Wondering why there is a wall around your flat roof? Understanding why parapet walls are installed around low-slope roofing systems will give you crucial insight to their function and necessity.

The professional roofers at New Image Roofing Atlanta assembled a comprehensive guide to parapet wall design, height, necessity, and waterproofing.

What is a Parapet Wall?

A parapet is a barrier that is an upward extension of a wall at the edge of a roof (seen in many flat roofing projects). This extension projects above the flat roof (can vary in height and width according to local building codes and its designed function). The word comes ultimately from the Italian parapetto.

Parapet Wall Design

A plain parapet wall is a simple vertical extension of the wall on the building’s outside. They are most common in commercial buildings without ornate decoration (it can be difficult to tell where parapet walls start looking from the building’s outside). They are generally more about functionality than design. Consider the following:

Purpose and Functionality – Parapet walls serve various functions for flat roofs, acting as aesthetic and functional elements. They provide a barrier that conceals rooftop equipment, helps prevent falls, and enhances the overall appearance of the building. Additionally, parapet walls are a crucial line of defense against water ingress, a common concern with flat roofs.

Aesthetic Considerations – From a design perspective, parapet walls contribute significantly to the visual appeal of a building. Architects often use them to create a uniform and pleasing silhouette, giving the structure a more finished and polished look. Parapets also offer opportunities for architectural creativity, with options for different materials, textures, and decorative elements.

Parapet Wall Height

Local building codes often determine how and when parapet walls should be constructed on commercial structures.

Building Codes and Safety – Determining parapet wall optimal height is a nuanced process that involves adherence to building codes and safety regulations. Building codes typically mandate minimum parapet heights to ensure occupant safety and prevent accidents. The International Building Code (IBC) and other regional codes provide guidelines on parapet wall heights based on factors like building occupancy, roof usage, and fire safety.

Read more about parapet wall specifications at codes.iccsafe.org/s/IBC2021P2/chapter-7-fire-and-smoke-protection-features/IBC2021P2-Ch07-Sec705.11

Wind Uplift Considerations – Parapet wall height is not solely about aesthetics and safety (it plays a crucial role in mitigating wind uplift forces). Tall parapets can act as a windbreak, reducing the impact of strong winds on the roof and preventing damage to roofing materials. Engineers must consider local wind patterns and calculate the appropriate parapet height to optimize wind resistance.

When Are Parapet Walls Necessary

Parapet walls are mainly found on flat roofs, extending a vertical wall at the side of a commercial, industrial, or residential structure past the roofline. Flat or low-slope roofing systems include:

• EPDM
• TPO
• PVC
• BUR

Parapet walls are typically required when the roof must double as something like a terrace, balcony, facilities area, lounging area, or walkway, helping keep the area safe.

Roof Access and Safety – Parapet walls become essential when rooftop access is necessary for maintenance, service, or other activities. They provide a protective barrier, considerably reducing accidental fall risks. OSHA (Occupational Safety and Health Administration) regulations often require the presence of parapet walls or other protective measures when employees work on flat roofs.

Read more about OSHA’s fall protection system criteria at osha.gov/laws-regs/regulations/standardnumber/1926/1926.502

Water Management – In regions with heavy rainfall or potential for flooding, parapet walls play a crucial role in:

• Managing water runoff
• Preventing water from cascading off the roof’s edge
• Reducing erosion and water damage to the building’s foundation and landscape

Properly designed parapets incorporate drainage systems to efficiently guide water away from the roof surface.

Concealing Rooftop Equipment – Flat roofs often house HVAC units, solar panels, and other equipment or activities necessary for building functionality. Parapet walls offer an effective solution for concealing these elements, maintaining a clean and uncluttered appearance while providing easy access for maintenance.

Waterproofing Parapet Walls

Like your roofing system, parapet walls must repel and shed water efficiently. Parapet walls that allow water infiltration will lead to costly structural damages.

Flashing and Sealants – Effective waterproofing is paramount for parapet wall longevity and performance.

• Flashing (water-resistant material) is installed at the roof and parapet junction to create a watertight seal
• Sealants are used to fill gaps and joints, preventing water infiltration

Cap Flashing – Cap flashing is an essential parapet waterproofing component (metal flashing installed at the parapet wall’s top, extending over the roof membrane). Cap flashing prevents water from seeping into the joint between the parapet and the roof, offering an additional protective layer against leaks.

Proper Drainage – Adequate drainage prevents water buildup on flat roofs and parapet walls. Scuppers (openings in the parapet that allow water to drain) are commonly used with conductors, gutters, and downspouts to ensure efficient water management. Regular maintenance, including clearing debris from scuppers, is crucial for the effectiveness of the drainage system.

Read more about roof maintenance plans

Quality Materials and Construction – Choosing durable and weather-resistant materials for parapet walls is fundamental to their long-term waterproofing. Consider the following:

• High-quality masonry, metal, or composite materials ensure durability and safety
• Professional construction practices, contribute to the parapet wall resilience against water intrusion
• Expert roof installation will ensure that parapet walls are protected and efficiently drain water

Tip: Thoroughly vet all of your contractors, verifying their credentials, past work, licenses, and insurance before contracting them.

Parapet Walls for Flat Roofs

In this article, you discovered crucial information about parapet wall design, height, necessity, and waterproofing for your commercial or residential low-slope roofing system.

Installing parapet walls around flat or low-slope roofing systems ensures occupant safety, building aesthetics, and supports effective water management.

Ignoring the need for parapet walls may leave your roof vulnerable to accidents and expose unsightly machinery or equipment on the rooftop, potentially decreasing your structure’s curb appeal and value.

Sources:
osha.gov/laws-regs/regulations/standardnumber/1926/1926.502
theconstructor.org/building/parapet-walls-types-uses/28646
codes.iccsafe.org