Study Shows Exterior Foundation Insulation Preferred.
Exterior basement insulation can play a number of roles within the basement envelope system (see Text Box 2). Since heat-loss control and ground-water management are the critical roles that any exterior insulation must play, both were assessed in the IRC study. Heat-loss control is dependent on many factors, including how well the basement wall system manages water (i.e., keeps moisture out of the wall system). The water-management capability of the insulation is related to the overall watermanagement strategy for the basement envelope system (see Figure 1). The diversion of ground water away from the basement is the primary means of controlling the quantity of water that the below-grade wall has to deal with. Surface-water control is seldom perfect, however, hence the basement envelope system must be designed to keep out any rain and melt water that finds its way below grade.
The most effective strategy for managing water is to provide two lines of defence. When exterior basement insulation is used, the first line of defence is the exterior surface of the insulation, which supplies a continuous means of managing water from the ground surface down to the gravel and drainpipe at the footing. The second line of defence is the outer face of the foundation (cast-in-place concrete, concrete block, or wood sheathing in a permanent wood foundation), which can handle the incidental quantities of water that may get by the first line of defence. Prior to this study, designers and builders had little factual information about how the insulations they specified would perform when placed on the outside of a basement wall in contact with the earth. But IRC’s continuous monitoring of the thermal performance of 13 different basement insulation systems throughout two heating seasons has provided some answers, including some understanding of how these systems manage water. The insulation systems were placed side by side on the exterior of two of the basement walls of IRC’s Test House #1 (see Figure 4). Thermal Performance The key finding from the study is that all of the insulation products provided sustained thermal performance over two full heating seasons, with each of the specimens showing only small variations from its average value (Figure 5 shows the R-value for a typical specimen).
Study Shows ICF industry has propagated a few myths, exaggerations and misstatements for many years.
“ICF’s are R-52 insulation value”. Not even close. The tested R-value of a typical ICF with 2.5” of EPS foam on each face is in the neighborhood of R-22. That’s because lab tests rate the individual components, not the wall assembly. The “R-52” statement is a spinoff of a study performed on several wall assemblies in different locations across North America comparing the field performance of ICF homes with that of typical wood frame construction.
“You don’t need to vibrate concrete….” Unless you use a self consolidating concrete mix design, concrete should always be vibrated to remove trapped air, and ensure consolidation. Studies at PCA have shown that internal vibration is the surest way to eliminate voids and honeycombing. It’s true that certain mix designs can forego internal vibration, however, few ICF installers are equipped to accurately do this. The discussion of whether or not to vibrate concrete mixes should be left to the structural engineer involved in the project.
“ICF’s are termite resistant”. EPS foam that is not specifically treated to repel termites are not “resistant” to tunneling termites. True, the concrete core within the ICF is “termite resistant”, but termites have been known to enter ICF structures and cause damage. While it’s true that EPS provides no food value for termites, they will tunnel through it searching for food and a place to live. And termites can find a way through a cold joint or other penetration that is not sealed. The only statement that should be made here is that the termites won’t eat the concrete, which is the structural element within the ICF. However, they could tunnel through the foam, and may get to wood trusses or floor systems.
“ICF walls won’t burn”. Composite cement-EPS blocks such as Rastra and Apex are fireproof, but traditional foam forms are still considered combustible construction. That’s because at about 1300º F, the fire retardant in the EPS boils away and the foam becomes fuel to the fire. ICFs need a fire-rated sheathing.
Study Shows that any insulation beyond R34 is not worth the Investment.
Most people imagine that the value of insulation is linear, so that, for example, doubling the R-value will double the amount of energy saved. The physics of the situation is quite different. While R is the measure of resistance to heat transfer for a product of a given thickness, the U-factor is the measure of overall heat transfer, and its value is the inverse of R. As a result, the conductive heat flow reduction achieved by adding insulation to the assembly increases at a decreasing rate. As Figure 1 indicates, 96 percent of all possible heat flow reduction is achieved at R 25. After that, as more and more insulation is added, the reductions will slowly, and at a decreasing rate, approach, but never reach, 100 percent. To illustrate, if you double the insulation to R 50, the heat flow is further reduced by only 2 percent. If you double it again, to R 100, the further reduction is only 1 percent more than R 50. So for the addition of four times the amount of insulation, the heat transfer reduction improves by only 3 percent.
Excessive insulation is often applied to or within the roof structure, largely because the deeper framing in the roof or attic floor accepts more depth of insulation fill, and on the mistaken belief that it will be more effective because “hot air rises.” Heat transfers in all directions from higher to lower temperature, seeking equilibrium (Second Law of Thermodynamics). The greater the difference in temperature (?t) between the two objects, the greater the flow of heat. Hot air rises in relation to cooler air, which, being denser, displaces it (Archimedes’ Principle). In a well-insulated, relatively airtight structure with modern environmental control systems, this stratification is largely absent.
Canada Housing & Mortgage Corp Study Shows that ICF isn't worth the added costs.
CMHC commissioned this study to update the economic assessment of residential basement insulation options to more accurately reflect the rising costs of basement construction and space-heating energy. An ICF basement adds over 35% extra cost to the installation, but only delivers a mere $10 per year savings on heat. ICF will cost you over $7500 additional lifecycle cost.