You do not need to pay for a professional energy assessment to identify where your home is wasting energy. A systematic DIY audit, working methodically through the building fabric, heating system, hot water and appliances, takes a single afternoon and will produce a prioritised list of improvements. Many of the issues you will find cost less than £50 to fix and pay back within a year or two.

This guide follows the sequence that energy assessors use: start with the biggest heat losses (roof, walls, floor, windows), move to the heating system, then look at hot water, ventilation and appliances. At the end you will have a clear picture of where your money is going and what to do first.

Before You Start: Gather Your Bills

Pull together 12 months of gas and electricity bills or smart meter data. Note your total annual consumption in kWh and your total spend. Ofgem’s typical medium-use household, on the figures it has used since 1 July 2026, uses about 9,500 kWh of gas and 2,500 kWh of electricity a year.1 If you are using substantially more than this, the audit will likely reveal why.

Also locate your property’s EPC (Energy Performance Certificate) on the GOV.UK register. You can download it free, and it shows the current rating, the home’s energy use and typical energy costs, and steps to improve its efficiency.2 Use it as a starting point, not a conclusion.

Step 1: Roof and Loft Insulation

Check: Open the loft hatch and look. Is there insulation? How deep is it? 270 mm is the figure everyone quotes, but it is a rule of thumb rather than a rule. Building Regulations set a U-value for the roof, not a depth: 0.16 W/m²K for an existing roof being renovated and 0.15 W/m²K for a new roof formed in an existing dwelling.3 At the 0.044 W/mK conductivity of ordinary loft roll, 0.16 needs closer to 300 mm, and 270 mm was the number when the target was looser.4 Older loft insulation is often only 100 mm deep or less.

What to look for:

  • No insulation: installing 270 mm in a loft of about 50 m² costs roughly £300–£550 in DIY materials, and the Energy Saving Trust puts a professional install from scratch at around £750.5 It also says an uninsulated home loses around 25% of its heat through the roof.5
  • Thin insulation: topping up to 270 mm in a loft of 30–50 m² costs roughly £120–£350 in DIY materials, or around £600 professionally from a 120 mm starting depth.5 The Energy Saving Trust puts the saving from that top-up at about £17 a year, so the thinner the existing layer, the better the return.5
  • Uninsulated or poorly sealed loft hatch: add draught-strip and 50 mm insulation board to the hatch lid, costs under £20 per hatch; saves £10–£30/year
  • Uninsulated water tanks and pipes in the loft: jacket and pipe lagging cost £10–£30; prevents freezing and reduces standing heat loss

Step 2: Cavity Wall Insulation

Check: Look at the outside of your property. If it was built from the 1920s onwards, it is likely to have cavity walls.6 The brickwork is a quick check: in a cavity wall all the bricks are laid lengthways, while a solid wall shows half-sized brick ends.6 Wall thickness helps too: the Energy Saving Trust says a brick wall between 260 mm and 350 mm thick is likely to be a cavity wall, and a narrower one is probably solid.7 Check whether the cavity has been filled. If you do not know, a local cavity wall insulation installer can usually carry out a borescope check, often free of charge.

Installed prices vary widely: quotes for a semi commonly start around £500, while the Energy Saving Trust puts a typical home in Great Britain at around £2,200.7 Which? puts the saving at £140 a year for a mid-terrace house, £240 for a semi and £410 for a detached house.6 It is one of the highest-return interventions available for cavity-wall properties. The Great British Insulation Scheme closed on 31 March 2026.8 ECO4, which funds insulation for low-income, fuel-poor and vulnerable households through the larger energy suppliers, runs until 31 December 2026, so check whether you qualify before it closes.9

Step 3: Floors

Check: Lift a corner of carpet or look at skirting board gaps. In suspended timber ground floors, there is often a significant air gap between floorboards. Gaps between boards, and between boards and skirting, allow cold air from the sub-floor void to enter the room.

