Now Boeing is grappling with the opposite problem: How to pack into its smaller Renton footprint the three full assembly lines it needs to build its single-aisle planes at a record pace.
Renton is crucial to Boeing's competitiveness as the sole location for 737 assembly, while Airbus steps up production of the rival A320 jet family at final-assembly lines in Europe, China and by 2016 at its newly announced plant in Mobile, Ala.
The inside of the Renton plant is a hive of activity as Boeing busily reshapes the interior to accommodate more planes, and more workers.
Within the next five years, the company will hire hundreds of new production workers, perhaps close to 1,000, to staff two assembly lines of the current best-selling 737 and one line of its newest variant, the 737 MAX. Boeing will add hundreds of engineering jobs for the MAX.
"I don't think anybody anticipated this back in 2003, 2004," said Alex Pietsch, the new head of Washington Gov. Chris Gregoire's aerospace office, who formerly led the city of Renton's economic-development efforts. "It's really astounding."
Ahead of last week's Farnborough International Airshow near London, Boeing gave a tour of the factory and provided new details of its expansion plans.
Eric Lindblad, vice president of 737 manufacturing operations, is tackling the challenge of making everything fit.
"We have to figure out how to get lean," said Lindblad, brimming with energy and enthusiasm. "Our employees are highly motivated to be the ones to build the 737 MAX. It's a wonderful impetus for continuous improvement."
Boeing's transformation of Renton shows an appetite for growth that contrasts sharply with the gloom in much of U.S. manufacturing.
Last month, construction workers laid concrete to extend one of two assembly lines for the current 737 NG model.
Boeing has already earmarked the space for a new third assembly line where by 2015 it will begin building the MAX.
And in an adjacent building where the 737 wings are put together on an innovative moving line, engineers were clearing the decks to install a second identical line.
In all this remodeling, Boeing dismantles and moves major fixtures only after installing new ones close by so that production is uninterrupted.
On the first of the 737's two assembly lines, seven of the planes sit nose-to-tail along the length of the building.
Fuselages delivered by train from Wichita, Kan., come in at one end; completed 737s, ready for delivery, roll out the other end through big doors facing Lake Washington.
A new assembly line for the MAX, parallel to this existing 737 line, will soon take up half the building.
But right now that area is a sea of prep work on engines, galleys, lavatories and tails.
Lindblad said the clutter will all be moved somewhere nearby on the Renton site to make room for the MAX.
While the first assembly line is already a model of efficiency, pumping out 21 jets every month, Renton's second line for the current 737 is housed in a slightly shorter building and can make just 14 jets a month.
Boeing's target of 42 jets per month by spring 2014 requires that second line to match the output of the first.
Since seven 737s won't fit nose-to-tail inside the shorter building, Boeing is reshaping the line to turn at a right angle and squeeze in a seventh assembly station.
Meanwhile, in a separate building, Boeing has significantly sped up how it makes 737 wings.
After five years of planning by a team of Boeing engineers, machinists and managers -- helped by experts from Japanese consultancy Shingijutsu -- the company in 2010 remade its wing manufacturing as a slower-paced cousin of Toyota's automotive moving assembly line.
The wings used to be built in heavy, towering fixtures; mechanics had to ascend tiered decks to work on the wings, which hung vertically.
Now the wings, lying flat as if on a dining table, move through three assembly stations and are advanced by a robotic tug every 5 hours and 22 minutes.
The plant builds 31.5 pairs of wings a month this way.
Off in one corner, 3.5 sets of wings a month are still built on the old vertical fixture.
Having worked out almost all the bugs from his new system, Lindblad is preparing to take down that fixture and install a second horizontal wing-assembly line.
On Boeing's current plan, the production rate in spring 2014 will be 20 percent higher than today. Then in 2015, Boeing will introduce the third line to build the MAX, which will mean more hiring.
"We definitely will bring new people on," said Beverly Wyse, head of the Renton plant. "We'll pull the most experienced workforce to the new airplane."
After the MAX line is perfected, Wyse said, Boeing will tweak the two existing lines so they can also build the MAX model.
According to the most recent filings with the state, more than 10,500 people work at Boeing Renton. About 4,800 are blue-collar production workers.
Boeing has made no detailed employment projections, but the rate increases already planned and the move from two to three production lines suggest a 20 percent increase in the production workforce toward the end of this decade is certainly possible.
Local government will work to help Boeing find all the room it needs.
Pietsch, the state's aerospace point man, said a proposed extension of Metro's Rapid Ride bus line to the plant could free up some of the 25 percent of the remaining Boeing Renton footprint now used as surface parking for workers.
Yet the crucial key remains Boeing's drive toward lean manufacturing, pushing constantly - and so far successfully - to produce more, faster and in less space.
"Do I think it can all fit in?" said Pietsch. "Sure. Boeing has been incredibly effective in leaning out the production lines."
Still, he said, Boeing might not have sold off the 65 acres across from its factory -- retaining about 145 acres -- if it had foreseen the ongoing rebirth of the 737 program.
"I don't know if they'd have made the same decisions had they anticipated the global demand for this class of airplane," Pietsch said.