The balance between modern lifestyles, ethical and environmental issues, and the practicalities of living can be seen in microcosm in the challenges of conserving energy in historic buildings. Energy conservation for historic buildings is widely discussed in articles, building standards, guidelines, and academic journals, and those interested in period properties face an often bewildering array of terms and concepts such as sustainability, home energy use, carbon footprints and the embodied energy of buildings.
With an increasingly drive for energy efficiency, many building owners will soon, if not already, face decisions on how best to balance the conservation of fuel and power with the need to conserve the building itself. However, there is generally no reason why historic buildings should not be reasonably energy efficient, comfortable and healthy without extensive and expensive energy conservation retro-fitting measures. The way to achieve this is to carefully select those measures which are sound economic investments, which will achieve the greatest savings without harm to the character of the building.
Firstly, it should be remembered that period properties were generally built in order to maximise natural light, heat and ventilation, and so tend to require significantly less energy for heating and cooling than a mid-20th century building. The thick masonry walls and the combination of relatively small window areas with wooden shutters and heavy curtains work quite effectively at retaining heat. The high thermal inertia of thick brick or stone masonry walls means that the energy absorbed by the external walls during one hour of strong sunlight may be transmitted to the interior over a period of six hours. It is a characteristic of older buildings that they tend to be cool during the day and warm in the evening. Many building owners have an uncomfortable room, where it heats up quickly, or becomes excessively cold in the winter. These are the rooms where passive or active measures to conserve energy are likely to have the most noticeable impact.
About 30% of the energy used in a building can be saved passively – by controlling how and when the building is used. These tend to be the most common “tips” offered – lowering central heating systems by a few degrees, turning off lights, being conscious of how you are heating the rooms in use and those not in use, and servicing radiators and other equipment to ensure maximum efficiency.
A further 20-30% reduction in energy use can be saved by undertaking new measures such as insulating roofs, changing doors and windows, controlling draughts, and even treating the exterior of the building. However, none of these are permanent solutions, and if carried out badly or overzealously can easily cost more than they are likely to save over their lifetime of use, and can damage both the fabric and the character of a historic property.
Draughts are a curse. No one likes them drifting through a room, and substantial heat loss occurs as cold outside airs infiltrates the building around the windows and under the doors and from cracks you never even noticed were there. However, older buildings need to “breathe” through the entire envelope of the walls, the floor, and the roof to allow moisture to escape and prevent damp and condensation. Reducing draughts should be the first priority for energy conservation. It’s low-cost, requires little skill and has substantial benefits. However, completely sealing the building is not wise, as without a level of air exchange appropriate for the building, condensation problems could occur throughout the building.
The roofs and windows are the primary pathways of heat loss, and normally the easiest to address. Insulating the attic is the easiest method to cost-effectively reduce heat loss through the roof. However, if the attic spaces are not properly ventilated because the insulation was not properly fitted, the insulation material can quickly become saturated and lose it’s effectiveness as a heat barrier, and potentially increasing the amount of heat lost. Windows are a poor thermal barrier and the most common source of draughts, and pose a number of challenges to allow improvement or upgrading of its thermal performance. The least intrusive method is to ensure that the sash windows common to most period properties sit snugly in their frame. Draught strip and draught brush systems can also be effective at further reducing both heat loss and air infiltration, and are generally preferable to the detracting from the character of a room and the exterior of the building by installing double-glazing or secondary glazing.
Wall insulation is a complex issue, and can result in serious technical and conservation problems if poorly carried out, and even more costly to correct. A significant number of plaster, external render, timber and sometimes building stone failures can be attributed to a poorly conceived or poorly executed attempt at wall insulation. Waterproof masonry paints and water-repellent treatments can similarly have unsatisfactory results. Building owners generally apply these coatings on masonry walls to keep water out, and so keep the masonry dry and warm. These treatments do stop the passage of water. However, traditional masonry almost always has a moisture load, and water passing into the building from anywhere (showers, a failed gutter, condensation from central heating etc) adds to this moisture load, and so the moisture starts to move. In a traditional building, this moisture is evaporated by wind and sun from the exterior of the building. With a waterproof coating, the moisture tends to build up behind the coating leading to the stone and brick flaking and crumbling, or migrates back into the interior of the building.
There is also a wide range of heating and air conditioning equipment, alternative energy technology exploiting solar and wind power, and other mechanical measures which can upgrade the energy efficiency of a historic building. These new technologies are becoming increasingly available, feasible to install, and cost-effective to achieve real energy efficiency savings. The installation of new services to a building requires careful consideration aside from the conservation of energy. It’s important that the installation process does not cause irreversible damage to the building, and should be installed in the knowledge that it will someday be removed and the system up-graded. The concept of invisibility and hiding all the services within walls and under floor may not be the best option for a historic building, and sometimes innovative approaches have to be balanced with common sense.
Finally, it should also be noted that while energy efficiency is desirable, it is not a panacea. A modern energy efficient building may use more energy over its lifetime than a less efficient building as it may use more energy for its construction and maintenance of both its fabric and its equipment. It should not be assumed that a new energy-efficient building is always the best option. Improving energy efficiency in historic properties is possible, feasible and sensible. Carrying out upgrades in phases is often useful, as it allows actual energy gains from passive energy-saving measures, and least-cost retro-fitting to be achieved by the property owner without vast expense, and without damage to the building.