how much should a flat roof overhang be

How Much Should a Flat Roof Overhang Be: A Comprehensive Guide

The design and construction of a flat roof is a multifaceted endeavour, requiring a meticulous approach to each element of its structure. One such integral aspect is the determination of the ideal overhang size. A flat roof overhang, the portion of the roof that extends beyond the building’s walls, serves a dual purpose, both functional and aesthetic. 

In this comprehensive guide, we will explore the multifaceted factors that influence the size of a flat roof overhang and provide in-depth guidance on how to calculate the perfect overhang size for your specific project, whether it’s a modern architectural masterpiece or a traditional structure.

Part 1: Understanding Flat Roof Overhangs

1.1 What Is a Flat Roof Overhang?

A flat roof overhang is a structural extension that gracefully protrudes beyond the external walls of a building. It transforms the otherwise linear boundaries of the building into an architectural feature that serves functional and aesthetic purposes. In addition to protecting the structure below, the overhang offers a contemporary flair to the overall design, making it an essential component of flat roof architecture.

1.2 The Importance of a Well-Designed Overhang

A well-designed overhang contributes to the structural integrity and visual appeal of a flat roof:

  • Rainwater Management: Among its primary functions, a well-designed overhang effectively manages rainwater. By preventing direct contact with the building’s exterior walls, it reduces the risk of water infiltration, safeguarding the interior.
  • Protection of Building Exterior: The overhang acts as a shield, protecting the exterior walls from the relentless forces of nature, such as intense sunlight, heavy rainfall, and snow. This protection ensures the longevity of building materials.
  • Providing Shade: In sunny climates, a strategically designed overhang can create shaded areas, improving outdoor comfort and reducing heat gain within the building. This not only enhances the quality of life but also promotes energy efficiency.
  • Aesthetic Appeal: From an architectural standpoint, a well-constructed overhang adds character and visual allure to the building. It can be tailored to complement the overall design, enhancing the structure’s aesthetics.

Part 2: Factors Influencing Overhang Size

2.1 Aesthetic Considerations

The dimensions of the overhang are significantly influenced by aesthetic considerations and architectural style. To determine the overhang size, it’s crucial to align with the overall design intent:

  • Architectural Style: Different architectural styles call for varying overhang designs. For instance, modern and minimalist designs often feature sleek, unobtrusive overhangs, while traditional structures may incorporate larger overhangs to evoke a classic look.
  • Visual Harmony: The overhang’s size should harmonize with the building’s proportions, lines, and materials. Achieving a balance between aesthetics and functionality is key to a successful design.

2.2 Functional Considerations

The functionality of the overhang is pivotal, and its size should be determined with care. Several functional factors come into play:

  • Climate: The local climate is a critical influencer. In regions with heavy rainfall, a larger overhang may be necessary to protect the walls and manage runoff effectively. Conversely, in sunnier areas, a more modest overhang may suffice to provide shading.
  • Rainfall Patterns: Understanding local rainfall patterns, especially during storms, is essential. This knowledge ensures that the overhang can divert water away from the building, reducing the risk of moisture damage.
  • Sun Exposure: Analysing the angle and path of the sun is crucial for determining the overhang’s size. The overhang should provide shade in areas where it is most needed to enhance comfort and energy efficiency.

2.3 Local Building Codes and Regulations

The significance of complying with local building codes and regulations cannot be overstated. These codes are in place to ensure safety and structural integrity, and they often dictate the size and design of a flat roof overhang. It is essential to be aware of these regulations and to obtain the necessary permits when designing and constructing a flat roof overhang to ensure legal compliance and safety.

Part 3: Calculating the Ideal Overhang Size

3.1 Measuring the Building’s Dimensions

Precise measurements of the building’s dimensions are the foundation of determining the ideal overhang size. The length and width of the building play a significant role in calculating the overhang’s length. To achieve accuracy, consider using modern measurement tools such as laser distance measurers.

