includes information on measures which could improve the building's efficiency and an indicative cost for each improvement²⁶.

Because EPCs are produced using standard information about buildings, they allow buyers and tenants to compare energy efficiency and likely heating and lighting costs before entering a contract²⁷. Certificates are required whenever a property is built or marketed for sale or rent²⁷, must be provided when a building is advertised for sale or let to a new tenant, and are also required on completion of construction of a new building²⁸. They must be displayed by certain large non-domestic buildings²⁸. Each EPC is valid for 10 years and can be used multiple times during that period²⁷.

Coverage is broad: EPCs cover around 60% of the housing stock in England and around 55% in Wales, based on Census 2021 analysis by the ONS²⁹. The register is active: in the quarter January to March 2026, 460,000 EPCs were lodged in England and Wales, a 2% decrease compared to the same quarter in 2025, of which 416,000 were domestic EPCs in England³⁰. In the 12 months to March 2026, 1,649,000 domestic EPCs were lodged in England, a 4% increase on the previous 12 months³⁰. One privacy point worth knowing: the certificate is publicly available, and some underlying data may be shared for monitoring and compliance of the EPB regulations, with government also able to use some data for research or statistical purposes²⁷.

For a household planning insulation, the EPC report is a free, personalised starting list of measures. Reading it properly, and knowing what the rating does and does not measure, is covered in Energy Performance Certificates and improving your EPC rating.

Revamped EPCs with standalone fabric scores

The current rating has a known weakness that matters to anyone weighing insulation against a heating change. A parliamentary committee reports that EPC ratings are based on the costs of home heating, rather than its carbon footprint, which means cheaper heating scores well regardless of emissions³¹. The same committee notes the perverse result that "replacing a gas boiler with a heat pump can, in fact, reduce a property's EPC score, which can negatively impact the property's value"³¹. A home that insulates well and switches to clean heating can look worse on paper than a gas-heated one.

Reform is under way, furthest advanced in Scotland. The Scottish Government's response to its EPC reform consultations commits to reform EPCs by introducing new ratings, redesigning the certificates, and improvements to the operational infrastructure²⁸. The announced shape of the domestic system is a new EPC rating system for domestic buildings "which will give clearer information on the fabric energy efficiency of a property; the emissions, efficiency and running costs of its heating system; and the cost of energy to run the home to standardised conditions"³². A separate new rating system is planned for non-domestic buildings³².

For householders, the significance is that fabric performance will become visible in its own right, rather than being folded into a single cost-based score. A well-insulated home will show its fabric rating regardless of how it is heated, which removes the penalty that today's rating can impose on low-carbon heating. The MEES rules for rented homes will interact with whatever rating system applies when the changes take effect.

Why insulating before installing a heat pump cuts bills

The connection between insulation and heat pumps is about the price of the fuel. Electricity is more expensive per unit than gas, so a heat pump in a poorly insulated home has to move more heat to hold the same temperature, at a higher running cost per unit of heat delivered. Official guidance is blunt: "If your home is not well-insulated, installing a heat pump may increase your energy bills instead. This is because electricity is more expensive than gas"³³.

This is the clearest practical argument for the fabric-first sequence. Insulation cuts the amount of heat the home needs, which shrinks the heat pump's workload and therefore its running cost. A household planning to move from a gas boiler to a heat pump benefits from doing the loft, wall and floor insulation first, both because the savings begin immediately and because the heat pump can then be sized for the smaller, post-insulation heat demand. What insulation a heat pump actually needs is covered in insulation and heat pumps.

The EPC interaction cuts the other way for now: because ratings are cost-based, a heat pump can reduce a property's score even as it cuts emissions³¹. Households should weigh that known flaw against the reform direction described above, which will separate fabric efficiency from heating costs in the rating.

UK suppliers and their product lines

The UK market for glazing and insulation is served by a mix of national manufacturers and specialist firms. On the glazing side, Anglian sells uPVC windows across a range of frame colours including black, and states that "our uPVC frames are guaranteed for 10 years"³⁴. The company also states that "we are proud to hold the Made in Britain accreditation on all our products. In fact, every part of your window is made i[n the UK]"³⁴, which matters to households weighing supply-chain security alongside thermal performance. Anglian's range is covered in more detail on Anglian windows and doors.

Other makers serve particular niches: Selectaglaze and Granada in secondary glazing for historic and bespoke windows, Internorm and VELFAC in high-performance triple glazing and roof windows, and a range of insulation material producers from Knauf and ROCKWOOL in mineral wool to Kingspan, Celotex and Unilin in rigid boards, Thermafleece in sheep wool and Warmcel in recycled cellulose. Households replacing windows should also be aware that some large glazing firms have failed in recent years: the collapses of Safestyle UK and Everest show why a manufacturer's guarantee is only as strong as the company behind it, and why checking a firm's status before signing matters as much as checking its products.

How insulation supports net zero and energy security

Insulation is the least glamorous part of energy independence and one of the most important. Properly installed insulation, energy efficient windows and doors and reducing draughts can significantly reduce energy use and reduce energy bills²⁵. Unlike a solar panel or a battery, insulation needs no maintenance, no installer visit and no app, and it keeps working through power cuts and price spikes. Every unit of heat a home does not need is a unit that does not have to be bought, generated or stored.

At national scale, the effect is measurable. The National Energy System Operator estimates that improved home insulation could reduce home electricity demand for heat by 11% by 2030³¹. That is demand that does not need to be met by generation, imports or infrastructure, which is why insulation features in every credible pathway to net zero. The parliamentary committee examining heat and buildings policy recommends that retrofit funding commitments continue until at least 2035³¹.

For the individual household, the honest summary is this: insulation reduces dependence on energy suppliers, because it cuts the volume of energy that must be bought from them, but it does not end it. A well-insulated home still needs a heating system, still draws on a supplier or a grid connection, and still depends on the installer and manufacturer behind the work. What it gains is resilience: lower bills on any tariff, a home that stays warm longer when heating fails, and a smaller, cheaper foundation for whatever generation and storage comes next. That fuller picture is developed in insulation, glazing and energy independence.