What fitting a VELUX yourself actually involves
Fitting a VELUX skylight is part carpentry, part roofing and part plastering, and each part has to be right for the window to stay dry and warm for decades.
On a straight replacement, the job runs like this. The old sash comes off its pivot hinges, the lining is freed, the old flashing is unclipped and the frame is unscrewed from its brackets and brought down into the room. Working out through the empty hole, you lift the tiles or slates around the edge, take away the old flashing and underfelt collar, and check the battens. The new frame goes in on fresh brackets, set square and level, with a new underfelt collar and drainage gutter above it. The flashing kit is laid from the bottom piece upwards, the covering goes back around it, and then the sash is refitted and the inside is made good. Our answer on replacing a VELUX window from inside covers that sequence in more detail.
A new window in a roof that has never had one is a different scale of job. You mark the opening between the rafters, strip the covering and battens, cut through the underlay, and usually cut at least one rafter. The cut rafter has to be carried by trimmers doubled up above and below the opening, then the frame, collars and flashing go in, and the inside needs a new plasterboard lining, insulation and finishing. The stages are set out in full in the VELUX window installation process.
The kit itself is easy to buy. Choosing the right parts is where people slip: the size code has to suit the rafter spacing or the old opening (see VELUX sizes and codes), and the flashing type has to match the roof covering and its profile (see VELUX flashing types). A flashing made for flat tiles will not keep the water out on a deep profiled tile, however carefully it is dressed.
Building Regulations and the notice duty
Fitting a roof window is building work under the Building Regulations whoever does it, so a homeowner fitting their own carries the same duty to notify as a firm would, and has to give that notice before starting.
A new roof window counts as a structural alteration because the roof is cut, and it also has to meet the thermal rules. Replacing a window is controlled work too. A firm registered with a competent person scheme can self-certify some of this, but a homeowner working on their own house normally goes to the council's Building Control, or to a registered building control approver. In Cambridge and South Cambridgeshire the council service is run through Greater Cambridge Shared Planning. The usual route for a small domestic job is a building notice, given at least two days before work starts, with a fee.
| Job | Roof cut? | Building Control |
|---|---|---|
| Same size swap | No | Notice usually needed |
| Bigger window | Yes | Notice needed |
| New opening | Yes | Notice needed |
| Loft conversion | Yes | Part of the wider application |
The inspector will want to see how the rafters have been trimmed, and the finished window has to meet the requirements that apply to it. Under Part L a rooflight has a limiting U-value of 2.2 W/m2K, which current VELUX double glazing is designed to meet. Part K expects safety glass overhead where people walk beneath, which is why an inner laminated pane matters. Near a boundary, Part B fire rules can limit where a rooflight may go. When the work passes, you receive a completion certificate. Without one, the missing sign-off tends to surface when you sell, and putting it right afterwards through a regularisation application can mean opening up finished work for inspection. Planning is a separate question: most VELUX windows fall within permitted development, with exceptions set out in our planning answer.
Working at height and the other risks worth weighing
The main risk in fitting your own roof window is the roof itself: working on a pitched slope at eaves height or above, with tools and heavy glass in hand.
A replacement done from inside keeps you on the loft floor with your head and shoulders out through the opening, which is far safer than standing on the tiles. A new opening, or a slate roof where the covering has to be worked from above, needs safe access outside. That means a properly erected scaffold or tower with edge protection, or at the very least a roof ladder hooked over the ridge and a secured ladder to reach it. The Health and Safety Executive names falls from height as a leading cause of serious and fatal injuries in building work, and the danger is the same on your own roof as on anyone else's.
The other risks are quieter and slower. A flashing laid in the wrong order, or an underfelt collar left out, can let water track behind the frame and into the ceiling long before anyone notices. Leaving out the insulation collar leaves a cold band around the frame where condensation gathers every winter; our guide to insulation collars and installation kits explains why they matter. On a new opening, a rafter cut without proper trimming can let the roof sag over the years. It is also worth reading the terms of the maker's product guarantee, as these generally assume the window has been fitted to the published instructions.
What doing it yourself can miss about the light
A DIY fit tends to put the window where the rafters make it easy, and the easiest spot is not always the one that lights the room well.
On a replacement this matters less, because the opening is already there. On a new window, the choice of slope, height and size decides how the room feels for years. A south slope over a Mill Road loft bedroom gives several hours of direct sun in summer and heat to match, so it may want solar protection glass and an external blind from the start. A north slope in a Trumpington Meadows home gives soft, even light all day and rarely overheats, but may need a bigger or taller window to feel bright. Set the window too high and you light the ceiling; set it too low and the sun patch falls across the desk or the bed at the wrong hour. Our page on how we plan the light walks through orientation, glass and position.
If you would rather hand the job over, we install and replace VELUX windows across Cambridge and about 30 miles around, handle the Building Control notification where the work is notifiable, and back the installation with a 10-year workmanship guarantee. See VELUX window installation in Cambridge, or book a light survey and we will set out the position, size and glass in a written light plan.
Questions people also ask
Can you fit a VELUX skylight yourself without scaffolding?
A like-for-like swap on a tiled roof can often be done from inside through the opening. A new opening or a slate roof usually needs safe access from outside, which means scaffold, a tower, or at least a roof ladder and edge protection.
Do I need Building Control to replace a VELUX myself?
Replacing a window is controlled work, so a homeowner fitting their own should normally give Building Control notice before starting. Enlarging the window or cutting a new opening certainly needs it, because the roof structure is altered. Your council's Building Control team will confirm what applies to your roof.
How long does a DIY VELUX installation take?
Allow longer than a trade fitter would take. A professional like-for-like swap is typically around half a day, and a new opening with lining a day or two. See how long a VELUX installation takes for what adds time.
Can I fit a bigger VELUX window myself?
It is possible, but it means cutting and trimming rafters, notifying Building Control and reworking the lining and the roof covering. Our answer on fitting a bigger VELUX window sets out what changes.
