We have sealed hundreds of roofs in Washington DC. Sealing a flat roof is tricky and understanding when to do it and over what is often misunderstood. The first thing to know is what type of flat roof do you have. There are typically only four different flat roofs found in the Washington Metropolitan area. These are Modified, TPO, EPDM and Built-up. Only one of these should ever be sealed and that is Modified. We run into situations where contractors actually seal an EPDM roof and if actually done can destroy any possibility of servicing it. The next thing to consider is why you should seal the roof. If you are experiencing a leak, sealing is not what you need. The leak simply needs to be found and repaired. Roof sealing is not a leak stopper, it is a way to prolong your aging flat roof. It will fill small voids in the membrane. A combination of properly repairing and sealing is many times an option, but make sure your roofing contractor knows what to look for when considering.