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Secondary Glazing: The Ultimate Solution for Heritage Homes & Listed Buildings
Secondary Glazing: The Ultimate Solution for Heritage Homes & Listed Buildings
📌 At a Glance: Secondary Glazing
- The Purpose: The only high-performance option for Grade II Listed or Conservation properties where window replacement is banned.
- The Power: Can reduce noise by up to 80% (better than double glazing) due to the large air cavity.
- The Efficiency: Reduces heat loss by creating a sealed thermal buffer, eliminating draughts from old sash windows.
Secondary glazing is often misunderstood. Many homeowners view it as a “compromise”—an ugly, clunky extra pane of glass you only install if the Council forces you to.
The reality is very different. Modern, slimline aluminium secondary glazing is a high-performance engineering solution. In fact, for acoustic insulation, it creates a barrier that even the best triple glazing struggles to beat.
Table of Contents
1. Why Choose Secondary Glazing?
If you live in a modern house, you replace the windows. But if you live in a period property in Hampshire, that might not be legal—or desirable.
Secondary glazing involves fitting a discreet, slimline aluminium frame with its own glass on the inside of your existing window reveal. This leaves your original timber sash or crittall windows completely untouched.
2. The Science: The 100mm Gap
The secret to secondary glazing isn’t the glass; it’s the gap. Unlike a double-glazed unit (which has a narrow 16-20mm cavity), secondary glazing allows for a massive air space between the old window and the new pane.
Optimising the Air Gap
Ideal Gap
20mm – 50mm
The Effect
Stops convection currents transferring cold air. Acts like a “double skin” for the house.
Result
Eliminates draughts and halves heat loss.
Ideal Gap
100mm – 150mm
The Effect
Decouples the two panes. The large air volume dampens sound vibrations.
Result
Reduces noise by up to 54dB (80% reduction).
3. Heritage & Listed Buildings
For Grade I and Grade II listed buildings, changing the external fabric is usually a criminal offence without Listed Building Consent. Local Conservation Officers in Hampshire protect the “historic character” of the glass and timber.
⚠️ The “Reversible” Rule
Conservation Officers generally approve Secondary Glazing because it is considered “Reversible.” It can be removed in the future without damaging the historic fabric of the building. However, you should always check with your local planning officer before proceeding.
4. Styles & Operation
Modern units are designed to align with your existing window sightlines (the bars), making them virtually invisible from the outside.
- Vertical Sliders: Perfect for Sash Windows. The panes slide up and down, counter-balanced by springs, matching the operation of your original window.
- Horizontal Sliders: Ideal for Casement or Crittall windows.
- Lift-Out Units: For windows you rarely open but need to clean behind.
📚 Related Guides
- Noise: Detailed Guide to Soundproofing
- Regulations: U-Values Explained
- Products: View our Secondary Glazing Range
5. Frequently Asked Questions
Yes, it is very effective. By creating an internal seal, it prevents the warm, moist air inside your home from hitting the cold single-glazed outer window. This stops the water droplets forming on the glass.
Absolutely. We design the secondary system to match your primary window. If you have a sliding sash, we fit a sliding secondary unit. You simply slide the inner pane up, then the outer pane up, to get fresh air.
If installed with a 100mm+ air gap and acoustic glass, secondary glazing can reduce noise by over 50 decibels. To put that in perspective, standard double glazing reduces noise by about 30-35 decibels. It is the difference between hearing a car drive by and silence.
Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
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