Secondary vs. Double Glazing: Cost & Performance Compared

It’s the classic renovation dilemma: do you rip out your old windows and start fresh with Double Glazing, or do you keep the originals and install Secondary Glazing behind them?

At KJM, we install both, so we can give you an unbiased answer. The “right” choice depends entirely on why you are upgrading. Are you freezing? Are you kept awake by traffic? Or do you just want lower bills? Let’s compare them head-to-head.

1. The Difference at a Glance

Double Glazing is a replacement product. We remove your old timber or steel frames entirely and install a new unit (usually uPVC, Aluminium, or Timber) containing two panes of glass separated by a gas-filled spacer bar.

Secondary Glazing is an addition. Your original window stays exactly where it is. We install a slimline aluminium frame with a single pane of glass on the room side of the existing window.

2. Head-to-Head: The 4 Rounds

The massive air gap in secondary glazing is what makes it superior for noise reduction.

3. The Elephant in the Room: Usability

This is where we have to be honest. While secondary glazing wins on noise and heritage, it has a practical drawback: Convenience.

• Opening the Window: To get fresh air, you have to open the secondary unit first, and then open the primary window. It’s a two-step process.
• Cleaning: You now have four glass surfaces to clean instead of two. While secondary panels slide or lift out for access, it is more work than a standard window.

Double Glazing is simpler. One handle, one movement, easy friction hinges for cleaning. If ease of use is your #1 priority, replacement windows win.

4. Cost & Payback

Because secondary glazing involves less material (single pane vs. sealed unit) and much less labour (no ripping out frames, no waste disposal, no plastering), it is significantly cheaper upfront.

5. Frequently Asked Questions