The short answer
A well-fitted roof window with a working lock and laminated glass is difficult to force from outside, and its height off the ground helps. The weak points are usually not the glass itself but easy access from a flat roof, porch or garage below, a handle left unlocked, and old hardware. Check those three things before you spend money on anything else.
Why height helps and where it stops helping
A roof window sits in a sloping surface with no sill to stand on and no ledge to grip, and from outside it is often out of reach. That alone puts it lower on an opportunist's list than a back door or a ground-floor casement.
What matters is how someone could physically get to the glass. A roof window above a single-storey rear extension, a lean-to, a garage or a porch roof can be reached by anyone who can climb onto that lower roof, particularly if a water butt, a wall or a fence gives them a first step. The same goes for a window above scaffolding that has been left up between stages of a job. Walk around the outside of your house and ask what a person could stand on to get within arm's reach of each opening. If the answer is anything at all, treat that window as a ground-floor window for security purposes.
A window in the main slope of a two-storey house, with only a drop to the garden below, is in a better position. Even so, a ladder left out in the garden changes that, so put ladders away.
Locks, handles and what the hardware does
Most roof windows close with a handle at the top or bottom of the sash that pulls the sash against its seal and engages a catch. Many models also have a ventilation position that holds the window a few centimetres open, which is useful for airing a room and a gap in your defences while you are out. Some can be fitted with a key-operated lock or a fixed restrictor that stops the sash opening beyond a narrow gap, and some are supplied with one. What is on offer depends on the maker and the model, so the window's own documentation is the place to look.
On an older window, ask whether the hinge, handle and catch are still doing their job. Seals that have perished, a handle that no longer pulls the sash tight and a catch bent out of line all make a window easier to lever. Our answer on looking after a roof window covers the upkeep side, and a handle that sticks or wobbles gets noted whenever we are up there.
A lock on a bedroom window
If a roof window is also the way out of a loft bedroom, think before locking it with a key. Approved Document B sets out what an escape window must offer where it serves a room: an unobstructed openable area of at least 0.33 m2, at least 450 mm high and 450 mm wide, with the bottom of the openable area no more than 1100 mm above the floor, and capable of staying open without being held. A lock that needs a key hunted for in the dark undermines the point of that window. If the window is an escape route, keep any key beside it and ask your building control body before you change anything.
Laminated glass and why it breaks differently
Glass choice matters because it decides what happens when something hits the window. Toughened glass, when it fails, breaks into small blunt pieces. Laminated glass has a clear plastic interlayer sandwiched between two sheets, so when it is struck it cracks but tends to stay in one piece, held by the interlayer. An intruder has to keep working at it, and the noise and delay count against them. The same property protects you if something falls onto the window from above.
Many roof windows come with a laminated inner pane, though the specification varies between models and years. Check the datasheet or the mark printed on the edge of the pane, or ask us to note it at the survey. Settle the glass when you choose the window, because upgrading afterwards usually means replacing the whole sash or unit.
Where the window sits in the room and the roof
Placement is part of security. A window on a landing or in a spare room is one nobody notices if the sash is left on the vent, while one over a desk is seen daily and its handle gets checked without thinking.
On the outside, think about sight lines. A window on the front slope is overlooked by the road, while one on a back slope facing a field or a hidden garden is not. Planting, trellis, drainpipes and wall-mounted fittings near the eaves can all act as steps. Planning a new opening? Our answer on whether skylights make rooms too hot covers summer heat, a placement question that often points the same way.
Where a window is going in above a flat extension, we raise the access issue at the survey. A flat roof you can walk across is one an intruder can walk across.
Insurance, replacement costs and what to do next
Some home policies attach conditions to locks. Your insurer can tell you whether a standard roof window catch satisfies yours; we do not advise on insurance.
Replacing a tired window with a lockable, laminated one is a bigger step. MyBuilder's 2026 guide puts fitting a standard roof window at about £350 to £600 for labour, with scaffold near £500 where needed; those are national ranges, not our prices. After the survey, our written quote covers scaffold, window, flashings and making good, with photographs of your roof.
Our 10-year workmanship guarantee is in writing. The sensible order is access first, then the catch, then the glass, and a new window last. For help with the wider roof window and skylight work we do, ring 01453 933613 or send the enquiry form with the rooms and what sits below each window.