What Is a Roof Curb?

If you are repairing a roof, installing new shingles or starting from scratch and building a roof, you will encounter and use a roof curb. This device is what it sounds like, a curb for the roof. It has many various features and functions that improve the roof's drainage and overall longevity.

What a Roof Curb Is

A roof curb is a piece of flashing, a metal sheet formed to fit around a chimney or vertically aligned vent on your roof. The roof curb is usually one single metal sheet with a beveled or curved bottom lip. The product looks like a sleeve that fits over the chimney. If you have used flashing to repair a roof, you know what a roof curb is. The two are similar. The only difference is the roof curb extends up vertically and is one piece.

What the Roof Curb Does

A roof curb's main function is channeling water away from the seam formed between the roof boards and the vertical chimney or vent. The curb's bottom lip, as it is formed to extend down and out at an angle, channels water away from this seam, which otherwise would become saturated with water and begin to rot. The protection of the roof system at the joints between the chimney or vent and roof is the main idea behind this part.

Types of Roof Curbs

There are many types of roof curbs used in a variety of situations for different types of chimneys and vents. Some roof curbs have additional vent holes that look like gills. These are used for kitchen exhaust vents, for instance. The vents are positioned near the top of the curb. Other major design differences include roof curbs built for flat roofs, non-insulated roofs and insulated roofs. The difference between the curbs for non-insulated roofs is they contain a layer of insulation.


The design and construction of roof curbs is fairly simple. Most are single welded curbs, which increases their efficiency. Having a single weld means there is only one seam in the roof curb. This reduces the chance of separation at the seam because there is only one seam to be concerned about. Each roof curb is designed to fit different-sized chimneys or vents in heights usually ranging from 8 to 24 inches. They may be built to fit pitched roofs, which are slanted, and flat roofs, most commonly found in commercial construction.

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