PATH - A Public Private Partnership for Advancing Housing Technology
PATH Case Study
Pulte's Switch to Panelization
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[IMAGE: Open metal web floor trusses are precisely positioned by the floor deck assembly machine.]
"We install 1" of rigid foam insulation on the exterior of our concrete foundation for optimal insulation performance and to manage condensation potential. If we do not insulate the exterior of the foundation, water may condense on the interior surface. By insulating the exterior, we move the condensate line to the outside of the foundation wall so it can drain properly, rather than allowing any moisture inside the basement."
"Over the top of the foam, we do a shotcrete finish for added durability. This is done in the field, which gives it a continuous seamless appearance. When you look at our foundation, you cannot see a difference between a poured-in-place wall and the product we deliver because of the shotcrete finish. So it has the same curb appeal."
A STRONG FLOOR SYSTEM
Once the foundation walls are installed, a pre-fabricated open-web floor truss is laid.
"Because they are built in the factory, we end up with a very low deflection: 3/16" maximum over 10 to 12 feet," Runnels says. "In addition, we get a very high deflection ratio in our floor system. Minimum code requirement is L/360. Our average is L/720. By raising the deflection ratio in the floor, we dramatically reduce the shake that occurs when someone walks up stairs."
"We provide a 7/8" decking on the floor system. With this decking, we can increase our floor truss spacing to 32" if we have to, but we keep our truss spacing to a maximum of 24". The thicker decking also adds stiffness to our subfloor to prevent tile cracking."
"We manufacture a SIP exterior wall, which we also use in walkout areas for the foundation," says Runnels. "The SIP consists of 7/16" Oriented Strand Board (OSB) that sandwiches a one-pound-density extended polystyrene (EPS) core. The layers are adhered together by a moisture-cured urethane adhesive. We use SIPs instead of a normal stud-framed wall because the 9'1"x 24' long SIP gives us more consistent wall insulation. At the same time, the wall has tremendous strength compared to stud framing. So we get the benefit of using the high sheer strength from the OSB, and we get energy-efficiency benefits from the foam."
INTERIOR STEEL WALL
"We also provide an interior steel wall," Runnels says. "Steel interior walls were chosen because they are light; they provide a straighter clean finish; and with the use of mechanical fasteners like self-tapping screws in steel, nail pops are virtually eliminated."
"We manufacture two walls at this time: 20-gauge (033-mill) for bearing walls and 22-gauge (027-mill) interior non-bearing for our usual 9'1" first-floor wall system and 8'1" second-floor wall system. Both have a high yield strength of 33,000 psi and a G-60 galvanized coating."
"The G-60 coating is a standard for us because we know the longevity is greater. There have been issues with lower galvanized coatings that may have come in contact with masonry, in the basement for instance. G-60 is recommended by the American Iron and Steel Institute and the Steel Framing Alliance to minimize corrosion."
HOW IT WORKS
Panelized components are wall, floor, and roof sections that are constructed in a factory, and then shipped and quickly installed on site. The panels form a structural envelope that eliminates the need for conventional framing, provides integral insulation, and can be assembled swiftly by less skilled laborers. Many panels are lightweight, and can be designed to resist earthquakes, high winds, debris impact, moisture, and insect infestation. Insulated panels also provide better overall air tightness and thermal performance than conventional wood framing. Panels can be produced in an automated factory environment using computer-controlled equipment that transfers panel-cutting instructions directly from digital CAD drawings. Once the panels are shipped to the jobsite, they can be quickly assembled, speeding the onsite construction schedule and allowing homes to be placed under roof more quickly.
READ THREE PATH FIELD EVALUATIONS:
"We look at the house as a system: we want to make everything work together--to simplify and speed up construction, and for better living," says Runnels.
"For example, we design the floor system to be able to handle our lateral pressure loads so we can backfill the foundation a lot quicker. There have been many cases in the Mid-Atlantic area where lateral pressure caused foundation walls to cave in. So code officials are requiring a lot of additional things to be done to the foundation walls before they can get backfilled. And framers don't like building over open digs anyway. But with our system, our decks are in panels, so they can be rolled out quickly. Within an hour or two, you can have the first floor deck on. In a couple more hours, you can have the bolting done, and therefore the shear diaphragm in the floor can handle the lateral pressure to the walls from the backfilled dirt."
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Content updated on 10/18/2006
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