Frequently Asked Questions

FAQs » COMPARISON TO OTHER PRODUCTS

Question: What other roofing products meet the most stringent reflectivity (>0.90) and emissivity (>0.80) benchmarks?

Answer:

No currently commercially available materials have reflectivity >0.90 and emissivity >0.80. Based on the measurements made to date by the various Research Laboratories, white single ply membrane has the highest R (0.85) and E value (0.93).

Question: What about comparisons with BUR, single ply, comp shingles including their color offerings? I heard a lot about comparing bare vs. black vs., white metal roofing. What about comparisons with BUR, single ply, comp shingles including their color offerings?

Answer:

The ORNL study has compared several BUR and membrane roofing materials over a 3-year period. Their report will be published in 2003. Generally speaking, smooth black BUR’s have R of 0.05 and E of 0.90 whereas shiny metals have high R and low E. The Lawrence Berkeley National Laboratory also has a database comparing thermal properties of a variety of roofing products.

Question: Most data presented dealt with coated/uncoated steel. How does aluminum compare?

Answer:

ORNL has not tested unpainted aluminum roofing materials but has measured the performance of bronze (PVDF resin) prepainted aluminum. Data indicate a reflectivity of 0.07 and emissivity of 0.87, however, with prepainted metal roofing, the substrate has no influence on the exterior surface reflectivity and emissivity.

Question: How long can steel roofs last in Florida?

Answer:

Using unpainted AZ55 Galvalume (AZ 165 g/m2) as the roofing material, the anticipated life of a low slope commercial roof in Florida is >25 years. Based on extensive building inspections carried out by the NamZAC Inspection Team, a roof life of 35 – 40 years is expected.

Question: Have traditional roof materials (asphalt, etc,) been compared to cool roof coated metal? How do they compare in similar colors such as light gray, dark gray, brown, black? If good can this be used to sell metal?

Answer:

Typical 25-year gray asphalt shingles have a reflectivity of 0.09 and emissivity of 0.91, while white prepainted steel has a reflectivity of 0.64 and emissivity of 0.83. Gray standard paint would typically have reflectivity values from about 0.30 for a light gray to about 0.10 for a dark charcoal gray. These values can be increased to around 0.45 and 0.25 respectively by using IR reflective pigments. The emissivity of these metal painted systems would be in the 0.8 to 0.9 range; the same as all painted metal.

Question: Regarding requirements for Chicago, which roofing materials meet them?

Answer:

Based on the 2002 draft of the cool roof requirements for the City of Chicago, no unpainted metal roofing material can meet the minimum benchmark. Painted metal can meet the requirements since the paint film is considered the exterior surface of that product. In moderate and cold climates, emissivity has a very much-reduced effect on heating and cooling energy loads. The use of roof insulation is much more effective in these climates.

Question: In the ORNL study, it would be useful to have comparisons between metal and competitive roofing materials.

Answer:

The Oak Ridge National Laboratory study has done exactly that. Over 50 roofing materials in several colors and material types have been evaluated over a 3-year period. Of the fifty materials, 11 are metal roofing systems; the others are asphalt, smooth BUR, ballasted BUR and several membrane systems. As stated earlier, their report is due in early 2003.

Question: Would unpainted metal include metal coated with metallic alloys?

Answer:

(Copper, coated copper, zinc-coated, tin coated, stainless and stainless coated)
Answer: Yes, unpainted metals include pure metals (copper, tin) and alloys. All the above materials have been used as roofing materials. Typically, unpainted AZ55 Galvalume Plus is used for low slope roofing and prepainted AZ50 Galvalume and galvanized are used for steep slope roofing.