The short answer
For most homes the sensible choice is a double-glazed roof window with a low-emissivity coating and a laminated inner pane. That gives good heat retention and keeps the glass together if it breaks. Triple glazing adds insulation and some sound reduction, and extra-acoustic glass helps most under heavy rain. Whatever you pick, a new roof window must meet 1.4 W/m²K or Band B.
Why roof window glass is different
A window in a wall stands upright, shelters under an eave and faces the weather at an angle. A roof window lies back along the slope, takes rain and hail directly and sits above the heads of the people in the room. Glass in that position is under more strain and carries a bigger consequence if it fails.
That is why roof windows are normally glazed differently from the windows below them. The outer pane faces the weather and the inner pane faces the room, and the two do separate work. The outer one has to resist impact from hail, branches and debris. The inner one has to stay in place if anything goes wrong, so that nothing falls on the people below.
What you buy is a factory-sealed stack of either two or three panes, each separated by a gap, held in a frame designed to shed water around its edge. Choosing glazing means choosing how that unit is built: how many panes, what each pane is made of and what is coated onto its surface.
Heat: double, triple and coatings
A roof window is a thin spot in the insulation, so its glazing matters to a room's comfort. The measure is the U-value, the rate at which heat passes through a surface, in W/m²K. A lower figure is better. Part L of the Building Regulations asks a replacement or new roof window to reach a U-value of 1.4 W/m²K, with Window Energy Rating Band B as the other route. A rooflight, the flat type that sits on a curb rather than in the slope, has a looser limit of 2.2 W/m²K.
Double glazing with a low-emissivity coating, a very thin metallic layer that sends warmth back into the room, is the normal way to reach that standard. The gap between panes is commonly filled with a gas that carries heat less readily than air. Triple glazing adds a third pane and improves the figure further, at greater weight and cost, and it is most worth considering for a bedroom or a room that is occupied all day.
The same coating can affect summer comfort. A loft room under a sunny slope can overheat, so a solar-control coating or an external blind is worth discussing at the survey.
Noise: what the glass can and cannot do
Rain on a window in the roof is louder than rain on a wall, because the glass is close to the sound and is not shielded by anything. Thicker or laminated panes reduce it. A laminated pane, two sheets of glass glued together by a plastic interlayer, damps vibration better than a single sheet of the same thickness, and so does a pane with different thicknesses either side of the gap.
Triple glazing helps modestly, but how it is built matters as much as the number of panes. A heavier outer pane and a laminated inner pane generally do more than a third sheet of ordinary glass. The frame, the flashing and the covering around the window shape the sound as well, and we deal with that side in our answer on whether roof windows are noisy in rain.
If noise is a concern, say so at the survey, because acoustic glazing is a specification choice that is cheap to make before ordering and expensive to change after the window is in.
Safety: toughened and laminated
The usual safety build for a roof window is a toughened outer pane and a laminated inner pane. Toughened glass is heat-treated so that it resists impact and, if it does break, crumbles into small blunt pieces. Laminated glass holds together when it cracks, because the interlayer keeps the fragments stuck in place.
Putting laminated glass on the inside is a sensible default. If hail or a falling branch breaks the outer pane, the inner one still keeps the room sealed and the pieces from dropping. Check what is on the specification sheet for the window you are quoted for, because the build differs between manufacturers and ranges, and some cheaper units use toughened glass on both faces.
Glazing and safety also link to escape. Whether a roof window can serve as a way out if there is a fire depends on height, 4.5 m from the ground at most, and on the opening size. Getting a heavy glazed unit into the slope is the subject of our note on fitting from inside.
Choosing, and what it affects
For a bedroom, a laminated inner pane and a low-emissivity double unit is a good baseline, with acoustic glass if rain noise would bother you. For a kitchen or bathroom, condensation resistance and an easy-clean outer surface matter more. For a south-facing loft room, think about solar control. In a conservation area, the frame profile and the glazing bars also need to suit the roof, which is a question for our guide to conservation rooflights.
Glazing is one part of the price. MyBuilder's 2026 guide gives typical UK installation of £350 to £600 for standard jobs, with the window extra, so a higher glazing specification affects the window cost and not the fitting charge. Our roof window cost guide goes through what moves the total.
Leaks around the glass are rarely caused by the glazing itself. A weep from a surround is more often a flashing problem, and you can read about that for a larger structure in why a dormer leaks. If you want advice on glazing for your own roof, ask for a survey, and the price we set afterwards is written down and fixed. Other options sit on our roof windows and skylights page.
