The Architect of the Capitol estimates a complete restoration of the Capitol Dome will cost $125 million, but that total might not be reliable, according to the Government Accountability Office.

GAO found the estimate “substantially comprehensive and well documented, but lacking key analysis that support accurate and credible estimates,” in a report requested by House appropriators who allocate money for AOC projects.

Those crunching the numbers for AOC did not use the most up-to-date figures from completed phases of the multi-year restoration project — such as the 2012 rehabilitation of the Dome skirt — when analyzing costs, according to the report released Tuesday. They did not accurately calculate inflation, instead relying on historical records and an industry database to support Dome estimates.

AOC also failed to include sensitivity, risk and uncertainty analysis in their estimate, or explain how the agency budgeted for unforeseen contingency costs, like the number of inches of stitching that would be needed to repair over 1,300 cracks criss-crossing the architectural icon.

“This report confirms what we suspected, that there’s little reliability in terms of our original estimates of Capitol projects,” said Rep. James P. Moran, D-Va., who has been on and off the Appropriations Legislative Branch Subcommittee for the better part of 20 years. Moran said he can’t recall a single major project that came anywhere near the original budget estimate.

He pointed to the Capitol Visitor Center as an extreme example of an Architect of the Capitol project that had exceeded its budget. The original budget established in 1999 was $265 million. A 2006 GAO estimate projected the CVC could cost as much as $555 million, then later pegged the figure at $584 million at completion. In late 2007, Architect of the Capitol Stephen T. Ayers and the GAO announced a November 2008 opening date and an updated total of $621 million.

“I do think that the Architect of the Capitol has gotten a little better,” Moran continued. “I think they’re determined to come up with more conscientious and accurate estimates.”

More recently, both the Dome skirt restoration and construction of stands for the 2013 presidential inaugural were completed on time and within budget constraints.

However, the GAO report also called into question the credibility of AOC’s estimated budget for the massive Cannon House Office Building renewal. Currently, AOC has a $753-million budget for the planning, design and construction phases of the project, targeted for completion by 2025. The GAO report does not detail what the agency believes might be a more reliable target; it only addresses the extent to which AOC follows leading practices for figuring out cost estimates.

House Legislative Branch Appropriations Subcommittee Chairman Tom Cole, R-Okla., told CQ Roll Call he’s got “no complaints” about the AOC, adding that the GAO does a terrific job. “That’s what they’re there for, to give Congress the means to double-check official estimates we get.”

At the time of the interview Cole had not yet had a chance to review the GAO’s findings.

Ultimately, GAO recommends that AOC incorporate some of its tested practices into its cost-estimating and keep Congress informed of its confidence levels in project estimates.

Architect of the Capitol Stephen T. Ayers concurred with the recommendation and responded with a letter, included in the 48-page report, that provides some context and clarification of its policies for estimating costs.

“We believe that implementing the recommendations will further improve our cost estimating process,” Ayers wrote. “At the same time, although we have not always fully documented all the steps we take, we have a robust cost estimating process that embraces industry best practices and produces credible and reliable results.”