  • Seal gaps with flexible filler or specially sized timber strips
  • Fit draught-proof strips around the perimeter under the skirting
  • Underfloor insulation (between the joists from below, or rigid board above if carrying out works): costs £800–£2,000 for a professional install; the Energy Saving Trust puts the saving at around £55 a year10

Solid concrete ground floors lose heat by conduction but cannot be insulated without raising the floor level by 100–150 mm (rigid insulation + screed), which is a major project only worth doing during a kitchen or bathroom renovation.

Step 4: Windows and Glazing

Check: On a cold day, hold your hand close to each window pane and frame. Single-glazed windows feel noticeably cold; the draught from poorly fitting frames is often detectable. Also check:

  • Are glazed units fogged or showing condensation between panes? The seal has failed, the unit needs replacing, not the whole frame
  • Are opening lights fitting squarely in their frames? A twisted sash or casement that does not close flush loses substantial heat
Window TypeU-value (W/m²K)Indicative Saving vs. Single Glaze
Single glazing5.0–5.8-
Old double glazing (pre-2002)2.8–3.2Some, but less than A-rated
Modern double glazing (A-rated)1.2–1.4About £85/yr (semi-detached)
Triple glazing0.8–1.0A little more than A-rated double

The Energy Saving Trust puts the saving from replacing all the single glazing in a semi-detached home with A-rated double glazing at about £85 a year.11 New replacement windows must reach a U-value of 1.4 W/m²K, or a Window Energy Rating of band B, under Approved Document L.3

Draught-proofing window frames (silicone bead to frame, compression strip to opening lights): costs £10–£30 per window DIY, and counts towards the whole-house draught-proofing saving in Step 5.

Step 5: Draughts: Doors, Floors and Services

Draughts are a significant source of heat loss in older UK homes: the Energy Saving Trust estimates that draught-proofing around windows, floors and doors could save around £55 a year in Great Britain.12 Systematic draught-proofing is one of the cheapest and fastest-payback improvements available.

Checklist:

  • External door frames: fit brush or compression strip draught excluders; £5–£15 per door
  • Letter boxes: fit a brush excluder; £8–£15 each
  • Keyholes: fit a cover plate; £2–£5 each
  • Loft hatch: seal as above
  • Redundant fireplace: fit a chimney balloon or seal the register plate; £15–£30; saving around £45 a year per open chimney, on Energy Saving Trust estimates12
  • Open flue gas fires and back boilers: check whether a pilot light burns continuously, even in summer, as it uses gas all year; ask a Gas Safe engineer whether it can be turned off safely
  • Service penetrations: where pipes and cables enter walls, fill gaps with fire-rated expanding foam

Step 6: Heating System

Check your boiler:

  • Note the installation date and model. Older non-condensing boilers often run at 80% efficiency or less, while a new gas boiler fitted in an existing home must now reach at least 92% efficiency (ErP)3
  • Is the boiler set to heat water on a schedule, or running continuously?
  • Is the flow temperature set correctly? A radiator flow temperature of about 60–65°C lets a condensing boiler condense and run more efficiently; many older installations are set to 80°C, which stops the boiler condensing and wastes energy13

Check the controls:

  • Room thermostat fitted and working? Turning the thermostat down by 1°C could save about 10% on your energy bill, on Energy Saving Trust estimates13
  • Thermostatic radiator valves (TRVs) on all radiators except the one in the room with the room thermostat?3
  • Timer/programmer set correctly for your occupancy pattern?
  • The Energy Saving Trust estimates that installing and using heating controls effectively could save around £100 a year.14
  • Hot water cylinder thermostat set to 60°C (legionella control minimum)?15

Step 7: Appliances and Lighting

Appliances and lighting use less energy than heating in most homes, but the checks are quick:

  • Fridge/freezer: check the door seal (a piece of paper should not pull out easily when the door is shut on it). an old fridge or freezer can use far more electricity than a modern one, so check its energy label before deciding whether to replace it
  • Washing machine: wash at 30°C unless heavily soiled and run full loads only; the Energy Saving Trust puts the saving from 30°C washes and one fewer wash a week at around £26 a year16
  • Lighting: replace any remaining halogen bulbs with LED equivalents; the Energy Saving Trust says swapping the remaining halogen spotlights in a home could save around £45 a year17
  • Standby power: the Energy Saving Trust says remembering to turn appliances off standby could save around £45 a year; use smart plugs or switch off at the socket16

