01The short version
Inside job or outside job?
The part you look at is inside. The part that keeps the weather out is outside. That split decides who does what.
People ask whether a VELUX can be swapped from inside because they have a finished room, a clean ceiling and no wish for a scaffold on the drive. It is a fair question for any skylight owner. The short answer is that it depends on what you mean by "replaced".
A VELUX roof window has two main parts in practice. The sash is the opening part that holds the glass and swings or pivots. The frame is the fixed box set into the roof. Around the frame sits flashing, the metal or composite skirt that overlaps your tiles or slates and carries rain past the edges. Swapping the sash is one kind of job. Swapping the whole unit, frame and flashing together, is another.
If you only need the glass or the sash, some models allow work from inside. If the frame, the flashing or the size is changing, the roof covering is opened, often working from inside. We say so up front on every free survey, because we would sooner you knew than found out halfway through.
| What is changing | Where the work happens | Roof opened up? |
|---|---|---|
| Sealed glass unit only | Often from inside, model dependent | Usually no |
| Sash and glazing together | Inside or outside, model dependent | Usually no |
| Whole window, same size | From the roof, with finishing inside | Yes, around the frame |
| Whole window, new size | From the roof and the rafters | Yes, and structure changes |
02Why the roof
Why a whole window comes out through the roof
A frame is fixed to the rafters and wrapped in flashing, so you cannot reach the joints that matter from below.
Think about how the window got there. The installer cut an opening between rafters, set the frame on brackets, tied it into the roof build-up, then dressed the flashing over the tiles around it. The overlap runs from the lowest edge upwards, so every piece sheds water onto the one beneath. Those joints sit on the outer face of the roof.
To take the old frame out cleanly you lift the flashing, slide the surrounding tiles or slates back, release the fixings and lift the unit away. The new frame then goes in the same way, with its own flashing kit sized to your roof covering. You can read how those kits differ in our guide to VELUX flashing kits.
Trying to push a new frame through from inside would leave the old flashing in place and no way to see whether the new joint had landed properly. That is not a fitting we would put our guarantee behind.
You can tidy a ceiling from below, but you cannot tie in a roof joint from below.
03Glass and sash
When the inside route does work
Where only the glazing or the sash needs changing, the frame and flashing can stay and the work is far lighter.
Some VELUX windows are built so the sash can be released from the frame and lifted out. Where that is possible, a new sash or a new sealed unit can be fitted without touching the tiles. It suits a window whose frame, flashing and lining are all sound but whose glass has misted, or whose older double glazing is cold to stand under.
Which models allow it, and how, is a matter for the maker's own instructions. We cannot promise a particular window will work this way until we see it, because the code printed on its label tells us the range, the size and the build. Our page on finding your VELUX window code shows where to look, and replacing just the glass in a VELUX covers that route in more detail.
Replacing only the sealed unit is not notifiable under the Building Regulations. A whole rooflight, frame and glass, counts as a controlled fitting under Part L. Building Control is notified, and the new window must meet the present window limit of 1.4 W/m²K or WER Band B. So if you want to replace velux from inside, that only works for the sash or glass. We handle the notification where the work is notifiable.
Inside route
Sash or sealed unit swapped. Frame, flashing and tiles untouched. Floors and furniture still protected, with little or no roof work.
Roof route
Whole window changed. Flashing lifted, frame replaced, roof covering made good, lining refinished from inside.
04Indoors
What still happens inside either way
Even a roof-side job leaves plenty of work in the room, and that is where the warmth is decided.
A full replacement is not all rooftop. Inside, the old lining comes away from the reveal, the gap between frame and roof insulation is checked, and the new reveal is formed so insulation runs unbroken to the edge of the frame. A gap there leaves a chilly band round the glass, however good the glazing is. Our warm specification page explains why we care about that joint.
Before anyone starts, we lay floor protection and clear furniture from the working area. One team stays with the job from the first visit to the last, so you are not explaining the room to a new face each morning.
Sash, frame or the lot: what can really be done from the room
Can I replace a VELUX myself from inside the loft?
Swapping a whole window is not a job to do from a loft hatch. The joint that sheds rain sits on the outer face of the roof, and it needs roof access and the right flashing. A sash or glass swap may be possible on some models, so check the maker's instructions for yours.
Will you need a scaffold to replace a VELUX?
Not always. It depends on the roof height, the pitch and whether the window sits near an edge. We assess access at the survey and give the answer in the written quote.
Can a bigger window go in the same hole?
Not always. A taller window can stay between the same rafters, but a wider one means altering them. See replacing a VELUX with a bigger one.
Does the work make a mess inside?
Some dust is unavoidable when the lining comes away. We cover the floors, contain the working area and clear up before we leave.
