In Manufactured We Truss

While no specific training is necessary to install manufactured trusses, it is important to have an understanding of framing and carpentry.  Photo courtesy of Wood Truss Council of AmericaWhile stick building remains the standard, remodelers are taking a cue from new home builders' use of pre-assembled trusses when it comes to big jobs. Manufactured roof and floor trusses can ease and expedite the process of installing the roof and floor systems in an addition, and more importantly, provide time, labor and material savings in the process.

"We always use pre-manufactured trusses. It is substantially faster," says Gary Potmich, a project manager with Kirk Development Co. The Phoenix-based remodeling firm typically works on homes built in the mid-1980s or earlier.

The ease of installation makes it easier for less-experienced workers to do the framing.

"Labor costs being what they are, this is a really good option. Also, we are finding that the professional expertise for stick building these trusses is rapidly disappearing," says Simon Evans, owner of Bay Truss, a San Francisco-area manufacturer.

In a 1996 project called "Framing the American Dream," the Wood Truss Council of America and the NAHB's Building Systems Council built two identical, 2,600-square-feet, multilevel homes in Houston. They discovered that using roof trusses saved 156.5 man hours and more than 4,000 board feet of lumber. For the floor trusses, the home with manufactured components required 26 fewer man-hours and 1,108 fewer board feet of lumber.

According to manufacturers, prefabricated trusses:

• Are structurally efficient. High-strength lumber is optimized by placing only where it is needed for large chord or web forces.
• Are capable of supporting heavy loads without interior bearing walls.
• Can be used in applications requiring longer spans.
• Are available in architectural grades, which can be left exposed.

This means you can order trusses to fit practically any addition.

Trusses are generally designed to fit a specific project. When ordering, provide all of the necessary dimensions and pitches, and identify whether you want a gable, hip or flat style on the plan.

"When getting ready to use prefab wood trusses in a structure, it's important to bring together design, installation and material specification," says William Plant, owner of American Pole & Timber in Houston. For material specification, a remodeler should not only consider high-quality plywood, spruce, and pine, but also decide on grade, treatment and finish.

It's also important to notify the manufacturer or supplier in advance. The amount of lead-time is often minimal, but make the call to be sure you will receive the trusses on time.

"From a local manufacturer, we can usually get them the same week, but as a practice we usually give them two weeks to be delivered," Potmich says. "In a pinch, we can order them Friday or even Monday and get them by Wednesday or Thursday."

As with any pre-manufactured element, it is important for the remodeler to get accurate plans to the supplier. However, for remodelers who have fickle clients or are dealing with large quantities, providing specific plans may be easier said than done. In these cases, you may want to consider using trimmable open-web floor trusses.

Codes generally do not permit prefabricated trusses to be altered on site. Trimmable floor trusses are the exception. They come in two types. The first is a hybrid of truss and I-joist technology. The main part of the truss has steel webs with top and bottom chords made from LVL or 2-by lumber. The web material for a short distance on each end is OSB, effectively forming an I-joist on each end that can be trimmed as needed.

The second type is an all-wood truss. This product has a section of dimensional lumber on the ends rather than an I-joist. The all-wood type does not rely on truss plates for connections like most open-web wood trusses. Rather, the chords and webs are connected using finger-jointing technology.

The trimmable end can be cut in the field up to 12 inches on each I-joist truss and up to 51/2 inches on each solid wood truss.

To help with safe installation, the Truss Plate Institute and the Wood Truss Council of America have published "The Guide to Good Practice for Handling, Installing & Bracing of Metal Plate Connected Wood Trusses" (BCSI 1-03). The guide stresses the importance of proper handling of trusses on site: checking the banding before moving truss bundles, picking up vertical bundles at the top cord, taking proper precautions when storing trusses more than a week, and allowing no more than 3 inches of deflection in every 10 feet of truss span. The WTCA and TPI cite poor handling as a major contributor to accidents and injuries that occur during truss installation.

After ensuring that the proper safety measures are followed, and the walls are plumb and square, you're ready for the pre-fabricated trusses.

"When you're installing an open-web 2×4 or 2×6 truss, whether it is flat or pitched, there is no special training required as long as you have a basic carpentry background," Potmich says.

The exception is if you are using a proprietary truss product, such as TrusJoist's TJI joists or Microllam LVLs.

"For proprietary trusses, there may be special requirements, but things like that are usually included in shop drawings," Potmich adds.

Manufacturers encourage remodelers to contact them for guidance when needed.

"In the end, our biggest single resource for our clients is the carpenter's pencil with our 800 number on it," says Evans. "We encourage people to call us whenever they get stuck."

Before raising the trusses, measure and mark on each cap plate where the heel of each truss will land.

Trusses are usually secured 24 inches on center, so start on one end by marking the first truss flush with the outside edge of the cap plate. Mark the subsequent trusses at 24-inch intervals. Then mark the truss positions on the opposing cap plate starting from the same end.

For a roof truss with a gable end, manufacturers often provide end trusses with more vertical members that support the sheathing:

1. Raise one of these end trusses into position first at one end, either by hand or by hoisting. Once raised, place the end truss flush with the outside edge of the cap plate and then toenail it in place. At this point, you will want to nail a few 2×4 braces from the truss to the ground.
2. Be sure to add any lateral or vertical bracing required by code in your area to resist high winds. BCSI 1-03 also suggests you always use diagonal bracing to secure the trusses
3. After securing the end truss, you can raise the other trusses onto the walls.

   On larger projects, contractors often hire a crane to hoist lift the trusses up. On smaller projects, or on a tight lot without room for a crane, you can place them by hand for less expense: