Extruded polystyrene boardstock and roof structure containing the extruded polystyrene boardstock

1. A polymer foam insulation board comprising a foamed polymer layer that includes one or more organic polymers, the organic polymers comprising at least 70% by weight of one or more alkenyl-aromatic polymers, the foamed polymer layer having opposing first and second major surfaces and a thickness orthogonal to the opposing major surfaces; a first facer sealingly bonded to the first major surface to form a first outer surface and a second facer sealingly bonded to the second major surface to form a second outer surface, wherein:

the foamed polymer layer has a foam density of at most 56 kg/m 3 (3.5 pounds per cubic foot), a thickness of at least 0.6 cm (0.25 inches), an RSI-value of at least 0.95 K·m 2 /W per 25.4 mm of thickness (R-value of 5.11° F.·ft 2 ·h/BTU/inch of thickness), and contains at least 0.25 weight percent, based on the weight of the foamed polymer layer, of an infrared radiation attenuating additive;

wherein the infrared radiation attenuating additive is one or more of graphite; carbon black; soot; a carbonized fiber, flake, or powder; carbon nanotubes, fullerenes, graphene, graphene oxide, or graphite nanoplatelets,

wherein each of said first and second facers is constituted by layers comprising films assembled into a multilayer structure, each of said first and second facers having a thickness of 19.05 to 63.5 μm,

the layers comprising, in order from the foamed polymer layer to an outermost surface of the polymer foam insulation board, an interior moisture barrier layer facing the foamed polymer layer, a tie-layer comprising polyolefin, an oxygen barrier polymer layer, a tie-layer comprising polyolefin, and an exterior moisture barrier layer, wherein the interior moisture barrier layer comprises ethylene-vinyl acetate polymer and the exterior moisture barrier layer comprises polyethylene;

wherein each interior moisture barrier layer has a thickness of 2.54 to 12.7 μm,

wherein each exterior moisture barrier layer has a thickness of 2.54 to 12.7 μm and further comprises a reflective filler, wherein the reflective filler, by itself, reflects at least 80% of incident visible light,

wherein each of the first and second facer has an opacity of at least 65%, an oxygen transfer rate of at most 0.65 cc/m 2 -day, an oxygen permeation rate of at most 0.9 cc-mil/m 2 -day, and an Elmendorf tear strength of at least 120 g/25.4 μm in at least one direction;

and

wherein each of the first outer surface and the second outer surface exhibits a surface solar reflectance of at least 35% as measured according to ASTM C1549.

2. The polymer foam insulation board of claim 1 , wherein the foamed polymer layer has a foam density of 21 to 56 kg/m 3 and a thickness of 7.62 to 15.24 cm.

3. The polymer foam insulation board of claim 1 wherein the alkenyl-aromatic polymer is a styrene-acrylonitrile copolymer that contains 10 to 22.5% by weight polymerized acrylonitrile and no more than 5 weight-percent halogen, based on the weight of the styrene-acrylonitrile copolymer.

4. The polymer foam insulation board of claim 1 wherein the foamed polymer layer contains 0.25 to 5 weight percent of the infrared radiation attenuating additive.

5. The polymer foam insulation board of claim 1 wherein the oxygen barrier layer comprises ethylene-vinyl alcohol copolymer.

6. The polymer foam insulation board of claim 1 wherein the reflective filler is titanium dioxide, calcium carbonate or both titanium dioxide and calcium carbonate.

7. The polymer foam insulation board of claim 1 wherein the first and second facers are the same.

8. The polymer foam insulation board of claim 1 which is rabbeted along one or more edges.

9. An inverted roof membrane assembly comprising:

a. decking;

b. a waterproofing membrane mounted directly or indirectly on top of the decking;

c. at least one layer of the polymer foam insulation board of claim 1 directly or indirectly on top of layer B; and

d. a ballast layer directly or indirectly on top of layer C.

10. The inverted roof membrane assembly of claim 9 wherein the ballast comprises gravel, stone, soil, one or more pavers, a green roof structure or component thereof, or a blue roof structure or component thereof.

11. The inverted roof membrane assembly of claim 9 , wherein the foamed polymer layer of the polymer foam insulation board has a foam density of 21 to 56 kg/m 3 and a thickness of 7.62 to 15.24 cm.

12. The inverted roof membrane assembly of claim 9 , wherein the alkenyl-aromatic polymer of the polymer foam insulation board is a styrene-acrylonitrile copolymer that contains 10 to 22.5% by weight polymerized acrylonitrile and no more than 5 weight-percent halogen, based on the weight of the styrene-acrylonitrile copolymer.

13. The inverted roof membrane assembly of claim 9 , wherein the foamed polymer layer of the polymer foam insulation board contains 0.25 to 5 weight percent of the infrared radiation attenuating additive.

14. The inverted roof membrane assembly of claim 9 , wherein the oxygen barrier layer comprises ethylene-vinyl alcohol copolymer.