Project Topaz

THE SITE

595 square metres in Accra, on a street where the houses sit close. There are neighbours hard against both flanks, and the plot meets the road along its front, where a wall and a slatted gate hold the line.

Nothing was standing on it. What already existed was a set of drawings, and the work began by modifying those. That is a narrower brief than designing from nothing, and a stranger one: the decisions have been made once already, by somebody else, and the job is finding which of them will not survive being built. The house went up from the revised set.

The client came back four years later with Project Onyx — inherited drawings again, but that time with the foundations for three buildings already in the ground, and the landscape ours as well.

THE HOUSE

Two storeys and a roof level. Lounge and living at ground, bedrooms and a family area above, and the first floor carried far enough forward to cover the parking without a separate structure for it. Floor to floor is 3300, and the section runs from a foundation at minus 1500 to a roof at 6600.

Four things changed in the inherited set. The stair was rotated. A room came out of the ground floor so the living and dining could be one larger space. A washroom went in at ground level, which means a visitor never has to go upstairs. And the master bedroom was reworked around a bigger bathroom and a walk-in closet.

Taking the room out is the one that needs defending. A room removed is a room that does not show up when a house is described by its count, and houses here are usually described by their count. What it buys is a ground floor that works as one space for the family actually living in it, which is worth more day to day than a door onto a room nobody uses.

The lounge is the exception to that arrangement. It goes up through both floors and takes glazing on two sides, which is what stops a plan of ordinary rooms reading as a house of ordinary rooms.

WHAT TO NOTICE

The walls are 400 millimetres thick, composite, with insulation inside them. The standard external wall in Ghana is a single leaf of sandcrete block at 150, uninsulated, with a split unit working against it for most of the year.

That wall costs more to build, and it takes floor area to do it: 400 millimetres of wall around a house is area nobody gets to stand in. What it buys is a slower house. Simulation work on insulated walls in tropical climates puts the annual saving above 20 per cent against an uninsulated one, and the arithmetic runs the same way everywhere — the build cost is paid once, the electricity is paid every month, for as long as anybody lives there.

WHERE THIS STOPS BEING TRUE

The 20 per cent is a simulation, not a bill. Nobody has measured this house against a version of itself built at 150 millimetres, and nobody is going to.

The mass question underneath it was a real one. Accra’s day-to-night swing is about four or five degrees, and in a climate with that little range a heavy wall is not automatically an ally: it takes solar heat up through the afternoon and gives it back after dark, and there is no cool night to lose it into. The insulation on this house sits outboard of the mass, which is the build-up that answers that. The insulation meets the sun, and the mass behind it is left to absorb what the household generates rather than what the sky does.

Where it stops is the glass. The lounge is glazed on two sides and runs up through both floors, and no wall thickness answers a window. Solar gain through glazing is the larger term in a house like this one, and the wall cannot be asked to carry it. If this house runs warm on an April afternoon, that is where to look first.