Solid walls can be insulated if you use the right materials. Using solid foam insulation, you can insulate any type of solid wall, such as the most common type, the concrete wall. Concrete walls do not provide the best insulation from cold, so adding a layer of foam insulation will increase heat retention and save energy. You can find these foam insulation boards at Home Depot or Lowes. They are rated for efficiency and heat retention. For instance, the typical R-18 boards are generally suited for moderate to cold climates, where temperatures reach as low as -17.8 degrees Carenheit in the winter.
Measure the height of the wall, then cut several lengths of 1-inch-thick by 2-inch-wide slatting boards to the height of the wall using a table saw or chop saw.
Place one slatting board along the edge of the wall. Use a level to ensure the slatting board is perfectly vertical. Then place a hammer gun with nail cartridge against the slatting board. Strike the head of the hammer gun with a mallet and drive the nail through the slatting board and into the concrete wall.
Measure the width of the insulation boards. Then install the next slatting board in the same manner as you did in step 2, so it is spaced this distance apart and the insulation board can fit in between the two slats. Continue to do this until the entire wall is slatted.
Lay one insulation board on a table face down, then apply a bead of concrete adhesive to the back. This bead should extend from one side to the other in a "z" pattern and be a continuous 1/4-inch-thick bead, and most important, there should be less than 6 inches of space on either side of the bead.
Set the insulation board between the first two slats so it covers the wall completely. Then repeat step 4 and five for each section of slatting. When you come to a corner, simply set the insulation board flush against the wall, then lay the next board on the adjoining wall flush against the surface of the insualtion board so they overlap.