Daniel C. Smith, P.E. - Advantages of Preassembly

Can use and supervise unskilled labor safely on the ground because of small work area
Seems to help with the organization of the trusses, trusses are pre-positioned with respect to the jig location and solves material handling problems. Instead of having 400 truss on the site, you end up with 80 packs of trusses ready to lift.
Vertical quality can be improved due to jig system and its stability when installed properly
Fewer people are needed to set large truss systems when preassemble is utilized.
Equipment uses of air guns and hoses is easier due to not being in the air.
Can get ahead of GC schedule, building roof on the ground while the upper floor walls are being constructed.
Crane time is reduced by 80%, you end up lifting 80 packs of trusses instead of 400 individual trusses.
The application of additional materials, like roof sheathing, sub fascia, dry in felt, safety rails, and other items becomes a larger part of the preassembly process the more that a subcontractor becomes comfortable with this process. And generally the quality improves due to this ease of installation.
Assembly line and mass production methods may be used due to set up of assembly yard.
Corner set systems can be done extremely accurately, square and with a 50% to 80% reduction in labor
Step down systems can be installed and framed more accurately with the preassembly system preparation on the ground.
Examples of Productivity Increases:

We have framed up an entire gable with a large roof rake and sheathing. The first one only about 30% of the work was performed on the ground (about 4 man days) and The remainder was performed over 4 days by 4 men in lifts and from the roof. The second gable, same size and complexity was framed 90% on the ground in two days, the 4 man crew spent 4 hours tying it to the main roof. We estimated a savings of 30%, in a much safer location – on the ground.
On a large project I had observed 4 men setting the king hip and corner jacks over a 8 hour period. Fortunately the other crew was much faster. On the next big job, Paul was able to get minor concessions from the architect to standardize the corners on 5 buildings – 61 corners. A jig was set up and two men did all 61 corner sets on the ground in 2 days. Each corner was lifted into place and tied to the girder and the walls. We were told by the GC that they were 3 weeks behind schedule when we walked on the job site. When we walked off the job site, they were 3 weeks ahead of schedule.

Supervisor is in the center of the Pack (work area) and within ear shot of a mis-placed nail
Quality control is improved due to easy access on the ground for the framing supervisor and an inspecting engineer. Great for training purposes for unskilled labor.
Pre-assembly forces the framer to think and plan ahead, which finds problems earlier.
Ideal situation for training unskilled labor.
The teaching of proper installation can be more easily done due to being on the ground and all can see when instructed.

90% of required labor will occur on the ground and 100 % of the unsafe crawling in the trusses is done on the ground. Always the use of unskilled labor is a safe situation.
Fall protection is easier to apply with this system and the written program is easier to write.
OSHA of Raleigh reviewed the system and encouraged it’s usage and further refinement
Teaching the subcontractor the basic principles of bracing and the distribution of forces becomes easier as the sub embraces this system.

Solves truss placement problems on the ground, if you find an error on pack #6, that the wrong truss was installed on pack #3, the repair is easy since everything is still on the ground. The error is found because you run out of a RT-1 truss or something similar. Most of the thinking is on the ground.
Can identify on the ground if a slope or truss length is incorrect.
Bracing can be installed more accurately because of ease of installation.

Trusses forces are distributed and shared between all of the trusses in the pack because of the quantity of bracing laterally, high, low, X bracing vertical and hortizontal.
Adds redundancy to the pack of trusses, if one truss fails it does not create a disaster due to the distribution of forces.
The forces in the x and lateral bracing are greatly reduced due to doing the x ing in every pack instead of every other 20’ increment.
Compression forces on webs, and bottom chords can be directed to the outside walls as a part of this system.
The engineer can inspect all preassembly on the ground, thus allowing a closer inspection of small details. Inspections in the air are at best difficult and more incomplete.

Advantages of Preassembly