We finished the repair work of a terrace in an attic. The reform consists of reworking the existing pavement and replacing the waterproof sheet to solve the humidity problems on the roof of the lower floors.
One of the keys to successfully waterproofing a flat roof is the treatment of singular points: perimeters, encounters with projecting elements such as drains, chimneys, etc … It must be taken into account if a sheet is made using sheet joints smaller ones, a good seal must be made by the applicator between sheets (taking care to also make a good overlap, of about 20 cm as a general rule)
We in this case have chosen a 1.1mm firestone butyl EPDM sheet in a seamless blanket as it allows us to depend less on the skill of the workmanship. The sheet is placed on a geotextile and under a geotextile, in this way it can expand freely from the layers with which it is in contact and can last many more years. In fact, the installers give us a 20-year guarantee.
On a terrace exposed to the sun, perimeter expansion joints are very important (and if we have very large roof panels, interior joints will also have to be made) since the roof must have a margin to expand, otherwise the pavement could crack.
Another important point when verifying the proper execution of a rehabilitation of a terrace or flat roof is the verification by means of a tightness test of the proper functioning of the roof. In our case we have carried out a flood test for 24 hours. One very important thing in this case is that if the drain is covered, it is necessary to have an overflow in case it rains since the overweight of the water is one ton per m3 and any structure could collapse for this reason.