Flat Roofs - Average Cost, Pros & Cons and Types

Everything You Need To Know About Flat Roofs

Flat roofs have long been used to create an architectural statement. They’re found on modern, Spanish-style homes and, in some cases, historic homes. In some Southwestern states, nearly half the homes have flat roofs.

Flat roofs are easier to construct and safer to stand on than sloped roofs. But if you have a flat roof, you know they’re inherently problematic. They are prone to leaks because rain and snow don’t slide off as easily, and they don’t last as long.

Flat roofs can cost anywhere from $200 to $700 per square to install (a square equals 100 square feet). For a roof with 2,500 square feet or 25 squares, which is fairly typical, that’s anywhere from $5,000 to $17,500.

Types of Flat Roofs

Before we get into pricing details, let’s go over the different types of flat roofs. This is important because the type of roof has a lot to do with the price. The five types of flat roofs are: built-up, single-ply membrane, spray polyurethane foam (SPF), asphalt roll and flat-seamed metal roofing.

• Built-up roofs, also known as hot asphalt roofs, tar-and-gravel roofs or multiple-ply roofs, are among the oldest and most reliable. Several layers of roof are laminated together with an oil-based product called bitumen. Then, that surface is coated with gravel or crushed rocks. Built-up roofs are the most common of flat roofs in cooler climates.
• Single-ply flat roofing, also called modified or torch-on roofing, is a rolled roofing product with rubber backing that is typically melted to the roof. However, newer versions have a peel-and-stick application that is great for DIY. This is the one of the lower-cost options.
• Spray polyurethane foam is sprayed onto the existing surface of your roof, with no need to remove the old layers. It is the most expensive of flat roof materials, but it is easy to maintain, energy efficient and waterproof.
• Asphalt roll is the least expensive, but it doesn’t last much longer than 10 years. The material is rolled onto the roof and either nailed down or attached with cement. The base material, covered in asphalt, can be felt or fiberglass.
• Flat-seamed metal roofing is made from small pieces of sheet metal that are soldered together. It is long-lasting but requires regular painting and maintenance to prevent corrosion. It also tends to be expensive.

Contrary to what most people think, flat roofs do have a small gradient, otherwise they would have no way to shed water. And despite the inherent problems with flat roofs, modern materials last longer than their predecessors.

Cost of a Flat Roof

Flat roof prices vary widely based on geographic location. In a state like Arizona, where they are plentiful, you can expect to pay less than $300 per square in most cases. In New England, where they aren’t as common, $600 or more per square is standard. These prices include installation but not tear-off of the old roof.

• Built-up roofs cost anywhere from $200 to $700 per square.
• Single-ply flat roofing costs about $150 to $400 per square.
• Spray polyurethane foam roofs cost about $300 to $500 per square.
• Asphalt roll roofing usually costs about $150 to $400 per square.
• Flat metal roofs usually cost $500 to $1,000 per square.

Also, budget an extra $50 to $100 per square if the old roof needs to be torn off.

Choosing a Contractor

Due to the inherent problems with flat roofs, you always want to choose a contractor with experience building them. Better yet - look for a contractor that specializes in flat roofs. If you live in an area where flat roofs are common, you should have plenty of options. If flat roofs are not common where you live, choices may be limited.

Always seek multiple quotes before hiring any contractor. Disregard any that seem suspiciously low or high. Make sure the company you choose is licensed and insured, and ask for proof. And be sure to check the company’s track record with organizations like the Better Business Bureau and the National Association of Home Builders.

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