Conservation Review of a Four-Iwan Seljuk Mosque
A twelfth-century congregational mosque in central Iran has a rectangular courtyard about 22 m by 28 m, four iwans, and a south dome chamber 11 m in diameter. The dome, brick masonry with a double shell, sits on an octagonal transition zone with muqarnas. The courtyard facades retain Seljuk brickwork, but most of the tile revetment is Safavid, and the mihrab was re-tiled in the 1960s with cement-based adhesive. A recent survey shows rising damp in the north iwan, a 15 mm wide crack through the dome drum, and loss of about 30% of the brick bond in the west arcade. The endowment board proposes three interventions: demolish the west arcade and rebuild it in concrete block with a brick veneer; replace the double-shell dome with a 120 mm concrete shell to permit a new prayer hall below; and add a 25 m high minaret at the main entrance to make the mosque more visible. The architect is asked to review the proposals and set a conservation strategy.
1. Interpret the spatial hierarchy and structural logic of the four-iwan mosque. Explain what each proposal would damage.
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The four-iwan courtyard is a hierarchy of movement and gathering: the courtyard is the public heart, the iwans frame the four axes, and the south iwan is the threshold to the dome chamber, the most sacred and structurally independent volume. The arcades are a repeatable bay system that defines the courtyard edge; the dome chamber is a single large volume with its own transition zone. Rebuilding the west arcade in concrete block with brick veneer would destroy the authentic brick bond and the structural rhythm, and the concrete would be stiffer and heavier than the original, attracting seismic forces. The minaret at the entrance would shift the hierarchy from the qibla axis to the street and add a tall, stiff element on old foundations. The proposals treat the mosque as a set of isolated objects rather than a linked spatial system, and they confuse visibility with significance.
2. Evaluate the proposal to replace the double-shell brick dome with a 120 mm concrete shell. Discuss structural and conservation issues.
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A 120 mm concrete shell is not a like-for-like replacement. It is thinner but much stiffer, and its thermal expansion and moisture movement differ from the brick drum; the connection at the drum would become a crack-prone interface. The original double shell controls temperature and acoustics and carries load through a brick vault; a concrete shell changes the load path and may increase thrust at the drum unless a ring beam is added. The 15 mm crack may be caused by settlement, thermal movement, or the dome's thrust; replacing the dome before diagnosing the cause is risky. Conservation requires monitoring the crack, checking the foundation, and repairing with lime grout and stitching. If a new shell is ever needed, it should be a separate, reversible structure inside the old dome, not a demolition and replacement. The concrete option also destroys the original fabric, which is the primary evidence of the building's history.
3. Set a conservation and new-intervention strategy. Address the west arcade, the dome crack, rising damp, the prayer hall, and the minaret.
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Strategy: minimal intervention, compatible repair, and reversible new work. First, remove the cement-based tile adhesive and 1970s plaster, re-point with lime mortar, and improve drainage around the north iwan to stop rising damp. Monitor the dome crack for a year; if stable, grout and stitch; if active, underpin and add a discreet ring beam. Rebuild only the lost 30% of the west arcade bond, using salvaged brick and lime mortar, and shore the arcade during work. For the new prayer hall, use a separate steel frame on independent footings, set back from the historic walls with a seismic joint, a lightweight roof, and reversible connections; its architecture should be quiet and clearly contemporary. Reject the minaret at the entrance; if a marker is needed, use a low, free-standing sign or a light tower away from the old foundations. The test is: can the new work be removed without damaging the old? If not, redesign.