R-value (insulation) contain no trapped CFCs or HFCs (e.g., half-pound low density foams). On certain brands, twenty-year tests have shown no shrinkage or reduction in insulating value. This has led to controversy as how to rate the insulation of these products. Many manufacturers will rate the R-value at the time of manufacture; critics argue that a more fair assessment would be its settled value. The foam industry adopted the LTTR (Long-Term Thermal Resistance) method, which rates the R-value based on a 15-year weighted average. However, the LTTR effectively provides only an eight-year aged R-value, short in the scale of a building that
American College of the Building Arts also specialized courses in drawing, design, materials science and construction management. ACBA maintains a low student-to-faculty ratio to ensure the highest standards of quality in its programs. The Byrne-Diderot Library is a major research resource for students and faculty. The library houses a specialized collection of books, periodicals, newspapers and audiovisual materials in the building, visual, decorative and liberal arts. The library's main collection contains over 6.500 items. The D.A.R. Special Collections room contains another 500 rare books, catalogs and periodicals, as well as examples of historical tools and 19th century Charleston iron work. American College of the Building Arts