Improving thermal efficiency to combat climate change. Could your old house become an eco-house?
In December 2015, the international community reached a landmark agreement within the United Nations Convention on Climate Change, known as The Paris Agreement. It aims to combat climate change and accelerate and intensify the actions and investment needed to create a sustainable low carbon future.
The UK Government has committed to a low-carbon economic future with the stated aim of achieving net zero carbon emissions by 2050. Substantial reductions have already been achieved. In 2020 over 40% of our electricity came from renewable energy sources, however, producing green energy alone will not allow us to achieve our target.
How do buildings contribute to carbon emissions?
Buildings are the third largest carbon-emitting sector. The temperate changeable climate of the UK means we use far more energy on creating heat than we do for powering lights and appliances. A BEIS report in 2020 noted that homes use 28% of all UK energy with 65% of that energy used for space heating. Consequently, tackling how we make our homes more thermally efficient and how we heat them has an important role to play in our route to a net zero future. With rising fuel costs and increasing numbers of households living in fuel poverty, making homes comfortable to live in, efficient, and affordable to heat is more important than ever.
The UK has some of the oldest housing stock in Europe, with approximately 20% of all houses built before 1919 and of solid wall or solid timber frame construction. Indeed, numbers of historic homes are increasing due to the splitting of larger properties and the conversion of non-domestic buildings such as mills.
Why does this matter?
Old buildings are typically less thermally efficient, use more energy, and are more costly to run. Carbon reduction strategies tend to focus on operational carbon emissions, that is the energy being used to run our homes, without taking into account embodied carbon, that is the energy required for their original construction.
Demolition of old houses and their replacement with new homes is associated with significant carbon emissions in the processes of transportation, recycling, disposal of materials, extraction and production of new building materials, and during construction. Consequently, although the building of new thermally efficient homes is important, we cannot simply build our way out of the climate crisis.
Besides, our historic buildings are valued for their historic and architectural significance, their character, and the contribution that they make to the sense of place and the local distinctiveness of our communities. Huge amounts of carbon are locked up or embodied in historic buildings in the UK and the important role they will play in tackling climate change has become the focus of much research in recent years.
Historic England has focussed its recent ‘Heritage Counts’ research on this subject. ‘Heritage Counts 2019 - There’s No Place Like Old Homes, Re-use and Recycle to reduce Carbon’ highlighted the need to recognise the amount of carbon already sequestered or embodied in our historic buildings and the important role refurbishment and retrofitting must play in tackling climate change.
‘Heritage Counts 2020 – Know Your Home, Know Your Carbon – Reducing carbon emissions in traditional homes’ focuses on the role of homeowners and occupiers of historic buildings highlighting the need to understand how your home uses energy, the importance of repair and maintenance, and the need to carefully plan any retrofit or renovation works.
Understanding your old building
Before embarking on any program of retrofitting or refurbishment it is crucial to understand how the building is constructed and how that influences its performance and use of energy. Modern and historic buildings differ in how they deal with heat, moisture, and air. Modern buildings depend on impermeable barriers to control movement of air and moisture and air tightness is important. Modern buildings have high levels of insulation allowing them to generate and sustain a comfortable temperature using less energy.
Historic buildings are usually of solid wall or solid timber frame construction with lime mortar and plasters a key component of their fabric. They take up moisture from their surroundings and release it according to local environmental conditions, a property often described as ‘breathability’. Traditional buildings typically heat up and cool down more slowly than modern buildings and have greater natural ventilation. Application of impermeable modern materials like cement render, concrete floors and plastic membranes interfere with the movement of moisture in old houses resulting in dampness, timber rot and reduced thermal efficiency. The equilibrium can also be disrupted by retrofit measures, such as the addition of insulation, if not carried out correctly. Consequently, it’s important to understand how the whole building operates before making changes.
Whole House Approach
The ‘Whole House Approach’ to retrofit is recommended by Historic England and the Society for the Protection of Ancient Buildings (SPAB). This approach is about getting the balance right recognising that there are three key areas for consideration:
Health (occupants and fabric)
Energy and Carbon (efficiency & reduction)
Heritage (significance and cultural well-being)
Each intervention proposed could have positive and negative impacts and these must be carefully balanced to avoid unintended consequences that can cause damage to buildings, occupants’ health, and failure to improve energy efficiency. For example, blocking up sources of draughts without considering how to control the ventilation of a house can lead to increased condensation, mould growth and associated health issues for occupants.
Each building is different and when considering retrofit measures ‘one size does not fit all’. Understanding interactions is the key to success and requires consideration of a variety of factors that affect the building, including its location, current condition, how it is heated and who occupies it.
The ‘Responsible Retrofit Guidance Wheel’ produced by the Sustainable Traditional Buildings Alliance (STBA) is a useful online tool that shows the impact of proposed energy efficiency measures on other elements of a building and considers technical, heritage and energy concerns.
How can we make our historic buildings more energy efficient?