Prioritisation Table

MeasureDIY CostAnnual SavingPayback
Loft insulation top-up£120–£350About £17 from 120 mm; more from a thinner layer7–21 years from 120 mm; shorter from a thin layer
Draught-proofing (doors, letterbox, chimney)£30–£80£45–£100Under 2 years
LED lighting (whole house)£50–£150About £451–3 years
Smart thermostat£150–£250 installedUp to about £100 (shared with other controls)2 years or more
Cavity wall insulation£500–£2,200 (installed)£140–£4101–16 years (shortest for detached houses)
Boiler controls upgrade£200–£600About £1002–6 years

Work from the top of this list downwards. Fabric-first (insulation and draught-proofing) before systems, and systems before renewables.

References (17)

Figures in this note were checked against the sources below on 2 October 2026. Superscript numbers in the text point to them. Every source the site cites, by topic.

  1. 1technicalvery strongOfgem, guidance.RN-JFYAIHOfgem's 2026 decision on typical domestic consumption values. Its Table 1 sets the new medium values, implemented from 1 July 2026, at 9,500 kWh a year for gas and 2,500 kWh for single-rate electricity.
  2. 2technicalvery strongGOV.UK, guidance.RN-L2XXSXAn EPC is required before a property is marketed for sale or rent and is valid for 10 years, rating the property from A at best to G at worst. Exemptions include temporary buildings in use for less than two years, stand-alone buildings under 50 square metres, industrial sites and non-residential agricultural buildings with low energy use, buildings due for demolition, holiday lets used for under four months a year, residential buildings occupied for less than four months a year, places of worship, and listed buildings where compliance would unacceptably alter their character or appearance. A fine applies where an EPC is required and not obtained. Assessors are found through the find an accredited assessor service.
  3. 3technicalvery strongMinistry of Housing, Communities and Local Government.RN-L0FCJXThe in-force U-value tables a DIY insulation or door note must quote, with the exact numbers. Table 4.2, limiting U-values for new fabric elements in existing dwellings, sets roof 0.15, wall 0.18, floor 0.18, swimming pool basin 0.25, window 1.4 or Window Energy Rating Band B minimum, rooflight 2.2, doors with more than 60 per cent of the internal face glazed 1.4 or Doorset Energy Rating Band C minimum, and other doors 1.4 or Doorset Energy Rating Band B minimum. Table 4.3, for existing elements, gives a roof threshold of 0.35 and an improved value of 0.16, which is the figure a loft insulation note needs: paragraph 4.12 says a retained element whose U-value is higher than the column (a) threshold, for example through a loft or garage conversion, should be upgraded to the column (b) value. Paragraph 4.13 allows a lesser upgrade only where the improved value is not technically or functionally feasible or would not achieve a simple payback of 15 years or less. Paragraph 4.8 requires a replacement element to be no worse than the one it replaces as well as meeting Table 4.2. Paragraph 4.10 gives the heritage exception: where character must be maintained, a centre pane U-value of no more than 1.2 or low-emissivity secondary glazing. Note 9 records that the timber window concession of 1.6 or Band C ended on 14 June 2023. The 2021 edition came into force on 15 June 2022; a 2026 edition exists at https://assets.publishing.service.gov.uk/media/69c122a6cfa346b9d4704a55/ADL1_2026.pdf.
  4. 4technicalsupplier figureSuperglass Insulation Ltd, guidance.RN-KXEFPBManufacturer product page for a standard glass mineral wool loft roll. It confirms the 0.044 W/mK declared conductivity used in the note's depth calculation.
  5. 5costfairEnergy Saving Trust, guidance.RN-I69XGOA price, true at 2026-09. Energy Saving Trust's consumer advice page on roof and loft insulation: recommended depths, the difference between insulating at joist level and at rafter level, and indicative costs and savings. EST is a consumer-facing body rather than the authority for the depth, so it is cited for the plain explanation and Approved Document L is cited for the requirement. The page blocks automated fetching, so it is described here from its title and publisher.
  6. 6technicalfairWhich?, guidance.RN-3GCYXSWhich? consumer guide to cavity wall insulation. It states that homes built from 1920 onwards are likely to have cavity walls.
  7. 7technicalfairEnergy Saving Trust, guidance.RN-54KWR6How to identify a cavity wall and what filling it costs. About 33% of all heat lost from an uninsulated home escapes through the walls. Houses built after the 1920s usually have cavity walls; pre 1920 houses are usually solid; houses from the 1990s onwards usually already have wall insulation. Identification: cavity walls show an even stretcher bond with all bricks laid lengthways, solid walls show an alternating pattern with header ends visible; a brick wall 260mm to 350mm thick is likely a cavity wall, narrower is likely solid, stone walls are solid up to about 500mm thick and earth walls run 300mm to over a metre. Typical installed cost around £2,200 in Great Britain and around £1,000 in Northern Ireland, with payback usually five years or less. Unsuitable where the wall is exposed to extreme weather or flooding, in poor condition, at risk of overheating, or where the cavity is narrower than 50mm. External repairs to brickwork, pointing, roofs, gutters and downpipes must be completed first or damp can be trapped. Underfloor grilles, airbricks, wall vents and trickle vents must not be blocked. Post installation damp is chased through the installer, then the Cavity Insulation Guarantee Agency guarantee or an independent insurance backed guarantee.
