Ponding water is defined as water left standing 48 hours after a rain. It is one of the most common challenges commercial roofing contractors face due to the severe negative consequences it can have on all types of flat roof systems. To prevent this problem in the first place, the National Roofing Contractors Association recommends that flat roof designs provide enough slope to make sure that the roof drains easily. The recommended roof slope is a minimum of ¼” per foot.
While proper structural design and construction can forestall this issue, oftentimes the contractor gets called in to fix it years after the roof was installed by someone else. In a previous article we talked about common causes of ponding water, in this article we are going to talk about why this issue is important.
The negative effects of roof ponding include:
Structural damage and deformation of the roof deck:
Water weighs about 63 pounds per cubic foot. A large pool of it, even at ¼ inch depth substantially increases the load on the roof system. As water collects, the roof deck begins to sag and the worse the problem gets for both the roof structure and contents in the building. Most roof decks are designed for specific loads and when you exceed that point, roof collapse is a real possibility.
Damage to the roof surface and membrane:
Winter freeze/ thaw cycles create ice composites that scrub the roof membrane and can cause substantial damage over time causing roof puncturing and leaks. Also, standing water acts like a magnifying glass, burning the roof membrane.
Algae & mold growth:
Pooling water and the heat on the roof surface creates a prime environment for algae and mold to grow when left unattended. This vegetation can deteriorate the roof membrane and often leads to a buildup of debris which can clog roof drains and make the ponding problem even worse.
Talk about an OSHA and insurance nightmare! In today’s legal environment, no one needs unnecessary lawsuits.
Bad news for onsite workers as well as anyone working in the building. Is your building in an especially sensitive environment like a Hospital or School?
Buildup of dirt and other pollutants:
These elements can compromise the roof membrane and lead to premature decay.
I spoke to a gentleman the other day that said his insurance company found ponding water on his commercial building and will not renew the policy unless fixed. This is common with most policies, better check the fine print!
Ponding water erodes the roof membrane faster resulting in premature failure of the roof system:
When water sits on a roof surface, it can create a capillary effect (moisture gets forced into the system) and moisture can get underneath the membrane, the insulation becomes compromised and loses effectiveness. Most importantly, moisture can cause serious damage to the roof deck and contents inside the building.
As you can see, ponding water is not something that should be taken lightly. The good news is, there are several proven and cost effective methods to eliminate it. In fact, it can be a good opportunity to open new doors for service sales and build trust with a client so when it comes time for the big re-roof job you’ll be the one they call on first. (See: Ponding Water: Problem or Opportunity?)
Feel free to contact us with any pics, questions or project specifications and we’d be happy to provide a free consult. With over 30 years experience in commercial roofing we’ve pretty much seen it all.
From my office on top of a bone-dry roof,
- P.W. Doc
The Ponding Water Doctor