The Cost of Doing Nothing: What Single-Glazed Sashes Cost You Each Year

Inaction has a price tag. Single-glazed Victorian or Georgian sash windows leak heat at roughly 5.0 W/m²K — three times the rate of even basic modern double glazing. For a typical London period semi with 12 single-glazed sash windows totalling 25m² of glass, that's around £400-£600 a year of avoidable heating cost. Over a decade, with energy prices likely to climb further, you're looking at a five-figure cost of doing nothing.

The Hidden Costs Beyond the Energy Bill

Heat loss is just the headline number. Add condensation damage (single-glazed windows pool moisture on the inside in winter, accelerating timber rot — typical sash repair runs £400-£800 per window once the rot sets in), sleep disruption (the British Sleep Society estimates a 30% productivity hit from sustained sleep loss), and the gradual devaluation effect on heritage homes that fail energy-performance certification. Total annual cost of doing nothing on a typical London period home: £900-£1,400.

What That Money Could Be Doing Instead

A £7,500 whole-house secondary glazing installation, financed against the £900-£1,400 annual cost of inaction, recovers itself faster than any straight energy-payback calculation suggests. And that's before considering the property-value uplift, the planning protection (no consent risk versus replacement windows), and the simple liveability gain of being able to hear the kettle over the traffic.

How the Numbers Are Built Up

A secondary glazing quote is built from four components: the glass (typically 30-40% of the total), the aluminium frame (15-20%), labour for survey and installation (25-35%), and overheads including delivery, sealants and warranty provision (15-20%). On a £750 single-window quote, that's roughly £270 in glass, £130 in frame, £225 in labour and £125 in overhead.

Use the bespoke project estimator for an installed price tailored to your window count and postcode, or compare against our full 2026 price guide for benchmark figures.

What Real Installations Actually Deliver

Marketing claims for acoustic glazing range from honest to wildly optimistic. The realistic benchmarks from our portfolio: a 10.8mm acoustic laminate system with a 150mm cavity achieves 42-46 dB total reduction (versus 22-26 dB for original single glazing), eliminates condensation on the inner pane within one heating season, and reduces heat loss through the treated window by 60-65%.

For thermal performance specifically, our thermal performance guide sets out the U-values; for acoustic numbers, the noise reduction guide shows real before-and-after measurements from London projects.

Customers consistently describe the post-installation experience in two phrases: 'I didn't realise how loud it was before' and 'the bedroom finally feels separate from the street'. Both are honest reactions to a 20+ dB drop in ambient noise — perceived by the brain as a fourfold reduction in loudness.

The Heritage and Planning Angle

For listed and conservation-area properties — which describes the majority of pre-1939 housing in London and the Home Counties — secondary glazing is the only thermally and acoustically meaningful upgrade that's reliably approvable. Replacement double glazing is refused as a matter of routine for listed buildings; even slimline heritage-style units rarely clear conservation review.

Our listed buildings guide sets out the reasoning conservation officers use, and our secondary glazing vs double glazing for listed buildings explainer breaks down the specific 'reversibility' test that decides which alterations get approved. The short answer: internal, removable, no damage to original fabric — and you're almost always fine.

For projects in particularly sensitive locations — within sight of a Grade I building, in a designated cathedral conservation area, or within a national park — we'll always advise a courtesy notification to the conservation officer before installation, even where strict consent isn't required.

Realistic Project Pricing for 2026

Per-window pricing for a single specification-grade secondary glazing unit in 2026 typically ranges from £550 (small thermal-spec casement) to £1,750 (large bay sash with 10.8mm acoustic laminate), all installation included. Whole-house projects unlock 15-25% discounts versus single-unit pricing thanks to fixed-cost amortisation across multiple windows.

For honest project budgeting, see our whole-house cost guide or run your own figures through the bespoke estimator — both tools include the per-window discount that whole-project quotes attract. Compare against the 2026 London price breakdown for benchmark per-window figures.

All quotes from our network include detailed survey, bespoke manufacture, professional installation, perimeter sealing, manufacturer's glass guarantee, and a 10-year installation warranty. Hidden extras (decorating reinstatement, scaffolding, structural alterations) are rare with secondary glazing because the work is internal and non-structural.

How to Take the Next Step

The standard project timeline runs roughly four weeks from first enquiry to completed installation: 3-5 days to first survey, 5 working days to detailed quote, 2-3 weeks for bespoke manufacture, then 1-2 days on site for fitting. Survey visits are free and non-obligation; quotes are detailed and itemised window by window.

Start with the online estimator for a tailored installed-price figure based on your specific window count and postcode, or browse our case studies to see comparable London and Home Counties projects with before-and-after photographs and measured acoustic data.

For specific local context — including which London areas and Home Counties towns we cover most frequently and the typical project specs in each — see our location pages. Every project we take on includes a manual survey verification before the final quote, so the figure you sign off on is the figure you pay.