Roofing over SIPs: One temperature snapshot
A question was recently raised elsewhere on this website about the temperatures and performance of roofing materials placed over SIPs. Two in-depth and on-going studies will eventually report on the key related subject-do asphalt shingles last as long when installed over unvented (in this case, SIP roofs) as they do over vented attics? The concern stated by roofers as early as 1987 is that the shingles over unvented roofs will run hotter so won't last as long. At least one of the studies won't be wrapped up for at least another two years. On a one-shot basis, the following temperature data set addresses the performance issue, though not the durability concern.
On two clear, hot, mid-July days in Denver, your site editor recorded the surface temperatures of light-colored asphalt shingles over SIPS and vented attics facing in various orientations. Additionally, a surface temperature was recorded for a neighboring vented roof with dark-colored shingles. Finally, several temperature readings beneath the shingles were also measured. Outdoor and interior temperatures were also recorded--including drywall surfaces beneath the SIPs and insulated, vented attics--using an infrared radiometer. Those data are listed below.
The key point: at its highest temperature, the surface of light-colored 12-year-old shingles tends to run 8-10 degrees hotter over unvented SIPs than over a vented attic facing the same orientation (south).
Related points:
- The difference between the surface temperature of the lighter and darker shingles of the same overall roof color on the same roof slope varies by 6 degrees (regardless of orientation or venting status of roof).
- The drywall beneath the SIPs heated up slightly more than the drywall beneath the vented attic, with identically colored shingles above each.
- However, the air temperature within the isolated SIP room remained slightly cooler than the room beneath the insulated attic, in some measure part due to better windows (R-3.5 vs. R-2), higher R-values in the SIP walls and roof (R-23/R-40 vs. R-18/R-35), and less internally generated heat.
- To this observer's untrained eye, there did not appear to be a significant difference between the shingles over the vented and SIP roof sections.
- The darker-colored shingle over a vented roof was hotter than the lighter colored shingled over an unvented SIP roof.
This one small set of data supports the notion that a minor performance advantage would be gained by venting above a SIP roof. Speculation here is that the benefits of venting above a SIP roof would be more substantial on the system durability side of the equation than on the comfort and energy side. Finally, color of shingle may have as much or more impact on shingle durability as the design of the roof assembly (vented vs. unvented).
Figure 1: Day 1
| Time of day and outdoor air temp; most measurements were taken during clear-sky conditions |
Shingle surface temp over south-facing SIP roof |
Drywall surface exposed to room beneath SIP |
Air temp of room beneath SIP |
Shingle surface temp over south-facing vented roof |
Drywall surface exposed to room beneath vented roof |
Air temp of room beneath vented roof |
| 10 a.m. - 73 deg.F | 154 deg.F | 69 deg.F | 70 deg.F | 148 deg.F | 72 deg.F | 70 deg.F |
| 1 p.m. - 84 deg.F | 190 deg.F | 75 deg.F | 72 deg.F | 182 deg.F | 76 deg.F | 73 deg.F |
| 2 p.m. - 88 deg.F | 182 deg.F | 77 deg.F | 73 deg.F | 172 deg.F | 76 deg.F | 73 deg.F |
| 3:30 - 86 deg.F, partly cloudy | 134 deg.F | 78 deg.F | 73 deg.F | 128 deg.F | 77 deg.F | 75 deg.F |
Figure 2: Day 2
| 1:30 pm, sunny day | Light-colored shingle | Dark-colored shingle |
| Above vented attic | 174 deg.F | 188 deg.F |
| Above unvented attic | 183 deg.F | N/A |
Figure 3: Day 2
Footnote: while these data weren't gathered under laboratory-type conditions, they are those prevailing in the real-world conditions experienced within a home. No air conditioning was supplied to the indoors.