What Is an Attic Truss?

Dan Cavallari
Dan Cavallari
An attic truss is typically used to support a peaked roof.
An attic truss is typically used to support a peaked roof.

An attic truss is a support feature found in many home or building attics. This structure will basically hold up the roof of the home or building and help the roof resist lateral stresses from wind, snow loads, and debris. A home is likely to have a series of attic truss supports running the length of the building — rather than just one — to ensure the load of the roof is adequately spread out and supported. Trusses are usually made from straight wood members, though steel and aluminum trusses are certainly possible as well.

The specific shape and structure of an attic truss can vary. The two most common types are king trusses and queen trusses. These two designs can be used independently or in conjunction with each other. The queen attic truss system is often used to transform an attic space from a simple storage unit into a usable living space by freeing up space in the center of the attic. The general profile of the system will create a large square in the center of the space, and the sides and top of the peaked roof will be supported by straight wooden posts oriented in triangular shapes. This provides strength for the roof while opening up usable living space in the attic.

King trusses are generally used for smaller roofs, or they are used on top of a queen truss. The king attic truss features a central vertical beam around which other support beams will be attached, creating a series of triangles. This design will not generally free up space in the attic, since the center beam will run right into the center of the room. When this is used independently, the attic space is usually used for storage. When it is used in conjunction with a queen truss, the king truss will only run from the peak of the roof to the top horizontal beam of the queen attic truss.

While most truss structures are designed to work in conjunction with peaked roofs, it is also possible to build an attic truss in a gambrel style home or structure. Gambrel roofs are peaked, but the roof will feature two angles of peaking: the lower part of the roof will be peaked at a steeper angle than the upper part of the roof. The truss itself is usually built to coincide with the joint between the two peaks.

How To Install Attic Trusses

Before figuring out how to install trusses, you need to know which type to install. To be clear, there are several types of trusses used to support the roof of a house. Many, like the queen post and fink styles, have W-shaped structures inside the truss's triangular design to aid in support. Similar styles include piggyback, Howe, double Howe, fan and Polynesian trusses.

In truth, the only truss style that's feasible for a usable attic is, unsurprisingly, the attic truss. This type of truss has some webbing surrounding an open square frame in its center. The frame creates a space for living or storage underneath the roof. The caveat is that the attic truss angle and subsequently your home's roof must be steep enough to accommodate the added space and comply with local building codes.

Installing any type of roof truss is a job best left to the professionals. But it doesn't hurt to have a general idea of how the process works. Before installing attic trusses, wall plates should already be installed and connected to load-bearing walls. There should also be a diagram that shows where each truss should be placed.

The process starts when the first truss is mechanically lifted to the top and then moved to the end of the roof. Truss number one is nailed to the wall plate and given temporary braces for short-term support. Subsequent trusses are placed, each facing the same direction as the first. The ridge beam is attached to the top point of each truss, ultimately extending to the far end of the roof.

You'll note that during installation, these trusses are not nailed to the top undesignated inside walls. This can cause major problems later on. Why? Well, truss materials expand or contract in minor ways as temperatures change with each season. Nailing down the trusses prevents the entire structure from moving as a unit, which can lead to cracking and warping as the wood expands and contracts,

Can You Store Stuff in a Truss Attic?

If your home had a truss attic when you moved in, you may be lamenting the lack of storage space. Unfortunately, your attic probably isn't conducive for storage in its natural state. That's because the bottom portions of the truss supports are not designed to bear more than 10 pounds of weight. Most of these trusses are constructed from lighter-weight wood. At most, they're meant to support its own weight plus the ceiling, insulation and light fixtures.

Converting a Truss Attic

Maybe your current truss attic looks like a no-go for storage. Can you modify it in some way to create a safe storage environment? Fortunately, it is possible. The existing structure must be re-engineered so it can safely support more weight. This sort of conversion is definitely a job for the pros. Unless you have extensive carpentry, construction and roofing expertise, you definitely should not attempt this conversion yourself.

Converting a truss attic into usable space involves careful planning and several important steps. Also referred to as a loft conversion, this type of project involves replacing the original truss structures with sturdier supports. Making your attic into a living or storage space will also require flooring to be installed, plus possibly knee walls and drywall painted in your desired shades. You may also need to have a code-compliant staircase and a dormer installed so the space has a proper entrance and egress for escape in case of a fire.

Before you start calling contractors, you'll need to take a few more things into account. Since many building codes have a minimum ceiling height requirement of at least seven or eight feet, you may literally need to raise the roof for your remodeled attic to comply. You may also have to meet a square footing requirement in your local building codes — usually 70 feet. Finally, raising your roof may be prohibitively expensive and/or cause you to run afoul of zoning laws.

Can You Walk on Attic Trusses?

Depending on your home maintenance needs, you may find yourself needing to access the attic. In a standard attic, this isn't a problem. But if your attic has trusses, and the space isn't converted, you will need to take some additional precautions. First, your trusses should be sturdy and relatively stable. Second, you should walk on the wooden beams themselves. Avoid stepping on the sheetrock areas in between the beams: They may not hold your weight and you risk cracking the sheetrock or falling right through the ceiling.

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    • An attic truss is typically used to support a peaked roof.
      By: mimadeo
      An attic truss is typically used to support a peaked roof.