the unit
The rooflight itself and its glazing
The unit is usually the largest single line. Its cost follows the type of unit first, then its size and glazing.
A fixed flat rooflight is the simplest product. An opening one adds a hinge, a seal and a winder or motor. An electric unit adds the motor, a rain sensor and a power supply that has to reach it. A roof lantern is a framed structure of glazing bars and panes, so it is priced as an assembly of parts. Walk-on glass is thick laminated glazing built to carry foot traffic, which puts it at the top of the range.
Size moves the price in steps. Roof windows come in fixed size codes, so a move from one code to the next can change the price noticeably. Flat rooflights and lanterns are often made to the opening, so the area of glass drives the figure.
Glazing adds its own layer of cost. Double glazing that meets the Part L figure for your type of unit is the baseline. Triple glazing, solar control coatings, self-cleaning coatings and integral blinds each add to it. Our guide to double or triple glazing sets out when the extra pane is worth paying for.
the opening
Replacement, new opening or structural work
Opening work is whatever the roof needs before the unit goes in. It varies more from job to job than any other line on the quote.
| Type of job | What it involves | Effect on the quote |
|---|---|---|
| Like-for-like replacement | Old unit out, new unit into the same opening | The least roof work |
| Larger unit, same position | Opening widened or lengthened, timber trimmed | Adds carpentry and roof covering work |
| New opening in a pitched roof | Covering stripped, rafters cut and trimmed | Structural work, Building Regulations approval |
| New opening in a flat roof | Deck cut, joists trimmed, kerb built, roof finish made good | Structural and roofing work combined |
A straight swap is quicker because the opening already exists, but it still needs measuring. An old roof window may not match a current size code, and an old flat rooflight may sit on a kerb that is now too low. We cover this in replacing a skylight without a new roof.
Cutting a new opening means altering the structure. On a pitched roof we trim around the cut rafters so the load still reaches the wall plate. On a flat roof the joists are trimmed in the same way and a kerb is built. That carpentry, and the approval that comes with it, is priced as its own line.
access
Getting to the roof safely
We settle how to reach the roof at the survey. A single-storey extension with a clear garden may need nothing more than ladders and roof boards. A two-storey house usually needs a mobile tower. A tall elevation, a steep slope or a job that runs over several days can need scaffold, and scaffold is hired, erected and taken down by a separate firm.
Terraced houses with no rear access, gardens reached only through the house and roofs above conservatories all change the method. We write the access we plan to use on the quote, so you can see why it costs what it does.
the roof edge
Kerbs and flashing round the unit
On a pitched roof, the flashing kit joins the window to the tiles or slates. The right kit depends on the covering: a profiled tile needs a different flashing from a flat slate, and a recessed fitting needs its own kit. Around the frame we refit the covering and battens and dress in an underfelt collar.
On a flat roof the kerb is the work. It has to stand high enough above the finished roof to meet the maker's minimum, often about 150 mm, and it may need to carry the fall if the unit does not build one in. The kerb is then wrapped in the roof finish, whether that is felt, EPDM rubber or fibreglass. If the existing finish is near the end of its life, we say so on the quote, before the job is booked.
inside
Making good inside, and the extras
Inside, a new roof window needs a lined reveal: plasterboard or a lining kit, insulation packed round the frame, then plaster or tape and fill. A flat rooflight or lantern needs its ceiling opening boarded and finished. We state on the quote whether we leave it ready for decoration or decorated.
Where the job is notifiable, sign-off under Building Regulations has a fee, either from BCP Council or the relevant authority for your address, or from a registered building control approver. The Building Regulations guide explains which jobs need it.
Other items appear only when chosen: blinds, a wall switch or remote, a rain sensor, removal of a ceiling that turns out to need replacing, or electrical work to bring power to an opening unit.
Lines that move a quote
- Unit and glazingType, size code or made-to-measure area, and any coatings, blinds or motors.
- Opening workA swap into the existing hole, a larger opening or a new structural one.
- AccessLadders, a mobile tower or hired scaffold, chosen at the survey.
- Kerb and flashingThe flashing kit for your covering, or the kerb height and fall a flat roof needs.
- Finishing insideLining, insulation, plaster and how far decoration goes.
the quote
How our written quote is laid out
Every quote is itemised. You see the unit named with its size and glazing, then the roof work, the access, the kerb or flashing, the work inside and any sign-off fee as separate lines. The survey sheet is attached, so each line can be traced back to a measurement.
Because each line comes from a reading, the figure does not need a margin added for surprises, and it does not grow once the roof is open. It changes only if something truly hidden turns up, such as rotten timber under the covering, and our terms set out how we handle that.
Each line of the quote traces back to a reading on the survey sheet.
To get one for your own roof, start on the quote page. The survey and the written quote are free.