The Importance of Basement Insulation

The Importance of Basement Insulation

The Importance of Basement Insulation

Basements are part of a home, within the building boundary—even those a lot of attempts are made to disconnect them from the living area. Because of this, basements have to be designed and constructed to be dry and conditioned. This is important for basements that contain mechanical equipment—so they won’t get damaged from the moisture. A dry basement or crawlspace is less likely to have pests and termites and that’s a big relief. If you are planning to use the basement for storage or as living space, it needs to be kept dry to avoid mold and dust mites. Basements should be insulated on their perimeters—they should not be insulated between floors.


Basement walls are the best thing to insulate in a home. It should be insulated with non-water sensitive insulation that prevents interior air from contacting cold basement surfaces. Allowing interior air (that is usually full of moisture, especially in the summer) to touch cold surfaces will lead to condensation and mold.  


Basement floor slabs are best insulated underneath with rigid insulation: both extruded or expanded polystyrene are a success. Although the energy savings of sub-slab insulation are not as significant as basement wall insulation, it does have a significant improvement in comfort and moisture damage resistance.


Basically, you have two options: insulate your basement ceiling or insulate your basement walls.

Insulating your basement ceiling means the warm air from your interior floors to the basement is slowed down, lowering the temperature and raising your chances of moisture problems or frozen pipes in the winter. You also don’t save nearly as much money on your energy bill as you hope.

The right material for basement insulation.

Rigid foam insulation consists of boards made of solid foam insulation and covered on one side with a radiant barrier. Rigid foam boards are attached to basement walls to seal and insulate the space. By insulating basement walls instead of the basement ceiling, the basement space is brought inside the home’s building envelope. The basement becomes part of the building’s conditioned space, which means that it will be more comfortable. Basement wall insulation also protects hot water lines and HVAC ductwork in the basement from cold winter temperatures that compromise the performance of your hot water and heating systems.

Rigid foam is ideal for the basement environment because of its water resistance and durability. Rigid foam won’t be damaged by leaks or mold, ensuring you have a long lasting solution for your home.

How to Insulate Your Basement?

Step-by-Step Basement Insulation Installation

  1. After the cement is set, apply a foam board adhesive to the rear of a polystyrene insulation panel. Then the second step is to press the panel to the wall.
  2. Next, you should create a wood grid that will hold the drywall in the basement. 
  3. The third step is to use a hammer drill and a 3/16-inch masonry bit, drill 5-inch holes through the 1×3 and into the concrete wall. This acts like a spring that tends to straighten out and anchor the spike into the concrete wall.
  4. Once you have set the horizontal boards, screw vertical 1x3s to the horizontal 1x3s with 1 ⅝-inch drywall screws. This will create a vertical and horizontal gap for any future electrical wiring to be installed. Space the horizontal 1x3s 16 inches on center, and finish installing the vertical boards.
  5. After all these steps your grid is in place, you can install your drywall. For basements, a moisture-resistant green board is best.

Insulate inside or outside?

Insulating on the outside is best, but it is often necessary to insulate from the inside for economical and practical reasons. Sometimes a combination of approaches is required. Examine the advantages of each approach carefully.

Insulating inside

This method will depend on a number of factors, including whether there are moisture issues, the need to account for moisture and air/vapour barriers, how you plan to use the space, and, finally, cost.

Advantages of inside insulation

  • It can be incorporated into a plan to finish the basement.
  • The work can be done at any time of the year and can be done one section at a time. Often all or part can be a do-it-yourself job.
  • It is often easier and cheaper to insulate the full wall and achieve high insulating values.
  • The landscaping and driveway will not be disturbed.

Disadvantages of inside insulation

  • Do not insulate a basement with moisture problems from the inside but if you have to, before taking measures to eliminate the moisture before adding insulation or your new walls will rot.
  • Adding insulation to the inside will make the foundation walls even colder. This means air humidity will get in contact with the walls and lead to mold. 
  • Obstructions such as electrical panels, wiring, plumbing, stairs, and partition walls make the work more difficult and the insulation and air barrier less effective. 

Insulating outside

This involves excavating around the foundation, waterproofing, and installing insulation. 

Advantages of outside insulation

  • The outside wall tends to be more continuous and easier to insulate.
  • You can effectively see and correct any moisture or structural problems (efflorescence, cracks, spalling and eroded mortar). 
  • There is no disruption in the house, no interior work, and no inside space lost.
  • Freeze-thaw stresses are eliminated, and frost is unlikely to penetrate down to the footings.
  • The mass of the foundation is within the insulated portion of the house and will tend to even out temperature fluctuations.

Disadvantages of outside insulation

  • Digging a trench around the house by hand can be difficult and risky.
  • Storing the dirt can be a problem.
  • Excavation cannot be done in winter and can be a problem in the spring.
  • Features such as non-removable steps, paved carports, shrubbery, trees or fences can make the work difficult.
  • Rubble or brick foundations could be partially supported by the soil.
  • It is expensive to obtain high insulation levels, and the retrofit may detract from the appearance of the house.

Why is the insulation of the basement important?

If you insulate your basement in a proper way, it can save you money on heating and have a very comfortable living space. In a lot of cases, a basement with insulation installed on its exterior walls it’s considered a conditioned space. The basement is more connected to other living spaces than to the outside, which makes basement wall insulation preferable to ceiling insulation.

In new construction, adding insulation on the exterior of the basement walls will do the following:

  • Minimize thermal bridging and reduce heat loss through the foundation
  • Protect the damp-proof coating from damage during backfilling
  • Provide some protection against moisture intrusion
  • Make the foundation part of the thermal mass of the conditioned space, thereby reducing interior temperature swings
  • Reduce the potential for condensation on surfaces in the basement
  • Conserve room area, relative to installing insulation on the interior.

In an existing home, adding insulation to the exterior of the basement walls is impractical. Interior basement wall insulation has the following advantages:

  • It is much less expensive to install than exterior insulation for existing buildings.
  • Almost any insulation type can be used.
  • It eliminates the threat of insect infestation.
  • No more cold floors in the winter
  • Greater indoor temperature stability
  • Reduced “stack effect”
  • Lower heating & cooling costs
  • Fewer indoor drafts

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