Energy Efficiency in Heritage Buildings

On 8 April I attended a talk by Daniel Ayre, from BDBC’s planning department, on energy efficiency in Historic Buildings.  Here’s my take on what he had to say.

Many of the houses in Silchester are in the Conservation Area, or are historic or notable buildings, and they require some different energy efficiency measures from more modern buildings.  Historic buildings work differently from modern buildings.  Modern buildings are “sealed units” whereas  historic buildings “breath”, letting moisture and air in at night and out during the day.  Any change to this can disrupt the function of the building and cause problems. For example, there may be condensation on the windows in the morning.  However, if you change the windows and stop the condensation, then you have to consider where  the moisture is going instead.  It may be somewhere less easy to deal with.   Similarly any wall insulation that stops the building breathing is likely to do more harm than good.

Although when we talk about energy efficiency, we are usually thinking about heating and electricity, Daniel observed that for buildings there are actually three sorts of energy that we should consider:

  • Embodied Energy – the energy of construction locked up in the building
  • Operational Energy – heating, lighting etc
  • Demolition Energy – the cost of disposal

A historic building has a lot of embodied energy, stored in some cases for hundreds of years and it is not necessarily energy efficient to demolish that to make small savings in operational energy.  For this reason, as well as the need to conserve the character of the area, the council will often recommend repair to existing structures rather than replacement.   Thinking again about the windows: many people think that energy efficiency requires moving to modern double-glazed windows.  This is possibly true if the existing windows are beyond repair (say, more than 55% of the frames would need replacement), but the energy in constructing a modern double glazed window in a factory far outweighs the cost of a local joiner building a replacement single-glazed unit.  And, when it fails, a double glazed window will need replacing in it’s entirety using yet more energy, a single-glazed pane of glass can be replaced.

 Energy efficiency measures that you might consider include:

  • keep the building in a good state of repair, and prevent draughts
  • repair what you have, rather than replacing with new
  • breathable insulation in the loft
  • secondary glazing
  • consider a heat pump, the steady heat can be better for a historic building than the heat-cool cycle of existing heating systems

Finally, historic buildings are often inherently more energy efficient than they appear, staying warmer in winter and cooler in summer than some modern properties.  So if you are lucky enough to have a historic property, enjoy it!