Big Ben has been silenced, and its chimes will not be heard for four years while London’s most famous bell tower is restored. With the $80- million project cost now more than double initial estimates, U.K. lawmakers are pondering how to manage renovation of the rest of the decrepit, 1,100-room Houses of Parliament, with a budget more than 60 times bigger.

Eroding stonework, leaking roofs, flooded basements, tangled wiring and wide-spread asbestos have left the of the House of Commons and the House of Lords “in a state of extreme disrepair,” according to a Public Accounts Committee report filed a few months ago. “The risk of a catastrophic failure is high and growing.”

To avert such a fate, officials over the past few years have devised a number of renovation options for Parliament members. Aiming to start work in 18 months, MPs will vote this year on the delivery approach, Andrea Leadsome, leader of the House of Commons, said in late October.

The most likely option, estimated to cost $5.2 billion, would be for everybody to relocate to nearby buildings, giving renovation contractors a clear run for six years. Keeping the buildings functional during renovation work could cost $7.5 billion and take more than 30 years, Leadsome added.

Since their completion some 150 years ago, the neo-Gothic Parliament buildings have never been seriously renovated, according to officials. The 300-meter-long Thames riverside complex replaced an original palace, which burned in 1834.

Only the 918-year-old Great Hall, with its 21-m by 73-m timber roof, survived. Numerous royal coronations and public trials have taken place there, including the one that led to the 1649 beheading of King Charles I.

Covering 112,000 sq m, the parlia-mentary complex includes 100 staircases, 31 elevators and more than 3 kilometers of passages over seven floors. The building was bombed 14 times during World War II. The House of Commons’ debating chamber was destroyed by an attack in 1941; after the war, the chamber was repaired and reopened, in 1950.

To manage the refurbishment, Parliament will likely create a sponsor entity to oversee a separate delivery unit, a strategy adopted on London’s current Crossrail project and on the 2012 Olympic infrastructure work.

To help with essential preparatory work in an “option-neutral” manner before final decisions are made, officials this July recruited the local office of CH2M Inc. to advise on project and cost management, says a spokeswoman. BDP Ltd., Manchester, joined as the team’s architect.

The new team could remain for the whole program of work. Meanwhile, by next spring, it is expected to spend approximately $16 million to plan future strategies and investigate the building’s condition. “Effort put into early planning is rewarded later with financial savings,” observes Brian Finnimore, managing director of Parliament’s Strategic Estates.

In estimating renovation costs, “there is a high level of risk included,” says a Parliament spokeswoman. But even the project’s 40% to 50% contingencies would not have been enough to cover the surprise cost hike for the Big Ben renovation.

The clock-tower contract is pre­ceding the main work, partly because it now fails to comply with fire regulations, which require the installation of a new elevator.

When locally based contractor Sir Robert McAlpine Ltd. was hired in 2016 for preconstruction services and to scaffold the bell tower, an in-house team had priced the renovation at $38 million.

But when McAlpine signed the main renovation contract in September, the price had risen to more than $80 million. Officials attributed some of the hike to the poor condition of stonework, greater complexity, more-than-expected groundwork to protect utilities and an increase in the budget contingency.

As well as repairs to the famous clock, the 96-m-tall stone Elizabeth Tower also needs attention. But Big Ben itself, which is actually the 13.8-tonne bell, is said to be in fine form.