A hidden roof is a pitched roof sitting behind a parapet, so from the ground the house reads as a flat-topped block with a clean horizontal edge. It has become one of the most requested things in contemporary Kenyan housing, and it is worth being honest about what it costs to do properly.

The appeal is obvious. You get the crisp modern silhouette without the problems of an actual flat roof, because there is still a pitch up there doing the work of shedding water. Light-gauge steel trusses make the pitch cheap to frame and let it span further than timber comfortably would, which opens up the rooms underneath.

The difficulty is that you have moved every drainage detail out of sight. On a conventional pitched roof, water runs to an eaves gutter hanging in the open where anyone can see it fail. Behind a parapet, the same water runs into a concealed gutter, and if that gutter blocks or the falls are wrong, the first sign is a damp patch on a bedroom ceiling.

So the details that matter are the ones nobody will ever look at. Adequate falls. Overflow provision, so a blockage spills outward and visibly rather than inward and silently. Access to clear the gutter without dismantling anything. Enough upstand at the parapet that wind-driven rain cannot get behind it.

We build them because they look right and clients want them. But a hidden roof is a detail that rewards being built carefully and punishes being built quickly, and the punishment arrives two rainy seasons after everyone has gone home.