What kind of insulation should you use for masonry walls and where should you install it?

ON THE EXTERIOR FACE

Masonry has a lot of thermal mass: it absorbs and stores much more heat than wood, metal, or other materials with little thermal mass. Placing insulation on the exterior face of masonry walls takes advantage of this thermal mass. Rigid foam board insulation, such as polyisocyanurate or expanded or extruded polystyrene, are used on the exterior of walls. The insulation boards are attached with adhesive or with mechanical fasteners.

IN THE CORES

Several types of insulation materials can be placed in the cores of concrete block. They include: granular materials such as perlite or vermiculite that are poured into the cores; preformed polystyrene inserts that are installed in the cores at the block plant or the jobsite; and foam that is pumped or poured into the cores.

IN THE CAVITY

The air space in a cavity wall acts as a layer of insulation. But adding real insulation to the cavity can further increase the thermal resistance of the wall.

ON THE INTERIOR FACE

Rigid foam insulation boards or glass fiber batt insulation can be attached to the interior side of masonry walls with steel or wood furring strips.

THE WALL ITSELF: LIGHTWEIGHT BLOCK

Lightweight concrete block also have insulating properties. Because they're made with lightweight aggregates that contain more air spaces, they conduct heat more slowly than normal or heavyweight block. Such aggregates include expanded shale, clay, and slate; expanded blast-furnace slag; sintered fly ash; coal cinders; pumice and scoria; and plastic beads.