Yes, double glazed windows are generally more secure than single glazed windows because they are physically harder to break through. A typical double glazed unit consists of two panes of glass, often at least 4mm thick each, separated by a sealed air gap. That makes it significantly more resistant to forced entry than a single 3-4mm pane (Secured by Design, 2026).
The security advantage depends heavily on the specific glazing type, frame material, and locking hardware. Standard double glazing uses annealed glass, which still shatters relatively easily. For genuine security gains, you need toughened or laminated glass combined with multi-point locking systems. Without these upgrades, the security benefit over a modern single glazed window is marginal.
Laminated glass provides the real security upgrade
The key variable is whether the double glazed unit uses laminated glass. Laminated glass has a tough polyvinyl butyral (PVB) interlayer bonded between two glass sheets, meaning even if the glass cracks, the interlayer holds the pane together. The Building Research Establishment (BRE) states that laminated glass can withstand repeated impacts from tools like hammers for several minutes, whereas standard annealed glass breaks in seconds. For security doors and ground-floor windows, laminated glass is strongly recommended over standard double glazing.
Multi-point locking systems are essential
Even the strongest glass is useless if the window frame can be forced open. Most modern double glazed windows come with multi-point locking systems, which lock the sash into the frame at three or more points. The TrustMark scheme requires that any window fitted under its accredited installer scheme must meet PAS 24 security standards, which includes multi-point locks. A single central lock is far easier to bypass with a crowbar. Always check for a British Standard (BS 7950) or PAS 24 certification on the window.
Frame material and installation matter too
uPVC frames are common but can be vulnerable if not reinforced internally with galvanised steel. Aluminium and timber frames offer greater inherent strength. The FENSA registered installer scheme confirms that proper installation is critical, a poorly fitted window, even with the best glass and locks, creates gaps that can be pried open. Ensure your installer is FENSA or TrustMark registered, and that the window meets the relevant security standard for your area. Double glazing alone is not a security guarantee; the combination of glass type, locking hardware, frame material, and professional installation determines the true level of protection.
A worked example
Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). The Energy Saving Trust estimates that upgrading from single to A-rated double glazing can save a typical semi-detached home around £195 per year on heating bills. With the added security benefit of laminated glass, which meets Secured by Design standards, the payback period for the security-focused upgrade is roughly 21.5 years based on energy savings alone, but the real value lies in the enhanced protection against forced entry. Over a 25-year lifespan, the total energy savings amount to approximately £4,875, effectively covering the upfront cost and delivering long-term peace of mind.
| Item | Figure |
|---|---|
| Upfront cost after grants | £4,200 |
| Yearly savings | £195 |
| Payback period | 21.5 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming that any double glazed window automatically provides strong security. The reality depends on the glass type and locking hardware, not the double glazing itself.
- Believing standard double glazing is security glass Standard annealed glass in double glazed units shatters just as easily as single glazing. For genuine security, you need laminated glass with a PVB interlayer, which holds the pane together even when cracked.
- Ignoring the locking mechanism Even the strongest glass is useless if the window frame can be forced open. A multi-point locking system with at least five locking points is essential to prevent the frame from being pried apart, and without it, a window rated as secure can be compromised in seconds.
- Overlooking frame material and installation A uPVC frame with a steel reinforcement core is far more secure than a standard hollow uPVC frame. Poor installation with weak fixings can void the warranty and leave the window vulnerable, costing you hundreds in potential replacement or repair.
Quick reference
- Laminated glass in a double glazed unit can withstand repeated impacts for several minutes, while standard annealed glass breaks in seconds.
- Multi-point locking systems with at least five locking points are required to meet Secured by Design security standards.
- Homes built before 2002 are eligible for ECO4 funding that can cover part of the cost of upgrading to secure double glazing.
- The payback period for security-focused double glazing is typically 20 to 25 years based on energy savings alone, but the security benefit is immediate.
- Fitting double glazed windows without proper frame reinforcement can void the warranty and reduce security effectiveness by up to 50%.
Frequently Asked Questions
Yes, double glazed windows are more secure because two panes of glass are harder to break than one. Secured by Design confirms that a typical double glazed unit with two 4mm panes is significantly more resistant to forced entry than a single 3-4mm pane.
For genuine security gains, yes. The Building Research Establishment states that laminated glass with a PVB interlayer can withstand repeated hammer impacts for minutes, while standard annealed glass breaks in seconds.
Multi-point locking systems are essential for security. Even strong glass is ineffective if the frame can be forced open, so look for windows with multi-point locks, ideally certified to PAS 24 or Secured by Design standards.
