Improving cavity wall insulation in older homes can be rewarding... or not.
If the cavities have been left unfilled or with low levels of insulation, filling them with insulation can be a way of improving comfort.
But not always. There are many cases where the best choice is... to left the walls uninsulated. Insulating, or improving the insulation levels of walls with moisture, or where it can be a problem, is an error.
Local contractors can provide advice, but they may not be informed enough. Consider hiring a consultant before installing any insulation.
Improving wall Cavity insulation with cellulose or Fiberglass fibers (Wood frame Walls)
Cellulose (or fiberglass loose-fill fibers) is an inexpensive way of improving cavity walls performance, in wood-frame homes.
You can buy some bags of cellulose at a specialty store, and rent a machine, and drill holes in the top and bottom of each wall cavity, and blow the insulation material into the cavity.
You will not achieve excellency, far from it. You will not be able to control the density of the insulation material; density will probably be uneven and spotty. But that’s inexpensive and a way of improving the energy-performance of the walls of old buildings without moisture problems.
You can also hire a contractor, to install dense-packed cellulose or fiberglass fibers.
Contractors have special machines, to control the density of the materials they install and their airtightness, and the walls will perform better, but it will be a lot more expensive.
Improving wall cavity insulation with sprayed foams
It's possible and advantageous to install spray foams in wall cavities of existing homes, including masonry and brick walls.
The spray is injected into the wall cavity, where it will expand and cover all the space available, providing airtightness and a higher R-value.
It’s a great choice when the insulation is installed correctly, though often expensive.
This "method" requires experienced contractors to avoid shrinkage and poor results.
When not to insulate wall cavities
Be aware. Do not insulate walls with moisture issues (cellulose is very moisture sensitive), or where moisture can occur. Do not install fiberglass in brick walls. Use insulation foams in masonry walls.
The insulation of the cavity wall drainage is also a very risky choice. The last thing you should want is to prevent the walls from draining and drying.
Choosing A Contractor
Retrofit cavity wall insulation with dense packed cellulose (or fiberglass) and sprayed foams is a professional job. It requires proper equipment, knowledge and experience. If your are looking for contractors, see:
USA and Canada:
Home Energy Rater (to find contractors in your area), or a member of the Insulation Contractors Association of America
The National Insulation Association (NIA), The Cavity Insulation Guarantee Agency (CIGA), The British Board of Agreement (BBA)
The Thermal Insulation Contractors Association