Anatomy of a Roof: Important Parts to Know About

May 12, 2014

Understanding what’s up there.

Roofs are complex and have many parts. A roof is one of those things that people rarely think about. Usually, a roof is just there, doing what it’s intended to do: protect the interior of a structure. Take a look at your roof. What do you see? To most people, it doesn’t look like much. There’s a lot more going on up there than you can see from the ground. Your roof is a complex system with plenty of parts. Want to know what they are and what they do? Read on.


The ridge is the highest part of a pitched—also known as “sloped”—roof. Most houses have pitched roofs for both aesthetic and practical reasons.

Roof Truss

Think of the truss as the skeleton of the roof. Comprised of beams fastened together in triangular patterns, the roof truss is the framework that holds the roof together.


Rafters are the parts of the truss that run all the way from the top of the roof to the bottom. There are principal rafters, common rafters, auxiliary rafters and compass rafters. Some rafters are called kings and some are called hips.

Decking or Sheathing

This is the part of the roof that covers the rafters and provides a flat surface to which the shingles are attached. The sheath or deck is generally made with large sheets of plywood.


The part of a roof known as the underlayment is usually made of super heavy felt, although synthetic materials are available. Also called tar paper, the underlayment is placed atop the decking prior to installation of shingles. The underlayment provides an additional layer of moisture protection. Here in the Pacific Northwest, we can use all of that we can get.


The fascia is a horizontal timber board that’s attached to the ends, or ‘feet’, of the rafters. Fascia is considered part of the trim and is the part to which rain gutters are attached.


The word eave means edge and that’s exactly what it is: the lowest edge of the roof. Fancy or plain, the eaves project beyond the side of a structure and provide an overhang to prevent rainwater from accumulating along the base of the building.


Stand under the eaves of your roof, look up, and you’ll see the soffit. It’s the finished underside of the eaves that project from the roof.


When two sloped roof planes intersect at an external angle of less than 180 degrees, it’s called a valley.


Whereas the valley of the roof describes the interior angle of two intersecting sloped roof planes, the hip is the external angle formed by the same intersection.


On a ridge roof, the gable is the triangular part of a wall just underneath the roof slopes on the side of a building.


In roof anatomy, the flashing prevents water seepage around things such as chimneys, vent pipes and valleys.

Your roof might just be the most important part of your house, and we’re glad you took some time to learn more about it. Bookmark our homepage and revisit us when you require an on-time, quality roofing contractor in the Portland, OR, and Vancouver, WA, areas. We are Interstate Roofing and we provide 24-hour emergency roofing services. Contact us online, or call 503.684.5611  to speak to a member of our helpful staff.