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If you own a building with a flat roof in Los Angeles, you might notice that water tends to stick around long after the rain stops. This standing water, technically known as ponding water, is the number one enemy of flat roofing systems. While a little bit of water right after a storm is normal, water that stays for days is a serious structural threat.
In this guide, we will break down exactly why this happens on your built up roof and, more importantly, how to fix it before it turns into a costly leak.
Key Takeaways
- Water remaining on a roof for more than forty eight hours is considered ponding and requires attention to prevent structural damage.
- You should inspect drains first because simple clogs are often the cause of water accumulation rather than structural failure.
- Installing crickets or tapered insulation is the most effective way to correct slope issues and divert water to drains.
- Upgrading to hydrolysis resistant membranes like PVC or silicone can protect roofs where perfect drainage is difficult to achieve.
- Addressing sagging decks from heavy roof over layers is essential to stop the problem at its source and prevent collapse.
The 48 Hour Rule
The first thing you need to understand is the difference between a wet roof and a ponding roof. Industry standards state that water should drain or evaporate from a roof within 48 hours of rainfall. If you still see puddles after two dry days, you have a ponding water problem. This standing water acts like a magnifying glass under the sun, accelerating the aging of your waterproofing membrane and adding immense weight to the structure.
Why Ponding Happens
Ponding rarely happens for no reason. It is usually caused by a combination of sagging roof decking, clogged drains, or poor initial design. One specific culprit we often see is the result of a roof over roof installation. When a new roof layer is installed over an old one without stripping it down, the added weight can cause the center of the roof to bow slightly, creating a bowl effect where water collects.
Immediate Solutions: Cleaning and Maintenance
Before you look into major construction, start with the basics. Often, the water is pooling simply because it has nowhere to go. Leaves, dirt, and debris can easily block scuppers and internal drains. You should schedule a time to clean your gutters and drains thoroughly. If the water drains away once the blockage is removed, your problem is maintenance, not structure.
Structural Solutions: Crickets and Tapered Insulation
If your drains are clear but water still sits, you likely have a slope issue. Flat roofs are not actually perfectly flat; they are supposed to have a slight pitch to guide water to the drains.
To fix a flat spot, a roofer can install what is called a cricket. A cricket is a rigid, triangle-shaped structure built underneath the roof membrane that works like a traffic director, physically diverting water away from walls and curbs toward the drains.
Another effective solution is installing tapered insulation. This involves placing wedge-shaped insulation boards under the roofing membrane to create a completely new slope. This method not only solves the drainage issue but also improves the building’s thermal efficiency.
Material Upgrades
Some roofing materials handle standing water better than others. If you cannot completely eliminate ponding due to the building’s design, you may need to upgrade to a more robust membrane. Single-ply membranes like PVC or TPO are welded at the seams, making them more resistant to standing water than traditional asphalt-based systems. Applying a high-quality silicone coating can also help waterproof a roof against the damaging effects of ponding, as silicone is inorganic and will not break down under standing water like asphalt will.
Ignoring ponding water is a gamble that rarely pays off. The added weight and moisture will eventually find a way into your building. Whether you need a simple drain cleaning or a slope correction with tapered insulation, acting now will save you from a complete roof replacement later. If you are tired of seeing puddles on your roof, contact us at LA Roofing Materials for a professional assessment.
FAQs
1. What is considered ponding water?
Ponding water is defined as any water that accumulates on a roof and remains for more than 48 hours after precipitation ends.
2. Can ponding water cause my roof to collapse?
Yes, in severe cases. Water weighs roughly 5 pounds per inch per square foot, so deep ponds add significant stress to the building’s structure.
3. Does a roof warranty cover ponding water?
Many standard manufacturer warranties exclude damage caused by ponding water, which is why correcting the slope is so important.
4. How do I fix a low spot on my flat roof?
You can fill low spots with roof patch compounds for minor issues, but significant depressions usually require installing tapered insulation or a cricket.
5. Is a flat roof supposed to be perfectly flat?
No. A “flat” roof should actually have a slight slope (usually at least 1/4 inch per foot) to allow gravity to pull water toward the drains.