Upgrading an existing house, rather than starting from scratch and building a new one is usually considerably more difficult for three main reasons
- historical building technologies may not lend themselves well to upgrading, especially around insulation and air tightness
- obtaining building materials which match existing ones may prove difficult
- there may be planning restrictions on what you can do, e.g. with listed buildings or conservation areas.
Given that the rate of replacement of old buildings with new ones is very slow then the challenge of upgrading the older ones becomes paramount. Leading the field at the moment are countries like Sweden, Germany, Austria and Switzerland where the Passivhaus standard is starting to be applied to existing buildings, including buildings of historic importance.
Here are some points to consider if you are dealing with a retrofit situation
- Possible standard to aim for
- Potential to make major improvements to the design
- Air tightness and how to achieve it
- Thermal massthis is about how much heat something can absorb - so it involves its specific heat capacity and its volume. It can be useful for levelling out the peaks and troughs of temperature within a house. See the page on thermal mass may be a quality worth exploiting
- Choice of fuel
- Materials compatibility. Traditional building methods may not be compatible with modern materials. There are several things to look out for.
- lime mortar is softer than cement mortar and allows for a degree of movement.
- traditional timber frame structures may move considerably with the seasons, particularly with changing humidity levels. It is important to allow for this.
- there may be situations where it is important to allow interstitial condensation to escape.
- The potentially tricky relationship of extensions to an existing building
- Potential for energy harvesting
- Potential for water conservation / rainwater harvesting
There is a considerable amount of information about retrofit at the low energy buildings database. These are mainly social housing examples but there’s lots of useful technical information.
Superhomes is a fairly new organisation dedicated to showcasing the best of eco refurbishment. Exemplar houses are open to the public at least one day a year.