3.2 Evaluating Environmental Factors

Environmental factors have a profound impact on the ideal overhang size. To make a precise calculation, evaluate the local environment:

  • Climate: The climate of the region has a direct bearing on the overhang size. In areas with frequent rain, a larger overhang may be required to protect the walls from moisture infiltration. In contrast, drier regions may necessitate a more modest overhang.
  • Rainfall Patterns: Study the rainfall patterns, especially during heavy storms, to ensure the overhang can effectively divert water away from the building. This prevents water-related damage.
  • Sun Exposure: To optimize shading, analyse the angle and path of the sun throughout the day and across seasons. This analysis ensures that the overhang provides shade when and where it is most needed.

3.3 Balancing Aesthetics and Functionality

Balancing aesthetics with functionality is a core challenge in designing the ideal overhang. To find this equilibrium:

  • Consult a Professional: Collaborate with an architect or designer to create an overhang that marries aesthetics with functionality. They can help you explore design options and test different overhang sizes and shapes.
  • Computer Simulations: Employ computer-aided design (CAD) software and simulations to model different overhang scenarios. This can provide a visual representation of how the overhang will appear and perform.
  • Physical Models: Create physical models or mock-ups to gain a tangible understanding of the overhang’s impact on the building’s appearance and its functional efficacy.

Part 4: Building a Flat Roof Overhang

4.1 Construction Methods

The construction of a flat roof overhang involves selecting from various methods and materials to suit the specific design, budget, and climate:

  • Materials: Overhangs can be constructed using a variety of materials, including steel, wood, and composite materials. The choice of materials impacts the overhang’s structural integrity and longevity.
  • Support Structures: The choice of support structures, such as columns, beams, or cantilevers, depends on the design and size of the overhang. The support structure must be robust enough to carry the overhang’s weight and withstand external forces.

4.2 Maintenance and Upkeep

To ensure the long-term functionality and visual appeal of the overhang, regular maintenance and upkeep are imperative:

  • Inspections: Conduct routine inspections to check for signs of damage, wear, or corrosion. Address any issues promptly to prevent structural problems.
  • Cleaning: Clean the overhang to remove debris, dirt, and algae that can accumulate over time. Keeping the overhang clean maintains its appearance and prevents damage.
  • Repainting: If the overhang is painted or finished, periodic repainting can rejuvenate its appearance and protect it from weathering.
  • Repairs: Address any damage or wear promptly. This includes repairing or replacing damaged materials, such as roofing, support structures, or finishes.


The size of a flat roof overhang is a pivotal consideration in flat roof design, and it profoundly influences the building’s aesthetics and functionality. By accounting for factors such as aesthetic preferences, climate, and local regulations, you can accurately determine the ideal overhang size for your specific project. Whether your goal is to create a modern architectural masterpiece, a traditional structure, or something in between, a well-designed overhang adds value, protection, and personality to your building. Thus, when planning your flat roof, remember the significance of this essential architectural feature. A well-designed overhang ensures the harmony of form and function, guaranteeing that your flat roof stands as a testament to both style and substance.

This comprehensive guide has provided you with an extensive understanding of the considerations surrounding flat roof overhangs, ensuring that your architectural vision aligns seamlessly with the practical demands of your building.

Key Takeaways

An overhang serves to protect the exterior of a house from strong winds and rain while at the same time providing shade from sunlight that might otherwise penetrate windows. To find a professional, you can click here for more information.

Flat roof overhangs should extend at least two feet from the home’s walls in order to provide adequate rain and snow protection, and any longer overhangs need external support for their structural integrity. 

If you’re planning to build a shed with an overhang, there are a few simple steps to follow:

First, determine how long your shed needs an overhang to reach the top edge of the wall, then calculate how many rafters will be needed for this length. 

The main overhang frame (called a king rafter) should be sized to fit the total length of the shed’s overhang, and then you’ll need smaller (jack) rafters that connect to it at 30 degree angles for a good connection.

