Buttress

A buttress, or payanda in Turkish, is a heavy block of masonry built against the outside of a wall, either vertical or slightly battered. Curved roofs such as arches, vaults and domes do not just press down; they push the supporting walls outward. The buttress uses its own weight to absorb that push and bring it safely to the foundation, so the wall neither leans nor splits open.

How the load path works

The inclined thrust coming from the roof combines with the vertical weight of the buttress. The steeper that resultant becomes, and the closer it stays to the middle of the base, the more comfortably the masonry works in pure compression. That is why buttresses are wide at the bottom and step or slope inward as they rise. The Gothic flying buttress follows the same logic in a lighter form: a half arch carries the thrust across open air to a separate pier.

• Plain buttress: a straight-sided mass bonded to the wall.
• Stepped buttress: narrows in stages as it climbs.
• Battered buttress: sloping outer face with a widened base.
• Flying buttress: transfers thrust through an arch to a remote pier.

Buttresses in surveys and restoration

On historic buildings some buttresses belong to the original design while others were added later as repairs after earthquakes or settlement. A measured survey separates the two by reading joint continuity, changes in material and whether the courses are toothed into the wall; the restitution drawings then assign each to its period. A vertical crack between a buttress and the main wall can point to unresisted thrust or uneven settlement, and it is logged separately during damage assessment.