Side aisle

A side aisle is the strip of space that runs along either side of the nave in a building divided by rows of columns or piers. It is narrower than the nave and usually lower. In a basilica it carries circulation and secondary functions; in a mosque it extends the congregational space of the prayer hall sideways.

Role in the building

Side aisles help the structure of the nave. The sideways thrust of a nave vault or tall nave wall is taken through the aisle roof and the outer walls, so the aisle covering acts as a kind of continuous buttress. In timber-roofed basilicas, the aisle roof is kept lower so that windows can be placed high in the nave wall.

• Single aisles: one strip on each side of the nave
• Double aisles: two on each side, giving a five-aisled plan
• Galleried aisles: with an upper gallery above

In survey and restoration

Because aisle walls and roofs carry thrust from the nave, they are a common place for structural damage: outer walls leaning out, cracked vaults or arcades out of plumb. In survey, measure each bay separately and record whether the columns are vertical. Later partitions or blocked openings in an aisle are documented as a separate phase in restitution work. Building the aisles as volumes separate from the nave in a 3D model makes phase analysis and sections easier to read.