HAVE OVER THE CENTURIES, CULTURE

Retrofitting listed and historic buildings has received relatively little attention, despite the fact that property age is the biggest single factor in the lack of energy efficiency and that older buildings account for a sizeable chunk of all UK homes.

Nearly one in four dwellings—6.2 million properties—in the UK were built before 1919, according to a study commissioned by the National Trust, Peabody, Historic England, the Crown Estate and Grosvenor. Addressing the energy efficiency of these often draughty old homes is essential, given the impending green building targets and that the built environment accounts for 25% of all UK emissions, as reported by the UK Green Building Council.

So the question is: can historic and listed buildings be retrofitted? The short answer is yes—but it’s not without its complexities.

Looking At The Bigger Picture

When it comes to retrofitting this type of property, Historic England guidance emphasises the need to take a “whole-building approach” because of the differences in construction methods between these homes and newer builds. While modern buildings depend on impermeable barriers to control the movement of moisture and air through their fabric, properties built using traditional methods absorb moisture from the air surrounding them and release it according to environmental conditions. Put simply, modern homes are designed to be airtight, while historic ones were made to breathe.

Although this simple principle applies to most traditionally built properties, individual homes can have their own characteristics as there were no set construction standards at the time; in comparison, more modern dwellings built from 1965 onwards follow the national building standards first introduced then by the Building Regulations Act.

“Every historic building's energy performance varies; there are many interacting factors involved, so there is no one-size-fits-all solution to making a building energy efficient,” explains a spokesperson for Historic England. “To understand the energy performance of any building and identify opportunities for improvements, all the factors that affect energy use and efficiency and how these are interlinked need to be considered.”

To understand the thermal performance of each historic building, several technologies can be employed, such as air pressurisation testing to determine how airtight a property is. In this procedure, a fan is set temporarily into a doorway to create a pressure differential, which allows the amount of air leakage through the building’s envelope to be quantified. This can be used alongside infrared video and still cameras to show surface temperature variation across the building envelope to accurately reveal cracks, open joins and other defects that can be fixed to prevent air leaking out and therefore heat loss.

In addition, the whole-building approach takes into account environmental, community, economic and cultural issues. With regard to the latter, retrofitting works must not reduce the building’s heritage value. “At its most basic, this could be looking at any listing or speaking with the local conservation officer or a heritage-accredited building professional but, more technically, it can involve carrying out an assessment of the building’s significance following the principles in documents like BS7913 and/or guides by organisations such as the Society for the Protection of Ancient Buildings and Historic England,” explains Matt King, senior building asset manager for land and nature at the National Trust. “Once you understand what makes your building significant, you can then review the retrofit measures available and consider the impact these interventions will have on the significance of the building—this is called a heritage impact assessment and is often needed for listed building consent.”

The preservation of a listed building’s cultural heritage adds even more complexity to the process of retrofitting these specific properties from a regulatory point of view. In addition to planning permission—which may be required for substantial retrofitting works, or if an article 4 direction is in effect in the area—anyone undertaking retrofitting works for listed and historic buildings must obtain listed building consent in order to carry them out. In general terms, listed building consent is required for all works of demolition, alteration, or extension to a listed building—or objects and structures within its curtilage, such as outbuildings—that affect its character as a building of special architectural or historic interest.

When applying for such consent, one must include sufficient detail to allow the impact of works to be properly assessed. This includes the provision of a site plan, location plan, design and access statement, and a heritage impact assessment. Once submitted, the local planning authority will confirm its decision within eight weeks—which includes a 21-day consultation period with neighbours and interested parties.

It is important to note that carrying out retrofitting works on a listed building without this consent is a criminal offence. The only acceptable defence for such an offence is if the works are urgently necessary in the interest of health and safety or for the preservation of the building, as long as the works carried out are limited to the minimum measures urgently needed and the person completing the works has notified the local planning authority and offered a justification as soon as possible.

Although historic and listed buildings need an individualised approach, some retrofitting measures are usually acceptable for many of them. “Roof insulation is one of the first things you’d look at trying to do. It’s an easy win, as there’s probably a void where you can put insulation in without affecting anything,” explains Katherine Watts, architect and leader of the conservation and heritage team at John McAslan + Partners. “Windows are another thing to look at; depending on how historic they are, you can either do secondary glazing or potentially replace them. For listed buildings, one of the criteria is that works should be reversible, which is why secondary glazing is preferred over window replacement, because you can obviously just take it out [if needed] and you haven’t lost anything.”

