The number of roof ventilation tiles (often called "chatières" or "cat-flap" tiles) required for a roof depends on several factors, including:

Quick definition

A ventilation tile is a perforated or vented tile that allows air to circulate in the space beneath the roof covering, preventing condensation and extending the lifespan of both the roofing and the insulation.

Factors to consider

1. Total roof area (in m²)

2.Type of roofing material (flat tiles, interlocking tiles, slate, etc.)

3. Presence or absence of a roofing underlay (breathable membrane)

4. Type of insulation (unconverted/cold attic vs. converted/habitable attic)

5. Local regulations or DTU standards (Unified Technical Documents)

6. Roof pitch

General recommendations (DTU 40.21 / 40.211)

If a roofing underlay is present:

• 1 ventilation tile per 20 to 25 m² of roof (projected area)

If no roofing underlay is present:

• 1 ventilation tile per 10 to 15 m²

For converted attics:

• Ventilation is required at the bottom (air intake) and at the top (air exhaust)

• Recommended minimum airflow rate:

1/500th of the insulated surface area

Simple calculation

example 100 m² roof with roofing underlay:

100 ÷ 25 = minimum of 4 ventilation tiles (2 at the bottom,

2 at the top) Without underlay:

100 ÷ 15 = minimum of 7 entilation tiles

Practical tips

• Distribute the ventilation tiles evenly across the roof slopes.

• Install an equal number of air intakes at the bottom and air outlets at the top.

• Provide continuous ventilation if possible (ventilated eaves, ventilated ridge closures, etc.).