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How To Slope A Flat Roof For Drainage

Posted on October 6, 2023

Estimated Reading Time : 5 Min.

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How To Slope A Flat Roof For Drainage

In this article, we will explore the importance of slope in flat roofing systems, the factors to consider when designing a flat roof, and how to slope a flat roof for drainage.

Factors to Consider When Designing a Flat Roof

Designing a flat roof involves several factors that impact the slope and overall drainage system. Here are some essential considerations to keep in mind:

1. Roof Design

The overall design of a flat roof plays a significant role in determining the appropriate slope. You should keep the design of the flat roof in consideration when thinking of a flat roof drainage system. The slope should complement the style of your home or building. Consulting with a professional contractor can help you determine the best design for your flat roof.

2. Roofing Material

The choice of roofing material is crucial in determining the slope of a flat roof. Different materials have specific requirements and limitations when it comes to slopes. Here are a few common flat roofing materials and their considerations:

  • Polyvinyl Chloride (PVC): PVC membranes are popular for their durability and resistance to weathering. They can be installed on slopes as low as 1/4 inch per foot.
  • Ethylene Propylene Diene Monomer (EPDM): EPDM roofs are known for their flexibility and longevity. They can be installed on slopes as low as 1/4 inch per foot.
  • Modified Bitumen: Modified bitumen is a popular choice for flat roofs due to its durability and ease of installation. The slope requirements may vary depending on the specific product.
  • Thermoplastic Polyolefin (TPO): TPO membranes are widely used for their energy efficiency and resistance to UV rays. They can be installed on slopes as low as 1/4 inch per foot.
  • Metal: Metal roofs generally require a minimum slope of 1/4 inch per foot for standing seam panels, to ensure effective water drainage. Some metal roofing systems can even accommodate lower slopes with additional features like lap sealant.

It is essential to consult the manufacturer’s guidelines and recommendations for each roofing material to determine the appropriate slope for your flat roof.

3. Climate and Rainfall

The amount of annual rainfall you get and the local weather in your region should be taken into account when determining the slope of a flat roof. Areas with heavy rainfall may require a steeper pitch to ensure proper water drainage. On the other hand, regions with minimal rainfall may allow for a lower-pitched roof.

4. Snow and Ice

If you live in an area that experiences heavy snowfall or ice accumulation, it is crucial to consider your roof’s ability to shed these materials effectively. Steeper slopes are generally recommended in snowy climates to prevent snow buildup and potential damage caused by the weight of the snow on a roofing system.

Ways to Slope a Flat Roof for Drainage

Now that we understand the importance of flat roof slopes, and the factors influencing it, let’s explore some effective methods to slope a flat roof for optimal drainage:

1. Underlayment

Roof underlayment plays a vital role in your roof’s protection from water damage. The underlayment can be installed on flat roofs to be fit for water drainage. During a roofing project, This can be created by using slightly thicker underlayment along the edges of the roof compared to the inside. This subtle difference in thickness creates a gentle slope, allowing water to flow off the roof and into the drainage system.

2. Pavers

How To Slope A Flat Roof For Drainage

On flat roofs with concrete, you can utilize pavers to create a slight slope. By positioning pavers with a thicker edge on one side, water is directed towards the lower edge, promoting drainage. This method is effective, especially when combined with a reliable drainage system.

3. Tapered Insulation

How To Slope A Flat Roof For Drainage

Tapered insulation offers a lightweight and cost-effective solution for creating a slope on a flat roof. These rigid insulation boards are designed with one thicker side and one thinner, to direct water toward the drainage system. Tapered insulation is easy to install and provides an efficient drainage solution.

Common Types of Flat Roof Drainage Systems

To ensure effective drainage, flat roofs are equipped with various types of drainage systems. Here are some common flat roof drainage systems:

1. Gutter Drainage

How To Slope A Flat Roof For Drainage

Gutter drainage is one of the most common and affordable flat roof drainage systems. It involves the installation of gutters along the edge of the roof to collect and redirect water as it runs off. Gutters can be made from galvanized steel, vinyl, or aluminum, but regular maintenance is required to prevent clogging and ensure proper water flow.

2. Siphonic Roof Drainage

Siphonic roof drainage is a system that allows rainwater to flush quickly from the roof. This system uses a minimal number of outlets connected to a single major pipe, creating a siphoning effect that rapidly drains water. Unlike other drainage systems, siphonic roof drainage does not require sloped pipes and can be effective in preventing ponding water. However, professional installation is recommended due to the complexity of the system.

3. Internal Drainage

How To Slope A Flat Roof For Drainage

Inner drainage is commonly used in commercial properties or buildings with large flat roofs. Pipes are placed beneath the roof or in parapet walls to ensure the water is drained away from the roof’s surface. This system provides a visually pleasing option as the pipes are hidden, enhancing the aesthetics of the roof. However, maintenance and repair of inner drainage systems can be more expensive compared to other options.

4. Scupper Drainage

How To Slope A Flat Roof For Drainage

Scupper drainage involves the creation of openings along the sides of the walls, allowing water to flow off the surface of the roof. Scuppers are effective in preventing debris from blocking water flow, and are also low maintenance as there aren’t any channels to clean debris from, and will require little to no repair as they don’t suffer from the expansion and contraction that typical gutters do. 

Are You Looking For A Commercial Roof Replacement In Tulsa, OK?

Now that you know the importance of flat roof slopes, you can imagine the adverse effects of not having a proper flat roof slope. Therefore, you need a skilled and knowledgeable roofing professional, well-versed in local area building codes and the weather patterns in Tulsa. 

If you are on the lookout for a flat roof replacement provider in Tulsa, you are in the right page. 

Contact A. Fricker Roofing & Waterproofing, the roofing company in Tulsa has gained a reputation through its dedicated, responsible, and professional team of roofers. Just call us today at (918)-402-7167 to speak with one of our roofing professionals.