A lunette is a small, subsidiary roof that is placed at right angles to the main roof and ‘pierces’ into it. The lunette intersects the main roof plane, creating a junction with a valley line. Lunettes are used to provide a roof for an extension, bay window or transversely placed section of a building that connects to the main roof.
Characteristics of a lunette
| Characteristic | Description |
|---|---|
| Position | At right angles to the main roof, joining beneath it |
| Ridge | Lower than the ridge of the main roof |
| Junction line | Valley line (internal angle) where the lunette meets the main roof |
| Size | Smaller than the main roof |
Difference between a lunette and a cross roof
- In a cross roof, both roofs are of comparable size and fully intersect one another
- In a lunette, the subsidiary roof is smaller and pierces into the main roof without reaching the ridge
- The ridge of the lunette terminates below the ridge of the main roof
Applications
- Extensions: a rear extension to a dwelling
- Bay windows: a projecting facade element with its own roof
- Side wings: a smaller transversely placed building section
- Dormers: larger dormers with their own roof that pierces into the main roof
Construction
- The lunette has its own rafters that bear against the main roof
- At the junction line, a valley rafter (internal angle timber) is formed
- The valley rafter carries the rafters of both the main roof and the lunette
- Proper waterproofing at the valley line is essential
Tips for the DIYer
- The valley line is the most vulnerable point: use lead flashings or a zinc valley gutter
- Match the roof pitch of the lunette to the main roof for a harmonious result
- Ensure that the valley rafter is adequately sized
- Check whether planning permission is required
Related terms
- Cross roof: two equal roofs that intersect one another
- Valley rafter: internal angle timber where two roof planes meet
- Valley gutter: gutter in the internal angle of the roof
- Gable roof: roof with two sloping planes