Walls
Most British housing is brick-built but not all walls are created equal. Construction methods have improved massively over the last century. Especially if you have a pre-1920s home, insulating your walls could be the most effective way to reduce your heating bills.
During the Victorian era fuel was plentiful and cheap, with coal being burnt in fireplaces for heat. Concepts such as global warming hadn't been conceived of, so insulation was a lesser concern. Smoke from the fireplaces meant that high levels of ventilation were required to maintain air quality.
Until around 1920 homes were usually built with a solid “single leaf” external wall. If you have single-leaf brick walls they will be approximately 225mm thick (you can measure at a window opening). Single leaf brick walls are particularly bad at keeping in heat and are an obvious candidate for insulation projects.
Solid brick walls were ubiquitous in British housing until around 1920. Walls like this have very poor insulating properties and adding wall insulation should be a priority. The hallmark of a solid brick wall is the presence of the smaller end faces of the “header” bricks.
Throughout the 20th century wall construction evolved, with cavity walls replacing solid walls from the 1920s. Cavity walls feature two “leaves” of brickwork with a gap between. This arrangement provides better insulating properties as well as reducing the risk of dampness reaching the inside of the home. If you have a cavity wall it will typically be 270 to 300mm thick and you will usually only see the long faces of the bricks (although some early cavity walls were built with bricks cut in half to give the same appearance as a solid wall). Depending on the age it may be built with both leaves in traditional clay bricks, or more recently with concrete blockwork for the inner leaf (which is hidden from view by plastering).
Early cavity wall typical of 20th century construction. There is a gap of up to 100mm between the two ‘leaves’ of brickwork. The insulating performance is better than the solid wall above, but is still poor. Cavity walls like this can easily be upgraded by blowing insulation into the gap - for more information see our page on Wall Insulation
Since 1995 Building Regulations have required that cavity walls are “filled” meaning that insulation is inserted in the gap to improve energy efficiency. If your home was built this recently it’s likely that it is already well-insulated, although the performance will be dependent on the quality of the construction as well as the age. Sloppy building practices such as not ensuring a tight fit between insulation boards can significantly reduce their effectiveness. The use of metal wall ties can also cause thermal bridging which reduces the effectiveness of the insulation layer.
Modern high-performance cavity wall with outer leaf of clay bricks, inner leaf of concrete blocks, and insulation between. A wall like this will achieve a U-value of around 0.3 - ten times better at retaining heat than the solid wall above.
Walls can be insulated by filling an empty cavity, or by attaching insulation to either the interior or exterior face of the wall. For more information refer to our section on Wall Insulation.