Historic Building Conservation in A Changing Climate

Guy Bowyer, York Conservation Trust's CEO, discusses the Trust’s approach, legacy and plans for stewardship of its estate, particularly in relation to the growing need for energy efficiency in our changing climate.

York Conservation Trust owns over 70 properties and is one of the largest private landlords in York. Co-founded by Dr John Bowes Morrell and his brother Cuthbert in 1945, the Trust became a charity in 1976, championing the useful life and comfort of historic buildings that play an important role in York’s commercial and residential streetscape.

Today, the buildings’ maintenance, along with sensitive retrofitting of energy efficiency solutions that respect heritage significance, is becoming more critical as our weather becomes warmer and wetter. So too is exploring greener, more efficient energy sources.

In a recent talk as part of York’s Festival of Ideas at De Grey House, the Trust’s York offices, Guy Bowyer outlines the Trust’s history and current position, together with the many challenges and opportunities it faces.

“York Conservation Trust is a building preservation trust, and our buildings form a rich part of the cultural and social history in the North and contribute significantly to the street scene in York. The history of the city reaches back to the Roman period and much of York's early history remains hidden underground in the archaeology.

“Most building preservation trusts are known as revolving trusts. These trusts don't always own buildings, they often repair and renovate them, passing them on to others to own and operate. There are also non-revolving trusts like us. In our case, we acquire and retain the buildings, using their rental income to repair and restore them. Our history of acquisition has led to us own some of York’s most important historic buildings including De Grey House, Herbert House, the Assembly Rooms and Theatre Royal. From the Morrell's original property company founded in 1945, the Trust will celebrate its 50th birthday as a charity in 2026. 

“Our charitable objectives are threefold: to preserve historic buildings for the benefit of people in York and North Yorkshire, to promote public knowledge and enjoyment of places of particular historic interest, and to advance education and skills in the conservation of buildings. The third and final objective we see as more far-reaching than our region; it’s a national and international role for the benefit of the heritage sector generally.

“Within 70 buildings we have 150 tenancies, with buildings divided up into different uses, split 50/50 between residential and commercial use. Economically, we find that as one sector is doing well, the other is not, and then it switches the other way, so having a 50/50 split works well to maintain our income. What is perhaps more remarkable about our estate is how many Historic England listed buildings we own: 10 grade I, 16 grade II* and 30 grade I, with grade I and II* buildings often posing the most difficult challenges.

“Our buildings are spread around the city with a few further afield, giving us the opportunity to influence conservation in outer areas. One such building is the Thompson Mausoleum in Little Ouseburn. This incredibly important building has links to Lord Burlington, architect of the Assembly Rooms, and is a highly influential piece of Georgian architecture. We also have three properties in Goathland, which were the holiday cottages of John Bowes Morrell and have been retained in the Trust's ownership. Most of our buildings display a small round green and gold plaque to identify them. Our office is at De Grey House where our small team is based. We also have 11 Trustees who act as Directors of the charity, many of which have direct family links to John Bowes and Cuthbert.

“With an estimated current portfolio value of around £35 million, from the beginnings of the organisation in 1945 when we had just eight properties, we grew steadily and in 1976 we became a charity owning 30 buildings. Between 1976 and 1994 10 more were added, showing we were acquiring a building every two years or so. However, between 1994 and 2023 we more than doubled in size and, although positive in terms of our turnover, this increase now presents us with particular challenges.

“The valuation of our buildings is difficult to assess, especially in the case of large, historic and civic buildings. Unlike residential properties, we don’t value commercial properties on their size or location, we value them on their rental income, which in many cases are very small. In this way they can become a liability rather than an asset; the enormous expenditure required to keep the building safe and operational far outweighs an achievable income. On the flip side, within our portfolio we own many historical buildings with a yearly rental income many times higher than their original purchase price. Overall, our rents and investments facilitate and support the future maintenance and management of all our buildings.

“It’s fair to say that we were developing residential space above many of our commercial properties in the 70s, well before the mainstream push in the 90s for living above a shop. We were just quietly getting on with the task of making sure our historic buildings were in full use.

“Post 2000, we went in a completely different direction, starting with acquiring the Assembly Rooms in 2002. The first neoclassical building to be built outside Italy, in many ways it is one of the jewels in the Trust’s crown. In 2005 we bought the De Grey Rooms and De Grey House and a year later Saint Anthony's Hall, one of only four surviving guildhalls in the city and one that required extensive conservation work. A year or two later we acquired Fairfax House and no. 1 Museum Street. We were simultaneously undertaking some extensive residential development projects when we acquired the Theatre Royal in 2015, famously for the cost of £1, although our bill for its restoration is now more than £4.3 million. We also acquired a substantial Georgian townhouse that was so decrepit it was literally falling down.

