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Sealing a Flat Roof: How To Waterproof Your Roof

Flat roofs offer unique architectural allure, but their low incline presents a different set of challenges compared to pitched roofs. One crucial concern? Keeping leaks at bay.

Unlike sloped roofs, they require specialized attention due to factors such as ponding water, which can affect their lifespan. Before delving into the sealing process, it’s essential to understand the unique characteristics of flat roofs and how they differ from traditional roofing systems.


Understanding The Quirks of Flat Roofs

Flat roofs like to keep things level, which means they’re not big fans of shedding water like their sloped counterparts. Instead, they tend to host a little pool party after heavy rain – we call it ponding water. Ponding water is standing water that puddles for more than 48 hours and can cause water problems that degrade your flat roof membrane.

Roofing Materials and Construction

Flat roofs often use different materials compared to traditional roofs. Bitumen, EPDM, and modified bitumen are common choices due to their flexibility and durability. Understanding the properties of these materials is crucial in selecting the right sealant and coating to complement the roof’s composition.

Maintenance Challenges

Unlike roofs with a little more slope, flat roofs need a bit more TLC. They don’t naturally let go of debris, so regular cleaning is needed to prevent debris buildup, which can compromise the integrity of the roof surface and contribute to ponding water.

Flat Roof’s Vulnerability to Roof Leaks, Blisters, and Membrane Damage

Blisters: Blisters on a flat roof are like little bumps that form beneath the surface of the roofing material. They’re caused by a combination of trapped moisture, heat, and sometimes inadequate installation.

These can weaken the roof’s integrity over time. Do it yourself (DIY) enthusiasts can identify blisters by visually inspecting the roof surface for raised areas, often with visible cracks.

Membrane Damage: Flat roof membranes, like EPDM or TPO, can sustain damage over time due to weather exposure, foot traffic, or the settling of the building. Damage may manifest as cracks, tears, or punctures in the membrane, compromising its ability to keep water out.

Flat Roof Leaks: The horizontal charm of flat roofs can make them more prone to leaks. Sealing the deal (pun intended) means paying attention to the nooks and crannies where water might sneak in – seams, flashings, and roof penetrations.

Which is why it’s important to ensure your flat roof does not leak as even a small amount of water can cause costly damages to your attic and ceiling, ruined insulation, mold, and much more that may lead to a complete flat roof replacement.

So, how do you fix a leak? It’s all about finding the right sealant.


What’s the Best Way to Seal a Flat Roof?

There’s no one-size-fits-all answer, as the best method depends on your roof’s material, condition, and budget. However, here are some popular options for homeowners and property managers alike:

Flat Roof Coatings: Liquid coatings like elastomeric roof coating, acrylic, or silicone form a seamless waterproof barrier, ideal for various substrates like concrete, metal, and even existing bitumen roofs.

Membrane Systems: Single-ply membranes like EPDM or TPO offer durable, long-lasting protection, often requiring professional roofer installation.

Built-up Roofs: This traditional method involves layering bitumen and gravel, providing excellent weather resistance but demanding significant maintenance.


Caulking for Flat Roof Protection

While coatings and membranes tackle large areas, caulking becomes your unsung hero for sealing those critical junctions and penetrations on your flat roof. Think flashing around vents, skylights, and chimneys, or seams where different roof materials meet.

Caulking Advantages

Targeted Sealing: Reaches tight spaces and awkward angles where coatings might struggle.
Flexibility: Accommodates roof movement and expansion/contraction due to temperature changes.
Leak Prevention: Plugs tiny gaps and prevents water infiltration around vulnerable points.
DIY-Friendly: Easy to apply with a caulking gun, making it a great option for small repairs.

Choosing the Right Caulking

Not all caulks are created equal! Opt for silicone-based caulks specifically designed for exterior use and metal surfaces. They offer superior weather resistance, flexibility, and adhesion.


DIY Flat Roof Sealing: Is It Safe?

Small repairs and preventative maintenance like applying sealant around roof penetrations can be tackled by DIY enthusiasts with proper research and safety precautions. However, extensive repairs or installing new membranes usually require the expertise of a professional roofer.

A flat roofing contractor will have experience installing protective equipment effectively to safeguard your roof against leaks. They will also ensure the proper installation of necessary hardware around penetration points including flashing, rain collars, wraps and flexible rubber pipe boots.


Let ACME Help!

Your roof is your home’s first line of defense against the elements. By sealing it effectively, you’ll enjoy peace of mind, lower energy bills, and a protected investment for years to come.

ACME Roofing, your trusted neighbor with over 20 years of expertise, is here to help. We can diagnose the problem, recommend the best sealing solution for your needs, and handle the repair with meticulous care.

Give us a call at (253) 564-2292 or visit our Roofing Showroom in Tacoma!



What is flat roof coating?

Flat roof coatings are liquid applied sealants that form a flexible, waterproof barrier on your roof surface. They come in various types like elastomeric, acrylic, and silicone, each offering unique benefits and lifespans.


What is the best flat roof sealant?

The “best” sealant depends on your specific needs. Consider factors like roof material, budget, desired lifespan, and ease of application. Popular options include silicone for flexibility, acrylic for affordability, and elastomeric for weather resistance.


How long do flat roof coatings last?

Lifespan varies depending on the coating type, quality, and proper application. Typically, expect 10-30 years for high-quality elastomeric coatings, while acrylics may last 5-10 years.


How often should a flat roof be resealed?

Resealing frequency depends on the chosen method and weather conditions. EPDM or TPO membranes may last 20-30 years without resealing, while bitumen roofs might require recoating every 5-10 years.


How do you apply a sealant to a flat roof?

Application methods vary depending on the chosen sealant. Always follow the manufacturer’s instructions carefully. Generally, you’ll need a roller, brush, and safety gear for proper application.