You ever hear the phrase “putting lipstick on a pig”? Well, that’s what it’s like to put fancy shingles or tile on a roof that doesn’t have a great structure. It’s kind of like putting nice clothes on – the shape of your body has a lot to do with how well you look in those clothes. When it comes to your roof, this is where trusses come in — there are a number of different designs for roof trusses and the best design for any building will depend on:
- The stresses the building roof is likely to experience. This could be snow loads, wind, Santa Claus, etc.
- The aesthetic preferences of the homeowner. What shape do you want your roof to have?
- The size of open areas within the building.
- The type of extreme weather conditions prevalent in the area where the home or building is being built. For example, here in the 4 Corners area, Dolores needs trusses that can withstand more snow than Cortez… Rico more than Dolores… and Telluride more than Rico.
Why Roof Trusses?
Trusses are used in a variety of applications where a lightweight, yet strong, structure is required. Trusses are used extensively in bridges, buildings (particularly roofing and flooring), radio and television towers, and space-based constructions.
Many home builders order prefabricated roof trusses from a manufacturer and have them delivered to a building site because building roof trusses is labor intensive and prefabricated roof trusses save time, materials, and money.
5 Advantages to using Roof Trusses:
- Carpenters with less experience can set trusses, lowering labor costs.
- Fewer interior load bearing walls are needed due to the trusses’ longer free span.
- Shorter lengths of stock 2×4 are used to build trusses, reducing material prices.
- Structural engineers design and certify roof trusses.
- Trusses can usually be set in 1 day, meaning the interior of the home is exposed to the weather for a minimal amount of time.
Roof Truss Considerations
When considering roof trusses for your home, they should not be chosen based on looks alone – an experienced architect, engineer, or truss designer usually helps to determine the roof truss design best suited to the building under construction. Someone with training specific to roof trusses will be able to make the most use of the room in your home, giving it the desired amount of space you are looking for.
For example, a different type of roof truss design can be used in various areas of your home, making it possible to customize the look you want in different rooms, while still maintaining the same exterior appearance.
Another thing to be aware of is that some roof trusses may be practical for the weather in a particular area, but may not be able to accommodate the desired design specifications for the building. Good architects and engineers consider both the building design and the stresses the roof will be subject to when choosing a truss design.
Basic Types of Roof Trusses
No matter how fancy the design, roof trusses are usually one of two types:
- Pitched Truss: The pitched truss has a triangular shape with additional structural members within the triangle, and is used primarily in roof construction.
- Parallel Chord Truss: The parallel chord truss consists of two parallel chords that make up the top and bottom of the truss, with diagonal and/or perpendicular webbing connecting the two parallel chords. The top parallel chord is usually in compression and the bottom parallel chord is usually in tension. (See my previous article on trusses for more info on chords, webbing, etc.)
More Roof Truss Types
- King Post: The king post truss is used for simple roof trusses and short-span bridges. It is the simplest form of truss because it is constructed of the fewest number of truss members (individual lengths of wood or metal). The truss consists of two diagonal members that meet at the apex of the truss, one horizontal beam that serves to tie the bottom end of the diagonals together, and the king post which connects the apex to the horizontal beam below. For a roof truss, the diagonal members are called rafters, and the horizontal member may serve as a ceiling joist. A king post truss can only extend up to 30 feet; therefore, they are unsuitable for longer spans. However, additional diagonal support can be added to make it a multiple truss system. This type of truss also does not provide storage space, because the frames are usually exposed, allowing no additional room. In addition, if one timber fails, it can create a domino effect by overloading neighboring timbers and endangering the whole structure. King post trusses are often used for barns, farm stands, pavilions, garages and carports. They are designed to add grace and elegance, as well as functionality to the home. The open, high-beamed ceilings also add a sense of space to a room. While the structure is simple and mainly uses only two angle struts, it is effective and can be altered slightly to create additional support.
