Updated 12 June 2026 · 9 min read
If you live in a period property in London or Hertfordshire, you know the struggle. Those original sash windows are the soul of your home — they're beautiful, full of character, and probably the reason you bought the place. But let's be honest: they can also be a nightmare.
Between the rattling glass, the icy draughts in November, and the constant hum of London traffic, "charming" can quickly turn into "uncomfortable."
At Presswarm Windows, we've been helping homeowners solve this exact problem since 1973. As a family-run business spanning three generations, we've seen every type of window issue imaginable. The most common question we get? "How do I make my home warm and quiet without ruining these windows?"
The answer is almost always secondary glazing. In this guide, we'll walk you through everything you need to know about sash window secondary glazing and bespoke secondary glazing, from why it's the gold standard for heritage homes to how it can slash your energy bills.
What exactly is secondary glazing?
Before we dive into the benefits, let's clear up what we're talking about. Secondary glazing isn't the same as double glazing. Instead of replacing your existing window, we install a slim, discreet second pane of glass on the inside of your room.
Think of it like a high-tech "internal storm window." It creates a sealed cushion of air between the original sash and the new pane, which acts as a powerful barrier against the outside world. Our bespoke secondary glazing is made to measure, so it suits the style and proportions of your existing windows.
1. The "big three" benefits: heat, noise and security
Why do Londoners choose secondary glazing over full replacement? It usually comes down to three major factors.
Stop losing money (and heat)
Original single-glazed sash windows are notorious for heat loss — in fact, you could be losing up to 25% of your home's heat through your windows alone. Our secondary glazing solutions are designed to cut heat loss by up to 75%.
Because we use A-rated materials and our own time-served installers (no subcontractors here), we ensure the fit is perfectly airtight. You'll notice the difference the moment we finish: the room stays warmer for longer, and your boiler doesn't have to work nearly as hard.
Total silence (almost)
If you live near a bus route, a train line, or just a busy London street, you know that traditional sash windows do almost nothing to block noise. Bespoke secondary glazing is the ultimate soundproofing tool. By creating an optimum air gap, we can reduce external noise by up to 80%.
Whether it's sirens, shouting, or the low rumble of traffic, secondary glazing turns it into a whisper. It's the difference between a restless night and a deep sleep.
An extra layer of security
Sash windows are beautiful, but they aren't always the most secure. Adding secondary glazing adds a second physical barrier that is incredibly difficult for an intruder to bypass. Our frames are made-to-measure and securely fitted, giving you that extra peace of mind.
2. Why it's the secret weapon for listed buildings
If you live in a listed building or a conservation area, your options are usually limited. Planning departments are very strict about changing the external appearance of a property.
This is where secondary glazing shines, because it is:
- Installed internally:it doesn't change the look of your house from the street.
- Fully reversible: it can be removed without damaging the original fabric of the building.
- Planning-friendly:in 99% of cases, you don't need planning permission or listed building consent.
At Presswarm, we specialise in heritage solutions. We understand the delicate nature of 100-year-old timber frames and treat your property with the respect it deserves — we treat every home as if it were our own.
3. Discreet style: you won't even know it's there
A common worry is that secondary glazing will look bulky or "cheap." If it's done right, you shouldn't even notice it. That's why many homeowners choose bespoke secondary glazing that is tailored to the exact look and layout of the original sash.
We use ultra-slim aluminium frames that can be powder-coated to match your existing window colours. For sash windows, we use vertical sliders. These are designed so that the meeting rails of the secondary unit line up perfectly with your original sashes — meaning you can still open your windows for ventilation just as easily as before.
4. The Presswarm process: what to expect
We believe in keeping things simple. When you work with us, you aren't dealing with a high-pressure sales team — you're dealing with a local family business that cares about its reputation.
- Friendly advice: we start with a no-obligation conversation, looking at your windows and giving you an honest assessment of what will work best.
- Expert measurement: our own experts take precision measurements. Everything we do is bespoke and made-to-measure, including sash window secondary glazing for period homes.
- Tidy installation:our time-served installers fit your windows efficiently and pride themselves on being tidy — we'll leave your home exactly as we found it (just a lot warmer).
- Guaranteed quality: every installation is FENSA registered, Which? Trusted Trader approved, and comes with a comprehensive insurance-backed guarantee.
Ready to upgrade your home?
Since 1973, Presswarm has been the trusted choice across London and Hertfordshire. Get honest advice and a no-obligation quote from our friendly family team.