Repair and Maintenance
Good maintenance is a key factor and homes must be repaired before retrofit measures are carried out. Simply put, the aim of house maintenance is to avoid the ingress of water into areas where it can cause damage and problems. Pointing, render, rainwater goods, slipped or missing roof tiles and slates, windows and sills, are all areas that can allow water penetration. There are many low risk and low cost measures that fall under repair and maintenance. The SPAB campaigns to highlight the importance of maintenance and offers advice including a downloadable calendar of maintenance tasks that can be carried out throughout the year.
Energy Supply, Efficiency & Controls
The efficiency of lighting, heating and hot water systems, the energy efficiency of appliances, and provision of good controls for heating and lighting can all reduce energy consumption. Upgrading elements of the heating system such as boiler, radiator valves, lagging to pipes, thermostats and controls are often straightforward changes with minimal risk to building fabric. Many modern systems have wireless thermostats that can be easily positioned allowing different zones of a house or building to be heated according to their level and time of use, improving operating efficiency and lowering energy use. Effective operation of services by homeowners and simple changes such as installing low-energy lightbulbs, ensuring new appliances are ‘A’ rated, and signing up to a ‘green energy’ supplier will also have a positive impact. Heat pumps that harness heat in the ground, air or water are increasingly popular but there are multiple factors to consider before installing them in listed buildings and Historic England has produced useful guidance.
Many historic buildings have traditional single-glazed timber or metal framed windows made from high quality materials that have considerably greater longevity than most modern windows. These windows are an integral part of the building’s design and contribute to their heritage significance and visual character. Nevertheless, owners and occupiers of historic buildings frequently enquire about replacing traditional windows with new double-glazed windows to reduce heat loss and reduce energy use. Indeed, a walk through most towns and villages is likely to yield examples of inappropriate replacement windows on historic buildings.
However, windows that appear to be in a very poor state can often be repaired and there are a variety of measures that can be used to improve their thermal performance. Simple draughtproofing measures are quick, inexpensive, and effective. Installing well-fitting blinds or heavy curtains, or using original shutters keeps heat in rooms on cold nights. Traditional windows can be upgraded to greatly improve their thermal efficiency by the installation of secondary glazing, with a wide range of systems available from DIY to bespoke systems. All allow traditional windows to be retained thus avoiding harm to the significance and visual appearance of historic buildings. Research shows a combination of the measures outlined above is highly effective in reducing heat loss via traditional windows.
The main function of the roof is to keep the weather out, resisting penetration of rain and wind. The roof also plays an important role in retaining heat in the house as up to a quarter of heat loss will occur through it if there is no insulation. Loft insulation installed above the rafters is usually inexpensive and straightforward to carry out if suitable materials are used and ventilation is sufficient to avoid the risks posed by condensation and mould in the roof space.
Attic rooms frequently contain no insulation, and the thermal upgrading of occupied roof spaces requires the creation of a warm roof. Creating a warm roof in a historic building with insulation applied above or between rafters is challenging and may only be possible if the whole roof is at the end of its life and being overhauled. Insulating the cheeks of dormer windows is also difficult as they are often thin with minimal space for insulation. Professional advice and design for a warm roof coupled with careful choice of the insulation materials to be used are necessary.
Wall insulation can improve the thermal efficiency of walls. However, its application to historic buildings of traditional, solid wall construction brings potential problems and risks. The suitability of internal or external wall insulation depends on many factors, including the construction of the wall, its thickness, location, exposure to weather and current condition. Wall insulation can interfere with the breathability of traditional construction methods and materials, resulting in moisture becoming trapped in walls, a phenomenon called interstitial condensation, causing damp walls and mould growth.
Both external and internal wall insulation can have a significant impact on the appearance and character of historic buildings. Externally historic buildings may have decorative brickwork, mouldings or bay windows; whilst internally features affected by insulation may include cornicing, skirting boards and architraves. Weak points in the insulation layer result in thermal bridges; points of high heat loss and low surface temperature that encourage condensation to accumulate.
There are specialist breathable insulation systems and insulating plasters available that may be suitable for use in traditional solid walled buildings. Specialist advice should always be sought before the application of wall insulation to address the potential risks to historic significance, building fabric and occupants’ health.
Homes are significant contributors to carbon emissions and energy use. There is a pressing need to make our homes more energy efficient. Historic buildings contain huge amounts of embodied carbon and their retention and reuse avoid carbon emissions associated with creating new buildings. Owners and occupiers of our precious historic buildings have an important role to play in reducing carbon emissions and energy usage. Small changes in behaviour such as reducing the thermostat temperature by one or two degrees, prioritising repair and maintenance, and introducing some of the simpler measures outlined above can have a big impact.
More comprehensive retrofit measures can reduce carbon emissions and energy use and maintain heritage significance if they are well designed and carefully executed. Homeowners should be aware that such works are likely to require planning or listed building consent and seeking professional advice at an early stage is recommended.