Rooflights and Roof Windows

Thinking about installing a rooflight or roof window? These fantastic additions fit seamlessly into your pitched or flat roof, designed to bring abundant natural light into your rooms.

However, before you begin, be aware that putting in a new rooflight almost always requires Building Regulations approval. Here’s why your project will likely need this official go-ahead:

• You will typically need to alter your existing roof structure to create the necessary opening.

• Your roof must be robust enough to support the additional weight of the new rooflight. If it isn't, you will need to reinforce the structure.

• The rooflight itself needs to offer excellent insulation against heat loss, making it energy-efficient.

• If the rooflight is situated close to a property boundary, you will need to give careful thought to its fire performance.

Modifying Your Roof's Structure

When you install a rooflight, you’ll frequently find yourself cutting through one or more of your roof's existing rafters (for sloped roofs) or joists (for flat roofs). The newly cut ends will then need fresh support, usually achieved by fixing two timber 'trimmers' horizontally across the new opening.

Additionally, the rafters or joists immediately adjacent to your new opening will now bear the increased load from the timbers you've cut. You might need to strengthen them by securing a new, full-length rafter or joist directly alongside the existing one.

Keeping the Elements Out

Once your rooflight is installed, you must ensure it’s completely weatherproof. This involves sealing the edges where the rooflight meets the roof, as well as making sure the glass itself is watertight.

You can commonly achieve this using traditional lead flashing or by utilising specialised kits that come supplied with the rooflight unit. It's always a good idea to consult the manufacturer, as they often provide detailed guidance on both installation and effective weatherproofing for their products.

Ensuring Good Airflow

You’ll need to make sure that the room which the rooflight serves has sufficient ventilation. Your rooflight itself can often provide this, catering for both rapid air changes (rapid venting) and continuous, low-level airflow (background venting).

Furthermore, don't forget to consider any existing roof voids or spaces; you need to guarantee that air can still circulate effectively within these areas.

Saving Energy

Every dwelling must be energy-efficient, and your rooflight contributes significantly to your property's overall energy performance, much like your windows and doors. You must ensure your rooflight complies with Building Regulations regarding heat loss.

This performance is measured by its U-value, which indicates how well a building component insulates (a lower U-value means better insulation). Crucially, your rooflight's U-value must not be higher than the permitted maximum.