Roofing Terms and Definitions for Layers of a Roof


Roofing terms and definitions for layers of a roof

Most homeowners will have an issue with their roof at some point. When your roof has a problem, you will likely contact a roofer to further investigate. However, this can seem intimidating for homeowners who know little to nothing about their roofs.

If you feel out of your depth discussing fundamental roof problems, that’s OK. Here are some basic terms for roofing layers.


Flashing is a flat, thin piece of sheet metal used to waterproof the perimeter and protrusions of the roofing system. It keeps direct water flowing away from the seams and joints and prevents it from entering the opening and cracks in a roof. Flashing is best applied to the roof’s joints, hips, valleys, chimneys, air vents, and dormers to prevent damage.

Roofing Square

A roofing square is a measuring unit equal to 100 square feet, or 10 feet by 10 feet. This measurement form estimates how much roofing materials are needed for a project, including the shingles and underlayment. Roofers use this measurement to calculate the costs for roof installation or repairs.

Roof Structure

The roof structure is the skeleton of your roof and the very bottom layer. It is comprised of individual wood or metal rafters that form a triangle-shaped truss. The system creates a frame that supports the sheathing and shingles, giving strength by transferring the weight of your roof or load to the exterior walls of your home.

Sheathing or Decking

A roof deck or sheathing is a layer of boards fastened to the rafters that cover your home. This material is typically plywood or oriented strand board (OSB). A layer of black roofing felt or synthetic underlayment is usually attached to the decking for added protection.


Many roofs have shingles that form the top layers of a roof covering. Shingles are made of a variety of materials, including asphalt, wood, tile, metal, and slate. Combined with underlayment, this layer creates a durable coating that protects the roof from wind, fire, and extreme weather.


Underlayment is a waterproof, paper-like material that overlaps sheets over your sheathing and vapor barrier. Underlayment works with the vapor barrier as a second layer of defense to protect your roof against rain and snow that can get trapped under your shingles. Furthermore, it helps the shingles lay flat and uniform.

Vapor Barrier

A vapor barrier is also known as an ice barrier or water barrier. This waterproof plastic membrane clings to the sheathing and works with underlayment to protect the sheathing from common winter roofing issues like ice buildup or rain.

Most homeowners are not qualified enough to work on their roofs. Furthermore, doing so can result in severe harm or additional roofing problems.

From roof leaks to missing shingles, CertainTeed professionals are at your service. Our professionals are fully licensed and insured to complete all roof work. We can spot any damage your roof has sustained and will take all the necessary steps to complete the job safely and thoroughly. Contact us today!



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