Letters

Professional Roofing welcomes letters to the editor. Views expressed in "Letters" are not necessarily those of NRCA. Letters must be signed and include a return address and telephone number. Professional Roofing reserves the right to edit letters for clarity and length. Send letters to Ambika Puniani, Editor, Professional Roofing, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018-5607; fax (847) 299-1183; or e-mail apuniani@nrca.net.

A different look at ventilation

"What's the value of ventilation?" March issue, page 20, stated that "ventilating the area under a roof deck reduces the average temperature by 0.5 degrees Celsius." This was based on computer simulation. Our experience with an actual roof test produced a significantly different result.

We at Cornell Corp., Cornell, Wis., installed a south-facing roof system with black shingles and roofing felt nailed to oriented strand board (OSB) sheathing. Half the roof system had our ventilated roof insulation product with a vent space between the OSB and polyisocyanurate insulation. On the other half, the sheathing was directly on top of the insulation. Below the shingles, we installed small thermocouples that could be connected to a temperature-measuring device. The device measured the temperature at the underside of the shingles. We found that the average temperature of shingles on a hot day was … lower in the ventilated area than it was in the nonventilated area.

Our tests show that on buildings where insulation has to be outside a structural roof deck, ventilated insulation lowers shingle temperature significantly.

Neil Goodall
Cornell Corp.
Cornell, Wis.

More information about snow guards

As a roof consultant who specializes in steep-slope roof systems in snowy areas, as well as a manufacturer of snow brackets, I noted some key concerns in "Snow guards for metal roof systems," March issue, page 62, by James R. Kirby, an NRCA senior director of technical services.

Kirby mentions that "it may be prudent to install snow guards during warm weather." I believe this should be a much stronger statement stating that it is mandatory to install snow guards [when the temperature is] above 40 F (4 C) with 30 days of cure time. In addition, I believe it also is necessary for the surfaces to be clean.

Kirby also notes that "it is best not to penetrate metal panels with exposed fasteners." As a consultant, I have experienced on many occasions panels torn off a roof system when snow guards only are adhered. This is because the clip that held down panels essentially was a wind-uplift clip that allowed a panel to expand and contract in the same direction of snow and ice movement. Attachment through the panel typically is done at the ridge. Therefore, the fasteners became the system's weak point, and with heavy snow loads, the metal panels pulled off a roof system.

I recommend that whenever a roofing contractor is installing snow retention, it should be done with snow brackets engineered from the system's fail point. It is a must to look for the weak link in a system and install brackets from the eave to ridge as they do in Europe.

Terry Anderson
Anderson Associates Consulting Inc.
American Fork, Utah

Following is Kirby's response to the letter:

"Thank you for your comments."

Clarification: In "Capitol Corner," February issue, page 12, it stated the nomination of Eugene Scalia for solicitor of labor was approved. The column also should have mentioned Scalia's nomination was a recess appointment by President Bush and bypassed a Senate vote.