Secondary Glazing vs Shutters vs Heavy Curtains: What Actually Cuts Noise & Heat

Before committing to secondary glazing, most homeowners try the cheaper alternatives first: heavy thermal curtains, internal plantation shutters, magnetic acrylic kits. These are real products that solve real (small) problems — but the physics of sound and heat transfer through a window are unforgiving, and none of them deliver the kind of step-change that a properly engineered secondary system does.

Heavy Thermal Curtains: What They Actually Do

A floor-length, interlined thermal curtain reduces heat loss through a window by around 25% compared to no curtain at all. That's a real saving on a heating bill. Acoustically, however, soft furnishings absorb mid-range frequencies and do almost nothing for low-frequency traffic or Tube noise — the perceived dB reduction is typically 2-4 dB, which is below the threshold of 'noticeable difference'. Curtains are a comfort upgrade, not a sound solution.

Plantation Shutters and Internal Acrylic Kits

Plantation shutters look beautiful and add maybe 10-15% thermal benefit. Acoustically they're worse than thick curtains because the slats leave continuous gaps. Magnetic acrylic kits perform better — a 4mm acrylic sheet with a magnetic seal can add 15-20 dB of acoustic reduction, and they're cheap. The catches: the acrylic yellows in 2-3 years, the magnetic seal degrades, and they have to be removed every time you open the window. They're a viable rental-property solution and a poor permanent one.

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.