There are a number of differences between flat roofs and sloped roofs that can affect how the roof functions, and are not always understood by property owners. The flat roofs require careful attention to drainage as well as the waterproofing system, without a steep incline to allow water to flow off rapidly. During times of failure of that system, water cannot flow off. It sits, seeps and gradually penetrates. Knowing the working principles behind flat roof waterproofing can save those who own a building from unpleasant surprises.

How Flat Roofs Differ From Sloped Roofs

Flat roofs are not 100% level. They are generally designed to have a little pitch to direct water flow towards drains. The water drains off of a sloped roof quickly due to the overlapping shingles, and flat roofs use membranes, coatings and careful drainage design.

This difference requires a waterproofing solution that is engineered to deal with standing water and slower drainage, not just materials engineered to shed water quickly.

Why Drainage Design Is So Important

One of the primary reasons for roofing issues on flat roofs is poor drainage. Roof drains, scuppers and gutters should never be obstructed or misaligned to ensure the water moves off the roof surface efficiently.

While a good waterproofing can be installed, if the water is consistently trapped in the same areas over time, it can lead to problems. Drainage is not an independent activity to waterproofing, but rather it works in combination with waterproofing.

Common Causes of Water Intrusion

Water tends to enter the building at small, unnoticed locations and not large, visible openings. Common causes include cracked or aged membranes, broken seams and broken flashing around vents and equipment.

If waterproofing materials are not protected from foot traffic by maintenance crews to rooftop equipment, they can be gradually damaged over time.

Waterproofing Systems and Membranes

There are a number of different ways to waterproof a flat roof such as single-ply membranes, modified bituminous and liquid-applied coatings. Different systems require various installation, life span, and maintenance protocols.

The selection will depend on the building's function, budget, and structure of the current roof. A professional evaluation is used to determine the appropriate system for the building—and not only its cost.

Understanding Ponding Water

Ponding water – water that stays on a flat roof for more than a couple days after rain. Ponding occasionally is a normal occurrence but if ponds are ponding all the time, there is a slope or drainage issue that should be addressed.

One of the more serious problems of the flat roof owner is standing water; it increases weight and contributes to roofing materials wear.

Seams and Penetrations Deserve Extra Attention

Any point of penetration of the roof surface through equipment, pipes or vents is a potential weak point. Wherever two membrane sections are connected together, there is a seam that could be vulnerable if not sealed at the time of installation.

Periodic surveying in these areas will frequently detect small leaks before they begin to leak in the main membrane, because penetrations are more likely to leak than the membrane.

The Role of Routine Roof Maintenance

A good roof maintenance plan is a significant part of the longevity of a waterproofing system. Regularly sweeping away debris, cleaning drains, and checking seams can keep little issues from growing into big ones if they are caught early.

A lot of flat roof waterproofing warranties stipulate that warranties are contingent upon documented maintenance, and you could find that taking $400 off the top of those warranties impacts both coverage and performance.

When Repair Is the Right Approach

If the damage is confined to a particular area, e.g. broken seam or small tear in the membrane, it may be possible to repair. When the remainder of the waterproofing system is in reasonably good condition, repairs are most effective.

A professional assessment provides information on whether or not the surrounding material is still structurally sound enough for a localized repair.

When Replacement Becomes Necessary

When too many of the membranes deteriorate, the leaks recur at various locations, or the system is at its end-of-service life, replacement is typically the answer. Repeated patching of an aging system can end up being more costly than a planned replacement.

When a qualified professional gives an honest evaluation, it aids property owners in determining if repair is no longer a financially sound option.

The Benefits of Professional Installation

The waterproofing level is greatly influenced by the installation method. Seams must be properly sealed, flashing must be properly detailed and drainage must be properly calculated. Years later there could be a leak from a small installation error.

These details can be taken care of properly the first time, because you can rely on a whole team that can provide you with full commercial roofing services, from the inspection to the installation.

Protecting the Building Over the Long Term

More than preventing leaks, flat roof waterproofing offers a number of benefits. It shields the insulation, interior finishes and the structure below the roof surface. A well-maintained system also helps to be energy efficient by preventing moisture from entering insulation layers.

While no waterproofing system is 100% waterproof and can last forever, a correctly installed and maintained system can greatly minimize risk during the life of the roof.

Frequently Asked Questions

What is the difference between waterproofing a flat roof and a conventional roof?

While sloped roof waterproofing is more dependent on rapidly draining membranes and coatings, the water in a flat roof is run at a slower pace, and will sometimes stand.

What's the lifespan of flat roof waterproofing?

When installed and maintained properly, lifespan is dependent on the material and maintenance, but can last up to 15 to 25 years.

Does a flat roof need to have some water on it?

Small temporary puddles are often seen following rainfall. If it has been several days or occurs on a regular basis, it indicates that there's a drainage problem and it needs to be assessed.

What is the recommended frequency of maintenance for a flat roof?

For most professionals, twice a year is the minimum inspection frequency, and after major storms or heavy rainfall.

Is it always possible to repair a damaged flat roof?

Not always. Damage may be repairable in certain areas, but if there is damage more widespread or if there are frequent leaks, it is likely that the leak needs to be replaced.

Does waterproofing make no leak at all possible?

All systems have some leaks forever. When installed properly, and maintained regularly, risk can be significantly reduced, but without a doubt, a leak will not be prevented.

The most important component of the performance of flat roof waterproofing?

Both the quality of the installation and the design of drainage systems are important, as are regular maintenance throughout the system's life.

Disclaimer

The requirements for waterproofing a flat roof depend on the building's size, condition of the existing roof (whether it is sheet or bituminous), drainage design and climatic conditions. This article is designed to give general information and cannot be a substitute for a proper inspection of your property.

Get Professional Roofing Help

Renewable Roofing Solution can assist you if you own a flat roof and need a truthful assessment of your roof's waterproofing system. Please visit renewableroofingsolution.com or call +1 (502) 664-8006 to schedule an inspection.