How To Install Rigid Foam Insulation On Exterior Concrete Walls

Rigid Foam Insulation On Exterior Concrete Walls

Rigid foam insulation is one of the most effective ways of insulating exterior concrete walls. It creates an air seal that keeps your home comfortable and optimizes energy efficiency. In addition, they are easy to install even with novice or intermediate level DIY skills.

Learning how to install rigid foam insulation on exterior concrete walls is easier than it seems. Gather your tools and equipment, prep and measure the exterior wall, cut your rigid foam insulation sheets, and install them.

Read on below for more detailed instructions for each step.  

Steps For Installing Rigid Foam Board On Exterior Walls

Image Source: Bilanol

1. Gather Your Tools And Equipment

You will need the following:

  • Adhesive
  • Drill hammer
  • Concrete fasteners
  • Rigid Foam
  • Hammer
  • Spray Foam
  • Tuck tape
  • Tape measure
  • Sealant
  • Utility knife or jigsaw
  • Worktable

2. Prepare The Concrete Wall

To prepare the concrete wall, dust it off and clean it with water. Let it dry completely. Notice if there are cracks on the wall and seal them.

Apply a moisture barrier once the wall is completely dry, e.g., a cement-based sealant or liquid asphalt. You could also use tar paper as a sealant. Cover the entire wall with the moisture barrier from top to bottom. Allow the sealant to dry fully before proceeding to install the rigid foam.

3. Measure The Wall

Using the tape measure, take the dimensions of the exterior foundation walls and compare them against the dimensions of the rigid insulation. Establish the best layout for the rigid foam board insulation. Determine whether you will need to cut some of the sheets and to what dimensions to fit the exterior wall.

4. Cut The Rigid Foam Sheets

Lay the rigid form board insulation on a worktable or a flat surface. Measure and make cutting lines per the required dimensions. Use a utility knife, circular saw, or a jigsaw to cut through the marked line. If need be, repeat the cut until the foam separates. Set the appropriately-sized foam sheets aside for installation.

5. Install The Rigid Foam

You can install rigid foam insulation on an exterior concrete block wall by either using adhesive or concrete fasteners. The adhesive works best if the walls are flat. However, you can use both mechanisms to reinforce the installation of your wall insulation.

When buying an adhesive, make sure to get one that is specially designed for foam board use. Other types of adhesives may contain chemicals that can react with the foam and corrode it.

Lay the rigid foam on a flat surface with the back facing up. Apply adhesive at the back of the foam. To do so, cut the tip of the adhesive tube and puncture the foil seal at the bottom of the tube nozzle using something sharp. Then, fit the tube into the caulk gun.

Squeeze the nozzle and apply the adhesive lines across the back of the foam sheet. Allow 10-12 inches between the lines and retain a distance of at least 1-inch from the edges of the board.

Hold up the foam sheet with the glued side facing the wall. Position it accordingly, stick it onto the wall. Press it against the wall for 30 seconds to one minute. This gives it ample time to begin to dry, and it can ensure a firm hold.

You can use a drill hammer at different points across the rigid foam. For example, you may drill a hole at each corner and two or three along the centerline. Styrofoam, the leading manufacturer of rigid foam insulation, recommends drilling one ½-inch long hole and using concrete fasteners that are long enough to ensure the sheets are firmly held in place.

Take the concrete fasteners and screw one in at a time in the holes. Then use a hammer to secure them in position. Apply adhesive on top of the nail to seal any spaces between the concrete fasteners and the panel.

When installing the next rigid foam sheet, apply a sealant or spray foam on the edge adjacent to the subsequent sheet. Then, fit it in closely and tightly to ensure there is no gap between the two sheets.

Repeat this installation process for all the rigid forms until the entire exterior concrete wall is fully covered.

6. Seal The Joints

Use tuck tape to seal the overlapping areas. While some people consider applying spray foam on already fitted foam sheets to seal these joints, the spaces are too tight, and the spray foam may not penetrate properly. Therefore, the best option is to lay tuck tape along the length of the joints.

7. Apply Spray Foam To Fill In Any Gaps

While you may have done an excellent job ensuring the foam is tightly fitted, there may be a gap at the top, bottom, or sides. If left unsealed, these gaps will allow water to seep in between the concrete and the insulation panel.

Use a gap and crack filler spray foam to fill in the spaces to ensure that the rigid foam is fully moisture-proof and airtight. This particular type of spray foam expands on application, completely filling up spaces.

8. Apply Paint To The Installed Rigid Foam

This step is optional but can improve the durability of the rigid foam. It can also be used to improve the curb appeal of the exterior walls or match it with the property’s overall aesthetic.

Only use water-based paints, acrylic paints, or latex paint on rigid foam insulation. Styrofoam recommends using water-based paints only on their rigid sheets. Once applied, water-based paint or acrylic paint dries off and provides a water-resistant seal on the foam insulation. Do not use solvent-based or oil-based paints as they contain chemicals that damage the foam.

9. Lay Loose Granules At The Bottom

Place loose granules at the bottom of the foam board panels to encourage water drainage. If there is poor drainage, water will linger near the panels for too long and begin to seep through.


Many energy experts recommend installing exterior insulation to improve energy efficiency in your home, especially if you live in cold areas. Rigid insulation is by far the best option. While you can hire a professional to install them for you, you could also install them by yourself or with a friend’s help. Follow the steps above to learn how to install rigid foam insulation on exterior concrete walls.

Frequently Asked Questions

Below are concise answers to the most common questions regarding installing rigid foam insulation on exterior walls.

Do you need a vapor barrier with rigid foam insulation?

It is not mandatory, but it helps to ensure that your rigid foam insulation is completely waterproof.

Can exterior foam insulation cause mold and moisture problems?

Unlike other insulation materials such as fiberglass, foam insulation is moisture resistant. Thus, it serves as a moisture barrier. As such, exterior foam insulation is not prone to mold and mildew growth.

Are there specific recommendations for the type of rigid foam to use for exterior walls?

Grooved foam insulation sheets are the best insulation option for use on exterior concrete walls. The grooves provide channels for water drainage to the ground on rainy days. In addition, consider rigid foam insulation that is impregnated with boric acid. The boric acid serves the critical purpose of repelling insects and reducing insect damage on the foam.

Go for extruded polystyrene rigid foam for outdoor application. It has a high heat resistance which means it can withstand high temperatures during hotter seasons. Besides, its high compressive strength prevents it from breaking due to pressure or extreme temperature changes.