A modern cavity wall is a watertight, energy-efficient masonry structure appropriate for external load-bearing walls. About a third of all the heat lost in an uninsulated home escapes through the walls. By building proper insulated cavity walls, you will save energy and save on your heating and air-conditioning bills.
A well-designed and properly constructed cavity wall is completely watertight, airtight and thermally efficient, ensuring that there is minimal heat loss through the walls during winter. If walls are made of a high density masonry material like clay brick – then cavity walls will also help to keep a house cooler during the summer.
Cavity walls offer two key benefits
- They provide excellent insulation from temperature extremes and noise.
- The cavity prevents the dampness from the outer leaf penetrating into the inner leaf.
Cavity walls were originally introduced in the early 1900’s to stop rain seeping through single solid brick walls. No matter how thick the wall or what it is made from, condensation will always be a problem if there is only a single walling layer or “leaf”.
Where does indoor condensation come from?
Think of your favourite ice cold beer! You take it out the fridge and within minutes water is dripping down the outside of the can and pooling on the table. Condensation is a result of cold beer inside the aluminium can or glass bottle, meeting warm air outside the container! Thicker glass slightly delays condensation, but won’t prevent it.
Similarly, you may have noticed that in cold weather, windows mist up on the inside, and form water droplets that run down the window and damage interior paintwork. But glass isn't the only construction material that "sweats".
Any solid, single leaf wall – even one made from thick concrete – will experience condensation. You don’t want that condensation weeping inside your house!
With a cavity wall, condensation still forms, but it gathers in the cavity behind the 1st wall and never reaches the 2nd interior wall. The house remains warm and dry.
DIY Moisture testing
A simple do-it-yourself moisture test that will give you a yes or no answer but not a numerical identifier is to use a piece of aluminium tinfoil or heavy plastic sheeting (preferably, but not necessarily clear) about 30cm square and tape all four sides down with duct tape in the center of the room (away from exterior walls). Wait 36 hours. If you see moisture on the plastic; or the slab is discolored from moisture as compared to the floor around it; then you have a moisture problem.