There are several types of flat roofs. A flat roof isn’t a roof with no pitch, but with a low pitch. Imagine a roof with no pitch.
Tar and Gravel
This type of roof consists from a layer of roofing felt and multiple layers of hot tar. Then gravel is added for Sun protection and aesthetic reasons. Because the installation process isn’t that easy and you can never know if it was done right, this roof solution has been almost completely abandoned.
Self adhered membranes
This is similar to the torch on method, but without the torch. The membranes have a self adhered layer. It has a protection layer that needs to be piled off. Then the membranes needs to be flattened by a 70lbs weight. The membranes are very easy to apply and they need no insurance. They are a little more expensive , but more efficient. One major drawback is that it can only be applied in warm weather.
It is, as you have guessed, made of rubber. One nice thing is that the coating can be applied over other types of coatings. It can be found in spray and roller form. The spray dries instantly, while the roller needs a few days to cure. Although the layer is fairly thin, you can add multiple layers. You can save a lot of money because you won’t need to remove other protective membranes or coatings. One major drawback is that the coating is quite expensive.
It’s a membrane that needs to be applied with the help of a torch. The flame is needed to seal the layers together. The problem is that you will need a special type of insurance to perform the installation. The coating is much cheaper then the self-adhered membrane and it’s very effective. The installation can be done in every season.