Energy Efficiency Measures for Older and Traditional Buildings

Introduction

Understanding how any traditional building was designed to work rather than just reaching for the retrofit is essential if we want to ensure or improve its energy efficiency.

Energy efficiency in any building depends on its design, the materials from which it is made, its location, condition and the way it is used. If we are to make a building more energy efficient, then we need to understand all of these factors, taking an holistic approach. Understanding the difference between older and newer buildings is also essential. The former are normally vapour permeable, in that moisture is let in and then evaporates, whereas the latter rely on vapour barriers and air gaps to keep moisture out.

Although solid masonry walls are common in older buildings, there are also many variations between one property and the next. Recognising a building type is also very important: by understanding its design, how it is constructed and the materials from which it is made, we can assess both how it performs and what affects that performance.

RdSAP also generates a recommendation of the works required to improve energy efficiency, and indicates what band could be achieved if these were undertaken.  Moisture is the biggest problem in an older building and, as indicated in BS 7913: 2013: Guide to the Conservation of Historic Buildings, building fabric that is damp could be 30% less energy efficient than dry building fabric. The control of moisture is therefore key to both energy efficiency and sustainability. This is where using building pathology is essential.

Getting an older building into good repair in a way that maintains or reinstate vapour permeability should be prioritised over energy efficiency measures, and it is important to understand that installing elements and materials that are impermeable could have a devastating effect on an older building.

Guidance and its limitations

When it comes to deciding what measures to install, it is important to continue thinking about vapour permeability and its overall effect on the hygrothermal performance of the building. Installing one measure could have consequences for many other different elements and aspects of an older building.

The thermal coherence of the external envelope is particularly important, and thermal bridging should be reduced as much as possible, so insulation should be carefully designed. In some places this will be very difficult: for example, at floor–wall junctions, timber joists bedded into the walls will form a thermal bridge and therefore be susceptible to interstitial condensation. This can be managed, however, provided that the building fabric around the timber joists is vapour permeable and thus allows such moisture to escape.

However, if there is cement mortar pointing or cement render on the exterior then this will inhibit evaporation and possibly put the ends of the joists at risk of becoming rotten. Another risk worth mentioning is that, if internal wall insulation is not carried through into the voids between ceilings and floors, then the whole horizontal strip could act as a thermal bridge and enable moisture to persist, with obvious consequences.

Many different types of insulation materials and products are available, and all have different installation methods. Careful selection is needed, especially when only slender sections can be installed – for example around window reveals – to provide thermal cohesion as much as possible, so materials may have to provide much better thermal performance for their thickness than those in other areas where greater thicknesses are possible.

Conclusion

While a great deal of expert effort can and should go into planning While a great deal of expert effort can and should go into planning and specifying work that will make an older building more energy efficient, this can all be severely compromised if it is not implemented properly. Adherence to BS 7913: 2013 on project management and supervision provides a robust approach, based on managing the risks of specification non-compliance.

Taking an holistic approach to improving the energy efficiency of older buildings need not be complex. It is initially about going back to basics and providing a building with its original performance characteristics so far as possible. It becomes complex and risky when retrofitting, and here again using vapour permeable materials is key. However, it will not be without its risks, and by following BS 7913: 2013 management of these will be more straightforward.