Insulating an old House
We all know that energy efficient systems and improved thermal performance in old houses will save on running costs, maintain comfort and reduce CO² emissions —and if you are able to achieve this by using materials that are ecologically friendly, you will be making an additional positive contribution.
However, adding insulation to old houses can often be extremely tricky, particularly where the walls are concerned. Modern materials and techniques can often be incompatible with traditional construction and the use of the wrong insulating materials could well cause serious harm to the building fabric. Most modern houses are built from hard, strong materials. To exclude moisture they rely on physical barriers such as damp-proof courses and membranes, cavity walls and cladding. Historic and traditional houses are completely different. Many have solid walls, and most have porous fabric, which both absorbs and readily allows the evaporation of moisture. This is often known as the ability of the building fabric to ‘breathe’. A more technical term for it is vapour permeability.
Wall insulation can be achieved by using a variety of materials including wood fibreboard, phenolic or urethane board, sheep’s wool, mineral fibre, newspaper, cork or hemp, or a hemp and lime mix. All these materials have their own advantages and disadvantages. Wood fibreboard is popular at present because it is entirely vapour permeable. The material – some systems are tongue-and-groove and others butt-jointed – is first screwed into position against the external wall, before being lime rendered and then color washed.
These boards have good sound-insulation properties as well as being able to achieve a U-value of 0.27. If you want to use entirely natural materials, it is possible to use one of the hemp or sheep’s wool-based breathable insulation products. These can be used externally by being attached to the wall and held in place by a wood fibreboard, which is again finished with a lime render and limewash.