Next, you can figure out how much each of these rafters will cost by taking the square footage of your rafters plus the overhang and subtracting the amount you’ll need to create a rake ladder. 

This will give you the total cost of each rafter, and it will also help you budget your rafters accordingly.

If you are considering building a new flat roof, it’s important to know how much it should overhang. The amount of overhang that you need depends on several factors, including the climate of your area and the number of windows in your home.

A common problem with flat roofs is water that pools on the surface because of a lack of slope. 

Typically, flat roofs are built on slight inclines, at least 1/8 inch per foot to drain water off and to direct it toward a downspout for drainage. This helps keep the structure from leaking and also saves money on roofing repairs.

Generally, the minimum size for overhangs is 2 feet–this length will protect your roof from most damage and allow it to function properly. 

Overhangs that extend longer than two feet lose structural integrity and may require additional support, such as posts or a truss system.


An overhang is an integral component of home design. It can protect exterior doors, windows, siding from raindrops and reduce solar heat gain while helping keep basements and crawl spaces dry.

Roof overhang length can vary significantly depending on where a home is built; homes in areas with heavy rainfall tend to feature longer overhangs than those located in cooler climates.

Once an overhang exceeds two feet, its structural integrity starts to degrade and may need additional support.

Homeowners deciding on the length of an overhang on their flat roof must consider its purpose and location when determining its length. An ideal overhang should provide sufficient sun and rain protection while still remaining short enough not to be blown off during strong winds.

An overhang should also be designed to minimise splashback, or the flow of water near the foundation, to the ground around a home.

Although no universal standard exists for length of overhangs, typical ones used to protect from rain are 16-18 inches wide while overhangs intended to shade windows from sunlight should measure at least 24 inches wide.


An overhang refers to any portion of a flat roof that extends past an exterior wall, or “eave”, and provides protection from rain or snow.

An overhang can help protect homes by keeping water from running down walls and damaging siding or the sides. Furthermore, an overhang provides additional wind protection as well as keeping snow and debris off roofs.

Ideal roof overhang dimensions should be 16-18 inches for rain protection and 24 to 36 inches wide for shade, depending on personal taste and design preferences of those living in each home. 

Overhangs can often serve as decorative features that reflect individual tastes of those residing within them.

The length of an overhang depends on both its climate and structure design, with anything greater than 24 inches requiring extra support; otherwise it could collapse under its own weight and break. To get expert help, our flat roofing in Sevenoaks can help.


Roof overhangs play an essential role in protecting windows, doors, siding and walls from rainwater seepage into their foundation; too little protection can allow rain into your home’s structure while too much can block sunlight rays making your house seem dark and uninviting.

A roof overhang’s height depends heavily on your local climate and chosen material; generally speaking, an effective overhang measures 16-18 inches wide.

An overhang on your flat roof can not only add style and charm, but it can also keep it dry! A small overhang will encourage water runoff into your gutter system instead of pooling at the foundation, while well-designed overhangs provide shaded windows to help keep the home cooler in hot climates or on sunny days. 

For guidance in selecting an appropriate overhang type for your property and circumstances, speak to a professional roofing contractor.


Design of a flat roof overhang is an integral component of building. These overhangs come in all lengths, styles and shapes to provide protection from rain, snow and sun as well as improve its aesthetics.

Homes in dry climates typically feature shorter overhangs than homes in wet or tropical weather, typically 16-18 inches from the wall of their home.

Some homebuilders opt for an overhang that fits flush with their structure’s roofline to achieve a modern aesthetic, which also allows for the installation of rain screen channels to divert water away from the home and its contents.

Flush overhangs provide effective protection from the elements, yet can also be damaged by wind. This is especially true during hurricane conditions where high speed gusts could dislodge it from its mount and take it with them off your roof entirely.

Read our article: Is a Flat Roof Cheaper Than a Pitched Roof?

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