THERE'S a character in the Asterix The Gaul comic books who constantly worries that the sky is going to fall on his head.

Vitalstatistix, the otherwise fearless chief of Asterix's village, walks around with his shield over his head just in case it ever does.

If he were ever to visit York, Vitalstatistix probably do the same whenever he stepped inside any of the city's historic Georgian houses. Except that it wouldn't be the sky he'd be worried about - it would be the ceilings.

First the Mansion House then the Assembly Rooms had to undergo urgent repairs after it was discovered that ornate plaster ceilings were pulling away from their supports - and could fall in.

Then, at the start of this year, Fairfax House - which likes to style itself 'England's finest Georgian townhouse' - discovered that it had a similar problem.

The house, run by York Civic Trust as a Georgian museum, boasts stunning plaster ceilings designed in the mid 1700s for Viscount Fairfax by the Swiss-Italian stucco artist Giuseppe Cortese.

In 2016, cracks were noticed running across the ceilings. It wasn't thought to be serious, but the cracks were monitored over the next four years by structural surveyors.

In January, however, when the house was closed for its annual winter clean, specialists from a company called Ornate Interiors were brought in to have a closer look. What they discovered was alarming.

"Movement in the ceilings around the cracked areas gave rise to concerns that parts of the ceilings may become loose and fall," says Guy Bowyer, an architect with the York Conservation Trust which owns the building. What's worse, it was feared that chunks of plaster up to 40mm thick could fall at any time.

Urgent repair work was called for. "It was not deemed safe to allow the public to access the building until the ceilings had been made safe," says Guy.

The house had been due to open for York Residents' Festival on January 25 and 26, to give visitors a chance to see 'behind the scenes' during the house's winter deep-clean.

Instead, it remained closed and there followed five weeks of intensive efforts involving experts from Ornate Interiors and the conservation trust, as well as Fairfax House staff.

Upstairs floorboards were taken up to study the ceilings below, joists were inspected, samples of plasterwork - which is attached to supporting joists by bundles of reeds put in place more than 200 years ago - were studied.

It wasn't always an easy process, admits Thomas Jacobs, Fairfax House's visitor experience and property officer. The gap between upper floors above and ceilings below was often filled with a type of Georgian sound-proofing which made it difficult to see what was going on.

But eventually it became clear. "The plaster was pulling away from the bundles of reeds along the ceiling joists that it was attached to."

It is not clear what had caused that to happen - though there are several possibilities.

The Georgians didn't really understand about foundations and ground conditions, says Guy Bowyer. It is quite normal to find houses from the period built on unsuitable ground without proper underpinning - the Mansion House was just the same.

The cracking got worse in 2016, and it may be that this was due in part at least to the floods of 2015, in which water levels rose and then fell very quickly. In the 1980s, the centre of Fairfax House was underpinned with a concrete 'float' - but not the sides of the building. This may have exacerbated some building settlement during the 2015 floods, leading to the cracks.

There are other possible causes, however - including poor drainage, or even the movement of heavy vehicles nearby. it is also possible that damage may have been caused when the building was used as a cinema (from 1920-1960) and dancehall (up until 1980).

Whatever the cause, once the problem had been diagnosed, it could be dealt with. Holes were drilled and special screws and washers made from steel were inserted along the joists to hold the plaster in place. The holes were then filled in with a special 'conservation' mix of lime and plaster. You'd never know those holes were there, says Thomas Jacobs.

The whole process took five weeks from start to finish, and cost the York Conservation Trust about £30,000.

Inevitably, the house's opening after its winter deep-clean had to be delayed. It was due to open on February 14. That has now been pushed back to March 27.

But at least it has given the house's staff a chance to give everything an even more through winter deep-clean than usual, says Martha Morley, the conservation and collections assistant. "And it has given us time to do a full collection audit," she says.

Every cloud has a silver lining...

It will now open with a bang on that Friday March 27, cleaned, spruced up, with those magnificently restored ceilings on display - and with a brand new exhibition.

That exhibition is 'Keeping up with the Georgians: Celebrity, Society and Satire.' The exhibition will feature, amongst other things, work by the Georgian caricaturist and printmaker James Gillray, who was famed for his scurrilous and sometimes bawdy political and social satires.

The exhibition is a meditation on how the the Georgians were just as obsessed with celebrity and with appearance as we are today, says Martha. And yes, that title is a play on Keeping up with the Kardashians...

Fairfax House re-opens on March 27. Find out more at fairfaxhouse.co.uk