— Donald Trump, interview with MSNBC, Feb. 9, 2016

Donald Trump put a price tag on the wall he wants to build on the 2,000-mile border with Mexico – $8 billion. He also described the wall in a bit more detail — it would be 1,000 miles long, made of precast concrete slabs, rising 35 to 40 feet in the air.

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Trump has repeatedly said Mexico will pay for the wall, though Mexican leaders dismiss that as a fantasy. He has suggested that the money would come from reducing the $50 billion trade deficit with Mexico — which as our friends at PolitiFact have documented, is simply nonsensical.

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But is his $8 billion estimate in the realm of possibility?

The Facts

As big government projects go, $8 billion is not a huge sum. A single aircraft carrier these days costs about $13 billion. But then that’s sophisticated ship — and Trump is just talking about a very long wall.

Under the Secure Fence Act of 2006, the United States has already spent $2.4 billion for fencing across nearly one-third of the border (670 miles). It’s unclear if Trump would replace the fence with the wall or supplement the fence with the wall. (The fence is mostly vehicle barriers and single-layer pedestrian fence, which presumably is inadequate for Trump’s purposes.)

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But the fence, while different from a wall, does provide some sense of the numbers involved. The Government Accountability Office in 2009 said the cost to build a mile of the fence initially averaged between $2.8 million and $3.9 million. But that was in the easiest areas, near metropolitan centers; other areas in the desert or mountains could cost as much as $16 million a mile.

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So 1,000 miles of fences is at best $3 billion, and certainly much higher than that. A concrete wall would clearly be an order of magnitude. (We have not even begun to consider upkeep and maintenance. The Corps of Engineers estimated that the 25-year life cycle cost of the fence would range from $16.4 million to $70 million per mile; the total cost of the fencing so far has been $7 billion, according to the Congressional Research Service.)

We can also look at the Israel’s experience with building a separation barrier between Israeli-held areas and Palestinian-held areas. For the first 525 kilometers (326 miles), the cost was $2.6 billion. A simple calculation of expanding that to 1,000 miles yields a calculation of $7.99 billion, suspiciously similar to Trump’s estimate.

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But only one-tenth (33 miles) of the Israeli barrier is an eight-meter (25-foot) concrete wall. The other 90 percent is a two-meter (six-foot) high electronic fence. Trump says he wants a 1,000-mile long concrete wall.

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Assuming the cost of the fence was equivalent to the U.S. fence ($3 million a mile), that suggests about $1 billion of the cost was for the fence; the other $1.4 billion was for 33 miles of the wall (which was built in mostly metropolitan areas). Believe it or not, that translates to $42 billion for 1,000 miles of a 25-foot wall. (Recall that Trump wants a 35-to-40-foot wall.)

In an interesting article for The National Memo, a structural engineer tried to do the calculations just for the concrete. He even produced a possible sketch.

His calculations were for a 2,000-mile, 25-foot-high wall, so we have updated them for a 1,000-mile, 35-foot-high wall.

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Foundation: 6 feet deep, 18 inch radius = 42.4 cubic feet

Column: 4 square feet area by 30 feet tall = 120 cubic feet

Wall panels: 35 feet tall by 10 feet long by 8 inches thick = 249.3 cubic feet

Total concrete per 10-foot segment = 411.7 cubic feet

1,000 miles = 5,280,000 feet = 528,000 segments (10-feet long each)

528,000 segments * 411.7 cubic feet per segment = 217,377,600 cubic feet = 8,050,666 cubic yards. (The cubic yard is the standard unit of measure of concrete volume in the United States.)

That’s about double the amount of concrete in the Hoover Dam. A cement manufacturer said prices are now running $85 to $90 a cubic yard, so that works out to about $700 million just for the concrete.

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As the engineer noted, a lot of reinforcing steel (rebar) would also be necessary. We figured that the steel would add up to about 1.6 million tons, which works out to about $1 billion at current per-ton costs, but perhaps Trump could get a volume discount.

So just for two raw materials, we are looking at nearly $2 billion. But of course, the wall would need to be designed, land would need to be acquired, environmental impact statements would need to be done, concrete-casting facilities would need to be built, materials would need to be shipped, and workers would need to be hired, housed and fed.

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We consulted with several experts, who said even a rough estimate of the total cost was extremely difficult. We will update if we obtain an estimate from a credible source.

Update: We spoke to a retired estimator and economist for one of the nation’s largest construction firms. He worked through some of the math, though he did not want to be identified publicly. Roughly, he said a wall of this type would cost at least $25 billion — and that is not counting a video system to keep watch on the border. Building the wall would also require at least 40,000 workers a year for at least four years, but he doubted it could be built so quickly.

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The concrete panels would need to be at least 8 inches thick and be 40 feet tall (35 feet above ground and five feet under ground). He estimated that it would cost about $10 billion for the concrete panels and $5-6 billion for steel columns to hold the panels, including labor. Concrete footing for the columns and a concrete foundation would add another $1 billion. A road would need to be built so 20-ton trucks could deliver the materials; that’s another $2 billion. Then you need to add another 30 percent for engineering, design, management and so forth. That adds up to nearly $25 billion–three times Trump’s estimate.

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Some of the calculations are staggering. The foundations would require nearly 2.5 to 3 million cubic yards of concrete, which requires poured-in-place concrete delivered in concrete trucks. “That’s 250,000 to 300,000 truckloads, 20-ton each of concrete,” he said. Then the excavated earth would need to be hauled somewhere and disposed–nearly 3 million cubic yards, or enough soil to cover 17 acres 100 feet deep. That’s 90,000 truckloads of 40 tons each.

Update, July 26: Bernstein Research issued a comprehensive report on the potential cost of the wall, concluding it would cost at least $15 billion and as much as $25 billion.

The Pinocchio Test

Trump’s claim that the wall would cost $8 billion is highly dubious. We would welcome a serious discussion of the costs, rather than mere assertions, and are open to new information, either from Trump or from experts in construction engineering who have crunched the numbers.

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But based on the costs of the Israeli security barrier (which is mostly fence) and the cost of the relatively simple fence already along the U.S.-Mexico border, an $8 billion price tag is simply not credible. We are open to adjusting the rating if credible new information or estimates can be obtained, but based on the information we have now, this is yet another Four-Pinocchio claim from Trump.

Update: In a Feb. 17 interview with MSNBC, Trump upped his estimate of the cost: “The wall is going to cost a fraction of that [trade deficit with Mexico], maybe $10 billion or $12 billion, and it’s going to be a real wall.” We still believe that figure is not credible.

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