Níall Hedderman: Extension daylight design

I have been designing house extensions since 2009. The projects that work, the ones clients are still happy with a decade later, are the ones where daylight was the first design decision, not an afterthought.

The projects that frustrate people are almost always ones where light was treated as a product added at the end, rather than a quality you design from the start. 

Windows and doors brings light just a few metres into a room. The deeper the extension, the darker it becomes. A long extension with only rear glazing will be bright at the garden end and dim everywhere else.

Roof apertures behave differently. Light entering from above reaches further into the space, it is more consistent across the day, and it changes the perceived height and volume of a room in a way that wall glazing can’t. A well-placed rooflight does not just brighten a room, it makes it feel taller, more resolved, more finished.

That distinction matters enormously when you are designing a kitchen, a family room, or any space where people spend serious time.

The best way I can explain this is through the projects I have designed. 

The first project is a flat-roof kitchen extension to a detached suburban house. The plan is wide, and from the outset I knew that rear glazing alone would leave the middle of the kitchen, the working heart of the room, permanently in shade. I designed three light sources working together: north-facing high-level glazing along one side for consistent, shadow-free light over the worktops; a large south-facing door fitted with privacy film on the other, connecting to the driveway; and a rooflight sitting centrally in the flat roof above the kitchen island, positioned between the two.

The rooflight is the control valve. The home-owner can use blinds to control the quality of light throughout the day rather than simply opening and closing things reactively.

The second project is a single-aspect listed basement flat in Edinburgh’s New Town conservation area, a challenging sites for an architect to work in.

Natural light came from one direction only. Adding the extension made the plan deeper and pushed the kitchen further from any daylight. The solution was a rooflight placed at exactly the junction between the new extension and the existing back wall of the flat: the precise point where natural light fades in the original layout. Light from above made this kitchen possible.

The third project is a mid-terrace townhouse where the neighbours above could look directly down into any south-facing rooflights. The obvious answer, privacy glass, was a non-starter, because the whole point of a rooflight is the view of the sky.

Instead, I specified rooflights that are relatively narrow in proportion to the depth of the roof build-up. The thickness of the roof construction itself restricts the angle at which anyone above can see into the space, without compromising the upward view from inside. 

Before you fix a layout, understand your relationship with the sun. Stand in your garden at different times of day. Know which direction your extension will face. Think about where the light will be at eight in the morning when you are making breakfast, and at four in the afternoon in January.

The roof is your most valuable surface. Once the structure goes up, your options narrow quickly. Decide early, and decide deliberately, not because a rooflight is a product worth adding, but because light is a quality worth designing.

An extension that gets this right will still feel like the right decision in 20 years. One that gets it wrong will feel like a missed opportunity for just as long.