EVERYTHING You Need to Know About Roof Truss Designs

Roof trusses play a critical role in providing support and shaping the overall structure of your building. With so many different truss designs available, how will you know which one is perfect for your project? Whether you are designing a vaulted ceiling in your master bedroom, looking for extra space in your attic or want to double your roof as an outdoor living area, understanding your options will help you make informed decisions. In this guide, we'll break down the most common types of roof trusses, their benefits, and when to use them.

Common Trusses

Common Trusses are the most frequently used trusses in residential construction and may be referred to as a regular or standard truss. The design features a peak in the top center and a flat bottom. These trusses can span from 8 to 80 feet and are primarily built with 2x4s. The span these trusses allow for are determined by the feet between panel points. The space between panel points are referred to as panels. For the top chords of the truss, there needs to be a panel point every 8 feet. For the bottom chord, there needs to be a panel point every 10 feet. A panel point is where the webs of the truss meet the top and bottom chords. If a truss only has 1 web, like a King Post Truss, it can only span 16 feet due to each panel only being able to go to 8 feet.

There are many kinds of common trusses due to how many webs can be added. A Queen Post Truss, also called a fan truss, has a post with two webs and can span 20 plus feet. The Fink Truss features a W pattern and the Howe Truss has four webs and a post. The Howe and Fink trusses are both named after the people who invented them. The Howe truss may also be referred to as a four over four common truss due to their being four panels on the top and four on the bottom. These styles may be modified to allow for a building with a greater span, up to about 80 feet total.

Vault Trusses

Vault is a generic term that implies the trusses are creating volume in the ceiling. The most common and simple type of vault truss is a Scissor Truss. The Scissor Truss has a slope on the bottom chord that matches the slope of the top chord of the truss and a bottom peak matching that of the top. It is ideal for creating more space inside of a building and can span buildings of 8 to 80 feet.

Scissor trusses present limitations about how far the bottom chord needs to be from the top chord for load-bearing, especially near the ends of the truss where the space is thinner. Some may opt to do a Parallel Chord Vault, where a web joins the edges of the top and bottom chord.

Other common vault trusses are the Partial, Offset and Barrel Vault Trusses. A Partial Vault truss is a truss that allows a builder to have a vault over a specific section of ceiling or room, leaving the rest of the ceiling flat. This truss has a bottom chord that slopes up and then drops vertically down, joining with the rest of the bottom chord, which is flat. An Offset Vault truss is similar to the partial vault, but the drop in the bottom chord may be a small slope instead of a vertical drop. A Barrel Vault Truss has a bottom chord that mimics a round vault.

Mono Trusses

Mono Truss is short for Mono Slope Truss or Single Slope Truss. They are essentially one half of a common truss. This design is often used against the side of another building. An example of this is in a Monitor-Style building, which has a peak in its center and a Mono Truss on each side. Many designs are available for Mono Truss, such as a Vault Mono Truss, which allows for more ceiling height.

Flat Trusses

Flat Trusses are popular for commercial applications, modern homes and even floors. Sometimes people have a flat roof built on their home that doubles as an outdoor living space. Three types of Flat Trusses are the Pratt Web Pattern, the Warren Pattern and the Mansard Truss. A Pratt Web Pattern Truss has a combination of vertical and diagonal webs. The Warren Pattern has alternating diagonal webs. Both the Pratt and Warren Patterns were named after the people who invented them. A Mansard Truss is a flat truss with a sloping roof on each side that is popular in commercial buildings. This design allows building owners to keep appliances, such as HVAC units, concealed on the roof. Builders may also choose to use a Sloping Flat Truss that works similarly to a vault truss in that it allows for higher ceilings.

Room in Attic Trusses

The main purpose of a Room in Attic Truss, also called a Bonus Room Truss, is to create usable space in the roof structure that is more economical than adding a second or third floor to a building. Extra space can be utilized for living, storage or mechanical purposes. A simple Room in Attic Truss has the structure of a common truss, but a collar tie forms the ceiling and the ends of the truss are supporting by knee walls. The Gambrel Truss Design is popular for attics because it has slopes outside that allow for a large space within a small span.

Conclusion

Selecting the right truss ensures your structure is not only strong and durable but also optimized for space, aesthetics, and cost-efficiency. Whether you want a common truss for a basic design, a vaulted truss for extra ceiling room, or a room in attic truss for living or storage space, knowing your options can help you make the best decision for your project. The staff at Truss Components of Washington are dedicated to making sure you know all the facts before choosing the perfect truss structure for you.

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