Answered · Skylight & Rooflight Installation & Replacement Chelmsford

How much does it cost to replace a skylight?

The short answer

The figure for a replacement is built from six things: the unit, the state of the opening it lands in, the roof covering around it, access, the glazing specification and whether the size is standard or made to measure. Sunspire quotes a range by email once the basics are known, then a fixed written figure after a survey.

Nobody can give a reliable number over the telephone, and a firm that does is quoting the easy version of your job. What follows is what actually moves the figure, in roughly the order it moves it, so you can work out before anyone visits whether yours sits at the bottom of a range or the top.

Why the number arrives in two stages

A replacement has one enormous advantage over a new installation. The opening already exists, so the largest unknown in the whole job has been removed before anyone starts.

That is why a range by email is usually tight. What it cannot know is what the old unit is hiding: the condition of the kerb timber at the deck junction, whether the covering has anything left in it, whether the opening is square. The survey converts the range into a fixed written price by answering those three questions, and after that the figure does not move unless you change what you asked for.

The unit, and where it sits in the total

People assume the glass is most of the cost. On a straightforward like for like replacement it is usually somewhere between a third and a half, and on a complicated one it is a good deal less.

Within the unit itself, the variables are size, opening mechanism and glazing build. A fixed light costs less than a manual opener, which costs less than an electric one, which costs less again than an electric unit with a rain sensor and a controller. Frame material moves it too, with powder coated aluminium over a timber core sitting above uPVC and below a slim cast conservation frame.

Whether the kerb survives, which is the biggest swing

This is the item that separates the bottom of a range from the top, and it is decided by a screwdriver rather than an opinion.

A kerb can be kept where the timber is sound and dry all the way down to the deck, the top is level enough to seat a new frame without packing, the height above the finished surface suits the position, and the covering dressed up its face is in good order. Where the bottom fifty millimetres has taken water, the upstand is rebuilt. That is roughly half a day of carpentry and it is the most valuable half day on the job. Where the timber has gone properly soft, the extent of the decay decides how far the work travels.

The covering, and how far it is disturbed

How much roof has to come back around the opening varies enormously by material, and it is the second biggest driver.

Covering	What has to happen	Effect on the figure
Single ply membrane	Cut back, new section hot air welded, joint tested	Modest
Torch on felt	Stripped back a course, rebuilt in layers	Modest
GRP	Cut back, new matting and resin laminated in	Weather dependent, adds a little
Concrete interlocking tile	Courses lifted, stacked, reset to a new kit	Moderate
Handmade clay or natural slate	Lifted individually, breakages hunted down	Significant
Asphalt	Hot work, specialist attendance	Significant

Access, and the line it occupies on a quote

A rear extension roof reached from a garden and a third floor slope over a narrow side return are the same installation with very different logistics.

Where a tower or a roof ladder does the job, access barely registers. Where a scaffold is needed, it brings its own hire period, erection and striking, and it sits on the quote as a separate item so you can see it. Powered access sits between the two. Whether your job needs any of it is covered in detail on access without scaffolding.

Size, and the point where the arithmetic changes

Cost does not track area in a straight line. Up to about a metre and a half in either direction you are buying more of the same thing, and the figure climbs gently.

Beyond that, three things happen at once. The glass becomes a special rather than a stock size. The unit needs more than two people to lift onto a roof, which sometimes means mechanical handling. And the structure below the opening starts to need designing rather than assuming. Those three together produce a step in the figure rather than a slope, which is why a small increase in ambition can produce a large increase in price.

Glazing specification, and where the money is well spent

Several options add to the unit cost and each buys something specific, so it is worth knowing which are worth having on your particular roof.

Solar control glass matters on any flat or south facing plane and does very little on a north slope. A laminated outer pane damps rain noise and helps where the roof is reachable from a boundary wall. An asymmetric build, where the panes differ in thickness, breaks up the drumming resonance. Self cleaning coating reduces washing rather than removing it. None of these can be added afterwards, which is the whole argument for deciding at order.

Standard sizes against made to measure

Openings formed before the mid nineteen seventies were set out in feet and inches, and a great many Essex roofs still carry them. Two by three feet, three by four, four by four.

Current ranges are metric and do not land on those numbers. A bespoke unit made to the measured size costs more and adds two to four weeks of lead time, but it leaves the structure completely alone, which on a trussed roof is frequently the cheaper answer once the alternative is priced properly. Easing an opening by twenty or thirty millimetres is often just the lining rather than the structure, and that is the option worth testing first.

What to send to get a range back

Four things are enough, and all four take ten minutes. A photograph of the unit from inside showing the reveal. A photograph from outside if the roof can be seen safely. The rough size of the opening measured at the ceiling. And what the covering is, in whatever words come naturally.

If there is a data plate on the sash edge or the frame face, a photograph of it is worth more than every other measurement combined, because it gives manufacturer, model and size code at once. The costs page explains how the ranges are built, and skylight replacement covers what the work itself involves.

Tell us about your roof

We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.

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