New building system at Stead

The gargantuan new General Motors

parts distribution center at Stead uses a

construction method that reduces maintenance

and energy costs.

The new GM parts distribution will

handle automotive replacement parts shipments

to more than 239 of its dealerships in

California, Nevada, Idaho and Utah, GM

officials said.

Clark and Sullivan Constructors of Reno

began building the massive 404,000-

square-foot warehouse facility in June 2002

and is expected to be finished by February.

The facility at 6565 Echo Ave., will house

384,000 feet of operating space and 20,000

feet of office space,

Its construction combines the traditional

form of tilt-up construction with an innovative

form of insulation built into the concrete

cladding of the walls.

The insulation is composed of 2-inch

pre-cut foam panels, or "sandwiches,"

embedded into two separate layers of concrete

to make the 12-inch thick concrete

walls. This differs dramatically from traditional

forms of tilt-up construction, where

7-inch concrete walls are erected, then insulated

with padded insulation and drywall as

the project nears completion

The extruded polystyrene foam panels,

which are produced by Dow Chemical and

are similar to other composite wall panels,

can have a R-value - the standard number

for measuring insulation efficiency - several

times that of traditional padding insulation,

reducing the amount of heat and energy

loss. Studies have shown that sandwiched

walls can have as much as an 80-degree difference

between its outside and internal

temperatures.

This is amplified by the use of 5-inch

vinyl polyurethane fasteners, which reduce

heat conduction better than their metal

predecessors and permanently bind the

panels to the sections of concrete.

Other advantages to building with a

sandwich panel system is that the exterior

wall doesn't have to be but it can be

painted or finished, and the thick concrete

of the interior wall is much more durable

than a sheet rock wall, which could be easily

damaged if, say, a forklift bumped into it.

The costs of building using this method

are high at first, notes Clark and Sullivan

Project Superintendent Ron Parks, but it

has both its short and long-run advantages.

"It costs more because you have to do

two separate [cement] pours," Parks said.

"But you can have several trades working on

the building at once, which increases the

turnaround rate."

In the first phase, after a perfectly flat

concrete base of the project has been

poured, a smooth 2 -inch layer of concrete

is poured into a 12-inch thick frame that

will be the wall panel. It is absolutely critical,

Parks said, that the pour be perfect

because it will be visible as the exterior of

the wall.

After the cement has been vibrated and

while it's still wet, the foam panel is fastened

using vinyl polyurethane connectors, which

go through the foam and into the concrete

leaving a peg on the top. The peg will fasten

to the final layer of concrete that will form

the back of the wall. Any doors or windows

are pre-cut and added into the wall's design.

The second phase begins after the concrete

has dried for a full 24 hours. At this

stage all fasteners, pick-up points, wire

mesh and supporting rebar are added much

in the style of traditional tilt-up models.

After everything is installed another 7 inches

of concrete is poured over the panels, creating

the back of the wall.

In the final phase a crane hoists the panels

using the pre-installed pick-up points

and sets them into pre-poured slots a couple

of inches deep. There the panels are fastened

to each other using traditional beams

and welding plates. Another stabilizing

pour is done around the walls and the roof

is added. The whole process in done on-site.

Parks added that warehouses using this

design are not prevalent, but he expects it to

take off. Clark and Sullivan Constructors

built the MSC Industrial Supply warehouse

in Fernley using a similar method, a project

that helped Clark and Sullivan win the GM

contract.

"There's no instruction booklet on how

to do this," Parks said of the new technology.

"You learn new things about it each time

you do it, sometimes by accident."