The 4th Kind of Flat Roof That This Old House Missed: Flat Roof Decks

While browsing the This Old House website, we came across an article titled “The 4 Kinds of Flat Roofs”, written by Max Alexander. It’s a great read—clear, concise, and packed with valuable insights. The article covers:

• Built-Up Roofs (BUR)

• Modified Bitumen Roofs

• Rubber Membrane Roofs (EPDM)

But… where was roof number 4?

There were no “Next” or “Read More” buttons—just three types of flat roofs. We were left hanging. Maybe it was an editorial oversight, or maybe they were just testing to see who was paying attention. Either way, we’re here to fill in the missing piece.

Let’s talk about the 4th kind of flat roof—one that turns underused space into something functional: Flat Roof Decks.

What Is a Flat Roof Deck?

A flat roof deck transforms a traditionally utilitarian flat roof into valuable outdoor living space. While providing proper structural support and safe access, a flat roof can double as a:

• Private outdoor lounge

• Rooftop patio

• Urban garden space

• Entertainment area

It’s a high-value upgrade for homeowners and a smart design feature for architects and builders.

Why PVC Sheet Membranes Are the Ideal Choice for Flat Roof Decks

PVC sheet membranes (commonly called vinyl decking) are the only flat roofing option that provides waterproofing protection and a walkable surface in one product. That’s why they’re the go-to solution for creating usable outdoor spaces on flat roofs.

Duradek’s PVC membranes are specifically engineered for roof-grade waterproofing and pedestrian traffic, making them the ideal choice for residential and commercial flat roof deck applications.

Benefits of PVC Roof Deck Membranes:

• Dual-function: roofing membrane + walking surface

• Low-maintenance and long-lasting

• Clean installation process—no open flames or messy tar

• Safe for occupied homes during installation

• Tested and code-compliant for both roofing and pedestrian use

Comparing Flat Roof Options: PVC vs. Traditional Systems

If you’re planning a flat roof project, it’s important to choose the right material for both performance and how you want to use the space. While traditional systems like BUR, modified bitumen, and EPDM rubber offer reliable waterproofing, they come with limitations—especially if your goal is to create a usable roof deck. Duradek delivers both waterproofing and a walkable surface in one smart solution.

Built-Up Roofing (BUR) vs. PVC Membranes

BUR, or built-up roofing, is the classic hot tar and gravel system. Contractors have used it for decades and still consider it a budget-friendly option. However, it’s far from ideal for modern residential needs:

• The installation is messy, involving multiple layers of felt, tar, and gravel.

• It produces strong odors, so experts don’t recommend using it on occupied buildings.

• Repairs are difficult, and tracking down leaks can be a challenge.

• Most importantly, it’s not a walkable surface and adds no usable outdoor space.

In comparison, PVC membranes provide a clean, efficient installation with no open flames or tar. Furthermore, they’re lightweight and installed using adhesives and hot air welding, making them safe for occupied homes. What’s more, they create a fully walkable surface, making them perfect for transforming your flat roof into an outdoor living area.

Modified Bitumen vs. PVC Membranes

Modified bitumen roofs are single-ply systems available in both torch-down and peel-and-stick options. Although these systems are more modern than BUR, they’re still not ideal for deck use:

• Torch-down systems pose a fire risk and aren’t recommended for residential settings.

• Peel-and-stick versions are easier to install, but still not suitable as a finished walking surface.

• To create a usable roof deck, you’d need to add extra layers and structural support.

PVC membranes eliminate that extra work. Moreover, they’re designed to handle pedestrian traffic from day one, requiring no additional materials or surface finishes.As a result, they combine waterproofing and walkability in one product, saving time and reducing complexity.

EPDM Rubber Roofing vs. PVC Membranes

Builders often choose EPDM, a rubber-based material, for its durability and cost-effectiveness. They can glue, fasten, or ballast it with stone, thanks to its lightweight design. Some homeowners even install it themselves. However, there are a few trade-offs:

• Standard black EPDM absorbs a lot of heat, making rooftop spaces uncomfortable.

• White or reflective versions are available, but they cost significantly more.

• EPDM is not designed for foot traffic, and it requires additional build-up to make the surface usable.

PVC membranes match EPDM in durability but outperform it when it comes to function and finish. With better heat reflectivity, integrated waterproofing, and a walkable surface, PVC is the only flat roofing option in this group that’s ready to use as a deck—right after installation. And with professional installation, it often comes backed by a solid warranty for added peace of mind.

Choose a Walkable, Waterproof Flat Roof Solution

When you’re planning a flat roof deck, Duradek PVC membranes provide a cost-effective, low-maintenance, and attractive solution. To ensure long-term performance and safety, make sure you choose a product that meets testing and approval standards for both roofing and pedestrian use.

👉 Download our free checklist:
Time, Tested and Approved – Walkable Roof Deck Product Testing Requirements (PDF)

See the Transformation: From Torch-On Roof to Vinyl Deck

Want proof? Check out Case Study #156: Roof Deck Renovation in Washington, DC. A tar-over-concrete roof was transformed into a modern, waterproof deck with Duradek.

Flat Roofs Can Be Functional and Fabulous

We had a little fun with the This Old House article, but in all seriousness—we’re big fans of their work. And if you’re one too, you might enjoy reading about how PVC membranes helped preserve a 200-year-old home in another This Old House renovation.

Ready to upgrade your flat roof into a walkable deck?
Find an authorized Duradek installer near you and turn that underused space into your favorite outdoor destination.