Construction Innovations
Manufactured Components in Residential Construction
By Perry A. Tabor, P.E.
Last month we introduced ourselves as Builder/Architect's structural engineering expert columnist, featuring our monthly "Structural Design Corner."
In our first article, we suggested fully engaging structural engineers throughout various project phases and encouraging them to present viable design innovations and alternatives.
This month, we are discussing the integration of one such innovation: manufactured components.
FLOOR/ROOF SYSTEMS
The use of pre-manufactured roof and floor truss assembly, within production residential construction, has been around for decades.
Roof wood truss assembly, for residential construction, became mainstream in the mid-'70s, following the valiant efforts of Gang-Nail and other innovative manufacturers that had the fortitude to "stay the course."
Floor trusses in residential construction began to establish a foothold in the mid-'80s, with the introduction of open-web trusses, but had their market share tempered by the introduction of "I-joist" around the same time.
Both truss products were introduced and became widely accepted within the residential industry to address one or more of the following:
- Skilled labor requirement reductions
- Time of construction shortened
- Quality of construction/performance level improved
- Simplification of construction
PANELIZED WALLS
Like the pre-manufactured roof and floor truss assembly, panelized wall assembly is not a new concept, but its success has been challenged. This was mostly due to manufacturers' initial struggles in developing processes to take projects from modeling into full construction.
My first knowledge of panelized residential construction came through stories of projects in Kansas City in 1976, when one of my framing crewmen (Toby, a transplant from KC) told of panelized roofs, walls and floor on a raised foundation. He claimed that they could frame an entire house in one day! Until then, we thought we were smok'n, as we had a three-man crew taking less than two weeks to post and beam the underfloor, lay 2x T&G floor deck, framing walls with windows and exterior T1-11 siding installed, roll roof truss with fascia boards and gable rafters, plywood sheath roof and frame kitchen soffits for a single-story 1,500-square-foot house with a two-car garage.
THE BASICS ON PANELIZED SYSTEMS
A panelized system consists of prefabricated panels that are fabricated within a highly automated factory, with "the (manufacturer's) floor" equipment and fabrication process, driven by a computerized building model.
In other words, the structural system is modeled down to the window cripples, screw/nail count and curtain rod back blocks. Every piece in the entire building is assigned an identification code (subdivision ID, lot number, plan number, elevation ID, building line and wall panel number) and the computer establishes the most efficient means to cut the materials before the computer data is actually released to "the floor."
Once the data is released to "the floor," precise pieces are assembled into wall framing panels, then progress to having structural shear, holdowns, hardware, etc., applied, all the while being flipped over by hydraulic arms and traveling along rollers towards the loading dock to be palletized/packaged for delivery via flat bed and to be erected, in simple terms, "by the numbers."
Prefabricated panelized systems require additional planning to ensure the panels are manufactured to specifications. However, they are generally easy to install and can provide significant labor and construction time savings.
Because the panels are manufactured in a factory environment, there is an assurance of quality and consistency. However, flexibility can be limited (e.g., concrete foundations must be placed accurately) and any on-site design changes (e.g., model walk changes) can be costly and difficult.
Although the initial cost of prefabricated panels may be higher than that of conventional framing materials, the labor savings is often significant enough to offset the initial cost difference. Additional benefits that the panelized system provides include structural capacity resistance to damage from earthquakes, wind, moisture changes (kiln-dried lumber) and insect infestation.
PANELIZERS/TRUSS MANUFACTURERS
Today, there are several combined wall panelizers and truss manufacturers that can readily supply the Bay Area. In particular, there are four noteworthy firms that produce roof trusses, floor trusses/joist, as well as wall panels.
Notable firms within the wood assembly arena include Forma Home Systems (formahomes.com ) and Compu-Tech Lumber Company (computechlumber.com ). Both firms are led by production housing veterans, having decades of home construction experience.
Two leading firms within the CFS (cold formed steel) panelization industry are FrameMax (framemax.com ) and NEXFRAME, LP (nucor.com), a joint venture established by the subsidiaries of Nucor Corp. and Lennar Corporation.
We hope that our introduction to manufactured components was informative and we look forward to covering other innovations in future articles.
April 2007 Builder Architect Edition Issue