The short answer
A roof window on a high slope is a hard target, and most designs have a lock or a restrictor that holds the sash shut. The weak spots are windows reachable from an extension, a garage or a flat roof. Laminated glass, a key-operated lock and a check of the fixings make them much harder to force. Ask your insurer whether it sets a standard for roof windows.
Where roof windows are weak, and where they are not
A roof window high on a pitched slope takes a ladder, time and noise to reach, and from outside there is nothing to grip. The risk changes with the building. A window on an extension roof that starts at head height, a window above a garage with a shed beside it, or one on a ground-floor flat roof can be reached with little effort.
Walk round the house, glance up at each slope and ask one thing: could someone stand on something and put a hand on the sash? If the answer is no, security is mostly a matter of keeping the standard lock engaged. If the answer is yes, those windows are worth strengthening.
Flat rooflights and lanterns deserve the same thought. Our page on flat rooflights explains why a ground-reachable one is a different matter to a pitched window on a second storey.
Laminated glass: the biggest single upgrade
Ordinary toughened glass is hard to break with a blow, but when it goes it falls apart into small pieces and leaves an opening. Laminated glass is made of two sheets fused to a plastic interlayer. If it is struck, it cracks but stays in the frame, so an intruder cannot just push through.
Many roof window makers offer laminated inner or outer panes as a standard option, and the same choice also helps in other ways. It holds together if a branch or a hailstone hits it, and it softens rain noise, as our page on roof window rain noise explains.
The cost is a heavier unit and a higher price. When you plan a new window, decide on the glass at the start, because it cannot be changed later without replacing the pane or the sash.
Locks, restrictors and ventilation positions
Almost every roof window has a handle that catches a latch. Many also offer a key-operated lock, either built in or fitted as an accessory, and some include a ventilation position that lets a few centimetres of air in while the sash stays held. A restrictor stops the sash opening further than a set angle.
Choose a window with a lock that engages automatically when the sash closes, or make a habit of turning the key. The best lock is useless if the key hangs on a nail by the window, so keep it out of sight from outside, and out of children's reach.
For escape windows in loft rooms, a lock must not trap a person inside. Approved Document B sets the openable size of an escape window and says it should stay open without being held, so a lock that needs a key hunt in the dark is a poor fit there. Check the arrangement with your building control body. We discuss this under loft conversion windows as well.
Fixings, frames and the flashing
A window is only as strong as the way it is fixed. A frame screwed to the rafters or trimmers at all the manufacturer's points resists being pulled or levered out. One that has been fixed with a few screws, or whose timbers have rotted, does not.
That is one reason to keep an eye on the surrounding woodwork. A leak that has softened a rafter or a trimmer weakens the grip of the fixings. If the frame has moved, the sash may no longer sit squarely on its seal, which can leave a gap.
Where a window is being fitted or replaced, the opening has to be trimmed to take the frame, and we cover that on the page about trimming rafters. A properly trimmed opening gives the frame firm timber to bite into on all sides.
Overheating, open windows and the habit of leaving them ajar
Security and ventilation compete. A roof window left open on a warm night is open to anyone who can reach it. The ventilation position that holds the sash a little way open, together with a restrictor, offers some air without a wide gap.
Top-floor rooms heat up under a roof in summer, which tempts people to leave windows wide open. Blinds, external shading and a cross-flow of air reduce that pressure, and our page on skylight overheating explains the options. Fewer sleepless nights mean fewer open windows.
Electric and solar models can be set to close automatically when it rains, but they do not make a window safer from intruders in themselves. Treat a powered window as you would any other and use the lock.
Insurance, cost and what we can do
Some home insurance policies set conditions for windows that can be reached from the ground or from a roof, for example a lock of a certain type. Read your policy wording or ask your insurer before you decide. Requirements differ between policies.
Costs depend on the model, the glass and the access. As a typical national guide, MyBuilder's roof window price guide, updated in August 2026, puts fitting at £350 to £600 for standard jobs including labour, and a scaffold at around £500. Our page on roof window cost lists the other factors, and the skylights hub links the rest.
If you want an existing window assessed, send us a couple of pictures taken indoors and out, or ask for a survey. We report on the lock, the glass and the frame, and a written quote follows, with photos of the actual roof. Sometimes all it needs is a better lock, and then that is all we suggest.