Natural light: enlarging an opening or adding a sun tunnel

A dark house is unpleasant to live in, and harder to sell. Enlarging an opening, creating a picture window or capturing light through the roof transforms a room, provided the structure and the planning rules are respected.

Enlarging a window or creating a picture window

Widening a window onto the garden, or turning it into a French window or a sliding picture window, changes the relationship between the house and the outdoors. In a load-bearing wall, the opening requires a properly sized lintel or beam. Any change to a façade generally requires a prior declaration (déclaration préalable) at the town hall, and must comply with the local planning rules (proportions, materials, colours).

A benchmark figure: one sixth of the living area

For new homes, the thermal regulations have required since 2013 a glazed area at least equal to one sixth of the living area. This is not an obligation in renovation, but it is a good benchmark.

The rules on neighbours

The French Civil Code protects the neighbours' privacy. A window or a picture window that gives a view onto the neighbouring property must be set back a minimum distance from the boundary.

Any closer, only “jours” are permitted: fixed glazing, which does not open, placed high up. This should be checked before designing the new opening, especially in Bordeaux échoppes (single-storey terraced houses) and semi-detached town houses.

The roof window

In a converted loft, a roof window lets in much more light than a window of the same size in a façade. Its position is chosen according to the orientation, and solar protection is planned for the summer, preferably an external shutter or blind, which is more effective against heat than an internal blind. As it changes the appearance of the roof, it also requires a prior declaration. On roofs with curved channel tiles, common in the Gironde, a flashing kit suited to this type of tile is used, and the window is often placed on the slope least visible from the street.

The sun tunnel

For a bathroom, a corridor or a room in the middle of the house, the sun tunnel, or light tube, captures daylight on the roof and directs it into the room through a reflective tube. It is an effective solution where no window is possible.

Sharing light between rooms

An interior glazed partition, a glazed door or a fanlight above a door lets light flow from one room to another. Light colours, bright floors and well-placed mirrors extend the effect.

Thinking about summer comfort and insulation

More glazing means more light, but also more heat gain in summer and more heat loss in winter. Choose high-performance windows and doors, comparing two values given by the manufacturers: the Uw coefficient, which measures heat loss (the lower, the better), and the solar factor Sw, which measures solar gain. Plan external solar protection on exposed façades, and keep a balance between light and comfort.

The steps in enlarging an opening

1. The study: checking the structure, the orientation and the distances from the neighbours.
2. The prior declaration: location plan, plans of the façades before and after, photos. The processing time is generally one month, extended to two months near a listed historic monument.
3. Ordering the windows and doors, made to measure, once approval has been obtained and the dimensions confirmed.
4. The opening: propping, cutting, fitting the lintel or beam.
5. Fitting the window or door, with particular care for air and water tightness and the junction with the insulation.
6. The finishes: external render, internal reveals, paintwork.

Mistakes to avoid

• Opening up widely to the west without solar protection: the low late-afternoon sun overheats the room in summer.
• Starting before the town hall's approval: a refused opening is not easily closed up again.
• Neglecting the junction with the insulation: around a poorly fitted picture window, cold air gets in and condensation sets in.
• Forgetting about privacy: a large picture window facing the street calls for curtains that are always drawn, which cancels out the benefit.

We assess the technical feasibility, prepare the works declaration and coordinate the creation of the opening through to the finishes.

Sources : Code de l’urbanisme, article R. 421-17 (déclaration préalable pour la modification de l’aspect extérieur) · Code du patrimoine, article L. 632-2 (avis de l’architecte des Bâtiments de France en secteur protégé) · Code civil, articles 676 à 679 (jours et vues sur la propriété voisine) · Code de l’urbanisme, articles R. 423-23 et R. 423-24 (délais d’instruction de la déclaration préalable) · Arrêté du 26 octobre 2010, article 20 (surface de baies des logements neufs : au moins un sixième de la surface habitable) · service-public.fr