A rooflight can transform an extension before the walls are even decorated. Positioned well, it brings daylight into the middle of a kitchen, makes a garden room feel larger and gives a flat roof a clean architectural finish. Knowing how to order bespoke rooflights properly is what turns that visual ambition into a product that fits, performs and arrives ready for installation.
A made-to-measure rooflight is not simply a standard size with a different label. The dimensions, glazing, kerb detail, roof build-up and finish all need to work together. Spending a little time on the specification before ordering helps prevent the most expensive problems: an incorrect opening, incompatible upstand or glass that is not suited to the room below.
Start with the rooflight’s job in the room
Before choosing a size, decide what you need the rooflight to achieve. A single large fixed rooflight can create a striking focal point over a dining table or island. Two or three smaller units may spread light more evenly through a long rear extension. In a room that runs deep from the external walls, a rooflight is often the most effective way to brighten the area that conventional windows cannot reach.
Consider sightlines as well as daylight. A rooflight above a kitchen island should feel centred when viewed from the main living space, while one above a stairwell may need to align with the flight or landing below. Looking at reflected ceiling plans, if available, can be useful for builders and architects. Homeowners can achieve a similar result by marking the proposed position on a simple floor plan before committing to a size.
There is a balance to strike. More glass can mean more daylight and a stronger connection to the sky, but it can also increase solar gain and make shading, ventilation or solar-control glazing more relevant. The best specification depends on the room orientation, how exposed the roof is and how the space will be used.
Measure the structural opening, not just the space you can see
This is the point where accuracy matters most. Rooflights are usually ordered to suit a structural roof opening or a defined external kerb size. These measurements are not always the same as the visible internal ceiling opening, especially where insulation, plasterboard and a plastered reveal reduce the finished aperture.
Confirm exactly which measurement convention the product uses before placing an order. Some rooflights are specified by the roof opening they fit over; others are sized by the external dimensions of the frame or by the upstand they sit on. The product drawings should state this clearly. Never assume that a rooflight advertised as 1000 mm by 1500 mm requires a 1000 mm by 1500 mm finished internal opening.
Measure the opening in several places, both lengthways and across the width. Roof structures are not always perfectly square, particularly on renovation projects. Record the smallest measurement and check the diagonals where possible. If the rooflight is going onto a builder-made upstand, ask the installer to confirm its finished outside dimensions, height and level before the product is manufactured.
Allow for tolerances and roof build-up
A rooflight needs enough tolerance for safe installation and weatherproofing. The installer will also need to account for the roof membrane, insulation, flashing details and any cladding or capping around the upstand. Ordering to the exact size of an existing hole without checking the manufacturer’s installation guidance can leave too little room for a proper weather seal.
The roof build-up also affects how the rooflight looks from inside. A deeper warm-roof construction may create a more pronounced internal reveal. This is not necessarily a drawback, but it should be considered early so the finished ceiling detail feels intentional.
Choose the right rooflight style
Fixed flat rooflights are a popular choice where the priority is maximum daylight, clean lines and low maintenance. They work particularly well over kitchens, dining spaces, hallways and single-storey extensions. Slim-frame designs can increase the visible glass area and provide a more refined finish from both inside and out.
Opening rooflights are worth considering where extra ventilation is needed. They can be useful in kitchens, bathrooms and spaces where warm air gathers beneath a flat roof. Options may include manual opening, electric operation and rain sensors, depending on the system selected. These add convenience, but they also require planning for controls, electrical supply and access for maintenance.
A roof lantern is a different proposition. Its raised, multi-panel form can create a dramatic centrepiece and suit larger traditional or contemporary extensions. A flat rooflight sits closer to the roofline and is often the better choice where a minimalist appearance, lower profile or uninterrupted view of the sky is the aim.
Specify glazing for comfort, not just appearance
The glass in a bespoke rooflight does far more than let light in. It affects insulation, solar control, safety, privacy and the amount of outside noise that reaches the room.
For most residential projects, insulated double glazing with a low-emissivity coating offers a strong combination of thermal performance and clarity. Triple glazing can improve insulation in some situations, but it is heavier and may not be necessary for every rooflight. The overall roof design, budget and product system should guide that decision.
South-facing or west-facing roofs can receive significant afternoon sun. Solar-control glass can reduce heat build-up and glare, making a bright extension more comfortable in summer. It may slightly alter the appearance of the glass or reduce the level of visible light, so it is a considered trade-off rather than an automatic upgrade.
Safety glazing is essential overhead. Rooflight glass should be specified to meet the relevant safety requirements, typically with toughened outer panes and laminated inner panes where appropriate. Laminated glass helps retain fragments if breakage occurs, providing reassurance for rooms used by families and for installations above seating or dining areas.
If overlooking is a concern, obscured or privacy glazing may help in selected locations, although it will change the view upward. For bedrooms, bathrooms or closely neighbouring properties, discuss the balance between daylight, privacy and planning considerations before ordering.
Confirm the kerb, upstand and waterproofing detail
Many flat rooflights are installed on an upstand, also called a kerb. This raised section lifts the rooflight above the roof surface and allows the waterproofing membrane to be correctly dressed around it. The required height and construction can vary by product and roofing system.
Some rooflights are designed for a site-built timber upstand, while others can be supplied with a proprietary insulated kerb. A proprietary kerb can simplify the installation and help achieve a consistent finish. A builder-made option may offer more flexibility on an unusual project, provided the dimensions follow the manufacturer’s requirements exactly.
Check whether the rooflight is supplied with fixings, cover caps, seals and any necessary flashing components. Your roofer needs this information before work begins, not when the delivery arrives. It is also wise to establish which trade is responsible for forming the opening, building the upstand, applying the membrane and fitting the rooflight. Clear responsibilities protect the programme and the finished waterproofing detail.
How to order bespoke rooflights without costly delays
Once the design is agreed, pull the key information into one specification. This makes it easier to compare products accurately and gives your supplier what they need to confirm suitability. Your order details should cover the following:
- the confirmed structural opening or external upstand dimensions
- the rooflight type, quantity and preferred frame colour
- glazing requirements, including solar control, privacy and safety options
- roof construction, membrane type and upstand arrangement
- whether the unit is fixed or opening, plus any electrical requirements
- site access, delivery timing and a named contact for the day of delivery
Bespoke products are normally manufactured to order, so changes after production has started may not be possible. Check the order confirmation line by line, particularly the dimensions and orientation. If your rooflight is rectangular, confirm which measurement is the width and which is the projection. It sounds simple, but a transposed size can disrupt a roof build and lead to avoidable remedial work.
For trade buyers, technical drawings and installation documents should be shared with the site team before the roof is formed. For homeowners, a short conversation between your supplier, builder and roofer can be just as valuable. Everyone should be working from the same dimensions and fitting method.
Plan delivery and installation around the build programme
Do not arrange delivery solely around the date you want the rooflight fitted. The opening, upstand and waterproofing should be ready, and the site should have safe access for unloading and storing the unit upright and protected. Large glazed units are heavy and need careful handling, often by more than one person.
Aim to install the rooflight as soon as practical after delivery, particularly if the roof opening is exposed. Your contractor should inspect the product on arrival and report any visible transit damage before installation. Keep packaging in place until the unit is close to being fitted, but remove protective films only when recommended so they do not become difficult to remove after prolonged sun exposure.
A bespoke rooflight is a visible investment in how a home feels every day. When the opening, glass and roof detail are specified with care, the result is more than a brighter room: it is a well-finished space that feels open, comfortable and built around the way you live. If any measurement or technical detail remains uncertain, Horizon Windows and Doors can help you check the specification before you place the order.
