SS Credit 7.2: Heat Island Effect: Roof

SS Credit 7.2: Heat Island Effect: Roof

LEED-NC Credit: YES | UNSURE | NO

Credit Intent

Minimize heat island effects that commonly plague roofs and can impact the microclimate and well as interfere with human comfort (indoors and outdoors) and wildlife habitat.

Feasibility

Despite Stanford’s red-tiled tradition and the need for the new GSB to follow suit, this credit should be sought. There are many materials available with high Solar Reflective Indices (SRI), which in this case must be higher than 29. Because there are no current plans for a vegetated roof (only smaller roof gardens), the choice of roofing material becomes the key to achieving this credit.

Figure 24: View of central campus’ red roofs from Hoover Tower.

Photo by John Millea, 5/14/07

Figure 25: GSB plans call for red roofing materials to match the Stanford campus.[1]

SS Credit 7.2: Heat Island Effect: Roof

LEED-NC Credit: YES | UNSURE | NO

Analysis

The project outline specifications call for a roof pitch between 30 and 35 degrees, within current Stanford design guidelines.[2] LEED-NC requirements dictate that any roof with a slope greater than 2:12 (or roughly 9.5 degrees) be designated “steep-sloped”, thus requiring an SRI of 29. It must be stressed that without a roofing material with an SRI of 29, this credit will not be attained.

The LEED-NC 2.2 Reference Guide lists several roofing materials and their SRIs, giving an SRI of 36 to “Red Clay Tile.” Therefore, it appears that if this type of tile is used, the credit can be achieved. In the project specifications, ARUP assumes that existing Serra Buildings 651 and 655 (see Figure 26) currently on the site have “clay tile” roofs.2 To receive credit, the entire roof area will need to be calculated, and its SRI values (by material) will need to be given.

To further increase the sustainability of the roof beyond simply earning this credit, the clay tiles can be used from the demolished Serra Buildings. ARUP notes that it is committed to recycling 75% of these buildings.2 If clay tiles are salvaged, the material cost of the new GSB roof could be greatly reduced.

Figure 26: Existing Serra Buildings 651 and 655, with possibly reusable clay

tile roofing, as seen from Hoover Tower. Photo by John Millea, 5/14/07.

Other sources also indicate that clay tile roofs have SRIs of 36, while concrete tile roofs have SRIs of 17.[3] It is important that roofing material with an SRI greater than 29 be used to achieve this credit. National suppliers of clay tile roofs, many in California, may be found at http://eetd.lbl.gov/coolroof/cmptile.htm.

[1] BCJ Architects, Plan sketch from Kathleen Kavanaugh’s presentation, 5/2/07.

[2] Schematic Narrative and Outline Specifications, BCJ Architects, 4/30/07

[3] Roofing Tile, http://eetd.lbl.gov/coolroof/tile.htm.