Other low-cost and low-risk options that are encouraged by Historic England include draughtproofing; thermal performance can be improved through curtains and blinds as well as putting rugs and carpets down on ground floors.

Risk From Modern Materials

A substantial issue when retrofitting historic and listed buildings is the type of materials and technologies used to carry out the works, as old and new buildings have different requirements. Specific materials, such as lime mortar, lath, plaster and timber, are often necessary to retrofit a historic property—however, they are not always used. “What often happens is that people try to make an older property perform like a modern building, but it doesn’t work like that. A lot of problems with historic buildings occur when you try to apply a modern method to it. For instance, if you try to put a vapour membrane inside a historic building, you could end up trapping the moisture and get a wet wall, which is much worse performing than a dry wall. So, you’re compounding the problem rather than solving it,” states Katherine.

Using the wrong materials can cause severe damage, such as condensation, mould growth, or dry and wet rot, which can affect the health of the building’s inhabitants. It can also mean a significant loss of historic fabric and value, failure to reduce energy consumption, and even do more harm than good in terms of environmental sustainability.

Solving this issue poses a much bigger problem than one might think. On top of the ongoing material shortage crisis, Victoria Herring, director of sustainability programme for the UK at Grosvenor, explains that there is a shortage of innovation when it comes to developing technologies to retrofit historic buildings, due to the lack of demand to carry out these types of projects—thus making it less appealing to invest and design new product for retrofitting historic homes. She adds that, despite this need for innovation, progress will not happen until there are clearer national and local policies that support and encourage sensitive retrofitting.

Inconsistent Officials

Despite the reports and guidance documents published by several national organisations, including Historic England, inconsistency of advice from local authorities and conservation officers and in rules with regard to retrofitting historic buildings appears to be plaguing the sector. “I know how hard everyone is working in this area, how under-resourced some offices are and the speed at which they are trying to upskill in what is a rapidly changing environment, but we certainly see examples of things like secondary glazing being acceptable in one area and then unacceptable elsewhere on a building of very similar style or significance,” states Matt. “That said, I also think building professionals can do better by ensuring that applications for consent are well thought out and follow Historic England’s guidance for the intervention being proposed.”

According to Rico Wojtulewicz, head of housing and planning policy at the National Federation of Builders (NFB), this is compounded by some heritage officers’ stringent view of what qualifies as cultural heritage. “Buildings have changed over the centuries, and culture changes all the time. I think we are too protective and specific as to what is acceptable. A good example of heritage mobility is vehicles—we’re now moving to electric cars, but what happens to all those heritage vehicles and trains? I don’t understand why on one hand we’re all about protecting buildings, but we’re happy to go the other way on vehicles. The balance really needs to be in the middle.”

When asked about the solution to this conundrum, Victoria, Matt and Rico all agree that a new national policy for retrofitting historic buildings is necessary to ensure advice given to people undertaking these projects is consistent. “That also requires the heritage sector to step back a little, accept change, and work with it to achieve the best outcome—not simply the outcomes it views as best,” adds Rico.

Specialist Building Workers

Another issue that complicates matters even more is the shortage of suitably skilled workers. “As you start working on statutorily protected buildings, the knowledge and skills required to successfully implement a retrofit are significant. This is not an area where you want to be working with someone who is applying knowledge of retrofit and energy efficiency measures from simpler buildings,” warns Matt.

NATIONAL POLICY AND YOU HAVE THE DEMAND, THEN YOU’RE NOT GOING TO GET PEOPLE BEING TRAINED AND UNDERSTANDING THESE BUILDINGS”

Rico underlines the importance of having skilled workers to retrofit a historic building, giving the installation of a suspended timber frame floor as an example: “This floor has got to retain the air so the flow continues, as that’s what keeps the foundation and structure of your building dry. You’ve got to do that in a very precise way to ensure you're not damaging the building. For instance, you may then need to have ventilation via either air bricks or telescopic air bricks so that you continually have that air flow. You may also need to fill some of the mortar joints around your bricks. There are lots of different elements that need to be done—that's why you need a skilled workforce, because they're the ones who will analyse exactly what needs to be done on a building in its entirety.”

Employing workers who do not understand traditional building approaches and the cultural value of such properties could result in damage to heritage significance through accidental alteration or removal of historic features. “You hear these horror stories of people going into heritage buildings and maybe stripping out period features without having consent and not understanding that they can work around those features with a bit of thought and understanding,” says Victoria.

