When you look at the roof of a house, the parts you will readily see are typically the roof covering and the gutters. Under the roofing, however, there is supporting framing. Most modern home builders use trusses for the roof framing of a stick-built house instead of lumber. Trusses are pre-fabricated, triangulated wooden structures used to support the roof as can be seen in the picture below. Using trusses for roof framing holds many advantages over other types of roof framing:
- Trusses are engineered to be very strong.
- They are usually much less expensive in materials than using 2×8 or 2×10 lumber
- They are also much less expensive in terms of time. Rather than having to have framers build the roof on-site from scratch, the trusses are manufactured in a factory and engineered there for strength. They are then brought already assembled to the site and simply need to be installed. This can usually be done in one day.
- You can have many configurations and variations, such as hip roofs, and vaulted or cathedral ceilings.
- The truss will typically span from exterior wall to exterior wall. This means that no interior walls are “load-bearing,” making moving interior walls easier if a homeowner wants to make plan design changes.
Types of Trusses
There are a number of types of truss used for different purposes. We will cover some of the more common ones here:
Gable trusses are the end trusses of a roof that has gable ends (as opposed to hip roofs). As you can see in the picture, the vertical framing is spaced at 16 inches on the center so that siding can be nailed to the truss.
A standard “W” truss is used over main areas of the home that will have flat interior ceilings.
In cases where a ceiling is vaulted, scissor trusses are used. In cases where only part of the ceiling width is vaulted but part will be flat, a partial scissor truss is used.
There are a number of other types of trusses for specialized purposes as well.
Mounting the Trusses
The trusses are raised to the top of the houses framing with a crane which is typically mounted to the back of the truck which delivers the trusses to the site. Once placed on top of the walls, they are spaced on 24-inch centers, meaning that the center of one truss is 24” from the center of the next truss. The trusses are tied to the walls with metal mounting plates. Once the trusses are in place, sheets of plywood or OSB are laid over the trusses and secured. Then the roofing material, such as shingles, is laid as the roof surface. Shingles are not just designed to make the roof attractive. They protect the framing from the elements, lengthening the life of the roof.
A common term you will hear is roof pitch. This is referring to the angle at which the roof rises to the peak of the roof. For example, as you see in the illustration a 6/12 pitch roof means that for every 12 inches inwards towards the peak of the roof, the roof angle rises 6 inches. Roof pitch explained picture here
The number 12 is always the same-1 foot. The other number is usually your choice. A 1/12 roof is extremely shallow and is more common in drier warmer climates. Most Pacific Northwest home builders use a steeper pitch from 4 to 8/12 as the steeper pitch helps gravity move snow and rain accumulation off of the roof.
Most stick-built homes today use what is called a ridge vent. This replaces the pipes that were commonly used years ago for venting the roof.
In the space between the trusses, hot and humid air rises and venting is needed to allow it to escape (breathing roof). The ridge vent is a cap the runs at the peak of the roof from one end of the ridge to the other end. It allows a space for the hot air to escape. in addition to being functional, it also looks much better than having pipes sticking out of the roof.
Home Builders in the Pacific Northwest usually use standard asphalt shingles for the roof. First, the roof framing is covered with building paper, or tar paper. The shingles then go on very quickly, usually a day or less.
In many areas of the Pacific Northwest, snow becomes an issue. Local building departments stipulate a certain weight. Most areas in Western Washington have a snow load between 20-25 lbs per square foot (psf). This means that the roof needs to be built to support 25 lbs of snow per every square foot of surface on the roof. In some higher elevations, snow loads can be much higher. In the mountains, it can be as much as 200-300 lbs psf. True Built Homes normally builds with the more common 25 lb snow load in mind. If the local building department requires a higher snow load capacity, then there are additional requirements, such as heavier duty headers, which we will have to meet. As a result, there might be a higher cost. Contact your home consultant if you have any questions about your area, or call your local building department
In areas of the Pacific Northwest coast, and some other parts of Washington and Oregon, local building codes also require additional bracing for higher wind zones. These are areas that receive more than the usual winds during storms. Some areas of the coast require homes to be built for 120 mph winds with increase periods of ‘gusts. Meeting the requirements of these codes often requires Pacific Northwest homebuilders to add additional bracing to the house. The roof often requires heavier sheathing, stronger nails and hurricane clips. While these requirements will incur a slightly higher cost, it must be remembered that these code are really for your benefit. Paying a bit more for the peace of mind knowing that your house will not fall down on your during a major storm is well worth the additional cost. Contact your home consultant if you have any questions about your area, or call your local building department