  8. 8technicalvery strongOfgem.RN-RDOIJRThe scheme, formerly known as ECO+, ran from April 2023 to 31 March 2026 and is now closed. It obliged medium and large energy suppliers to deliver measures reducing energy use in the least energy-efficient homes in Great Britain. Eligibility was homes with an EPC rating of D to G in Council Tax bands A to D in England, or A to E in Scotland and Wales, plus low-income and vulnerable households. Unlike ECO4, which funds whole-house packages, GBIS mostly delivered a single insulation measure per home. This is the page to cite when a note has to say a grant route has closed rather than leave a reader chasing it.
  9. 9technicalvery strongOfgem.RN-FPPUSLECO4 is the fourth phase of the Energy Company Obligation across Great Britain. It applies to measures installed from 1 April 2022 and runs until 31 December 2026 following a nine-month extension; ECO3 closed on 31 March 2022 and ECO4 came into force in July 2022. The scheme places a Home Heating Cost Reduction Obligation on medium and large energy suppliers to promote measures that improve the ability of low-income, fuel-poor and vulnerable households to heat their homes, funding insulation and heating upgrades for both homeowners and tenants. Ofgem also lists the Great British Insulation Scheme as a separate obligation on this page.
  10. 10costfairEnergy Saving Trust, guidance.RN-9FOXX3A price, true at 2026-09. Floor insulation performance targets, savings and cost. Target U-values: 0.25 W/m2K or lower in England, Wales and Northern Ireland, and 0.18 W/m2K or lower in Scotland, achieved with at least 70mm of high performance rigid foam or around 150mm of mineral wool depending on floor type and construction. Replacing 50% or more of a floor triggers the duty to insulate to those standards even if insulation was not in the original plan. Insulating under the ground floor boards saves about £55 a year in Great Britain and £70 in Northern Ireland, rising to up to £85 in GB and £120 in NI for a detached house, and cuts about 180kg of carbon in GB and 260kg in NI. A typical suspended timber floor installation costs £1,400 to £2,500 by house type, and solid floor insulation costs considerably more. Suspended timber floors are typical of homes built between the 1850s and the 1950s, identified by airbricks below floor level; solid concrete ground floors are common from the 1950s onwards, and floors built since the early 2000s are usually already insulated.
  11. 11costfairEnergy Saving Trust, guidance.RN-SS1KSRA price, true at 2026-09. Glazing performance, life and price. A set of A-rated windows for a semi detached house typically costs around £4,800. Replacing single glazing with A-rated double glazing across a semi detached house saves £85 a year in Great Britain and £140 in Northern Ireland, and cuts 290kg of CO2 a year in GB and 550kg in NI. Triple glazing costs around 20% more than double glazing, justified mainly in cold or noisy locations. Good quality, correctly installed and maintained double glazed units last 20 to 35 years and can go well beyond 35 years where the seals and gaskets are checked and the units kept clean and ventilated.
  12. 12costfairEnergy Saving Trust, guidance.RN-FRD5VYA price, true at 2026-09. Draught proofing costs and savings. Professional draught proofing of windows and doors across a whole house costs around £250, with DIY cheaper. A terracotta chimney pot cap starts at around £150 and also keeps out moisture and birds. Savings: around £55 a year in Great Britain and £80 in Northern Ireland from draught proofing windows, floors and doors, plus around £45 in GB and £60 in NI from draught proofing an unused open chimney. A draught free home is comfortable at a lower setting, and turning a thermostat down from 22 degrees C to 21 degrees C saves £120 a year in GB and £80 in NI. Warns that further draught proofing of an already well sealed home raises the risk of poor indoor air quality.
  13. 13technicalfairWhich?, guidance.RN-QF3WMZWhich? heating advice. It recommends a 60–65°C flow temperature so a condensing boiler condenses, and cites Nesta research on turning combi flow temperature down from 80°C.
  14. 14costfairEnergy Saving Trust, guidance.RN-1B36CGA price, true at 2026-09. Energy Saving Trust's consumer advice on thermostats and heating controls: room thermostats, programmers, thermostatic radiator valves and zoning, with indicative savings. Useful as the plain-English explanation of what each control does; the compliance requirement for controls on a new or replacement system sits in Approved Document L, not here. The page blocks automated fetching, so it is described from its title and publisher.
  15. 15technicalvery strongHealth and Safety Executive, guidance.RN-RLI5PMHSE guidance on legionella control in hot and cold water systems. It states that hot water should be stored at 60°C or above to kill legionella.
  16. 16costfairEnergy Saving Trust.RN-HYQVG1A price, true at 2026-09. The Energy Saving Trust's quick tips put the saving from washing at 30°C and running the machine once less a week at £26 a year in Great Britain.
  17. 17costfairEnergy Saving Trust.RN-F75XBGA price, true at 2026-09. The Energy Saving Trust's lighting guide says replacing the remaining halogen spotlights in a home with LED bulbs saves about £45 a year in Great Britain.