“During this period of growth, we were also increasing our requirement to keep on top of the maintenance of disrepair to roofs, rainwater goods and windowsills: damage compounded by our changing climate. Our issues were perhaps brought to a head by repairs required to the Assembly Rooms ceiling, identified in the nick of time as it was judged as being on the verge of collapse. The restaurant that current leases the Assembly Rooms had to close for three months while we saved the ceiling. A following root and branch survey of our entire estate brought more issues to light and a ten year plan has emerged to manage, protect and enhance our estate, which has included some strategic disposals to fund the works. In this vein, we're also looking at alternative investments through development on land we own adjacent to some of our buildings.

“Our historic buildings are now regularly surveyed. We try and find out how a building is constructed, what the fabric is, whether there's any safety issues and whether they're suitable for their intended use; in terms of any additional requirements and responsibilities that we need to consider. With any type of building there are risks that you don't see unless you really look, but there also are opportunities as well.

“To date we've undertaken 25 fully detailed surveys, which we call Quinquennial Inspections. We expect to repeat these every five years to improve our knowledge. Importantly, we’ve also inspected all our buildings of a lower historical significance and, unsurprisingly, have discovered plenty of defects. Across all our buildings there’s a pressing need to improve their resilience to climate change, their sustainability and energy efficiency. Currently, our repair bill over the next 10 years is estimated at around £14 million with about £2 million of additional sustainable improvements needed.

“I feel it’s very important to promote the benefits of historic buildings in the context of sustainability because I think they are often (and wrongly) seen as the old fashioned, ailing relative of modern builds. So, I’m going to explore how we can preserve our historic buildings, making them more resilient to the direct effects of climate change, more comfortable, energy efficient and cost effective; buildings that retain their rightfully important role in our communities.

“In terms of promoting the benefits of historic buildings, I want to explore the use of carbon. Modern buildings are often seen as more sustainable. In York we have a range of new developments on former brownfield sites, where concrete buildings of the 60s and 70s are being demolished and replaced by updated concrete modular systems, similar in footprint and scale.

“Compare this to a 14th century building that has been continually adapted over the years and has largely remained as it was on the same site and refurbished in the early 20th century. Which do you think would have the lower energy performance rating? You may be surprised to find that in our case they achieved the same score. They both got a B.

“So, how is that possible? The modern residential building will have been built to our current high standards. Its much older counterpart required no such standards and today has a commercial use as a restaurant. Ultimately, you could say that this comparison highlights how poor the EPCs assessments are because of the disparity of commercial and residential standards. To achieve a B for the historic building, along with other minor changes, we changed all the lighting to LED and installed a condensing gas boiler. Whereas the developers would have had to go to much greater lengths to achieve a B for the modern residences. However, for me, there's a wider discussion here around the value of embodied carbon energy in our old buildings.

“Carbon, its use, its loss and impact on our planet and energy costs makes it a focus of sustainability because we can measure it. However, in this respect, we pay less attention to the carbon already in the ground, in terms of the benefits of our historic housing stock.

“Modern buildings by and large have a 50 to 75 year cycle from ground works to demolition. The process then starts again. Consider the materials needed to be sourced, transported, erected then dismantled, removed and disposed of at end of life. Then compare this cycle to an historic building that has sat on the same site for centuries hosting a lot of embodied carbon, which isn't appreciably measured. It's not even thought about. Think too about how it was built. In York, timber would be locally sourced: recycled from other buildings, dismantled ships or floating debris hauled out of the river. Everything would have been handmade, including scaffolding, which, in turn, would also be reused and recycled; everything local, everything sustainable.

“Today, buildings have a much shorter life and little, if any, material is recycled and reused in new construction despite, as in the case of my earlier example of the modern block in York, being similar in size, footprint and principal structure to the building it is replacing. There are many examples like this, highlighting a disturbing mindset in planning, design and construction, a lack of creativity and unsustainable levels of resource consumption.

