Secondary Glazing Installation Guide

For UK homeowners living in conservation areas or listed buildings, secondary glazing is often the only viable option to reduce heat loss and block external noise. It is significantly more affordable than full window replacement and causes minimal disruption to your home's fabric.

What Does the Work Involve?

• Initial Survey: A specialist measures each window aperture precisely, checking for "out of square" frames and handle protrusions.
• Design Selection: Choosing between fixed, horizontal sliding, vertical sliding, or hinged units to match your existing window operation.
• Surface Preparation: Cleaning the existing primary window and inner reveal to ensure no dust is trapped between the panes.
• Frame Installation: Fixing the new aluminium or timber sub-frame to the window reveal or the face of the primary window.
• Glazing Fitting: Inserting the glass panels—often using toughened or acoustic glass—into the new internal tracks.
• Sealing and Finishing: Applying specialist perimeter sealants to eliminate draughts and ensure an airtight finish.

Typical Costs

Prices for secondary glazing vary based on the frame material, glass type, and the complexity of the opening mechanism. Professional installation typically accounts for 20-30% of the total project cost.

Costs are influenced by the size of the windows and the "reveal" depth. Bespoke shapes, such as arched or circular windows, can increase prices by 50% or more due to specialist manufacturing requirements.

How Long Does It Take?

• Site Survey: 1–2 hours depending on the number of windows.
• Manufacturing Lead Time: 3–6 weeks for custom-made units.
• Installation (Single Window): 1–3 hours per unit.
• Full House Installation: 1–2 days for an average semi-detached home.

DIY or Professional?

While basic magnetic or film-based kits are available for DIY enthusiasts, they lack the durability and airtightness of professional systems. Professional installation is highly recommended for permanent aluminium systems, especially for large sash windows or when acoustic performance is the priority.

Professional installers ensure the "air gap" is optimised—usually between 100mm and 200mm—to achieve maximum sound reduction, which is difficult to manage with DIY kits.

Choosing the Right Tradesperson

• Check Accreditations: Look for installers registered with FENSA or CERTASS, or members of the Glass and Glazing Federation (GGF).
• Acoustic Expertise: If soundproofing is your goal, ask for "weighted sound reduction" (Rw) data for their specific glass types.
• Portfolio: Ask to see photos of previous work in similar properties, particularly if you live in a period home.
• Questions to Ask:
  • Will the secondary glazing obstruct my original window handles or stays?
  • What thickness of glass do you recommend for my specific noise/heat issues?
  • How do you manage ventilation to prevent condensation?
  • Is there a warranty on the powder coating and the moving parts?

UK Regulations

• Listed Buildings: While usually permitted, you should notify your Local Planning Authority (LPA) as some may have specific requirements regarding frame visibility.
• Building Regs Part L: Secondary glazing is a recognised method for improving thermal performance in existing dwellings.
• Fire Safety (Part B): Units must not obstruct designated fire escape windows (Egress windows).
• Safety Glass (Part K): Glass in "critical locations" (low level or in doors) must be toughened or laminated to BS EN 12600 standards.

Common Problems

• Condensation: If the primary window is not perfectly sealed or the secondary unit lacks a small vent, moisture can become trapped between the panes.
• Access Issues: Poorly planned installations can make it impossible to clean the back of the original glass or operate the original catches.
• Acoustic Bridges: If the secondary frame touches the primary frame directly without an insulation break, sound vibrations will pass straight through.
• Cheap Materials: Plastic or thin acrylic sheets can yellow over time and scratch easily compared to glass.

Frequently Asked Questions

Is secondary glazing better than double glazing for noise?

Yes, often it is. Because secondary glazing allows for a much larger air gap (up to 200mm) than standard double glazing (16-20mm), it is significantly more effective at blocking low-frequency traffic noise.

Will it stop condensation on my windows?

It can reduce it by keeping the inner glass warmer, but it won't "cure" it if there is high humidity in the room. Proper balanced ventilation is required to ensure moisture doesn't get trapped between the two windows.

Can I still open my windows for fresh air?

Yes, provided you choose a sliding or hinged system. These are designed to align with your existing window's opening mechanism so you can still access the handles and open both panes.

How much will I save on my heating bills?

Secondary glazing can reduce heat loss through windows by up to 60%. For a typical UK home, this can translate to a saving of £100–£150 per year, though the primary benefit is often improved comfort and fewer draughts.

Does it look ugly from the outside?

If installed correctly, secondary glazing is virtually invisible from the street. The frames are designed to be slimline and are usually colour-matched to your existing window frames or masonry.