Yes, double glazed windows are significantly harder to break than single glazed windows. A standard double glazed unit consists of two panes of glass, typically 4mm each, separated by a 12-16mm gap filled with argon gas. That makes it substantially more resistant to impact. The Energy Saving Trust confirms that double glazing reduces heat loss and improves security due to its multi-pane construction (Energy Saving Trust, 2026).
The difficulty of breaking double glazing depends on the glass type used. Standard annealed glass breaks relatively easily, but modern double glazing often uses toughened or laminated glass, which is far harder to shatter. Laminated glass, for example, has a plastic interlayer that holds fragments together even after impact. This applies to most homes fitted with double glazing after 2002, when Building Regulations Part L and Part Q began requiring improved security standards.
Standard double glazing resists blunt force
A typical double glazed unit with two 4mm panes of standard float glass requires considerably more force to break than a single 4mm pane. Research from the Building Research Establishment (BRE) indicates that a double glazed unit is around twice as resistant to impact from a blunt object compared to single glazing (BRE, 2026). The air or gas gap between panes also absorbs energy, meaning a burglar would need repeated, forceful strikes to penetrate both layers. This added resistance is a key reason why double glazing is recommended under Secured by Design standards.
Toughened and laminated glass offer much higher break resistance
If your double glazing uses toughened glass, it is four to five times stronger than standard float glass of the same thickness. Toughened glass must meet British Standard BS EN 12150, which requires it to withstand impact forces that would shatter ordinary glass (GOV.UK Approved Document Q, 2026). Laminated glass, meeting BS EN 14449, is even harder to break because the plastic interlayer prevents the pane from separating. Both types are common in modern double glazed units, particularly in ground-floor windows.
Double glazing is not unbreakable but meets security standards
No window is completely unbreakable, but double glazed windows must meet minimum security standards under Building Regulations Part Q, which came into effect in 2015. This regulation requires that all replacement windows in England and Wales be tested to PAS 24 or equivalent standards. This ensures they resist forced entry for at least three minutes (GOV.UK, 2026). Laminated or toughened glass double glazing typically exceeds this requirement. For maximum security, choose windows with a Secured by Design logo and multi-point locking systems.
A worked example
A typical 1930s semi-detached house in Manchester replacing 10 single-glazed windows with A-rated double glazing costs around £7,500 after the 0% VAT reduction (in place until March 2027). The Energy Saving Trust estimates annual heating savings of £195 for a gas-heated home, rising to £235 with oil heating. Over 25 years, that works out to £4,875 in energy savings alone. The security upgrade is harder to quantify but adds significant peace of mind. If you qualify for ECO4, you may receive a grant covering the full cost. Payback on energy savings alone takes roughly 38 years, but the comfort, condensation reduction, and security improvements make it worthwhile long before then. The Energy Saving Trust confirms that double glazing raises a home’s EPC rating by up to 2 bands.
| Item | Figure |
|---|---|
| Upfront cost after grants | £7,500 |
| Yearly savings | £195 |
| Payback period | 38 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming all double glazed windows offer the same level of security. Here are three critical errors homeowners make.
- Thinking standard glass is unbreakable Standard annealed glass in older double glazing shatters easily with a sharp blow from a brick or hammer. The right choice is laminated or toughened glass, which resists impact far longer and can void your home insurance claim if absent.
- Ignoring the frame quality Many people focus only on the glass and forget the frame. A weak uPVC frame with single-point locking can be prized open in seconds. Modern Part Q compliant windows require multi-point locking systems to meet Building Regulations.
- Believing a broken pane means replacing the whole window Double glazed units can be repaired individually without replacing the entire frame. A single sealed unit costs roughly £150–£300 fitted, far less than a full window replacement. Ignoring this leads to unnecessary expense.
Quick reference
- Double glazed windows are roughly twice as impact-resistant as single glazing according to BRE research.
- Laminated double glazing holds glass fragments together after impact, preventing easy entry.
- To meet Building Regulations Part Q (security), windows fitted after April 2002 must have multi-point locking.
- Replacing a broken sealed unit costs £150–£300, far cheaper than a full window replacement.
- Never assume a window is secure based on the glass alone, check the frame and locking mechanism.
Frequently Asked Questions
Yes. A standard double glazed unit with two 4mm panes is around twice as resistant to blunt force impact as a single 4mm pane, according to the Building Research Establishment (BRE, 2026). The gas-filled gap between panes also absorbs energy, requiring repeated forceful strikes to penetrate.
Laminated glass is the hardest to break. Its plastic interlayer holds shattered fragments together even after impact. That makes it far more difficult to penetrate than standard annealed or even toughened glass.
Yes. Since 2002, UK Building Regulations Part L (energy efficiency) and Part Q (security) have required improved security standards for replacement windows, including tougher glass options in many cases.
