Kelda Bath HouseReykjavík, 2022

Kelda is a public bath house on the harbour edge in Reykjavík, with three geothermal pools cast in situ in low-carbon concrete. The building steps down toward the water in three terraces, so every pool keeps its view across the bay, and the changing rooms sit in a thick concrete volume on the upper terrace that shelters the pools from the north wind.

A bath house is a moisture problem dressed as architecture. Warm pool water, cold sea air and concrete that takes years to dry make condensation and slow damage the main long-term risks, so we embedded moisture probes in the slabs and walls during the pour and tied the ventilation to them from the first day of operation. Pool hall humidity is held at 62 percent, within two percent of the design value, and the concrete has dried to 3.1 percent moisture by mass. Four years of data now set the maintenance plan for the pool linings instead of a fixed schedule.