Rooflight and skylight costs in Southampton

Every rooflight job has two halves. One is the product: a roof window, a flat rooflight, a lantern, a conservation unit or a sun tunnel, each made by a manufacturer who sets its price by size, frame and glass. The other is the work of fitting it into your particular roof, which depends on what the roof is made of, what holds it up, how you reach it and what the room below needs. The first half can be looked up. The second half can only be priced by looking.

We could publish a table of starting prices, and plenty of firms do. The trouble is that a starting price describes a job that rarely exists: a stock unit in a tiled roof at bungalow height with nothing to trim and nothing to make good. Real jobs have a kerb that is a little low, a truss in the wrong place, scaffolding to put up or a plasterer to fit around. A starting price then becomes the first of several conversations about extras.

So we do it the other way round. We survey the roof and the room, or work from your drawings if the build has not started, and we send a written quote that covers the whole job. It names the unit, the glazing, the access we have allowed for, the lead time we expect from the maker and anything that depends on your builder. If something on the day turns out differently from what we could see, we tell you before we carry on, not afterwards.

The biggest single choice is the kind of unit, because each type is made differently and fitted differently.

Within each type there is a wide range. A small fixed flat rooflight over a utility room and a large frameless unit over a kitchen island are both flat rooflights, but they are very different jobs. The same is true of roof windows, where a basic centre pivot window and a top hung window with an electric blind sit far apart.

Size is the most obvious factor. Larger units cost more to make, and they are heavier to carry, lift and fit. A large lantern or walk-on panel may need more hands on the day or lifting gear, which we allow for in the quote.

Glazing is the next. Every unit we fit has sealed glazed units, and the options add up. Triple glazing gives a better energy figure and a quieter room. Solar control coatings reduce heat gain on south and west facing roofs. Self-cleaning glass keeps the outer pane clearer between cleans. Laminated inner panes are specified for overhead glazing above rooms people use. Each of these is a separate line in the maker's price. We set out each option with the reason it might suit your room, and we leave out the ones that would not earn their place.

Opening units cost more than fixed ones. A manual opening rooflight has hinges, a stay and a seal that has to work every time it closes. An electric one adds a motor, a control and often a rain sensor, and it needs an electrician to bring power to it at first fix. If you are not sure you need ventilation from the rooflight, we talk through what the room already has before you pay for an opening unit.

A rooflight is only as simple to fit as the roof allows. Interlocking concrete tiles on a regular pitch are the easiest covering to open up and make good. Plain clay tiles take longer because there are more of them. Natural slate needs care, matching slates and often some new battens around the opening. Old roofs with lime mortar, lead flashings or fragile tiles take longer still.

Flat roofs depend on their covering and its age. Single-ply membranes, GRP and modern felt systems each have their own way of being turned up a kerb and sealed. If the roof is being laid new, the roofer does that as part of the job and the cost of the rooflight work stays low. If the roof is already finished, it has to be cut open around the new opening and made good again, sometimes by the original roofer so their warranty is kept.

Condition matters too. A roof that is already sagging, leaking or due for re-covering around the opening is a poor base for a new unit. If we see that, we say so in the quote and suggest whether the rooflight should wait for the roof work, or the roof work should happen first.

Forming a new opening means dealing with whatever carries the roof. In a traditional cut roof, a rafter or two is trimmed and the load carried around the opening with new timbers. In a roof built with trusses, the trusses cannot be cut without an engineer's design, so the window is usually sized to fit between them. On a flat roof, joists are trimmed and a kerb or upstand built to the height and size the unit needs.

On an extension or loft conversion under way, this structural work is usually your builder's, done to the opening size we send in writing. That keeps the cost of our part down and means the opening is formed once, in the right place. On a retrofit into an existing roof, we carry out the trimming ourselves or agree with you who will, and it appears in the quote as its own line.

The cheapest opening is the one formed once, at the right size, by the trade already on the roof.

Getting safely to the roof can be a large part of a small job. A bungalow or a single-storey extension can often be reached from a mobile tower. A two-storey house usually needs scaffolding with edge protection, and a three-storey townhouse or a roof over a busy pavement may need a licence from the council for the scaffold. If your builder already has scaffolding up for their own work, we arrange to use it while it is there, which saves you paying for it twice.

Heavy glass is the other part of access. Large lanterns, walk-on panels and big frameless rooflights may need lifting gear, a small crane or simply more people on the day. Where the only route is through the house, we plan how the glass comes in and protect the rooms on the way. All of this is priced in the quote, so it is not a surprise on the morning of the job.

