birds eye view of skyscrapers with flat roofs

Flat Roof Components & How They Function

In News by Infinity Roofing

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Low-slope or flat roofs are a product of the Industrial Revolution, first gaining traction as a way to decrease construction costs for large commercial buildings in the late 19th century. The style quickly gained popularity as a modern alternative to more traditional sloped roofs, with many buildings mimicking the look with “false-fronts.” Now over a century later, flat roofs are commonplace on commercial buildings as well as residential properties. Here are some of the most important flat roofing components and how they work to provide shelter for your business or home. 

Flat Roofing Components 

While flat roofing might seem like a simple concept compared to sloped roofs, it still involves many components. Even though there are many different types of flat roofs, understanding the terminology used in single-ply roofing will give you a better idea of the basic structure. 

Roof Deck 

The roof deck is the structural surface that provides the base for the roofing system, including the insulation. Roof decks — typically made of steel, concrete, or wood — support the roof’s weight so it doesn’t come falling down. 

Roof Insulation 

Applying insulation is material applied underneath the roof’s membrane to reduce heat build-up. In single-ply roofing, the insulation usually consists of various size boards. There are many different types of thermal insulation available for low-slope roofs


The term “substrate” refers to the surface where the roofing material is applied. This surface could include the structural deck or the insulation where subsequent layers will be placed. 


The roofing membrane is either a flexible or semi-flexible covering that seals the roof to protect it against the elements. The primary purpose is to expel water and help with leak prevention. There are several different types of commercial roofing membranes:

  • EPDM (ethylene propylene diene terpolymer)
  • TPO (thermoplastic polyolefin)
  • PVC 
  • Elastomeric Coatings


In a ballasted roof system, the ballast refers to the stone (typically river-washed stone) that goes on top of the roofing components. The weight of the stone helps protect the roof and keep the components secure. 


Contact adhesive is applied to both the roofing substrate and membrane to achieve proper adhesion. Adequate flash-off time is required on each surface to ensure the adhesion is set and ready between bonding the surfaces together. 

Wet lay adhesives only apply to the substrate before adhering the membrane to the substrate. The adhesive needs to be wet for the membrane to bond to the substrate. Different contact and wet lay adhesives are used for certain applications.


A splice in single-ply roofing refers to the joining of two pieces of material to act as one. Splices are important because it’s how seams between different sheets of membrane are sealed to be both secure and watertight. 

A fishmouth, or an opening between the two layers of membrane, may if occur if splices are not joined correctly. A fishmouth is usually the result of poor workmanship. 

Roof Penetrations

Roof penetrations include objects like A/C units, skylights, or other equipment that penetrates the roof structure. Proper flashing of penetrations helps prevent leaking.


Raised structures known as curbs often support roof penetrations. They’re what goes under an HVAC unit or other equipment that might be on the roof. 


A penthouse is just a raised structure on the roof of a building that sits within the outer walls. 

Roof Hatch

A roof hatch is a type of curb that provides access to get on and off the roof. 

Parapet Wall

Parapet walls go around the perimeter of the roof. They may vary in height and width. Although they are fairly common, not every flat roof has a parapet wall. 

Counter Flashing

Counter flashing is formed metal that is secured on walls, pipes, curbs, or other roof surfaces to provide protection and help shed water away from the material below. 

Roof Drains

Drains are what allow water to exit the roofing system. As with penetrations, they must be flashed to make sure they don’t leak. 


A roof cricket is an area between the drainage points that is raised to divert water and ensure proper drainage. 


A scupper is an opening in the roofing that helps channel water away. For instance, a scupper may be a small opening in a parapet wall used for drainage. They also need to be flashed to ensure they are sealed properly. 

Wood Nailer

A wood nailer is a solid piece of wood that acts as an effective substrate for other roof accessories. Typically wood nailers are used with metal edge details, which come in many different types. 


Copings are metal or concrete coverings that are placed on exposed walls to provide extra protection. For instance, they may be used to cover a single-ply membrane on top of a parapet wall. 

Expansion Joint

Expansion joints are a structural separation between two building elements. They reduce the stress and movement of the building components to reduce splitting or damaging the roof membrane. 

Want to Learn More About Flat Roof Components?

If you’re looking for more information about flat roof components, we’d love to answer any questions you have and discuss what flat roof options are available for you.

Infinity Roofing & Siding offers reliable residential and commercial roofing services in Richmond, Williamsburg, Fredericksburg, Virginia Beach, and the surrounding areas. Whether your roof is pitched or flat, shingled or metal, old or new, the roofing specialists at Infinity Roofing & Siding can assess your roof for storm damage and provide high-quality roof repair, restoration, and replacement. Reach out to us for a free inspection and quote!