The Heritage and Carbon Report estimates that 100,000 people are currently working on historic buildings, and a further 105,000 full-time workers—including 14,500 more electricians and 14,300 more plumbers—will be needed each year until 2050 to focus solely on upgrading buildings built before 1919.

In order to do so, both Victoria and Rico believe further training is required to extend the skilled workforce needed to carry out retrofitting works to the millions of historic buildings in the UK—a suggestion echoed in the Heritage and Carbon report, which calls for the government to allocate unspent funds to training more people with heritage retrofitting skills. “Unless you have an overarching national policy and you have the demand, then you're not going to get people being trained and understanding these buildings,” says Victoria.

Rico believes a steady supply of work is also necessary to drive this, in conjunction with training schemes. “No company will train somebody over three years without any pipeline of work afterwards; the finances just don’t work. If you want to ensure your workforce has greater capacity, it’s not simply about training people—it’s also about ensuring you have a pipeline of work so that people are retained,” he explains. “When the government gives a signifier to the industry that it is going to back this and there is a pipeline of work, the market will then move itself to provide the capacity and the innovation.”

A BIG CHEQUE FOR A BIG JOB—SO WHO PAYS?

Aside from being a complicated task, retrofitting a historic building doesn’t come cheap—particularly as the lack of skilled labour drives the already high prices up even further. “It’s a skilled job and there are very few people doing it, so it’s a ‘name your price’ situation,” states Rico.

So how expensive is it to retrofit a historic building? Victoria explains that it is hard to estimate an average, as the cost will depend on the complexity of the works required and where the building is located. However, based on 2019 costs and using Grosvenor’s previous work as an example—done in central London, where the firm primarily operates—she estimates a simple retrofitting project would cost roughly £10-15 per sq ft, going up to £33 per sq ft for complex work.

“Lime mortar can be two or three times the price of ordinary plaster, while a timber window is six times the price of a uPVC window. And, of course, skilled workers are few and far between, so they rightly charge more for their works to be done to high standards. You’ve also got to consider the costs of enabling that work; you may need an architect, so it might cost you a few thousand pounds just to get the technical drawings done,” explains Rico.

Rico adds that the lengthy process of applying and obtaining for planning permission and listed building consent—which he claims could take 6–12 months—could also see costs driven up due to material price increases and inflation during the waiting period. “As complicated as that is for charities that own heritage buildings, at least they have some level of security as they have reserves. If you're an ordinary person living in one of these buildings, you don't have as much capital or financial reserves”, he adds.

Rico’s calculations paint an even bleaker picture, as he claims it would cost about £2 trillion to retrofit all UK buildings in need of this—of which minimum £40bn would be solely for listed buildings—and decarbonise their energy sources. “If you do that, you also need to decarbonise the [whole electricity] grid; the figures there are between £2.8 trillion and £3.8 trillion, so you’re looking at a total of £5 trillion—and I think I’m being conservative,” he elaborates.

Such a hefty bill begs the question: do we have enough funding for this? Victoria and Rico don’t think so, which is why they believe the government needs to step in. They recommend several options, such as the partial or full reduction of VAT for retrofitting works on historic buildings to match the policy for certain energy-saving materials introduced by the government in March 2022. “There’s nowhere near enough funding but, if we're being completely honest, if we want the government to put their hands in our pockets—as it's taxpayer funding—we need to make sure we're getting value for money,” states Rico.

HIGH RISK, HIGH REWARD

With such a complex process, sprinkled with many difficulties, it’s understandable why some may be put off from retrofitting historic buildings. Nevertheless, the benefits this brings to the table are just as big as the challenges. According to Victoria, successfully retrofitting a historic property can result in up to a 90% reduction in carbon emissions and greater energy efficiency, depending on the complexity of the works done, leading to a significant drop in bills for inhabitants.

At a larger scale, Historic England predicts that if the UK refurbishes and retrofits 50% of its pre-1919 housing between 2021 and 2031, this could reduce 39.6 million tonnes of carbon dioxide emissions by 2050. Not only this, but the Heritage and Carbon report estimates that scaling up the construction sector with the skills necessary to retrofit the UK’s historic buildings would lead to an additional £35bn of output annually, supporting around 290,000 jobs.

Although the process of retrofitting all of the UK’s historic buildings seems to be a long, arduous and expensive process, there is no denying that this is indeed possible—and necessary to fulfil the country’s ambitious sustainability plans. As Historic England states, it’s not a question of “if ” change can be accommodated, but rather “ how ”.