Access depends on height, roof type and weight of glass
Three things decide how we reach a rooflight for replacement: how high the roof is, whether it is flat or pitched, and how heavy the new glass will be.
Scaffolding is one answer among several. The Work at Height Regulations 2005 ask any installer to plan the job so nobody can fall, choosing the safest practical equipment for the task and how long it lasts. For a short swap on a low flat roof that can mean a secured ladder and temporary edge protection. For a two-hour sash change on a loft roof window it can mean no outside access at all. For a four-metre lantern above a kitchen it can mean a proper tower or a scaffold with a loading bay. The survey is where we decide which, and the written quote says so before anyone arrives, so there are no surprises on the day.
Pitched roof windows: often changed from inside
A modern top-hung or centre-pivot roof window is designed to be fitted from within the room, which makes a like-for-like upgrade much simpler than people expect.
If the frame and flashing are sound and the pane has misted, a new sash can go in from the loft with no work on the tiles at all. Our guide on replacing a misted roof window covers when a new sash is enough and when the whole window should go. Where the full window and its flashing are renewed, someone does need to work on the roof around the opening. On a loft in a Romsey or Mill Road terrace, that can usually be done by leaning out through the opening itself with a roof ladder hooked over the ridge, as long as the slope, the tiles and the working height allow it safely. A steep slate slope three storeys up on a De Freville villa is a different job, and a scaffold on the rear or a tower from the garden becomes the sensible choice.
If you only want the glass changed on a VELUX, read can you replace VELUX glass only?, since that route rarely involves any exterior access.
Flat rooflights and domes on single-storey extensions
A flat roof skylight on a kitchen or side-return extension typically sits about 2.5 to 3.5 metres off the ground, which is well within reach of lighter access kit.
For an old dome or a tired flat rooflight on an upstand, the usual arrangement is a ladder tied at the top, temporary edge protection along any open roof edge, and boards laid on the membrane so the roof finish is not marked. A small mobile tower in the garden is a common alternative where the ground is level and there is room for it. The work itself happens on top of the roof: lifting off the old unit, checking the kerb, and bedding and sealing the new one. Our guides on replacing an old flat rooflight and replacing dome rooflights explain what changes at the upstand.
Weight is the thing that changes the plan. A 1000 x 1000mm double glazed flat rooflight is a two-person lift. A larger triple glazed unit can weigh well over 100kg, and carrying that up a ladder is not acceptable. In those cases we bring in a tower with a hoist, a vacuum lifter or, where the drive and garden allow it, a small crane or lifting machine.
Roof lanterns and large units: lifting is the deciding factor
A roof lantern is heavier and more awkward than its size suggests, so replacing one nearly always needs a stable working platform around the upstand.
The glazing panels go in one at a time, and the fitters need to stand safely beside the kerb while they place and secure them. On a flat roof with a parapet this can sometimes be done from the roof itself with edge protection. On an open-edged extension, a perimeter scaffold or a tower on each side is the safer way to do it, and the difference shows in the finish because the fitters can work square to the frame. Replacing a failed roof lantern goes through the full sequence.
Terraced streets, pavements and the licence question
Scaffolding on a public pavement or road needs a licence from the highway authority, which in Cambridge and the surrounding district is Cambridgeshire County Council.
That matters on terraced streets where the only practical access to a front roof slope is from the pavement. Rear rooflights are nearly always reached from the garden, but on some mid-terrace houses in Petersfield and Chesterton the garden can only be reached through the house, so every pole, board and pane of glass comes through the hallway. We look at this at the survey and say in writing how materials will arrive, where the kit will stand and whether a licence is needed. If a reroof is planned anyway, using that scaffold for the rooflights too is the cheapest route of all; see replacing rooflights during a reroof.
How access usually works, by situation
This is a guide to the kit each type of job tends to need; the survey confirms it for your roof.
| Rooflight | Typical height | Usual access |
|---|---|---|
| Roof window, sash only | Any | From inside |
| Roof window, full unit | Loft | Roof ladder or scaffold |
| Flat rooflight or dome | Single storey | Ladder, edge guard or tower |
| Large glass or lantern | Single storey | Tower, scaffold or lifter |
| Any unit | Two storey | Scaffold or tower |
Access equipment is a line of its own in our quote, so you can see what it adds and why. The other things that shape the price are set out in what affects the cost of replacing a misted rooflight, and the full range of upgrades is on our misted and failed rooflight replacement page. To have your roof looked at, book a light survey.
Questions people also ask
Can a skylight be replaced from inside the house?
A roof window sash or pane can usually be changed from inside. A flat rooflight, dome or lantern sits on an upstand outside the roof, so it has to be lifted off and set down from above, even if some of the lining work is done from the room below.
Will the scaffold damage my garden or roof?
Scaffold and tower feet stand on boards to spread the load, and boards go down on any flat roof membrane the fitters walk across. Inside the house, our answer on whether replacing a rooflight damages the ceiling covers how the finish around the opening is protected and made good.
How long does scaffolding stay up for a rooflight replacement?
For a single rooflight, access kit is usually up for the day of fitting, with a scaffold sometimes going up the day before and coming down once the flashing and seals are complete. A lantern or several units can take two to three days.
Do I need to tell my neighbours?
If the scaffold or tower needs to stand on their land, or a crane will lift over their garden, you need their agreement first. It is also a courtesy to let them know about deliveries and noise on the day.