- Queen Post: A queen post is a tension member in a truss designed to span longer openings than a king post truss. A king post uses one central supporting post, whereas the queen post truss uses two. Even though it is a tension member, rather than a compression member, they are commonly still called a post. Queen post trusses should be used when there is a large span that needs to be covered. They are relatively inexpensive and can be made to fit almost any size or shape roof. They transfer the weight load of the roof to the eave posts and allow for a clean, open space that needs no internal posts that might affect the architectural design of the building. The queen post provides excellent structural support and can be adapted and combined with other types of roof trusses for unique roof designs.
- Modified Queen Post: A modified queen post truss can be used in bay barns or something that requires an even longer span than what a queen post truss can handle. These trusses have added members that provide compression and tension support over the longer span of the truss.
- Fink: A Fink truss is one of the most commonly used types of residential construction trusses. It is a symmetrical truss that has arms which angle upwards from the bottom chord, forming V-shaped webs, which support the interior of the structure. These trusses can cover over 80 feet when the web pattern is duplicated. Fink trusses were used frequently in bridges for railroads and are now commonly used as roofing trusses today. This type of roof has under a 35-degree pitch. Anything steeper than this must use trusses that are more substantial to support the building. The Fink truss has been a popular style for many years, because it can accommodate many different rooflines and provide the structural support necessary to uphold the roof. In addition, this type of roof truss can extend over a distance while still accommodating the load path that is needed. They can also be stacked together to assist in building several more styles of roof profiles.
- Double Fink: A single Fink Truss can be up to 33 feet in size, while a Double Fink Truss can be up to 54 feet. It is even possible to create a Triple Fink Truss.
- Howe: The relatively rare Howe Truss, patented in 1840 by Massachusetts millwright William Howe, includes vertical members and diagonals that slope up towards the center. The diagonal web members are in compression and the vertical web members are in tension.
- Double Howe: Howe Trusses are meant to span up to 36 feet and a Double Howe is rated for as much as 60 feet. The longest Howe Truss design is the Triple Howe, and it is designed for spans ranging from 54 feet to 80 feet in length.
- Fan: The Fan Truss resembles a triangle with inverted triangular webs on each side of the apex, both supported by central vertical posts. Fan trusses do not contain a main king post or center post, and are available in double and triple fan styles. Double Fan Trusses reach a width of up to 36 feet and a triple fan may span as much as 80 feet of open space.
- Hip: A Hip Truss is a truss that has a flat top instead of the common peaks you see on traditional homes. A Hip Truss is used for a Hip Roof. Also called a hip-roof or hipped roof, it is a type of roof where all sides slope down towards the walls, usually with a fairly gentle slope. So it is a house with no gables or other vertical sides to the roof. A square hip roof is shaped like a pyramid. Hip roofs on houses could also have two triangular sides and two trapezoidal ones. A Hip Roof on a rectangular plan has four faces. They are almost always at the same pitch or slope, which makes them symmetrical about the centerlines. They are available in four basic types:
- Terminal Hip Truss System: These are best suited for relatively short spans of 32 feet or less. The hip jacks extend directly to the peak. The distance from the end wall to the face of the girder is equal to one half the span, provided the slopes are equal.
- Hip Master Truss System: The Hip Master Truss System provides an efficient method of framing complicated Hip Roofs. It supports the hip portion of the roof which is framed conventionally, speeds cutting of hip members and eliminates excessive bracing required in conventional framing.
- Step Down Hip Truss System: Step-down trusses are produced in the same size as the standard trusses and gradually decrease in the flat top dimension to form the sloping hip roof line.
- Dutch Hip Truss System: The Dutch Hip Roof gives the architectural appearance and features of both the hip and gable roof. The eave of the roof line continues around all four sides of the building. The small gable end breaks the symmety of a full hip or gable roof.
