Will it look like double glazing?

No. Vertical sliding secondary glazing is designed to follow the lines of a traditional sash window, with a discreet slim frame that sits quietly behind the original.

Can I still open my sash windows?

Yes. The secondary units slide vertically just like your sashes, so you retain full access for ventilation and cleaning.

Does it work with curved or arched sashes?

We make every unit to measure and can accommodate most shapes. We confirm the best approach for arched heads at survey.

How much noise will it cut?

With acoustic laminated glass and a wide cavity you can achieve up to 80% perceived noise reduction, ideal for homes on busy roads or near railways.

Is it suitable for listed buildings?

Yes. As a reversible internal system it is widely accepted for listed sash windows and rarely needs listed building consent, though we recommend confirming with your local authority.

Secondary Glazing

Sash Window Secondary Glazing

Vertical sliding secondary glazing made to mirror the look and operation of traditional sash windows. Keep your original box sashes and gain modern warmth and quiet — the discreet choice for period and listed homes across London and Hertfordshire.

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Close-up of a sash window with internal secondary glazing

Built for sash windows

All the character, none of the draughts

Original sash windows are one of the most beautiful features of period homes, but single glazing and gaps around the sashes make them draughty, cold and noisy. Replacing them is expensive, often restricted, and means losing irreplaceable original joinery.

Vertical sliding secondary glazing solves the problem from the inside. A discreet inner sash is fitted to the room side, creating a sealed insulating cavity while perfectly matching the sliding operation of your existing window. You keep your original sashes, and gain a warmer, quieter, more comfortable home.

Why choose it

The benefits of sash secondary glazing

Matches your sash sightlines

Vertical sliding units mirror the meeting rails and proportions of your original box sashes.

Full access retained

Both panels slide so you can open, clean and maintain your original sash windows with ease.

Up to 75% less heat loss

A sealed cavity traps warmth that would otherwise escape through single-glazed sashes.

Quieter rooms

Acoustic glass options cut traffic and street noise dramatically in busy locations.

No damage to originals

Fitted to the room side, the system leaves your historic sashes completely untouched.

Discreet slim frames

Slimline aluminium sections in your choice of colour all but disappear against the window.

Compare your options

Sash window secondary glazing vs sash window replacement

Both improve performance — but the right choice depends on the condition of your sashes, your budget, your heritage protections and your goals.

Factor	Sash Window Secondary Glazing	Sash Window Replacement
Original windows	Retained and protected	Removed and disposed of
Listed building consent	Usually not required	Almost always required
Conservation area consent	Usually not required	Often required
Heat loss reduction	Up to 75%	Up to 80%
Noise reduction	Up to 80% (acoustic glass)	Up to 50%
Installation time	1 day per room	1–2 days per window
Reversibility	Fully reversible	Permanent change
Typical cost per window	£400–£900	£1,200–£3,500+
Lifespan	25+ years	25–40 years
Best for	Heritage homes, listed buildings, conservation areas, period properties with sashes in good condition	Properties where sashes are rotten, beyond repair, or already non-original replacements

The honest answer: if your original sashes are in sound condition, secondary glazing almost always wins on cost, planning, heritage protection and noise reduction. Full replacement makes sense only when the original windows are beyond repair, or where you want to upgrade modern non-original windows.

Transparent pricing

What does secondary glazing cost?

Secondary glazing is priced per window, and the final cost depends on size, system type, glass specification and frame finish. The figures below are typical retail ranges for installed secondary glazing units in London and Hertfordshire — every survey we provide is fixed, written and free of obligation.

System type	Typical size	Standard 4mm glass	Acoustic / thermal glass
Lift-out / fixed panel	Small (up to 0.8m²)	£350–£550	£450–£700
Horizontal sliding	Medium (0.8–1.5m²)	£450–£750	£600–£950
Vertical sliding sash	Medium (0.8–1.5m²)	£550–£900	£700–£1,200
Side-hung casement	Medium (0.8–1.5m²)	£500–£850	£650–£1,100
Bespoke bay / angled	Per bay (3–5 panels)	£1,400–£2,800	£1,900–£3,800

Prices include survey, manufacture and installation. Frame colours, hardware finish and glass specification are all included in your fixed written quote — no hidden extras.

Volume discounts available for whole-house installations (5+ windows). Many of our customers spread payments across a 2–3 month installation programme — ask us about phased works during your survey.

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How it works