Rooflight and skylight fitting in Patchway

In the 1950s and early 1960s a large bungalow estate was built at Stoke Lodge, next to Patchway Common. A bungalow keeps every room on one level, and the loft above is one space left to grow into. Roof windows can give that space daylight through the slope itself, wherever a loft room has no outside wall to hold an ordinary window.

October is a good month to judge one. The sun is lower than in summer, the mornings are cool, and the light that reaches a loft room comes in at a shallow angle. That tells you quickly which parts of the slope give the room its light and which are shaded. It is far better to find that out in the planning than after the window is in.

Bungalows on an estate can stand close together, so privacy is a point to settle early. A roof window high in the slope looks at sky rather than at the garden next door, while a lower one can look across a fence. Stand in the loft with a tape and a helper and the sightlines show up in a few minutes. The survey does the same job properly, and it is also when the position gets set against the rafters.

A loft used for sleeping brings a safety question with it, which is how a person gets out if the stairs are blocked. The route out of a new loft bedroom is a Building Regulations matter under Approved Document B, and the survey looks at the existing stairs and windows below. Nothing here is a reason to shelve the idea; it is a reason to include building control from the start.

On the slope itself, blinds are worth planning with the glass. A loft bedroom wants a blind that darkens the room for the mornings of June, and a window set low in the slope is far easier to reach for that. Once the lamps are on, the pane turns dark and the bedroom is what you see in it. A blackout blind is what keeps a loft bedroom dark in the early hours of June, and it is the first thing to settle after the position of the glass. The VELUX windows hub covers the range, and what fitting a VELUX costs gives the price picture.

The width and height of a roof window come from a standard list, so reading it helps, and a loft room that needs more daylight can take two windows side by side or one above the other where the rafters allow. Reading VELUX size codes shows how.

Is that old roof window still doing its job? An older roof window can be a tired thing, with a frame that has faded, glazing that has misted and a seal that no longer holds. April's long afternoon light shows the faults: the low sun shines straight through the glass and lights every mark and every smear.

When a roof window is replaced in England, the new unit should have a U-value no worse than 1.4 W/m²K, or a Window Energy Rating of Band B or better. A rooflight, which stands on a kerb or upstand instead of sitting in the plane of the roof, has its own limit of 2.2 W/m²K. Those figures come from Approved Document L, and the good U-value for a rooflight answer explains the units.

Swapping the glass alone, or fitting a window into the frame it already has, does not count as supplying a controlled fitting, and the energy limits are not triggered by it. The choice between the two jobs is a real one, and it turns on the state of the frame, the seal and the age of the unit. A sound frame can keep going, while one that has warped or faded is a reason to start again. If the frame is sound and only the glass has failed, the answer on replacing just the glass explains that route.

Where the whole window comes out, the work usually needs Building Regulations approval, and the council's building control team or a registered building control approver is who deals with the notification where the work is notifiable. We handle that for you. Fitting a new unit is also the moment to rethink the blind, since the blind on an old roof window can be the part that has aged worst. A fresh blackout blind keeps a loft bedroom dark on June mornings, and the shading for a south-facing slope is better settled with the glass than added later.