- Gambrel: The use of Gambrel Roof Trusses on roofs goes back centuries in American architecture. In fact, the earliest documented use of the Gambrel Roof was in the 1600’s. Often mistakenly called a Hipped Roof, the Gambrel Roof is used on homes in a style referred to as “Dutch Colonial”. Gambrel Roof Trusses give the roofs of the structures that use them a barn-like appearance. The Gambrel Roof is a symmetrical, double-sided roof with a double slope on each side. The lower slope is at a steep, almost vertical angle. Additionally, the distinctive line of the gambrel roof is not limited to barns and storage buildings – Colonial Style architecture, for example, makes frequent use of Gambrel Roof Trusses. The Gambrel Roof design is very attractive, but it is even more practical since trusses in Gambrel Roofs allow for the maximum amount of storage space in the attic area and do not require interior walls or support posts. Unlike most pitched roofs, where sharply angled walls make much of the space unusable, the pitch breaks in the Gambrel Roof mean that very little of the interior space is rendered unusable by the slope of the ceiling. Because of this, most of the interior space directly under the roof can be utilized as living space. Haylofts are a common example of the amount of space afforded by the use Gambrel Roof Trusses. Another advantage to the Gambrel Roof is that exterior design elements like dormers, which increase the sidewalk appeal and value of a home, are easily incorporated in the rooflines supported by Gambrel Roof Trusses.
- Bowstring: Named for their shape that resembles an archery bow, Bowstring Trusses were first used for arched truss bridges, often confused with tied-arch bridges. Bowstring Trusses are great for spanning large distances – thousands of Bowstring Trusses were used during World War II for holding up the curved roofs of aircraft hangars and other military buildings. Many variations exist in the arrangements of the members connecting the nodes of the upper arc with those of the lower chord. Sometimes, the lower sections of the bowstring truss go up at a slightly steeper angle than the other sections of the truss, which allows water to run off more easily. An advantage of roofs built over Bowstring Trusses is that there is no need to cap the ridge at the top of the roof, saving time and money in the construction process. (A ridge cap normally runs along the length of a roof, covering the seam where the materials forming each side of the roof join at the very top of the roof. Bowstring Truss Roofs are arched, so there is no point at the top where two sets of roofing materials meet.)
- Polynesian: A Polynesian Truss has two pitches – a lower pitch on the bottom part of the roof, and a steeper pitch on the top part of the roof. Typical pitches would be 17.5 degrees and 35 degrees.
- Mono Pitch: Mono Pitch Trusses are usually used in shed-type roofs and lean-to roofs. They are basically half of a normal truss.
- Dual Pitch: The Dual Pitch Truss has a different angle or slope on each side of the truss apex. This type of truss is very commonly used, and can conform to the design of many homes.
- Scissors: Scissor Truss Roofs create a unique sloped ceiling inside your home. The pitch of the roof defines how steeply the ceiling will slope. This is a very common type of roof truss used in residential home construction. Also, Scissor Trusses are often used to design cathedral ceilings since this type of roof truss does not require a bearing beam or wall to support the roof, and it has a greater load limit than many other types of trusses. Also, in areas where there are extreme weather conditions or where the soil is unstable, this type of roof is particularly useful because it can increase the stability of the building. It is often combined with other types of roof trusses when constructing a home. In order to form these trusses, two inside beams are placed to rise up to meet in the middle, creating a “scissor” look. This gives the vaulted appearance of the ceiling in the home. They usually shouldn’t span more than 48 feet.
- Cambered: To camber means to slightly curve or bend. The word camber is typically used in describing a type of arch, truss or beam. So, “Cambered” Trusses arch upward. This type of truss will give your ceiling an arched look.
- Inverted: An Inverted Truss is used to create cathedral and vaulted ceilings with great spans. Scissor trusses are usually used in homes, whereas Double Inverted Trusses are usually used commercially, and for churches. However, there are also some creative things you can do with this truss to create a modern look for your home’s rooflines.
