Roof Waterproofing & Insulation: The Complete Guide
Reading the Warning Signs
Part 2 of 4
Because water doesn't always travel in a straight line through a concrete slab, the signs of a failing roof don't always show up where you'd expect. It's worth learning to read them correctly, both up on the roof itself and on the ceiling of the floor below.
On the roof, the first thing worth checking is whether rainwater drains quickly toward the gutters or pools in certain spots for more than a day or two after rain. Standing water is a sign of insufficient slope, and it's also exactly where any failure will show up first. Also check the joints around parapets, vent pipes, and any air-conditioning fittings — these are the points where the waterproofing layer is interrupted, and statistically the most common source of leaks.
On the ceiling below, a yellowish or brown stain that gradually grows after each rainfall is the clearest sign. If the plaster around the stain has started bubbling or detaching, the problem has already been going on for several months. In more serious cases, you might see water droplets forming directly on the ceiling during or right after heavy rain.
A less obvious but equally telling sign is higher-than-usual air-conditioning bills in summer, with no obvious cause. A roof without thermal insulation, or with worn waterproofing, can reach a surface temperature of 70°C+ on hot days, transferring a significant share of that heat into the room below.