Here are two definitions used in this article. The “R-value” of a wall or a sheet of insulation is its ability to resist heat flowing through it, due to the reflection of heat radiation and also the conduction through it. It does not indicate how much energy is lost due to air leaking through the wall. Dead air insulation is a space where air is trapped. When heat energy passes through this space, the space provides insulation, because heat is not conducted through air as through solid materials, and because the surfaces on either side of the space effectively resist heat transfer by radiation.
Brick Veneer Walls
Brick veneer walls have one layer of brick covering a framed wall. Presumably all brick homes built in the past 100 years have one layer. Prior to that, many homes had two layers of brick and no wooden framing.
If your walls are brick veneer, do not fill the space behind the bricks with insulation because this drains away water that condenses after contacting cold bricks in winter. In summer, moisture or rain water entering the home through the bricks drains through the gap.
Solid Masonry Walls
If your walls are brick, block or stone with no wooden framing, there are several ways that a do-it-yourselfer can add insulation to the walls.
A. If the tops of the walls are accessible from the attic, there should be a space between the plaster (the inside surface of the walls) and the bricks or blocks. You can pour in vermiculate or perlite insulation balls. If you have block walls you can pour the balls into the walls through the holes in the blocks. If your home is two or three stories, you can only insulate the top story with insulation balls for any of these types of walls.
B. If your walls are brick with no frame, there may be a gap between two walls of brick. This insulates the house and also drains water that seeps in to prevent it from damaging the plaster during a rain. The gap can be filled with liquid foam insulation by an insulation contractor by drilling holes between the bricks of the outer wall and shooting in insulation in liquid form. It is hard to estimate the increase in R-value because the gap that would be filled is dead air insulation, but the increase in R-value will be much less than the R-value of that thickness of insulating foam.
C. If your walls are solid masonry and your climate is very cold, you could install siding with insulation sheathing behind it. Your energy savings would not be enough to justify the cost, but if your walls are unattractive, it could significantly increase the property value of your home. Aluminum siding may be the easiest type to install, and this can be done by handy do-it-yourselfers. Other types are more difficult, and some types should only be installed by “factory-trained” installers. See DIY Wall Insulation for more about different types of siding.
Frame Walls with No Insulation
To check if your walls have insulation, touch the walls on a very cold or very hot day. If they feel cold or hot they are not insulated. To be certain, remove a switch plate cover and look in the wall using a flashlight.
If you have frame walls with no insulation, as a do-it-yourselfer, you could fill the walls with loose fill cellulose insulation, which is made from shredded paper, treated with fire retardant. A do-it-yourselfer could also fill frame walls with loose fill mineral wool insulation. This is made from rock or slag. The only other option is to hire a contractor to spray in foam insulation.
Three Types of Insulation Used to Fill Walls
Type 1. Loose fill cellulose insulation is made from shredded paper, treated with fire retardant. Blowing it in can be a do-it-yourself project if you can rent a blower. The only part of the project that some homeowners could not do is repairing the 3” diameter holes in the wall that they would cut to blow in the insulation, but you could hire a painter for this. You can rent a cellulose insulation blower from a hardware store or rental store and buy the insulation at a home center.
Frame walls with wood siding and no insulation behind the siding (insulation sheathing) and no insulation in the walls typically have an R-value of about R-5 or R-6. If filled with loose fill cellulose insulation they are typically about R-11 or R-12, which is similar to walls with fiberglass batt insulation, which is in almost all homes built for many decades.
To put in loose fill cellulose insulation, cut one or two 3” diameter holes every 16” horizontally, stick the tube into each hole and blow in the cellulose. Watch a DIY video on insulating your walls with loose fill cellulose insulation.
Loose fill cellulose insulation has several problems. In very cold climates, filling the walls with any type of loose fill insulation could cause the walls to become damp inside from condensation because warm air escaping through the inner walls condenses when it contacts cold outer walls. This is because a vapor barrier cannot be inserted into the walls, which is done when walls are built. Another problem with loose fill cellulose insulation is that some fire retardants which have been used lost some of their effectiveness over the years.
Type 2. Mineral wool loose fill insulation is made from rock or slag. It is used because it is more fire-resistant than cellulose. It is much less popular than loose fill cellulose, presumably because it is more expensive and has a lower R-value. It can be put in by a do-it-yourselfer using the same equipment and methods as loose fill cellulose.
Type 3. Foam insulation can be sprayed in by an insulation contractor. It is recommended in very cold climates, because air cannot pass through it and condense to leave vapor in the walls. It is very expensive, and is only cost-effective in very cold climates. The contractor drills one or two small holes every 16” and sprays in the insulation
How to Insulate Wood Siding in Poor Condition
If you have wood siding that is making your home unsightly, you could lower your utility bills by covering it or replacing it with attractive insulating siding. This can be a do-it yourself project if you use aluminum siding. Other types are harder to install, and some types cannot be installed by do-it-yourselfers.
Insulating siding can be either aluminum siding with foam insulation bonded to it, or siding installed over insulation sheathing. If you install new siding over old siding, air trapped between the two will be “dead air insulation, which adds much insulation value if the siding behind it is fairly air-tight.
Removing and replacing your wood siding allows you to use thick, high R-value rigid foam insulation sheathing. The best is 1” thick and made of polyisocyanurate, with a reflective surface on one side to reflect heat. Removing your siding to install thinner, less expensive insulation sheathing may give you no better than covering over the old siding if the old siding is clapboard, because clapboard has air spaces in front of it when covered by insulation sheathing.
If you are installing new siding over the old, use 3/8” rigid foam insulated “fanfold” underlayment insulation, with a reflective surface, because this is the thickest available.
Lower Your Energy Bills 