Stains on a flat commercial roof may only seem like a cosmetic problem, but they can indicate more severe concerns. Determining the cause of the stains can help guide the proper repair steps. 

1. Ponding Water

Often a stain on a flat commercial roof is indicative of ponding water, which is a sign of drainage issues. Ponding water stains tend to be dark in color due to mold or algae growth that occurs in these damp spots. There may also be collected dirt and debris in the affected area, which further darkens the stain. Although the stain itself is not immediately damaging, the cause can lead to leaks or even a collapse due to the excess weight of the ponding water. Drains may need to be cleaned or installed in order to solve the issue.

2. UV Damage

Over time, damage from sunlight can cause commercial roofing membranes to break down. You may first notice a slight discoloration on the affected areas. The discoloration may give the membrane a white or yellowed appearance, and the membrane in the affected area may seem more brittle than it should be. Once affected, replacement of the membrane is needed. In the future, you can help prevent UV discoloration and damage by having the roofing membrane recoated every few years to help guard against UV radiation. 

3. Bird Stains

Birds are much more than a nuisance when they gather and nest on your flat roof. Bird dropping stains have a mottled light and dark appearance. Not only is this unattractive and odorous, but the acid in bird droppings will also slowly eat away at your roof membrane. Prompt cleaning will remove the stains, fortunately. You can then have the roof recoated to help protect it against further acid damage. It's also a good idea to install some bird prevention devices, such as roof pegs, so that the birds don't return and cause more damage.

4. Corrosion Issues

A commercial roof has quite a few different appliances and vent pipes installed upon it. Each of these items is flashed around the base with metal or rubber in order to prevent leaks. As metal flashing fails, it may begin to corrode or rust, which can leave reddish-brown stains on the roof. Although this problem doesn't affect the roofing membrane, it does indicate that the flashed areas may be more prone to leaks as the flashing fails. Replacement of the flashing is needed to solve the problem.

Contact a commercial roofing company, like Tillotson Enterprise Inc, if you have further questions about roof staining.