In the United States we measure the effectiveness of insulating materials with the R-value. Technically this is known as the Coefficient of Thermal Resistance, measuring the resistance of a given material to the flow of heat, so a higher R-value number is better. According to the 'Zeroth' Law of Thermodynamics, if there is a difference in energy between two systems, there will be a net exchange of energy between them unless or until they are in thermal equilibrium. And only heat energy can move; there is no such thing as 'coldth'... there is only the absence of heat.
In Europe it is customary to measure the effectiveness of insulating materials using the U-value, which is simply the reciprocal (inverse) of R-value, so a lower U-value number is better. However a European U-value number for a product is not directly translatable to American R-values because we use different measurement units. To convert an American R-value into a European U-value, divide 1 by the R-value, then multiply the result by 5.682. To convert a European U-value to an American R-value, multiply by 0.176, then divide 1 by the result.The Difficulty With R-value
For example, in a study done by the TNO University in Summer ’97, two identical houses in Delft, Holland were insulated to the same rated R-27 value, but with a different density of insulating materials. One had fiberglass of 1.25 lb/ft3 density and the other had cellulose of 4.37 lb/ft3 density. As the outdoor temperature fluctuated by 30 degrees during testing, TNO's measurements showed considerable differences in response between the houses. Whereas the house with fiberglass insulation had its indoor temperature vary by an average of 13 degrees, the house insulated with cellulose insulation varied only 3 degrees during the testing period. This illustrates the benefit of using insulation that has 'thermal mass', i.e. the ability to moderate daily temperature fluctuations.
The actual test for R-value simply places a burner under the insulating material in ideal conditions, to measure simply resistance to heat flow, with no consideration given to other aspects of thermal isolation. So traditional R-value is inadequate to convey attributes such as thermal mass, thermal storage, prevention of air passage and convection. As shown by this study and others, houses with denser insulation have much better temperature isolation (slower heat loss) over time than those insulated with fiberglass and other low-mass materials.
This means that if you insulate to R-38 with heavier insulation materials you get better results, and if with concrete+EPS foam, the best possible. A structure insulated with Insulated Concrete Forms provides a superior result because it is much denser than cellulose or fiberglass, plus we combine it with the insulative resistance of foam, for multiple-aspect thermal isolation. And to insulate the attic rafters with Air-Krete, seals and completes the envelope.
Advanced construction materials and methods like Insulated Concrete Forms give an optimal mix of thermal resistance (foam), thermal inertia (concrete), and ultra-tight sealing to set a new standard of low energy consumption, and provide a safe, quiet, and comfortable environment year-round.Thermal Protection in Summer
If Summer heat under the roof is not taken into consideration during design stages, the interior climate will experience much greater heat swings. This can create an uncomfortable living environment, so dealing with the problem of heat generated under-roof should be integral to the design and planning of any project.Facts
Summer overheating effects can be reduced by controlling the gains of solar energy. A larger roof overhang ensures that the windows are kept shaded from the Sun when it is high in the sky. And in Winter the Sun is low in the sky, so its rays can enter the house interior directly.
A similar effect can be had with shading from roller blinds or shutters, awnings or climbing plants, which do not shade the window area in Winter. And the use of heat retaining interior construction components such as concrete floors and Trombe walls also reduce the degree of overheating.Design
Intelligent architecture means limiting heat that reaches the interior of the house. Facades and roof surfaces that stand out from the house or are ventilated underneath, draw off so much heat that even with conventional construction, interior wall surfaces remain markedly cooler than for example, a composite insulation system with the same R-value.
Here's an excellent Building Sciences article about air gaps and the value of drainage planes. Bottom line is that behind any stucco, HardiPlank, or stone veneer should be a vapor barrier or house wrap, even with ICF. Recent claims against the Hardie company illustrate the need for an air gap to allow for condensation.
As with thermal and moisture protection during the Winter, the air-tightness of components and their construction is of great significance:
Similar to the R-value in Winter, roofs and walls can similarly be assessed in Summer. The decisive parameters here are Amplitude Suppression and Phase Displacement.
Amplitude Suppression is the relationship between external temperature variation and interior temperature variation. For example, if the external temperature variation is 80°F and the interior temperature variation 8°F, the value of the Amplitude Suppression is 10. (80°/8°)
In other words:
The Phase Displacement is the time span between the highest external temperature and the highest interior temperature – in the above example, 12 hours (between 2:00pm and 2:00am). And so 12 hours in this case is the Phase Displacement.
A key goal of thermal protection in Summer is to retard temperature penetration of a roof or a wall such that the highest temperature of the day only reaches the interior when the outside temperature is so low that the heat can be driven out by ventilation. The target here is a Phase Displacement of 10 to 12 hours, given the outdoor heat cycle of the day, so that a portion of the heat stored in the construction components is then returned to the exterior of the house.
Construction materials most suitable for Summer thermal isolation are materials which exhibit low thermal conductivity, but which also have a high bulk density and high specific thermal storage capacity. We believe that Mineral Foam insulation offers the best combination of thermal resistance and thermal mass, of any insulation choice. This closely mimics the complimentary benefits of ICFs.Especially important: Roof Surfaces
The roof surface, which conducts heat, is rather large in relation to the living area beneath it. A conventional roof is normally protected by insulating material such as fiberglass, which has almost no storage mass; plus fiberglass is notorious for allowing thermal convection currents, a phenomenon which is not accounted for in R-value testing, and which seriously reduces effectiveness. A sealed insulation surface is best to prevent convection currents.
In the attic space the significance of construction methods and materials is somewhat different than walls: The low angle of the roof means that it absorbs more heat than the walls, and so temperatures under an unvented roof covering may reach 150°F. It is important to understand that over time, high roof temperatures with insulation directly below can cause asphaltic roofing materials to age prematurely, so we recommend that an air-gap be installed below the roof surface. There are corregated PVC panels for just this purpose.
In summary, it is especially important that a Phase Displacement of 12 hours is achieved, by using an insulating material that has a high temperature resistivity and a high thermal mass, such as Mineral Foam.
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