It’s not as if you’re going to go out and build a roof over your house, but understanding roof structure, framing, and types of roofs might make it easier when talking with an architect, builder, or roofing contractor in the Dallas and Fort Worth area.
In this post, we take a quick, not-too-technical look at roof structure, framing, building regulations, parts of a roof covering, and types of roofs. We’re ignoring shingles because we’ve covered that material in several previous posts.
Roof Structure and Framing
Essentially all the elements that make up a roof combine to create a waterproof layer. Some roofs will have all the elements mentioned below; others only have some, but the principles tend to remain the same.
If a term doesn’t make sense, ask the Dallas or Fort Worth-area roofing company or roofing contractor you are working with to install a new roof or repair the one over your home.
Roofs are supported by:
- outside walls,
- ceiling joists
- interior load bearing walls.
Roofs are sheathed in layers of:
- and shingles.
The roof’s job is to shed water away from the structure, provide a location to mount a satellite TV dish, and collect poorly-thrown frisbees.
We’re not going to get deep into building regulations for roofs, other than to say that you must check with Dallas, Fort Worth, and surrounding city building authorities regarding codes and requirements for installing new roofs or repairing existing ones.
Dallas, Fort Worth, and surrounding cities usually have requirements for every detail, including materials, ventilation, and fasteners. The regulations are much stricter when it comes to historic buildings or structures in historic locations, for which certain styles may be required. There are also requirements for attic conversions. Even home owners associations may weigh in what your roof can look like.
Parts of a Roof Covering
This is standard on most residential roofs:
- To shed water properly, materials are overlapped.
- Typically material is installed from the bottom of the roof toward the ridge, so that the lower layer is overlapped by the next layer of the same material.
- A typical roof is constructed from a truss, covered with sheathing, underlayment, and a covering on top. The layers are carefully overlapped to ensure the roof is fully waterproofed.
Most roofs have some kind of asphalt shingle or tile covering to provide the waterproofing, but we will not go in detail here as we’ve discussed shingles in several previous posts.
Battens provide attachment points for tiles and hold down felt. They are evenly spaced to give the correct overlap between rows of tiles. The spacing (gauge) depends on roof pitch, tile type and fastening method, and climate. Roofs covered with asphalt shingles do not need battens.
Felt, or another kind of underlayment (including synthetics) (images), is laid below shingles to create a waterproof barrier. It is now required by building regulations in Dallas, Fort Worth, and surrounding cities, but felt may not be present on older buildings. It is laid over the sheathing, which may be made of plywood or another material, in overlapping horizontal strips.
Boarding laid on top of the rafters is known as sheathing and is required by local Dallas, Fort Worth, and surrounding city codes. Sheathing adds rigidity to the roof frame and provides a nailing surface for fasteners. OSB (oriented strand board or sterling board), particleboard, and plywood are common sheathing materials.
Each sheet of sheathing is centered on a rafter below. If you are planning to install wood shakes or shingles, your roofing contractor will space sheathing to provide more ventilation, as it helps to dry out wood roofing materials after wet weather.
If your roofing company is replacing your roof or repairing sheathing, make sure you hire contractors who are carefull. Roofers should walk only where the rafters run underneath to help prevent any bowing from occurring.
Types of Roof Design
As you’ve probably figured out, roof designs can be complicated.
In order to shape a roof, hips and ridges combine with the trusses to create the spaces inside the home. The shape of the roof must also shed water effectively.
When a roofer is detailing a roof hip or ridge, it is important to make the connection secure and to properly install the sheathing, underlayment, and flashing materials so that water does not enter the structure.
A valley is used if the external walls of the home turn an internal corner. It is designed to direct water down towards its intersection point, and then the water runs down the valley and off the roof.
A hip design can sometimes be found at a corner of the external walls of the home. Just like a mountain, a hip allows rainwater and snow to fall off either side of the hip and then slide off of the roof.
Typically, deep eaves should have 12 inches or more continuously vented to ensure that sufficient air intake is available. This is required to properly vent the attic.
Typically, shallow eaves have less than 12 inches of continuous venting. This is popular among more contemporary designs. You must also vent to ensure proper air circulation in the attic.
Outlook overhang is on the gable end of the home. It is supported by look-outs, which extend from the adjacent rafter. It requires more material and is sturdy.
Ridgehung overhang is less material intensive than outlook overhang. In this design the overhang is hung from the ridge at the apex of the roof. The boards are installed flat.