Skip to Content

How to Slope a Flat Roof for Drainage


Whether residential or commercial, flat roofs are not technically flat. They must contain a minimum slope to allow water to drain. Proper drainage prevents problems such as leaks, mold, or structural deterioration. The state of Florida imposes building codes to ensure that every type of roof has a form of drainage.

If you have recently noticed that your roof has water puddles, rotting framework, or leak stains along the walls or ceiling, there may be a problem with drainage. Below we look at what a flat roof is, the types of flat roofs, and how to slope a flat roof for drainage. If you have any further questions, feel free to contact Quality Roofing. We are your leading roofing contractor on the coast.

What is a Flat Roof?

A flat roof is a roofing system that is nearly level with a slight slope. The reason why it is called a flat roof is that it meets the bare minimum for a required slope, or it is flatter than any other type of roof. Roofing contractors often refer to the slope of the roof as the pitch.

Flat roofs require a specific type of construction, which usually includes a reinforced structure made of concrete or masonry. It is typically covered by some type of membranes, such as modified bitumen roofing or thermoplastic roofing (TPO or PVC). Flat roofs have several applications in both residential and commercial buildings.

How the Pitch is Determined in a Flat Roof

There are several items that roofing contractors’ factor in when determining the pitch of the roof, including:

  • Amount of rainfall
  • Drain speed requirements
  • The roof designs
  • Likelihood of snow and ice during winter
  • The structural stability of the framework
  • Any items on the roof
  • Roofing standards and building codes

The primary consideration is the amount of water or ice that can potentially collect on the roof in torrential rain or heavy snow. Although snow and ice are not a significant problem in Florida, heavy rains frequently occur – especially during hurricane season. Roof designs on many houses in the area are also more complex and made of specialized materials such as metal or tile. All of these factors help contractors determine the proper angle of the slope when designing the roof.

What Are Requirements for Flat Roofs in Florida?

For drainage purposes, the current building codes require a minimum two percent slope or a one-fourth unit vertical for every 12 units horizontal. In other words, the roof must slope one-fourth of an inch for every 12 inches. The slope is barely noticeable to the naked eye. In most cases, if you were to eyeball a roof, you would not notice that there is a slope.

However, a two-percent slope is plenty of pitch for proper water drainage. It also meets building codes in almost any roofing application. When working with a roofing contractor in Florida you need to ensure that the building meets all codes. Doing so gives your roof a longer life, keeps all occupants safe, and reduces the number of repairs you have to make on the roofing system.

What Are the Benefits of a Flat Roof

There are several benefits of installing a flat roof on your house or commercial property, such as:

A Cost-Effective Solution

The materials and labor needed for a flat roof are much less than those of a sloped roof. For instance, TPO is mechanically attached or adhered to a roof surface. This method of applying a roofing system requires fewer materials and much less labor than trying to manually attach roofing material to a sloped roof, where it takes more effort to complete the job. You spend less money without sacrificing the quality of craftsmanship.

Easier Access to the Roof

Roofing contractors generally recommend that you stay off the roof. However, there may be times when getting on the roof is necessary. Some roofs have features such as balconies or other amenities that give you access to the roof. If so, accessing a flat roof is far easier than trying to scale a sloped roof.

Height Allowance

Some communities in Florida impose height restrictions on new construction. A sloped roof may give you less livable or workable space if you have to adhere to the height restrictions. If you have a flat roof, you can add more livable space without exceeding the restrictions. For instance, in a commercial building, you may be able to add another floor if you choose a flat roof.

Types of Flat Roofs

Not all flat roofs are built the same. You do have some options for the type of roof you install. Three of the most popular roofing materials include:

Metal Roofs

Today’s residential and commercial metal roofs far surpass the older products, changing the way home and business owners look at metal. Metal roofs are durable, non-combustible, and can reflect the heat off of the roof. Metal roofs are also easy to install and replace. They can be customized to fit around nearly any roof feature or protrusion.

Modified Bitumen Roofing

Modified bitumen roofing is an asphalt-based form of roofing specially designed for flat roofs. Due to its flexible design, you have more options for installing the roofing system on your building. Roofing contractors install modified bitumen roofing using self-adhering sheets. Most jobs can be completed quickly without the use of high-tech equipment, large work crews, or volatile organic chemicals (VOCs).

Thermoplastic Roof Membrane (PVC or TPO)
A thermoplastic roof membrane is a reinforced roof layer that provides more strength and stability for your building. Most membranes are made from PVC alloys or thermoplastic Olefin (TPO). Most TPO surfaces are white, which does an excellent job of reflecting the sun’s rays. Seams are sealed by heat-welded hot air. Contractors can attach the membrane by adhesion, ballasts, or mechanical attachments.

Get a Free Roof Replacement Estimate

Quality Roofing offers premier roofing services for homeowners in Florida. To find out more about our roofing replacement solutions, call (850) 753-0041 or fill out the quick form on our contact page.

The post How to Slope a Flat Roof for Drainage appeared first on Quality Roofing Solutions.

Share To: