Short answer
Sometimes. A roof window can often be fitted from inside the loft when the roof pitch, the unit size and the covering allow the fitter to work through the opening, which means fitting velux from inside without a full scaffold. Larger units, steep or fragile roofs, and anything needing work on the external flashing at height usually call for scaffold or a tower. The survey decides and the job plan records it.
When fitting velux from inside works
A roof window is dressed into the covering from the outside, but much of the work can be done from within. The fitter marks the opening, cuts the sheeting and battens from below, and lifts the new frame up into place through the gap. When the roof is a moderate pitch, the window is a standard size and the covering is easy to lift, that approach is practical and tidy.
Working this way suits a straight like-for-like swap better than a new opening. The old frame is already there, the position is fixed, and the rafters are known. Most of the effort is below the roof line, with only the flashing dressed from the slope. It is a real way of installing a rooflight without scaffolding for the main stage of the work.
Safe working is the test. A fitter inside a loft can brace against the rafters, but lifting a frame over a gap with the roof open means the rest of the roof and the room below must be protected. A clear floor and a second pair of hands for the lift are all part of the plan, and a roof that cannot be worked safely this way is moved to the scaffold route at the survey.
One practical question follows: what happens to the dust and the old frame? In a loft job the floor below is covered before anything is cut, the old sash and frame come down through the opening in pieces small enough to carry, and the loft is swept before the new frame goes up. Hatch size matters here, because every part of the new unit has to pass through it or be lifted from the slope. The survey measures the hatch as well as the roof.
What decides whether it can be done from inside
Four things decide it. The first is pitch: a very steep roof makes reaching out onto the slope unsafe, and a very shallow one makes it hard to get through. The second is the size and weight of the unit, since a large frame is awkward to pass up through a loft hatch or a tight opening. The third is the roof covering, and the fourth is how the roof can be reached at all.
A covering like slate or old clay tile may be brittle, and walking or kneeling on it can crack it. In that case the work needs a safe way across the slope, which is generally scaffold or a tower and not a ladder on the gutter. The same goes for any roof with a poor edge, a weak fascia or a surface that cannot be crossed without damage.
- Roof pitch that allows safe reach to the flashing
- A unit small enough to pass through the loft
- A covering that can be lifted without breakage
- A safe way to reach the slope when the flashing is dressed
When scaffold or a tower is still needed
Scaffold goes up when the work at height cannot be done safely any other way. A new opening, a larger unit, a roof above a certain height, or a complicated flashing over a slate covering all point that way. A two-storey house usually needs scaffold at the eaves for anything beyond a small swap, and a tower may suit a lower roof where a full scaffold is more than the job needs.
The general rule is that safe working comes before convenience. Work at height has its own rules, and the decision between inside access, a tower and scaffold is made on the roof, on the survey. A scaffold also gives a platform for the weathering, making the covering good around the flashing neatly. For the cases where the old frame is staying in an opening that cannot be reached, the roof window installation page covers the fuller job.
Building Control and the order of work
Fitting from inside does not change the regulations. Putting a roof window into an existing roof is building work whichever side the fitter stands on, and a full swap of frame and glass is notified to Building Control too. The chosen unit is picked to meet the energy limit for roof windows, and the notice is sent by us where the work is notifiable.
If the opening is a different size from the old one, rafters are cut or trimmed from below, and that is structural. Matching a new VELUX to an old opening shows when a straight swap is possible and when the opening has to change. A like-for-like swap keeps the rafters as they are.
Order matters on the day. The inside work starts with protecting the floor and the room below, then the old sash and frame come out, the new frame is lifted in and fixed to the rafters, and only then is the flashing dressed from the slope. By evening the slope is sealed, and the lining and finish follow.
How access is written into the job plan
The survey notes how the roof is reached, whether the loft allows inside working, and whether scaffold or a tower is needed. That becomes its own line in the written plan, so you can read how the team gets to the slope before agreeing to anything. If scaffold is needed, the plan records when it goes up and when it comes down.
That is the reason access is not left to the morning of the job. The cost of scaffold, if needed, is a visible item in the written quote, and the plan shows how long the roof is open. Where a tower will do instead, the plan says why. Either way the arrangement is settled at the survey, with the neighbours' access and any parked cars considered, so the fitting day starts on time. For the whole sequence from survey to sign-off, see the VELUX window installation service, and use the VELUX replacement guide if the window is already there.