Working with your builder or architect

Most of the rooflights we fit go into a roof that somebody else is building. A rear extension, a loft conversion, a flat roof being stripped and re-covered, a kitchen knocked through with a new roof over it. The homeowner has a builder, sometimes an architect, and a programme that runs for weeks. The rooflight is one line in that programme, and it is the line most likely to hold the others up when it is late or the wrong size.

This page explains how we work alongside the people already on your job. It is written for homeowners who want to know what to expect, and for builders and architects who want to know what we will send them and when. If you are one of the latter, you will find nothing here that asks you to change how you run a site. We fit around you, and we put everything you need from us in writing.

Retrofits follow the same thinking on a smaller scale. When we add a roof window to a finished loft or replace an old dome on a garage, there may be no builder at all, but there is still a sequence: the opening, the weathering, the inside finish. We plan it the same way.

The first thing your builder needs from us is a size. Not a brochure size, and not the size of the glass, but the size of the opening or kerb they have to build for the product in question you have chosen. Makers size their rooflights from the kerb. Some quote the external dimensions of the upstand, some the internal clear opening, and the difference is twice the thickness of the timber plus any insulation fixed to it. A builder working from the wrong one builds a kerb that is out before it starts.

So we send a kerb drawing. It is a simple dimensioned sketch for the unit you are buying, with the numbers the builder needs and nothing they do not. We send it as early as the drawings allow, which on an extension is often before the walls are finished, because the opening is fixed by the structure, not the brickwork.

For a pitched roof the drawing is about the opening between rafters or trusses: the clear width and height the roof window needs, the trimming above and below, and the batten heights the flashing kit expects. For a lantern or flat rooflight it is about the kerb: its size, its height, the fall taken up in the timbers so the top stays level, and the detail where the roof covering meets it.

If your builder prefers to build the kerb first and have us measure it, that is fine too. We measure the finished kerb against the maker's requirement and say plainly if anything needs adjusting ahead of ordering. The point is that somebody checks, in writing, before money is spent on glass.

Made-to-measure rooflights and lanterns are built after the order is confirmed with final sizes, and the maker sets the lead time. It varies with the product, the size, the frame colour, the glass and the time of year. We cannot shorten a lead time. What we can do is start it at the right moment, and that moment comes from your builder's programme.

We ask your builder one question: when will the roof be ready for the rooflight? That means the deck laid, the insulation in and the covering turned up the kerb, or on a pitched roof the opening formed and battened. We take the production wait, work back from that date, and agree an order date with you and your builder. The order goes in once the kerb size is confirmed, and we send everyone the delivery date the maker gives us.

The chart above shows the idea on a loft conversion. The windows are ordered as soon as the opening sizes are agreed, so the lead time runs while the builder opens the roof and trims the rafters. By the time the openings are ready, the windows are on their way. On an extension with a lantern the bars move, but the principle is the same: the order goes in early enough that the roof never waits for the glass.

If the maker's date moves, we tell you and your builder the day we hear, not the day before fitting. That gives the roofer and the plasterer time to rearrange rather than turning up to an empty opening.

A rooflight sits where several trades meet, and each of them needs the one before to have finished. Getting the order right is most of the job. On a typical extension or loft conversion it runs like this.

Two details cause most of the trouble when this order slips. The first is the membrane. On a flat roof, the covering has to be dressed up the side of the kerb and finished where the rooflight maker says, before the unit goes on. If the rooflight is fitted first, the roofer has to work around it, and the joint that matters most is the one hardest to reach. We check the membrane detail before we fit, every time.

The second is the reveal. The inside of the kerb or opening has to be insulated before it is boarded, or it becomes a cold band where condensation forms. Electric rooflights and lights set into the reveal need their cables in place before the plasterboard goes up. We agree with your builder who fits the insulation and remind the electrician what is coming, so the plasterer is not boarding over a problem.

Each trade finishes once. That is the whole method, and it is why the size goes to your builder before anyone else touches the roof.

On a flat roof, the joint between the covering and the kerb is the one that decides whether the rooflight stays dry for decades. Every covering handles it differently. A single-ply membrane is bonded up the face of the kerb and finished with a termination detail. A GRP roof is laminated up the upstand with a formed angle at the base. A torch-on felt system has its own capping sheet and fillet. The rooflight maker then says where their frame sits relative to all of that: over the top of the covering, or with the covering run up under a trim.

