Second-storey additions

What is already under the house

A single-storey house on a slab was footed for a single storey. Adding above it means establishing what the footings are, what the soil under them will bear, and whether the existing walls can carry a floor and a roof rather than just a roof.

That is a geotechnical and structural exercise before it is an architectural one. Sometimes the answer is straightforward. Sometimes it means underpinning or new footings inside the existing house, which is a different project and a different number.

The stair costs more room than people expect

A compliant stair needs a run, headroom above it and a landing at each end, and it has to come down somewhere useful on a floor plan that was drawn without it.

This is where most second-storey designs get reworked. Placing the stair first and fitting the new rooms around it produces a better plan than the reverse.

Roof tie-in and the weather

Part of the existing roof comes off. Between that moment and the new structure being dry, the inside of your house is exposed, so the sequence, the temporary protection and the weather window are planned rather than hoped for.

Summer here is the constraint on the finishing trades as much as the framing: concrete, exterior plaster, roofing and paint each have a temperature window that a July afternoon sits outside.

Height, massing and the committee

A second storey is the most visible change you can make to a house. In any community with architectural review it will be judged on height, roof line, massing and what it does to a neighbour’s view, and some associations refuse them outright.

We confirm that before design rather than after, because it is the one answer that can end the project.