Flat roofs are highly affordable, provide more usable space for a patio or garden, and provide better accessibility when cleaning gutters, making repairs or installing things like satellite dishes or solar panels. Flat roofs are typically paired with a 10- to 20-year warranty but can last up to 25 years or longer if properly installed and maintained.
Meeting Minimum Code Standards
Whether building a new flat roof, or repairing an old one, to meet standards we want to build up the sidewalls, to keep water confined to the roof, and not leaking into places it isn’t supposed to. The ability to manage the water should be the top priority and main concern when installing the flat roof. The code states any standing water on a roof needs to be drained and dried within 48 hours of rain. This requires some extra building up of the slope to ensure for proper drainage of water.
How to Allow Water Drainage
First, the flat roof needs to be free of any divots or craters that would pool water in them, causing sinking or collapsing of the roof over time. So, first make sure the slope is enough to guide the water down and out of the gutter, downspout or leader. The parapet walls should also be built up to help guide that water down along the edges of the roof and not pooling in the edges or center. The angle of the slope is generally 1-2% on flat roofs (so they aren’t actually flat).
Flat Roof Maintenance and Preventative Care
Flat roofs are sometimes known for being problematic, mostly due to the low slope and water pooling. They are generally chosen for commercial buildings as they are cost-effective and energy-efficient because there’s less volume and space to heat or cool, and they can even be turned into extra patio or garden space in the city. There are some things one can do to prevent water pooling or leaking. First, regular maintenance checks to clear out roof outlets like gutters, downpours, etc. is very important. A clogged roof outlet is a recipe for disaster. Leaves, dirt, snow, ice, can all plug those outlets and trap water from getting out. Water pooling and remaining on the roof for over 48 hours is not only against code but can begin to seep into the roof ruining insulation, windows, apartment ceilings, etc.
Materials used to waterproof and build up flat roofs generally have a lifespan of 20-30 years if well maintained, so it is very important to check the integrity and quality of these regularly. You will also want to be clear about your insurance coverage for your flat roof, especially as a commercial property owner. In a place where snow and ice can cause problems on flat roofs, make sure you have the coverage you need if a major repair occurs down the road.
Types of Flat Roofing and Materials
Built-Up Roof (BUR)
A built-up roof provides the traditional form of hot-tar-gravel and is constructed from three or more piles of waterproof material alternated with hot tar and ballasted by a smooth layer of river stone. In the past, BURs consisted of simple tar paper, however, these types of roofs are shifting with the use of more complex materials such as fiberglass membranes.
Pros of a BUR: When you choose a BUR, you get excellent protection from fires, as well as an attractive place for windows and decks that overlook the roof. It’s also one of the most affordable options of the four flat roof types.
Cons of a BUR: BUR materials are severely heavy meaning joists will need to be strengthened in some cases. It’s also a messy and smelly installation process, meaning you probably won’t be able to occupy your home while it’s being laid. Additionally, gravel can clog gutters and leak sources can be hard to pinpoint.
Modified bitumen roofs are a single-ply rolled roof that acts as an ice-and-water protectant, and is saturated with a mineral-based wear surface to provide extra protection. Through a torch-down approach, the adhesive is heated as the material is unrolled. Peel and stick systems have also been introduced which makes the process simpler and safer.
Pros of Modified Bitumen: Modified bitumen has a light-colored mineral surface which is great for reflecting heat which will slash your energy bills. The peel-and-stick option is also perfect for DIYers who want to work on their roof themselves. In terms of price, it’s not the most expensive, but also not the cheapest, making it a good middle-ground option.
Cons of Modified Bitumen: If you choose the torch-down application, you’re opening up your home to fire risks, and you won’t be able to occupy the building during installation. It also isn’t as resistant to scuffing or tearing as rubber-membrane roof materials.
A rubber membrane roof consists of ethylene propylene diene monomer (EPDM) and is durable enough to resist sun damage. EPDM can be mechanically anchored to your structure with special fasteners, stone or glued.
Pros of Rubber Membrane Roofs: These types of flat roofs are perhaps the most homeowner-friendly to install and maintain. EPDM material is highly resistant to scuffing and tearing, while also remaining relatively lightweight. Leaks are also very easy to repair.
Cons of Rubber Membrane Roofs: With rubber membrane, the black material that comes standard is capable of absorbing heat, while lighter-colored coats (which are more expensive) are better for warmer-temperate climates. While this type of flat roof is popular, it costs more than both BUR and modified bitumen.
Spray foam roofs are ideal for those homeowners that want a cost-effective and long term solution to their roofing problems. You’ll see huge energy savings when you choose to protect your roof with spray foam.
Pros of Spray Foam: Spray foam features advanced tensile strength and durability that’s highly comparable to that offered by more traditional roofing systems. Additionally, it’s completely seamless, waterproof and a fully adhered to the existing roof substrate.
Cons of Spray Foam: Spray home cannot be applied by the everyday DIYer and has to be applied by a professional. This type of roof has rigorous specifications and requires steady expert hands for effective application.