- Cathedral: A Cathedral Truss can be used to create a vaulted ceiling, although Scissor Trusses are more common for this purpose.
- Studio: A Studio Truss is basically a common gabled truss roof, but with one ceiling raised to accommodate a studio room, while the other half of the roof has an ordinary flat ceiling.
- Attic: Some truss designs make it difficult to impossible to have attic space. However, there are Attic Truss designs that leave open space that may be used for storage or converted to additional living space. Attic Roof Trusses are usually designed to give the building a standard eight-foot tall attic space. The design of the trusses does not change the exterior appearance of the home. The most common type of attic truss design in residential construction is the Double Cantilever style. Unlike standard roof trusses, an attic truss leaves most of the area beneath the roof open and framed, so adding walls and a ceiling at a later time is fairly inexpensive and can be easily accomplished even as a DIY project. Although Attic Roof Truss designs are more expensive than other types of trusses, they offer savings over stick construction and add value to a house. For example, if a family needs more space they can add an additional room or two to the attic, instead of selling the house and moving to a larger one. More square footage, whether it is finished or unfinished, equals money when selling a house – houses with attics and/or basements are priced higher and are more attractive to buyers than those without extra space.
- Stub: A Stub or Bob-Tail Truss is a gable shaped truss that is clipped at the end. This truss may be used where a triangular truss will not fit. It is usually stubbed to match an existing ridge line with a shorter span or to change to a vaulted ceiling in the opposite direction. This type of truss has the same pitch on each side; however, the peak is not usually in the center of the span. This results in one end of the truss having a taller heel than the other.
- Piggyback: Piggyback Trusses are used when the height of a required roof truss exceeds the limit allowed by a state’s transportation department for transport on the back of a truck. Depending on the state, the limit is usually around 12 to 14 feet. So when your truss height exceeds that limit, a Piggyback Truss is needed to transport it to your house.
- Flat: A Flat Truss is used in roofs or floors. It may be designed as top or bottom chord bearing, or for simple or multiple spans. It may also be cantilevered at one or both ends. When used as a roof truss, they are not actually flat, but slightly sloped, which prevents water from pooling on the roof and collapsing or damaging the structure – flat roofs generally have a pitch of less than 10 degrees. Flat Roof Trusses are one of the more common types of roof trusses. However, they are more inefficient than other types of trusses because stress on the webs of flat roof trusses is greater than other types of trusses. Therefore, in order to have a safe web connection structure that can withstand the weight of the roof materials, it will probably be a more complicated and expensive construction process. Because of this, they are generally used when specifically requested by the homebuilder or to compliment the particular design of the building, such as a Southwest or Pueblo style home. Building a flat roof has special considerations – it will need to support a heavier load than a pitched roof, which would allow snow and water to slide off more easily. Needless to say, it is not recommended to use a flat roof in areas that get a lot of snow.
- Sloping Flat: A Sloping Flat Truss is used to create a vaulted ceiling. It may be top or bottom chord bearing. This truss has parallel chords, both of which slope at the same angle, with a vertical post at each end.
Of course, now that you have a general idea of what kinds of trusses can be made for your home, it is still a good idea to have an experienced architect, engineer, or truss designer create your truss plans. You’ll need an engineer’s stamp of approval to pass inspection, and any one of these professionals will be able to give you truss plans that have an engineer’s approval.
Here at the ProBuild Truss Plant, for example, our talented truss designers will know what kinds of trusses to use to meet your design and building code needs, and their plans come with an engineer’s stamp of approval. This is all part of the service of giving you a bid on building your trusses. Feel free to come down to the ProBuild on County Road M and Highway 145 and ask for Derek, or give me a call at my number listed below.
Derek Alvarez sells pre-built roof trusses and building materials at ProBuild here in Cortez, Colorado. If you have any questions for Derek, you can contact him at 970-739-9911. *The views and opinions expressed are those of Derek Alvarez alone and do not necessarily represent the views of ProBuild.