27 Nov 2019

Property conversion in the face of climate change

Historic buildings account for more than a quarter of our existing building stock, and a surprisingly large number of ‘self-build’ properties are converted historic buildings, writes Melissa Osborne, Principal Building Surveyor at Trident Building Consultancy.

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A centuries-old home restored in 2020 may remain for centuries to come, but in a very different climate – one of wetter winters and hotter, drier summers, storms as well as rising sea levels. What can we do to prepare for change, mitigate the challenges that it presents and create environmentally-responsible buildings?

The long-term forecast

By the 2050s, a maximum daily temperature of 26°C plus is projected to occur approximately 50 days a year, compared to 18 days currently. Homes have been built to provide thermal comfort – prioritising heat retention and sunlight over cooling. They are ill-equipped to meet our needs, and they too will suffer from raised temperatures – from pests (specifically woodworm) to biodegradation. Prolonged periods of drought have caused soil shrinkage, leading to subsidence in older properties (particularly those situated on clay), and as recent news reports have shown, flooding causes significant damage to the buildings’ structure, services and contents. Longer-term, changes in the water table can cause heave and – again – subsidence.

The Met Office reports that of our 17 record-breaking rainfall seasons since 1910, nine have occurred since 2000. Based on the assumption that temperatures rise by 4º, the number of UK households at significant risk of flooding will more than double – reaching 1.9 million by 2050.

With 20% more rainfall today than in the 1960s (a worrying increase of the 70% in the north and west of Scotland), existing gutters, downpipes and drains struggle to cope with volumes and intensities of rainwater. This leads to greater risks of water penetration and damage to the structure and internal finishes.

Historic building materials are more permeable than those of modern buildings, and changes in moisture content rapidly activate damaging cycles of salt crystallisation. Furthermore, storms can be particularly detrimental – saturation of masonry; for example, as a result of increased rainfall, combined with high winds may lead to structural failure.

Along with increased temperatures, an increase in humidity can cause corrosive chemical reactions, and changes in radiation damages materials, particularly bituminous roof felt, paintwork and timber.

So renovating an older home with hopes of longevity in the face of accelerated change is a challenge, but not without solutions.

Preparing for higher temperatures

The good news is that traditionally constructed (specifically stone) homes are often better able to remain cool than their modern counterparts as a result of thermal mass. And as over-heating was invariably not a consideration when they were first constructed, there are opportunities for improvements.

We do not need to create new methods, as there is much that can be learnt from warmer climates. Shelter from the sun was the main objective for traditional North African and Mediterranean architecture. Homes in these locations have been found to feature Passivhaus techniques and materials many hundreds of years before the invention of the building standard. Typically, such buildings feature shutters and awnings to create shade, cool stone floors, light-coloured surfaces to increase reflectivity, ventilated roof spaces, cavity wall and roof insulation. Shaded, openable windows prevent the ‘greenhouse effect’. More recent techniques include double (or triple) glazing with low e-coatings or solar heat gain coefficient (SHGC) glazing, multiple layers of reflective roof and ceiling insulation, and elevated floors with reflective, closed-cell bulk insulation to resist upward heat flow and condensation.

Individual thermostats are considerably more effective than those that serve an entire property, and air-conditioned or heated spaces are sealed to prevent loss.

Preparing for flooding and storms

Sadly, in the case of flooding, there is significant evidence of good intent leading to further problems. Waterproofing, while logical, can do more harm than good as once water is within the fabric of a building, waterproofing will reduce its potential to dry out. Practical solutions to address flooding include keeping gutters clear, sealing gaps around pipe and cable entries, repointing brickwork, fitting non-return valves on mains drains and introducing flood-resistant materials – such as replacing wooden floorboards with solid concrete and steel in place of wooden skirting boards. This should be complemented by initiatives to enable natural ventilation, such as air bricks. Porous external surfaces, gardens and green roofs are beneficial in reducing excess water, as is rainwater harvesting.

Would-be renovators should mitigate for storms by reinforcing the building structure (including the roof) and increasing the capacity of guttering, drainage down-pipes and rainscreen cladding.

Taking responsibility for the future

The bottom line is that the ultimate home of the future – whether brand-new or centuries-old – is one that looks ahead by minimising its own negative impact.

Of course, careful consideration will need to be given to the impact on the character and structure of the building: it is not always possible to position a wind turbine or solar panels on a listed building. But there is always potential for energy generation. Unobtrusive possibilities include ground and air source heat pumps, energy exchange systems, reed bed sewerage/water purification systems and use of ‘grey’ water, hydropower, improved and more extensive use of thermostats, and switching to lower-carbon energy supplies.

Regular reviews are fundamental in implementing a systematic and preventative maintenance programme. Prior to considering any substantial changes to a historic building, it is important to ascertain whether the building is listed or located within a conservation area.

While adaptations to older buildings might appear complex, from a sustainability point of view, conversions of existing properties is always seen as the responsible option. The greenest building is the one that is already built, and that’s a great start.

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