EPC Compliance Hub: Secondary Glazing for London Properties
Everything we have published on improving Energy Performance Certificate ratings with secondary glazing — U-value mechanics, SAP scoring, MEES Band C deadlines, listed-building routes, real London costs and payback modelling. Start with the core reading, then follow the compliance route that matches your property.
The numbers that decide EPC compliance
5.8 → 1.8 W/m²K
Typical window assembly U-value after secondary glazing
5–15 points
Usual SAP/EPC point gain for a whole-property install
Band C by 2030
Expected minimum standard for privately rented homes
Estimate your upgrade cost and target band
Set your property type, window count, glass specification and current EPC score to see an indicative London installation cost and the band your property is likely to reach.
EPC compliance calculator
Estimate the secondary glazing spend and likely EPC band outcome for your London property. Indicative only — a SAP assessor confirms the final rating.
Single-glazed timber sashes — the biggest heat-loss element in most London terraces.
Assembly U-value after installation: 1.8 W/m²K
The number printed on your certificate, out of 100.
£5,280 – £6,750
Around £730 per window, including survey, manufacture, installation and VAT.
Band D → Band D
58 → 66 points (+8 SAP points from the window upgrade alone).
Secondary glazing gets you close, but you would still need roughly 3 more SAP points — typically loft or floor insulation, heating controls, or a low-E glass upgrade.
Projected EPC band shift
Victorian / Edwardian terrace with 10.8mm acoustic laminate across 8 windows — SAP score before and after, against the Band C threshold of 69 points.
- G · 1–20
- F · 21–38
- E · 39–54
- D · 55–68
- C · 69–80
- B · 81–91
- A · 92–100
Bars show the SAP points modelled from the window upgrade only. Loft, floor, heating and lighting measures are assessed separately by your SAP assessor.
Core EPC reading
The four pages that answer most EPC questions: how the rating is calculated, what secondary glazing changes, and who installs it.
- EPC & MEESDoes secondary glazing improve EPC ratings? Landlord guide 2026U-values from 5.8 down to 1.8 W/m²K, typical 5–15 SAP point gains, MEES Band C timelines and the listed-building exemption route.
- ReferenceEPC & thermal efficiency guide for London propertiesHow SAP assessors score windows, which evidence to supply, and how secondary glazing is recorded on the assessment.
- TechnicalThermal performance guide: U-values, air gaps and glass specsThe physics behind the numbers — cavity depth, low-E coatings and how each variable moves the assembly U-value.
- ServiceThermal secondary glazing installation across LondonThe survey-to-install service that delivers the measured U-value improvement your EPC assessment needs.
Compliance routes by property type
Period, listed and conservation-area properties reach Band C differently from modern stock. These guides cover the thermal, damp and consent considerations for each.
- BenefitThermal insulation benefits: cut heat loss by up to 60%Measured heat-loss reductions per window type and the running-cost savings landlords can pass into EPC modelling.
- BenefitCondensation control and damp preventionWhy raising the internal pane temperature removes the surface condensation that drives damp and mould claims.
- BlogCondensation on period windows: why secondary glazing stops the rotThe dew-point mechanics behind winter condensation in single-glazed sashes, and the specification that ends it.
- SolutionListed buildings: compliant thermal upgrades without consent riskReversible, conservation-approved systems that raise EPC scores where replacement windows are refused.
- BlogSecondary glazing for listed buildings: planning & thermal guideListed Building Consent, conservation-officer expectations and the thermal gains achievable within them.
- BlogConservation areas: Article 4 directions and planning rulesBorough-by-borough rules that decide whether your EPC upgrade needs consent at all.
Costing, payback and budgeting
Build the business case before you commission works — capital cost, energy savings and the point at which the upgrade pays for itself.
- ToolROI & payback calculator for thermal upgradesModel capital cost against annual energy savings and portfolio-level payback before you commission works.
- ToolEnergy savings estimator by window countEstimate kWh and £ savings from cutting window U-values across a whole property.
- BlogSecondary glazing cost London 2026 by property typeReal per-window prices for flats, terraces and mansion blocks — the budget line for your compliance plan.
- PricingFixed London secondary glazing pricingPer-window prices by glass specification, opening style and size, inclusive of installation.
EPC compliance questions
Does secondary glazing count towards an EPC rating?
Yes. A SAP assessor records secondary glazing as part of the window assembly. It typically lowers the assembly U-value from around 5.0–5.8 W/m²K to roughly 1.8–2.0 W/m²K, which usually adds 5 to 15 EPC points depending on the window-to-floor-area ratio.
What EPC rating do London landlords need by 2030?
Under the proposed Minimum Energy Efficiency Standards trajectory, privately rented homes are expected to reach EPC Band C. Properties currently in Band D often need only a fabric-first window upgrade to cross the threshold.
Can listed buildings improve their EPC without replacing windows?
Yes. Secondary glazing is fully reversible and is routinely accepted by London conservation officers, so listed and conservation-area properties can improve thermal performance without altering the original sashes.
How long does an EPC-driven secondary glazing project take?
A typical London property is surveyed within a week, manufactured in three to four weeks, and installed in one to two days per property. A re-assessment can then be commissioned immediately.
Do I need planning permission for secondary glazing on a rental property?
Internal secondary glazing rarely requires planning permission. Listed Building Consent may be required for Grade I and Grade II listed properties, and some conservation areas carry Article 4 directions.
Explore our secondary glazing services across London
Browse the full range of secondary glazing services, the specific benefits they deliver, and the London boroughs where we install every week.