Leaving a Slab Edge Un-insulated is like Leaving a Window Open


Climate zones

Improving the energy efficiency of a structure’s building envelop doesn’t end with the walls, windows and attic.  The foundation of a home whether a basement, crawl space or slab on grade needs to be insulated as well.

The International Energy Conservation Code (IECC) requires slab edge insulation and 36 states have adopted this IECC standard. The IECC code requires R-10 at the slab edge.  The requirement runs from the Canadian border (and Alaska) south, covering Climate Zones 4 and above. In California Title 24 mandates insulated edges for radiant slabs even if in Zones 1, 2, and 3, which predominate in the state.

As we have seen over the past 20 years, there has been a move to improve energy efficiency in all parts of the building envelop.  This is evidenced by the move to 2 x 6 wall construction to increase the amount of insulation in walls, the recommendation for increased amounts of attic insulation, and increased use of energy efficient windows.

Slabs have a stem wall that is similar to a foundation wall but without a basement. 60% of heat loss from the foundation occurs in the top eight inches of the un-insulated stem wall/slab edge; insulating these eight inches results in a tremendous amount of energy savings.

If your home is built on an un-insulated slab, the first 10 feet of floor from the slab edge will conduct cold because concrete has little R value (it takes 10 feet of concrete to achieve an R-10 insulation value).  Considering the overall footprint of an average home is approximately 25’ x 50’ there is a significant amount of first floor area that will remain chilled.  In fact, a properly insulated slab edge is estimated to save at least $200 a year in energy costs in addition to increasing comfort in the living space. 

There are products designed to insulate the slab edge for both current and new construction. For retrofit applications EnergyFlash® protects insulation that can be adhered to the slab edge and provides a durable decorative finish.  For new construction, EnergyEdge® forms and insulates the slab at the same time.  It provides the required R-10 value for slab on grade construction and is a great product for the contractor because once done pouring the slab no return trip to the job site is required to strip forms; also eliminated is the disposal of old wooden forms.  The builder benefits by eliminating the additional cost to insulate the slab after the pour.  

EnergyEdge saves time, money and energy. 


  1. I really regret why I didn’t immediately worked on my home’s insulation. You can really save a lot by having your home a properly insulated. You’re AC works less to keep a room cool if hot air can leak into your house.

  2. Pingback: Insulating the foundation for radiant heat « Raising Modern

Leave A Reply