Can any building be made energy efficient? This is one of the most common questions I am asked. Here are a few tips when assessing a building for a low energy renovation.
1. The form (ie: shape) of the building matters
One of the first steps when assessing a building for a low energy renovation is to understand how efficient the form of the building is. Generally speaking, the more compact the building, the more cost efficient and easier it will be to carry out a low energy renovation.
Compact building types include terraced/semi-detached homes and apartment buildings.
Less compact buildings include bungalows and small detached homes.
A good exercise to carry out is a heat loss form factor calculation. New Zealand based architect Elrond Burrell has a great explanation of this here.
2. Orientation (ie: the way the building faces) is important
Low energy and Passivhaus buildings heavily rely on the sun for heat in lieu of a heating system. In the northern hemisphere, an ideally orientated building will have a façade facing south that can accommodate a reasonable amount of glazing. This bank of glazing can then be used to heat the building in the winter.
Highly insulated buildings have a greater risk of overheating in summer. To mitigate this, the façade can be shaded using external fins (known as brise soleil), shutters, fabrics (ie: awnings or sails) or vegetation. Shading could be mounted onto the building or situated close by.
It is straight forward to shade glazing that is south facing because the azimuth and altitude of the sun is relatively stable during the summer months.
By contrast, because the sun rises and sets at a broad range of points along the horizon throughout the year, east/west facing glazing is harder to shade.
3. Insulate and Ventilate
Any upgrade in insulation needs to be accompanied by a review of the ventilation strategy. A good ventilation strategy will ensure that the air quality is high and humidity is balanced. Poor ventilation can cause dry skin, aggravate allergies and cause mould. A common solution for this is to install a mechanical ventilation system.
4. Retaining the external appearance of the building
If the external appearance needs to be retained, it is possible to internally line the building with insulation. However, this requires great attention to detail, both in the design and construction, to ensure that there is no risk of interstitial condensation (ie: a build-up of moisture between the layers of new and old construction). Some parts of the building fabric may also rely on exposure to air to stay dry. It is essential that the existing characteristics of the building are well understood so that renovation work is compatible.
5. Payback periods
There have been a number of studies into low energy retrofits to check if they pay themselves off in a reasonable period of time. The Passivhaus Trust has a number of useful resources on this topic. Generally speaking, retrofits can take between 12-30 years to pay back. Therefore, if you plan on staying in your home for a relatively short period of time, be sure to seek advice from an estate agent on the value that carrying out renovation works could add to the property.
6. Can any building be made energy efficient? Yes, but at a cost.
The Economist carried out an interesting study into the general cost of upgrading and retrofitting properties in the UK. A link to this study is here. Their conclusion was that a 'deep retrofit' for a typical UK semi-detached home could cost approximately £67,000 excluding any works to enlarge the property (ie: extensions). Detached homes could be significantly more.