From the room below, a rooflight is the glass and the reveal around it. For a roof window, the reveal is often finished with the maker's own lining kit, which is quick and tidy. For a flat rooflight or lantern, the inside of the kerb is insulated, boarded and plastered so it runs into the ceiling. That plastering may be ours, or your plasterer's if they are on site anyway; the quote says which.

Extras come at the end of the list but can matter. Blinds for roof windows and lanterns are made to the finished size. Electric units need power brought to them by your electrician at first fix. Decorating after the plaster dries is usually yours or your decorator's. We list what is included and what is not, so you can compare our quote fairly with any other.

Some of the biggest costs on a rooflight job are not on the rooflight's own invoice. They are the return visits and the waiting. When a unit is ordered late, the roof is covered with a temporary sheet, the roofer has to come back to open it up and dress the membrane again, and the plasterer either works around a hole or makes a second trip. Scaffolding stays up longer than planned. None of that is unusual, and all of it is paid for by someone, usually the homeowner.

Planning the rooflight into the build avoids most of it. When we send the kerb or opening size to your builder before the deck goes on, the opening is formed once. At ordering against the programme, the unit arrives when the roof is ready, so the roofer finishes the membrane in one visit. When we fit in step with the plasterer, the reveals are done with the rest of the ceiling. The rooflight costs the same; the job around it costs less.

Replacing a rooflight that has misted, cracked or simply aged is often less work than forming a new opening, because the structure is already trimmed and the inside already finished. The cost then depends mainly on the new unit and on the state of what it sits on.

On a pitched roof, a replacement roof window may fit the existing opening exactly if the maker still makes that size, or need a small adjustment to the lining if not. On a flat roof, the old kerb has to be measured, checked for rot and checked for height, because older kerbs were often built lower than a modern unit needs. Where the kerb is sound, the swap is straightforward. Where it is not, the kerb is rebuilt and the covering made good around it, which we price as a separate item.

Sometimes only the glass has failed. If the frame is sound and the maker can supply a new sealed unit, replacing just the glass can be the sensible option, and it is not notifiable work. We will tell you honestly when that is the better route.

If you are collecting more than one quote, the useful comparison is line by line rather than bottom line. Check that each quote names the same unit, the same glazing and the same opening type. Check who forms the opening, who makes good the roof, who finishes the inside and who handles Building Control. Check what access has been allowed for and whether the lead time is stated.

A quote that leaves several of those blank is not necessarily cheaper; it may just be describing less of the job. Ours lists each item so you can see what is included and ask about anything that is not.

A new rooflight, or a whole replacement unit, is work that has to meet Building Regulations, including the energy limits in Approved Document L and the rules on structure and glazing. Where the work is notifiable, we handle the Building Control notification, and that cost is built into the quote rather than added later. Where the rooflight is part of a bigger project that already has its own Building Regulations application, it is covered there and we provide the product information your inspector needs.

Every job we fit comes with our 10-year workmanship guarantee, and the maker's own product cover sits alongside it. What each covers is set out on our guarantee page.

A rooflight on an extension or loft conversion can be priced before there is a roof to look at, and it is often better that way. If you have plans from an architect or a designer, send them with your enquiry. From the drawings we can see the size and shape of the opening, the roof build-up, the fall on a flat roof and how the room below is laid out. That is enough to recommend a unit, price it and give you the lead time to plan around.

A price from drawings is firm for the unit and the fitting as drawn. What it cannot see is how the building turns out on site: a kerb built a little differently, an extra layer of insulation, a change to the roof covering. We visit once the shell is up to check the opening before the order is confirmed, and if anything has moved we tell you and your builder straight away, with any change to the price in writing before work goes ahead.

• The unit by maker, type, size and glazing, with the energy figure for the whole unit
• The expected lead time from the maker, and when we would place the order
• The opening or kerb size we will send to your builder, where they are forming it
• Structural work, roof making good and the inside finish, and who carries out each
• Access we have allowed for, from a tower to a full scaffold or lifting gear
• Building Control notification, where the work is notifiable
• Anything we could not see on the survey and how we would deal with it

If your project is still on the drawing board, we can price from the plans and confirm on site once the shell is up. That gives you and your builder a figure to include in the overall budget, and a date to plan around. To start, book a free survey, or read our answer on what it costs to fit a skylight for the short version.