A flat roof window is an insulated daylight opening with flat glazing, installed on a kerb in a flat or low-pitched roof. It may also be referred to as a flat glass rooflight or glazed rooflight.

Unlike a traditional domed plastic rooflight, a flat roof window has a flush, contemporary glass surface. A white, low-maintenance internal frame provides a calm interior finish. Depending on the version, it can be fixed, open electrically for ventilation, provide roof access or incorporate walk-on glass.

The right dimensions depend on the floor area and depth of the room, ceiling height, layout, roof construction and desired amount of daylight. A centrally positioned window produces a different light pattern from one located close to the façade. Multiple windows can distribute daylight more evenly.

Before design and ordering, check the direction of the joists and the available space between structural members. Have any changes to joists, beams or other load-bearing elements assessed. Use only the technical information for the selected model and size when forming the opening.

A flat roof window must be installed at a sufficient angle so that rainwater drains from the glass and connections. Standing water increases soiling and can place additional stress on junctions and sealant. Intura models are generally suitable for roof pitches of approximately 2 to 15 degrees.

Check the actual fall on site, as a flat roof may not be level or uniform throughout. The kerb, roof construction and finish must together achieve the prescribed pitch.

The roofing is dressed against and around the kerb in accordance with the installation instructions. The exact method differs for bitumen, EPDM, PVC and other roofing materials. Corners, overlaps and terminations require particular care.

Waterproofing, insulation and airtightness are separate layers, all of which must remain continuous. Make sure the roofing contractor and carpentry or finishing team understand in advance where their work interfaces.

Condensation occurs when warm, humid indoor air meets a cold surface. Control indoor humidity, ventilate the room and provide continuous thermal insulation and an airtight connection around the kerb and internal finish.

A thermal bridge or air leak can cause locally low surface temperatures. Allow air to circulate across the glazing when designing the reveal. Moisture on the room side does not automatically mean that the window is leaking; moisture between the panes may indicate a failed insulated glass unit.

Solar-control glazing is particularly useful for large glazed areas, sunny roof positions and rooms that heat up quickly in summer. It reduces a proportion of solar heat and intrusive glare while retaining natural daylight.

Glazing is only one part of summer comfort. Glass area, orientation, internal heat sources, ventilation, night cooling and blinds also matter. Where comfort requirements are high, additional adjustable shading may be required.

An electrically ventilated PGC model can be opened for purge ventilation and to release warm air. It is a useful addition but does not automatically replace the continuous ventilation required in a home, bathroom, kitchen or commercial space.

Coordinate the window with the ventilation strategy and plan the electrical supply and controls in good time. Consider maintenance, accessibility and safe isolation during work.

• Confusing the commercial size with the external dimensions or structural opening.
• Checking the supporting structure only after the opening has been formed.
• Providing insufficient fall or inadequate drainage.
• Interrupting insulation or airtightness around the kerb.
• Underestimating solar exposure and the risk of overheating.
• Failing to plan power and controls for an electric model.
• Treating a standard flat roof window as though it were suitable for foot traffic.

If in doubt, have the complete configuration checked before ordering. Include the required size, roof construction, roofing material, pitch, photographs and a drawing showing the proposed position.