Regent Street Disease, or Deansgate Disorder, is a blight that affects early 20th century steel framed buildings, especially those clad with stone or terracotta.
It occurs when water penetrates the building façade, causing the steel to corrode and expand, cracking the surrounding masonry. If left untreated it can have dire consequences as sections of the stonework fall away, endangering passers-by.
The condition, which some professionals prefer to term “steel frame corrosion” is named after the streets in London and Manchester with which it has become most frequently associated. But despite its colourful monikers, it is not restricted to the UK. It has also cropped up in US cities including New York and Chicago and can occur anywhere in buildings of a certain type.
Modern steel frame buildings use cavity wall construction techniques. However, in the early years of steel frame building, ornate masonry or stone façades were frequently wrapped tightly around the metal. Architects and engineers expected the stonework to provide sufficient protection, but water, sometimes inadvertently trapped by architectural detailing, can nonetheless penetrate masonry, particularly a porous material like Portland Stone.
At-risk buildings usually date from the first half of the 20th century, especially the 1920s and 1930s. “It is very common throughout the country in buildings of that age. It is not confined to grand, pseudo-Georgian façades in in the West End. It could just as easily be in Southend-on-Sea,” says Trevor Rushton FRICS, group chairman at property and construction consultancy Watts.
The problem often comes to light through a survey carried out before a sale. It can also be uncovered when a tenant’s responsibility for dilapidations is assessed at the end of a lease, or during planned preventative maintenance.
While the issue does not usually lead to collapse of the entire structure, leaving it untreated is not an option. “I have been involved in some projects where there have been quite serious collapses of masonry or stone as a result of it,” says Rushton. “At one London girls’ school, a large section of cornice collapsed because the frame was corroded.”
Where a case of Regent Street Disease is suspected, it is essential to make an accurate diagnosis and not rely on assumptions, he says. “The other thing is not to underestimate the scale of the problem. It can be a lot worse than you think it is.” In serious cases, or for larger affected buildings, surveyors will usually seek the advice of a structural engineer, he adds.
“I have been involved in some projects where there have been quite serious collapses of masonry or stone as a result of it” Trevor Rushton FRICS, Watts
Cracking up
While the effects are invisible at first, over time the rusting steel “grows” outwards. Often, the symptoms become apparent in the form of vertical cracks that follow the lines of the steel frame. Bill Keane, principal director at structural engineering firm Fairhurst, says identifying a correlation between the stone cracking and embedded steel is essential, otherwise you could be causing unnecessary destruction and disturbance to the building fabric.
“Stone is a natural product, it will crack over time, and quite a lot of the buildings in London suffered blast damage in the Second World War,” he says. “You need to understand how the building was built and what are you looking at. You're a bit like a doctor really.”
Robert Greer is a director at contractor Paye Stonework, a specialist in conservation of historic buildings. The company has has worked on many Regent Street Disease remediation projects, including the Savoy and Ritz hotels, BBC Broadcasting House and buildings on Regent Street itself. He says diagnosis usually starts with high-resolution photography, sometimes carried out by drones “so we can start to map the joints to see where movement has occurred, where there's staining and displacement.”
Thermal analysis can be used to identify areas where the façade remains damp overnight, showing that it has not drained properly. Ground penetrating radar can be employed to scan the façade to map where the steel fame is and compare it with the areas of cracking.
Such methods are not sufficient by themselves though, argues Keane. “Ultimately close-quarter tactile inspection is required, particularly if the location of a defect may impact on the need to erect emergency scaffold or netting to keep the pavement and retail units open.”
US cities like Chicago and New York were at the forefront of early steel frame construction, says Greer. “It is definitely a North American issue as well.” However, Richard Jantz, executive managing director at Cushman & Wakefield in New York, says that today the problem is rarely encountered there.
“You need to understand how the building was built and what are you looking at. You're a bit like a doctor really” Bill Keane, Fairhurst
He observes that it mainly affects low-rise masonry buildings, and most skyscrapers are curtain wall structures in which the free flow of air between structure and wall avoids the chain reaction that causes the condition. Meanwhile the city’s Local Law 11 requires every masonry building to undergo a five-yearly physical inspection and a remediation plan for cracking or masonry failure. “I believe that the proactive Local Law approach to documenting and repairing masonry buildings is preventative and may have short-circuited much of this occurring in NYC,” he says.
Once diagnosed, the usual treatment is to open up the building fabric by removing sections of stonework so that the corrosion can be remediated by sand blasting and the application of a protective coating before the façade is restored. It can be a time-consuming, expensive, disruptive and noisy process. The bill can run to millions of pounds for a large building, with scaffolding typically staying up from 18 months to three years.
Carrying out that work on a large mixed-use asset like an office block with retail below, which is usually occupied by several businesses brings a host of challenges. That is where a building surveyor’s involvement is most required, says Phil Speller MRICS, a partner at Cushman & Wakefield in London. “We manage the requirements of the occupiers while trying to complete the project on time and on budget for the landlord, as well as working with stakeholders like the owners and occupiers of neighbouring properties.”
The cost of repairs is usually borne by the tenants under the terms of their lease, which can create controversy. “What is the type of repair that's appropriate for that type of building and meets the tenant’s repairing liability?” asks Speller. “A tenant, at the end of the term, should not be paying for the landlord to future proof their building for the next 20 years or for ongoing repairs.”
It is not in the interests of either party to put up with the inconvenience and cost of swathing the building in scaffolding for a year to treat one area, only to have to put it up again the following year to repeat the process, says Speller. “It is better to plan it in advance and do it all at once.”
“A tenant, at the end of the term, should not be paying for the landlord to future proof their building for the next 20 years” Phil Speller MRICS, Cushman & Wakefield
Cathodic protection
From the 1990s onwards, cathodic protection techniques applied to treating corrosion of reinforced steel in concrete have sometimes been used to address Regent Street Disease. Cathodic protection involves passing a DC current into the steel frame to reverse the direction of electric currents associated with the corrosion process. It does not repair the damage, but it can suppress the rate of deterioration.
Cathodic protection is technically challenging, requiring a specialist designer, says Keane. It also requires historic buildings consent for protected structures, as well as needing ongoing monitoring and maintenance, and if applied wrongly, can speed up the corrosion.
To his knowledge there are no buildings on Regent Street where cathodic protection is installed, and among the many such façades he has surveyed he has only seen one building with such a system. “I’m sure there are some others, but it is not commonplace,” he says. “Building blight is a very sensitive issue with property investors, therefore some property owners take the view that why should they draw unnecessary attention to a building by installing it?”
In most cases Keane says that landlord and tenants settle on a “pragmatic” approach that involves immediately opening and treating the worst-affected areas, and any nearby areas that come to light, to make the building safe. A regular inspection routine is then agreed upon to assess whether any further action is needed on a five-yearly basis.
In most cases Keane says that landlord and tenants settle on a “pragmatic” approach that involves immediately opening and treating the worst-affected areas, and any nearby areas that come to light, to make the building safe. A regular inspection routine is then agreed upon to assess whether any further action is needed on a five-yearly basis.
For property owners, Regent Street Disease, is a headache. But most experienced landlords owning or buying early 20th century steel framed assets know they will have to deal with it, says Speller. “It doesn't generally come as a shock.”
Most surveyors recommend putting in place a regular and thorough ongoing preventative maintenance plan for buildings that might be affected, so that unexpected costs can be minimised and the potential for collapses eliminated.
