Lightweight Well Insulated Envelope

I have watched the transition in housing construction from solid brickwork, through cavity walls with brick and subsequently thermal block inner skins, the addition of cavity insulation to reduce heat flow to brick veneer with insulated structural timber frames.

Some variation from brick veneer to reverse brick veneer has attempted to bring more thermal mass within the insulation of the external envelope but it is a slow process to what we all know we choose when we want to keep something either hot or cool. A polystyrene esky!

This is the simplest method of maintaining the internal temperature, either hot or cold and creating an environment that needs least energy input. Put a hot or cold brick inside and it will remain the same for many hours without any energy use. The resistance to heat flow, in either direction, means that the energy input to keep the interior at a comfortable temperature is less than in a building envelope that will allow heat to pass through easily. Materials with low resistance allow heat to pass through – R0.5 – a cavity brick wall – and high resistance – R3 – fibreglass insulation in your roof – stop the heat passing through.

Normal thickness masonry veneer cannot stand on its own and needs to be tied to a structural frame. The frame carries the loads above so what is the masonry for? The reason for the change from masonry veneer to reverse masonry veneer has been to increase the internal thermal mass within the insulation of the envelope but still the masonry does not carry the loadings above and the exterior still has to be clad to be weatherproof.

The key here is that the move to well insulated external envelopes in a framed structure does the entire job. We will talk more about masonry internally under THERMAL MASS later.