The discussion of how and why to insulate a basement always begins with what is required. Most builders and homeowners ultimately are not concerned with what will perform best for the life of the structure. The guidance comes from the International Residential Code (IRC) in section 402.1.1. The case is clear that for most of the country-except areas roughly south of the middle of Tennessee and along the West Coast up to Oregon-a basement must be insulated to an equivalent of R-10 if continuous insulation is used and R-13 if cavity insulation is used. Thus, direction is given for the vast majority of today's basement market.
The myths in this equation are that insulating basements is difficult, expensive, and ineffective. In fact, today's concrete foundation contractors are well equipped to offer a variety of insulation options to suit the builder, homeowner, site conditions, or any other variable that may place limits on the construction of the home. One quick look at the methods for insulating today's modern foundation is all it takes to determine how effective this decision can be on both the aesthetics and the performance of the quality living space that has been added to the home.
Usually insulation choices are based on the position of the insulation in relation to the structural concrete wall. In order to provide continuous insulation-thus meeting the lower R-value requirements-decisions include insulation on the exterior or interior of the foundation wall or even within the foundation wall-also referred to as a sandwich wall. The systems in use today are not at all like the methods that have been used for decades to place insulation against a layer of solid concrete.
No longer is insulation glued or otherwise stuck to a wall, nor is it placed between pieces of wooden furring or studs (this would be considered cavity and require an R-13). Today, rigid insulation that does not absorb moisture and does not break apart, is set into the wall forms prior to the concrete placement. High-tech form tie modifications firmly secure the insulation against either the inside or the outside wall form while concrete is placed into the remaining cavity. The resulting wall has a structural thickness and reinforcement as required for the structural design along with energy code compliant insulation mechanically secured with the structural wall. These systems also provide easy attachment of common wall treatments such as drywall, siding, and masonry to the high-density composite plates securing the insulation to the wall. They maintain equal effectiveness for waterproofing, as today's spray-applied and sheet membrane systems effectively are applied around the foundation-whether they are put on exterior insulation or directly to the concrete wall.
Finally, the decision can be made to provide continuous insulation within the concrete. This method also maintains the R-10 value but results in exposed concrete on both the inside and outside. Structural composite wall ties firmly hold the insulation in the middle of the formed wall. This separates the concrete into two structural layers that work together with the insulation layer to easily create the required load capacity for the weight of the house and the earth forces applied to the sides. The system goes one step further to provide the aesthetics of modern concrete treatments while maintaining current methods for waterproofing.
Rather than defining a difficult condition that the builder must achieve, today's insulation systems define cost-effective and unequaled performance opportunities to enhance new living spaces for the homeowner. For more information on these methods of insulating basements and other features of foundations, visit the Concrete Foundations Association's Web site at www.cfawalls.org.
— Jim Baty, firstname.lastname@example.org, is technical director of the Concrete Foundations Association and the Concrete Homes Council, both in Mt. Vernon, Iowa.