Replacing a thirty year old VELUX without disturbing the covering
A roof window replacement is a job most people expect to be disruptive and it usually is not. On a covering that is uniform and a unit that is a current size, the work is contained within a small area around the opening and finished the same day.
This page is about the method and what it involves, rather than about choosing the unit.
The principle: work within the flashing zone
The area that has to be disturbed is the area the flashing kit occupies, plus enough beyond it to lift and reinstate the covering cleanly.
That is a band around the opening rather than a large part of the slope. Everything outside that band stays where it is, and on a well executed replacement it is never touched.
The size of that band is set by the flashing kit and by how far up the slope the underlay has to be reached, and both are known before work starts.
The sequence
- Protect the room below, because a roof being opened produces dust and debris.
- Lift the covering around the window, working from the top down, and set it aside in order.
- Remove the old flashing kit, which is scrap rather than something to reuse.
- Take out the old unit, which frequently means cutting old fixings rather than backing them out.
- Inspect the opening: trimmers, underlay, insulation, condition of the timber.
- Correct anything that needs it, which is the moment for that and the only one.
- Set the new unit and fix it into structural timber.
- Fit the underlay collar and the insulation collar.
- Fit the new flashing kit, dressed to the covering.
- Reinstate the covering with the original material.
- Make good the reveal inside.
Working from the top down
The covering above the window has to come off before the covering beside it, because every course laps the one below and the fixings for each course are underneath the one above.
On slate that means cutting nails with a ripper or lifting the courses above. On nibbed tiles it means lifting rather than sliding. On pegged tiles it means lifting each one clear of its peg without breaking it at the hole.
Doing it in the right order is what keeps the disturbance small. Doing it in the wrong order breaks things unnecessarily.
Setting the covering aside
Everything that comes off is stacked in order, on edge rather than flat, and protected.
On a uniform modern covering the order matters less. On hand made tile or on slate it matters a great deal, because putting the same units back in roughly the same place is what makes the finished job invisible.
New material, where any is needed, goes where it is least conspicuous rather than in a neat rectangle round the window.
How much breakage to expect
Some, always, and how much depends on the covering and its condition.
| Covering | Breakage | Replacement |
|---|---|---|
| Concrete interlocking tile | Low | Readily available, matches after a season |
| Machine made plain tile | Low to moderate | Available, colour settles |
| Welsh slate | Moderate, nails are the issue | Reclaimed, and matching takes effort |
| Hand made peg tile | High on an old brittle roof | Reclaimed, scarce, buy before opening up |
| Horsham stone | Low if handled properly, catastrophic if not | Effectively irreplaceable in matching condition |
Where an allowance is needed it is established at survey by looking at the condition of the covering, and the material is sourced before the roof is opened rather than after.
Old fixings
A thirty year old window is held by thirty year old fixings, and within a mile or two of the sea those are frequently unrecoverable.
Heads round out because the drive recess has corroded shallow. Heads shear because the neck has lost section. Threads turn endlessly in timber they have corroded away from. Each of those turns a quick removal into careful work with a drill.
It is why we survey a coastal replacement without committing to a fixed duration until a unit has been off, and why we say so at quotation rather than on the day.
What we find underneath
The same list, on almost every unit of this age.
- No underlay collar, which explains a leak the owner had stopped mentioning.
- No insulation carried up to the frame, which explains the cold reveal and the winter condensation.
- A flashing kit that never suited the profile of the covering.
- Trimmers soft at one end where water has been getting in.
- Occasionally, no trimmers at all: a rafter cut and the window fixed to what was left.
None of it is unusual, and every one of them is cheap to correct at this moment and unreachable at any other.
The bit that is not optional
Where a trimmer is decayed, it is replaced. Where there are no trimmers, they are formed.
That is not an upsell and it is not discretionary. A new unit fixed into soft timber is a new unit that will move, and the whole point of the replacement is that the next thirty years are better than the last.
