Frequently Asked Questions about the ASTEC Systems

3. What is the k-value or the R-value of ASTEC and how do these values compare with mass insulation?

The R-value is the measure of the resistance of a material to heat flow (or heat gain) by conduction only. The k-value is the measure of thermal conductivity; it measures the rate of heat transfer by conduction through a material from face to face.

The R-value is always the reciprocal of the k-value. For instance, R = L/k and k = L/R where,
R = thermal resistance,
L = thickness,
k = thermal conductivity;
R-19 means 19 hr ft² ˚F / Btu or 3.34 m² ˚C/W.

ASTEC's thermal conductivity (k-value) is very low (0.00345 W/m °K or 0.00199 Btu/h ft °F). A very low k-value indicates a good conductive insulator. But the R-value depends on thickness and the thickness (L) of ASTEC is so small that the resistance (R-value) is not given serious consideration. What really counts in preventing heat transfer is solar reflectivity. R-value (resistance) is only valid when "managing" heat which has already transferred.

To compare ASTEC's thermal resistance (R-value) to the thermal resistance of polystyrene or of fiberglass, is to compare materials acting on different heat transfer modes (radiation vs. conduction). There is no common ground between radiation and conduction except the calculation of the end results (actual heat transfer) in terms of W/m2 or Btu/hr/ft2.

The reflectivity and emissivity of most roof surfaces is extremely low (less than 0.20) when compared with ASTEC's high solar reflectivity (p-value: 0.85) and thermal emissivity (ε-value: 0.9).

Therefore, to avoid heat transfer, the best way is to reflect radiant heat (stop the heat from coming in the roof to begin with) and to quickly emit any radiation that is absorbed. In dealing with radiation, thickness has no useful value and R-values or k-values are not useful anymore. High reflectivity and emissivity become important.

If, on the other hand, you don't effectively deal with heat transfer by radiation, you will then be stuck and forced to deal with heat transfer by conduction once heat penetrates the roof; then, R-value which is directly proportional to thickness, becomes an important factor.

The comparison of a structure with ASTEC's roofing system purely on the basis of conduction factors (thickness, k-value, density, heat resistance) is counter-productive. Such a comparison does not do justice to the end-users.

In conclusion, there is no acceptable direct comparison between the prevention of heat transfer by radiation and the subsequent management of heat transfer by conduction. A better alternative may be to determine when a total system like ASTEC is superior to mass insulation and when both systems may be complementary.

If the roof heat transfers are the only valid points of comparison, let's look at three types of roofs with the ASTEC system and without the ASTEC system on a clear, summer, noon-time condition with:

1) No insulation;
2) One (1") inch (2.5 cm) of mass insulation; and
3) One (1") inch (2.5 cm) of mass insulation and gypsum board covering.

Thus, ASTEC reduces the roof heat transfer by more than 70% over the uncoated roof for all three roof types.

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