Use a straightedge and a utility knife to slice through the insulation then snap the board along the cut line to get a.
How to insulate concrete walls with foam board.
The insulation may be rigid board extruded or expanded polystyrene or polyisocyanurate closed cell spray polyurethane foam cellular glass fibrous batt or fibrous blown in insulation note however that fibrous insulation is susceptible to moisture.
Lay a panel of polystyrene.
Now as you glue the panels to the exposed concrete blocks leave a inch gap at the floor and ceiling and cut holes in the panels to fit around outlets and wall switches.
Interior insulation refers to insulation applied to the interior side of the concrete masonry as shown in figure 1.
After the adhesive cures add extension boxes to the outlets and switches and spray foam into every gap top bottom and around each box.
After that thin furring strips are installed on top of the foam to provide a firm base for the drywall screws and drywall.
The concrete should be dry and free from cracks before installing foam insulation boards.
If necessary address moisture problems and seal cracks before you begin.
Cut each sheet of rigid foam insulation to fit the crawl space wall height.