In reality, there cannot be a literately flat roof because it will not drain any water. When it rains, the water will remain there until when the roof begins to leak. So, what is being referred to as flat roof is actually low-sloped roof. It is not as sloppy as the pitched roof. Actually, flat roofs usually have about 10 degrees slope.
The commonest kind of flat roof is built up roof. Even though it is also referred to as hot-tar-and-gravel roof, tar is no longer in use. Instead, asphalt built up roof is now the order of the day. This is because asphalt lasts longer than hot tar.
Some of the benefits of built up roofs are outlined below:
Since flat roofs drain water less than pitched roofs, water stays on it a little longer. So, built up roofs offer fantastic waterproof protection. This helps to prevent leaking. It also protects the building from the ultra-violet rays of the sun. Needless to say that UV rays are dangerous to human health.
Another benefit is that it requires relatively low maintenance cost and it can withstand harsh weather conditions. It is very tough and durable. Gravel is a very good fire retardant so built up roofs protect the whole building from being razed down. Secondly, gravel beautifies the siding, deck and the windows of your house.
As beneficial as built up roofs are, they have their own drawbacks. They are quite difficult to install. The difficulty also affects the speed of installation. In other words, they are very slow to install. Secondly, the installation emits fumes and vapors that are harmful to human health.
Even though built up roofs have a very low cost of maintenance, their cost of installation is on the high side. When a built up roof begins to leak, the leaking spot is always difficult to figure out because gravels sometimes clog the scuppers and gutters. Finally, built up roofs are quite prone to water and wind damages.
Common issues with built up roofs are open joints, undulations and cracks.
To repair any open joint, first apply some cement on the opening. Then, you hold it down so that it can stick to the substrate. This method sometimes fails. If it does, then you have to cut a felt and nail it down over the open joint and pour some cement of the nail and then spread some gravel over the cement and allow it to harden up.
To fix this, you need to level up the sunken areas by adding some layers on them. The substrate has to be in perfect condition for you to be able to fix the problem of undulations.
First of all, you need to clean the area and then add a coat of asphalt cement to it.