Flat commercial roofs can present unique problems in regards to drainage, and it’s important that property managers and owners take steps to ensure that drainage is maintained over time and not left to chance. Without proper maintenance, a pool of water can develop on the roof surface, which can lead to long-term damage and costly repairs. Below, we cover the key aspects of maintaining drainage on flat commercial roofs.

How Flat Roofs Drain Water

Flat commercial roofs are designed to drain water in one of two ways. The simplest drainage system is the one designed with a gentle slope to shed water from high points to lower points. The second type is a roof built with precise drainage channels distributed throughout the roof like a network of “sub-roofs” that carry water away from the roof’s surface in a series of parallel lines.

Gravity vs. Center-Discharge Drains

Gravity-discharge drains are less-common but still relevant in certain flat roofing systems. In this system, water is passively discharged off the roof without the use of a pump or a catchment system. On the other hand, center-discharge drains are more commonly used in flat roofing systems. This method of drain use a catchment system, typically a collection of pipes, to channel water down to a lower-ground point.

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Replacing Saturated Insulation

Drain failure can lead to water sitting on the roof or standing puddles, which can lead to the saturation of insulation. It’s important to check on the insulation to see if any repairs need to be done. The insulation must be dry and free from any signs of saturation before reinstallation.

Inspecting And Repairing Seams And Flashing

A critical aspect of maintaining a well-draining flat roofing system are the seams and flashing. Flashing is the metal, rubber or plastic material that is used to join two pieces of material together, direct water away from roof crevices, penetrate skylights and other roof locations. Damaged flashings and seams should be inspected and repaired regularly to ensure a continual flowing of water off the roof.

Checking Downspouts And Gutters

Before the rainy season, make sure to inspect the downspouts and gutters of your flat roof. Any debris that has accumulated in the downspout needs to be cleared out and the gutters should be checked for signs of damage or wear and tear. Damaged gutters and downspouts will not be able to adequately carry water away from the building or prevent water saturation of the soil below the building.

General Roof Inspection

It’s important to do an overall inspection of your flat roof regularly, including removing debris and dirt to ensure a free-flowing drainage system. In addition, check for signs of mold, mildew and other signs of damage or potential damage, such as raised seams or signs of sagging or wear and tear.

Answering Frequently Asked Questions on Drain Maintenance

How do I clean a flat roof?

Flat roofs can be cleaned by using a special mold-resistant cleaning solution and a soft-bristle brush. The cleaner can be sprayed directly on the roof, then a soft-bristle brush can be used to clean the surface. Additionally, a soft bristle pressure washing system can also be used, but extreme caution should be taken not to damage the roofing material.

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How often should I inspect and clean my flat roof?

Your flat roof should be inspected annually and cleaned semi-annually, or more often if needed. The frequency of cleaning and inspection will be dependent on your local climate, the amount of debris falling on the roof, and the type of roofing material.

What can cause water pooling on flat roofs?

Water pooling can be caused by clogged gutters, clogged discharges, improper roof slope, damaged seams, cracks and holes in the roof, and debris blockages.

What are the most common roofing materials for flat roofs?

The most common roofing materials for flat roofs are ethylene propylene diene monomer (EPDM) rubber membrane, thermoplastic polyolefin (TPO) membrane, asphalt modified bitumen, and metal roofs. Selecting the right roofing material for your flat roof requires considering factors such as cost, durability, and local climate.

Final Words

Maintaining drainage on flat commercial roofs is important for property managers and owners to ensure that their building is not subject to water pooling or damage from standing water. An annual inspection, regular cleaning, and repair of the drainage systems are necessary to avoid costly repairs. With proper care and routine maintenance, a flat roof can provide many years of reliable protection without any issues.