  1. Review of typical domestic consumption values: decision, Ofgem, accessed 30 September 2026. ofgem.gov.uk

  2. Buying or selling your home: Energy Performance Certificates, GOV.UK, accessed 30 September 2026. gov.uk

  3. Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments, Ministry of Housing, Communities and Local Government, accessed 14 September 2026. assets.publishing.service.gov.uk

  4. Multi-Roll 44, Superglass Insulation Ltd, accessed 30 September 2026. superglass.co.uk

  5. Roof and loft insulation, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  6. Cavity wall insulation costs and savings, Which?, accessed 30 September 2026. which.co.uk

  7. Cavity wall insulation, Energy Saving Trust, accessed 2 October 2026. energysavingtrust.org.uk

  8. Great British Insulation Scheme, Ofgem, accessed 7 September 2026. ofgem.gov.uk

  9. Energy Company Obligation (ECO), Ofgem, accessed 30 September 2026. ofgem.gov.uk

  10. Floor insulation, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  11. Energy efficient windows and doors, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  12. Draught-proofing, Energy Saving Trust, accessed 30 September 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  13. Top tips to reduce your heating bills, Which?, accessed 30 September 2026. which.co.uk

  14. Thermostats and heating controls, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  15. Hot and cold water systems: things to consider, Health and Safety Executive, accessed 30 September 2026. hse.gov.uk

  16. Quick tips to save energy at home from the experts, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk

  17. Lighting, Energy Saving Trust, accessed 2 October 2026. Priced at 2026-09 and left there. energysavingtrust.org.uk