We send your roofer the maker's detail for that particular unit before they start, because a covering finished a few millimetres too high or too low on the kerb is hard to put right once the rooflight is on. On the day, we check the detail, fit the unit to it and seal the frame to the maker's instructions. If anything looks wrong, we stop and talk to the roofer before we fit, not after.

The same care applies to the upstand height. It is measured from the finished roof surface, so insulation, deck boards and covering all count. A kerb that looks tall enough on the joists can end up too low once the roof is built up around it, which is why the height on our kerb drawing is always stated above the finished surface.

If you are drawing the project, we can help you specify the rooflight before the drawings are issued. We recommend units that suit the roof, the room and the budget, and we provide the maker's product data: dimensioned drawings, kerb or opening requirements, weights, and the thermal performance of the whole unit.

For work to existing dwellings in England, Approved Document L sets limits of 2.2 W/m²K for rooflights and 1.4 W/m²K, or a Window Energy Rating of Band B, for roof windows. We give you the figure for the unit chosen and glazing, so the specification and the Building Regulations submission agree. Where a roof window is meant to serve as a means of escape, we check it against the opening size the regulations require and remind you that this only works for rooms within 4.5m of the ground; a loft on a two-storey house needs a protected stair instead.

We are equally happy to work to your specification. If you have already chosen a unit, we will tell you its lead time, check the kerb detail against the maker's current instructions and flag anything that has changed since your drawing was produced.

Builds move. Steel arrives late, the weather stops the roofer for a week, a client changes the kitchen layout and the lantern has to shift with it. None of that is unusual, and the rooflight plan has to move with the rest of the job rather than against it.

If the roof date slips, we tell the maker and, where they allow it, hold the delivery so the unit is not sitting on site getting knocked about. If the opening size changes before we order, we send a new kerb drawing and withdraw the old one, so there is only ever one set of numbers in circulation. If it changes after the order, we tell you straight away what can still be altered, what it costs and how it affects the date, and nothing goes ahead until you agree.

The habit that makes this work is simple: one person on our side looks after your job from survey to sign-off, and every change is confirmed in writing to you and your builder at the same time. Messages are not passed along a chain, and nobody finds out about a change on the morning they arrive.

Not every job comes with a builder. Adding a roof window to a loft that is already a bedroom, putting a sun tunnel into a dark landing or swapping a cloudy dome on a garage roof are jobs we carry out ourselves from start to finish. The sequence still matters; it is just shorter, and we run all of it.

We survey the roof and the room, agree the unit, and plan the opening from inside and out so the light lands where the room needs it and the opening misses rafters, cables and pipes. On the day we protect the room, open the roof, trim the structure, fit and flash the unit, and line the reveal. Where plastering or decorating is needed afterwards, we tell you in the quote whether it is ours or yours.

Your builder runs the site, and we work to their rules. We confirm our day with them as well as with you, arrive when we said we would, and keep to the area we need. Where the roof is reached by their scaffold, we check it is safe for our use and leave it as we found it. We never stand on glass; we work from the deck or the scaffold beside the opening.

Large units are delivered as close to the fitting day as the maker allows, so crates are not sitting in the way of other trades. When we finish, we tell your builder and the next trade that the opening is ready for them, take our packaging away and leave the roof weathertight.

Who builds the kerb?

On a new extension or a new flat roof, your builder usually does, to the size we send, because they are already framing the roof. On a retrofit into an existing flat roof, we can build it or agree it with your roofer.

Can you supply the rooflight for my builder to fit?

Our service is supply and fit, because the sizing, ordering and fitting are what make the rooflight work in the programme. We are glad to talk your builder through any detail they are unsure of.

How early should I get in touch?

As soon as you have drawings or a builder's start date. The earlier we agree the unit, the earlier the kerb size reaches your builder and the more room there is to order without the roof waiting.

Do you work with architects as well as builders?

Yes. We provide product data and kerb details for drawings and specifications, and then work with whichever builder carries out the job.

When the rooflight is part of a bigger project with its own Building Regulations application, it is inspected with the rest of the work, and we give your builder the product information the inspector asks for. When we fit a new rooflight or replace a whole unit as our own job, the work is notifiable and we handle the notification, so you receive the completion paperwork without chasing it.

You also receive the product details from the maker and our 10-year workmanship guarantee. Keep them with the house papers; a buyer's solicitor will ask for them one day. If you are starting a project and want to see how this would work on yours, book a free survey or send us your drawings, and read our costs page for what moves the price.