We flag it when we find it, with a photograph, rather than springing it as a cost on the day.
The roof is never left open overnight
A replacement is planned to open and close within the day, and it is not started when the forecast will not allow that.
Where the roof has no underlay, which is common on the older village stock, that rule is not a nicety. An open roof in a Channel squall puts water straight into the ceiling below.
Practically it means these jobs are weather dependent, and moving a start date is better than opening a roof into a poor forecast.
Access, and what it costs
How the roof is reached varies enormously across our patch and it is a real proportion of the job.
On a bungalow at Ferring or Rustington the roof is low, the ground around it is usually open, and a ladder and a small tower are enough. On a two storey semi at Durrington it is a tower or a modest scaffold. On a four storey terrace in Hove there is no side access at all, the route is through the building or a scaffold onto the pavement, and a pavement scaffold frequently needs a licence from the highway authority.
That is why we establish the access route before quoting rather than after, and why doing everything a roof needs on one visit is much better value than returning. On a terrace the access can cost more than the window.
Getting the old one out and the new one in
A sealed glass unit is heavy and awkward, and the route it travels is worth establishing at survey.
Most domestic roof windows can be handled by two people through a house and up a loft ladder, and that is how most of this work is done. Where the staircase has a tight half landing, or where the loft hatch is small, the unit may have to go up the outside instead.
Occasionally that constraint decides the size: a narrower unit that can be carried in beats a wider one that needs plant. Better to know that before the order than on delivery day.
Keeping the house liveable
A single window replacement is a day, and the room is usable again that evening.
What we protect is the room below and the route through the house, because a roof space holds decades of dust and a staircase carries everything in and out. Floors get covered, the route gets protected, and the debris leaves with us.
On a loft bedroom the practical advice is to clear the space under the window and take anything precious out of the room, which takes ten minutes and removes the only real risk to your belongings.
What happens inside
The reveal is the part the room sees, and it is worth setting expectations.
Where a new unit is the same size as the old one, the existing reveal frequently survives with making good at the edges. Where the size has changed, or where the insulation collar is being fitted for the first time, the linings come off and are remade.
Decoration is not usually included in a rooflight quotation, and we say what will need painting rather than leaving it to be discovered.
Dust, and how much
Less than people fear and more than nothing.
An old roof space holds decades of dust, and opening a hole in a ceiling releases some of it. Furniture is covered or moved, floors are protected, and the opening is sheeted from below where the room is finished.
On an unconverted loft with a boarded floor it is negligible. In a finished bedroom it needs the preparation.
How long it takes
On a uniform covering, a current size, and sound trimming, a single window is a day.
Add an obsolete size needing the opening adapted, or decayed trimmers, or coastal fixings that have to be drilled out, and it is longer. Add hand made tile or stone and the covering work alone doubles it.
We give the realistic figure at quotation with the unknowns named, because a roof nobody has been inside is a roof with unknowns in it.
Several windows at once
Where a house has two or three of the same age, doing them together is considerably better value than one at a time.
The access is set up once, the covering is handled once, the material allowance is bought once, and the crew is on site once. It also means the roof ends up consistent rather than carrying one new unit and two old ones.
Where budget only allows one, the one to do first is whichever is leaking, or whichever is in the room that matters most.
Doing it while the roof is being recovered
If the covering is within a few years of needing replacement, the cheapest version of this job is to wait and do both together.
With the covering off, the battens being replaced and the structure visible, a new window is built into a roof being reassembled rather than cut into a finished one. The saving against doing the two jobs separately is substantial.
We will say so at survey where it applies, even though it means not selling a job this year.
How we work on a VELUX
We work within the flashing zone and keep the disturbance to it, set aside and reinstate the original covering, and inspect the trimming, the underlay and the insulation while the unit is out. We fit both collars and a new flashing kit matched to the covering, and we never leave a roof open overnight.
A replacement done properly is invisible from the ground and better than the original in every way that is not visible at all.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.