“The case for retaining and reusing our historic buildings is clear in that they’ve been sustainably made and have occupied the same footprint for a very long time, avoiding the cycle of change and carbon loss. They also represent the heritage and unique character of the United Kingdom’s built environment with the crucial bonus of being in daily use. However, the drive for improved green credentials often puts historic buildings at a seeming disadvantage. Asking historic buildings to achieve the same environmental standards as new builds is a tough challenge and, I feel, unjustifiably given, as I’ve highlighted, that they are already ahead of the game in terms of sustainable construction and embodied carbon. We may risk simply retaining the facades of the buildings and taking out their guts to meet ever stringent requirements; is that an answer? I would prefer a far more balanced approach to historical significance and sustainability.

“One of our biggest challenges is ensuring our buildings are more resilient to climate change through adaptation and retrofit. An example would be external render, which offers an additional insulating layer. On one of our buildings in Goodramgate the much older render was removed in the early 20th century during critical conservation work because the architects at that time didn’t like the ‘look’; they didn’t think it was correct. This has materially impacted its green credentials today, so should we put it back? We are also aware of problems created using modern insulation materials that accelerate the decay of ancient wooden timbers because the use of those materials effectively reduces that building’s ability to ‘breathe’; our old buildings were built to allow water in AND out.

“Historic buildings require materials that allow the transfer of moisture. Here we have a dry building where breathable materials have been used, as opposed to a very wet building suffering from black mould. The high moisture is the result of modern interventions to try and make it more like a 20th century building, including the use of concrete slab, non-breathable plaster on the inside, non-breathable render or pointing on the outside, hard nonporous ground surfaces and blocked drains. Cementitious pointing which shows the brickwork ‘blowing’. Not only is it unsightly and a loss of historic fabric, but the face of a brick fails making it more porous allowing more water to get trapped inside the fabric of the building.

“To keep an old building dry, ideally, lime plaster and pointing is a key material that allows moisture transfer and evaporation. Our 20th century solutions to this were cavity walls, as a way of shedding water to keep the inner skin dry while the outer skin could get very wet. And more modern architecture has moved in the direction of rain screen cladding systems that let water run away off the surfaces, and any residual moisture in the building’s fabric is ventilated.

“Paint too can pose problems because many are oil-based and create an unbreathable layer on surfaces, causing a problem for older buildings. We found this to be true for the De Grey Rooms, one of our larger buildings. For some years it was covered in a bright white oil-based external paint. Archive research showed that the building would not originally have been bright white, but more of a buff colour to sit with the surrounding York walls. As we investigated the history, we also peeled back the layers of paint where it was bubbling away and found water damage eroding the render. For the refurbishment that followed, the Trust’s largest outlay was removing the exterior paint and repairing the damaged render. Today, it has breathable cream exterior paintwork closer to its original livery that should protect the render underneath.

“As the pace of climate change increases, so too does the frequency of high intensity rain events, meaning the fundamental understanding and needs of our historic building stock will become more and more crucial to mitigate the effect of higher levels of moisture. Old buildings are simply not designed to cope with the onslaught. Interestingly, it is not, as many believe, more insulation that’s needed to reduce running costs and increase comfort, it's keeping them dry. You can’t warm a wet building, it’s simply not possible.

“Traditional timber gutters are a good example of historically accurate rainwater goods that are regularly failing the very buildings they were meant to protect. Fast growing vegetation in rainwater hoppers and spouts is another issue, together with a lack of regular maintenance. Inundated guttering, blocked hoppers and overwhelmed spouts pour water down walls and into basements, soaking facades and creating water damage. This is a problem we are faced with at the Assembly Rooms. Completed in 1735, Georgian guttering is simply not designed to take today’s weather, combined with moss-blocked sumps and overflowing hoppers meant water was washing down the front of the building, damaging the stone façade. We have deployed wider guttering, larger hoppers, mesh filters and waterspouts. We're struggling to get permissions to replace our timber guttering elsewhere on the estate because of evidential historic value, but I really would encourage the sector moving towards allowing that change to help preserve the buildings themselves.

“Moss, grass and bushes of all description flourish in moist environments and, with less hard frosts, are increasingly establishing themselves on and in the fabric of the city’s buildings, compromising their ability to move water away from walls. Clearing vegetation also creates its own issues around further damage to stonework and drains, all affecting the integrity and lifespan of the buildings.

“Once dry, how do we keep our historic buildings warm? Roof insulation is something that we can do without affecting the historic significance of the buildings through adding physical, thick layers of insulation, as well as more modern, ultra-thin membranes above rafters. We also add insulating lime-based breathable renders and plasters.

