Kerrottamalla

Kerrottamalla is a Finnish term that describes a type of passage or corridor that runs along the side of a multi‑storey building and provides access to all floors. The word is a combination of *kerros* (floor) and *tall* (building or structure), with the suffix *-alla* indicating location, so the literal sense is “on the floor building.” In practice, a kerrottamalla functions as a continuous vertical and horizontal link that connects staircases, elevator shafts, and interior rooms on each level.

Architecturally, the kerrottamalla is usually situated in the core of a building. It may run the full height of the structure, providing a covered walkway that offers protection from the elements while allowing natural light and ventilation. The corridor can be paved with stone, metal, or composite flooring, and its width is governed by local building codes, typically ranging from 1.5 to 2.5 meters to accommodate foot traffic and wheelchair accessibility. In addition to serving as a circulation path, the kerrottamalla often houses utility conduits, dead‑bolt firestops, and, in some designs, small service areas such as storage or maintenance rooms.

In Finnish schools, hospitals, and public buildings, the kerrottamalla is a common feature because it simplifies the layout and makes emergency evacuation more efficient. The design is also favored in apartment complexes, where it ensures each unit has internal access without requiring external staircases. Modern adaptations sometimes include fire‑resistant cladding and acoustic treatments to meet contemporary safety regulations.

Historically, the concept of the kerrottamalla predates modern construction techniques, found in old wooden townhouses and wooden bridges that exploited timber framing to create protected walkways. Today, standard building codes define kerrottamalla specifications in terms of fire rating, load capacity, and egress width. Because of its multifunctional nature, the kerrottamalla remains a staple feature in Nordic architecture, embodying a blend of functionality, safety, and aesthetic consideration.

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