A roof is a complicated system. Made up of trusses, supporting beams, decking, underlayment, and roofing material, there’s a lot that goes into keeping any building standing strong against all of the elements. Whether you’re thinking about getting a new roof, or you’re planning to build a pole barn, shed, or barn from scratch, it’s important to understand the main components of a roof so you end up with a completed project you can be proud of, and that will stand the test of time.

Here are some of the most important roofing terms you should know, including terms related to roof trusses and the roof system itself.

Roof Truss Terms

Whether you’re planning a DIY project like a shed or garage using roof trusses, or you’re interested in learning more about manufactured construction components, here are some of the basic terms to know about roof trusses:

Roof Truss

Before we can get into the components of a roof truss, it’s important to know what a roof truss is.

A roof truss is a pre-manufactured roofing component — what you’d typically consider to be the rafters of a roof. Trusses are manufactured offsite, and then shipped already assembled to a construction site to reduce on-site labor and speed the building process along. They’re also handy for DIY outbuilding construction because they’re made precisely, with little room for human error, ensuring your building has the support it needs.

Now that we have a clear definition of a roof truss, what are some of its main components? (Take a look at this image, courtesy of Technistrut, for a better visualization of each of these components.)

anatomy of a roof truss


The apex of a truss is its top-most point. On a common or attic style roof truss, which are triangular, this will be the top peak of the roof. On roofs with a flat top, like a hip or flat roof, it is the top and center point of the truss.

Bottom Chord

This is the long, horizontal beam on which the rest of the truss is built. In some cases, where a roof truss has a triangular base, rather than a flat base, there are two bottom chords that form the support and structure for the rest of the truss.


How far the top chord hangs over its bearing support. When a roof is complete, the overhang is the distance from the bottom of the roof to the building itself.


Smaller beams that run perpendicular to the top chords of each roof truss. Purlins are used to support the decking of a roof.

Top Chord

The top-most beams of a roof truss. In most common roof styles, these are the two slanted beams that hang over the side of a building.


The beams that join top and bottom chords in a triangular pattern. Webs carry tension and compression stress, keeping the truss from bending.

Standard Roofing Terms

Now that you have many of the common roof truss terms down, let’s talk about overall roofing terms that are good to know.

Drip Edge

An L-shaped metal strip that’s installed along roof edges to keep dripping water clear of siding, eaves, and the rest of your home.


The horizontal lower edge of a sloped roof. This is where the edge of your roof levels off, rather than slanting to a point.


The flat board attached to the outer edge of a roof. Your gutters are attached to the fascia board of your roof.


A secondary layer of protection for the roof deck. Felt or underlayment is most often waterproof, and occasionally referred to as tar paper. It’s applied on top of the decking to add another barrier against water and the elements under the shingles.


Waterproof material used to prevent water from seeping through particularly vulnerable portions of your roof. Most often seen around chimneys, vent pipes, joints to vertical walls, and roof valleys.


Oriented Strand Board. It’s a material commonly used as decking for roofs, made from wood chips and lamination glues pressed together to make a cheap, durable material.


Rafters are the exposed beams you see in the ceiling and at the peak of a building that’s under construction. If you’re using manufactured roof trusses, this is the part that you won’t have to build yourself.


The top edge of two intersecting sloping surfaces. A common ridge is the peak of your roof. Most roofers apply an additional, overlapping layer of shingles to the ridge to prevent water seepage and damage.

Roof Valley

The depression between two roof peaks. For example, if your garage roof has a peak, and your home’s roof has a peak, the valley occurs where those two roofs meet at the bottom of the slope.


Sheathing, also known as decking, is the material that is nailed onto purlins, and that makes up the backing for a roof. Roofing materials, like shingles, are applied to the decking or sheathing of a roof.


The material most commonly used on the exterior of residential roofs. Shingles are most often made of asphalt and are nailed on in strips of 3-5 shingles at a time.


How steep your roof is. Roofers measure slope by the rise in inches for every 12 inches of horizontal length. For example, a roof that rises 4 inches for every foot of horizontal distance has a 4-in-12 slope.

We hope this glossary of roofing terms helps you tackle your next project with confidence! Whether you’re looking for a new roof or considering a roofing project of your own, Zeeland Lumber & Supply would love to help.

We manufacture and ship our own roof trusses directly to our customers and we supply a number of roofing materials from top brands like CertainTeed. Or, if you just have a question about roofing or roofing materials, we’re always here as a resource for you. Give us a call at 888-772-2119, or contact us online — we’re here to help, whether you’re looking for products or answers.

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