“In terms of sustainable, renewable energy use, the jury is still out on heat pumps for historic buildings. We've not used one yet, but we have plans to do so. We are also experimenting with other electric systems and would advocate the removal of gas where possible. One of the easiest ways to do it is to go fully electric and get a green energy tariff. We have also recently installed far infra-red heating systems in some buildings. A low energy, low cost electric system not widely used, far infra-red heats the physical elements, not the air in a room and is quite effective. The placing of panels appears to work best when ceiling mounted.

“To address a major driver of heat loss, we also cover the basics including draught proofing windows, including the use of traditional awnings and shutters, that not only work for draughts and heat loss in winter, but also as a sunshade in summer. Layered curtains, tapestries and other textiles also offer the same properties. We tend to overlook these more tried and tested traditional methods of temperature control. Easily cleaned and replaced they are also more cost effective in older buildings. Secondary glazing, a window system that sits behind the original glass, can support heat retention like double glazing. It's easily removed, although often awkward to open and close, and we would advocate using a thin system where possible. Then we move into the difficult and slightly polemic area of double glazing.

“Replacing original historic glass is often not desirable simply because of the loss of original building material. Also on cost grounds; although effective, double glazing and newer highly effective single glazing options, are expensive and may well be less economically and materially effective than adding to roof insulation. Modern glass also brings issues around its greater reflective quality, materially altering the nature of the street scene; it’s a balancing act that undoubtedly needs to be considered.

“A building’s interior décor also brings challenges for retrofit insulation. The removal of historic and traditional features, including cornices, dados, pelmets and skirting boards, to install interior insulation robs buildings of their historic significance and character. To measure how our buildings are coping with issues such as condensation, we’re using small Tinytag® Data Loggers, which measure temperature and humidity, alongside CO2, power usage and other environmental parameters. We have deployed these small devices in one of our grade I listed buildings that has very thin wall construction, because we were concerned about how much interior insulation would be needed to make the building viable for use. What we found surprised us. The building performed better than we thought, with no condensation risk within the fabric whatsoever. This means that when we upgrade it, we can be much more sensitive to the original fabric, because the building's impressive thermal buffer indicates extensive retrofit insulation will not be necessary. The unobtrusive, more sensitive and removeable interventions such as curtains, blinds and rugs will be sufficient.

“Akin to double glazing, solar or PV (photovoltaic) panels also divide opinion for their deployment on historic buildings and the impact on roofscapes. Whilst in some settings it wouldn't make a huge difference, York has acres of terracotta pantile roofs, which make the use of large black PV panels visibly insensitive. Recent development of PV technology has made strides in the use of smaller tile sized panels that look like slates, but not pantiles. The requirement for regular cleaning and maintenance also presents us with logistical challenges, which are difficult to overcome at this time.

“So perhaps the answer is to consider alternative locations and co-investment initiatives to put them on other, less historically sensitive buildings like supermarkets, car parks, outer park and ride facilities, or on other community assets like schools. In this way we can spread out greener energy production further afield, whilst retaining the visible integrity of our historic building stock. York Minster is currently locating an array of PV panels on largely unsighted parts of its roof and within its estate elsewhere; such use should be supported and can also be used as a blueprint for other historic sites of that nature. Another key aspect to improve historic buildings’ green credentials is low energy lighting systems. A good example in York is the recently refurbished Guild Hall; City of York Council have used LED lighting to good effective across the full range of their estate.

“Today, we’re drawing on old building methods and all emerging retrofit technologies to inform how we best conserve, protect and upgrade all our building stock. We are holding workshops and seminars, education days and engagement events, and we welcome fundraising opportunities to help us progress our work. Soon we will be moving into an 18 month programme of work at Herbert House; a much loved, iconic and ancient York building that needs around £3 million investment to ensure its viable future.

“We know it’s important to learn from retrofit mistakes we’ve made in the past; given the rate of climate change we can’t afford to make those mistakes again. I feel strongly that planning regulations need to afford historic buildings more latitude to explore better, more efficient ways of removing water, through the use, location and materials of rainwater goods and roofs. That said, the adoption of new materials also needs to be approached cautiously. With little proof of concept data in historic building settings, we need to ensure we are not storing up trouble for the future as we have done unintentionally through damaging early 20th century initiatives.

“Our current strategy for the Trust’s portfolio is one of consolidation and repair, research and considered experimentation; fully focused on ensuring the buildings in our care are in the best shape possible for future generations’ use, enrichment and enjoyment.”

Guy Bowyer, De Grey House, York, 2024