There is a strong argument that a cavity wall without insulation is only half a wall. The function of a wall is to keep the weather out which does not just mean the rain, but the cold as well. An increasingly important function of a wall is to keep the heat on the right side: inside in winter and outside in summer. Which means installing insulation, and in the right way.
Getting cavity wall insulation (CWI) wrong can be a disaster and expensive as, being inside a wall, it can be very difficult to access. But there are only two fundamental issues to getting CWI right:
1 Use the right amount and type of insulation. The majority of expense is in the work involved in installing it, not in the material itself.
Install it with the same care and attention to detail that would