CORNELL CORPORATION
808 South 3rd Street
P.O. Box 338
Cornell , Wisconsin 54732
Tel: (888) 439-6411
Fax: (800) 267-8368
E-Mail: cornell@cornellcorporation.com
Web site: www.cornellcorporation.com
Cornell Corporation has been a leading roof insulation manufacturer since
1955. In response to the need for nailable insulation above the structural roof
deck in cathedral or vaulted ceiling applications, Cornell Corporation introduced
ThermaCal® in 1979, which started the nail base roof insulation industry.
In response to the shingle manufacturers’ requests for ventilation, we
introduced Vent-Top ThermaCal in 1987. Cornell Corporation is your ventilated
roof insulation specialist!
Please see the attached table for a quick selection guide to Cornell’s
roof sheathing and insulation products in both polyiso and XPS — ThermaCal®,
ThermaCal® X, Vent-Top ThermaCal®, Vent-Top ThermaCal®
X, and CVRS.
Most of the better ridge vents have a ventilation capacity of 18 sq. in. of net free area per foot of ridge. This is 9 sq. in. per foot on each side of the ridge. The eave vents and the vented insulation should also have a capacity of at least 9 sq. in. per foot after deducting for spacer strips.
If the roof deck below the vented insulation is steel, plywood or nominal 1" wood then the screws are going to penetrate through the deck. If you specify that the screws are to be fastened into the upper flange of the steel deck, they will be harder to see from below. Figure approximately one screw for every two square feet of roof insulation.
High humidity buildings such as swimming pools should have a vapor retarder between the roof deck and the insulation. Your Architect or Engineer should determine whether a vapor retarder is required.
Roofs with hips, dormers and valleys need to have ventilation both up the slope and across the slope. Cornell Corporation products have individual spacer blocks that leave 50% open for lateral ventilation.
With tile or slate roofing use the optional heavier top sheathing for better nail holding. 5/8" and 3/4" oriented strand board or plywood is available. Vent-Top ThermaCal 2 with two layers of sheathing gives higher compression resistance for heavy roofing loads.
Cornell Corporation panels have machined edges that provide the proper clearance between the wood sheathing on adjoining panels. Products that have to be spaced apart will allow heat loss at the joints that may need to be caulked.
Cornell Corporation panels with the no-cost option tongue and groove on all four edges of the foam will reduce the heat loss at the joints.
Remember a wood roof deck and shingles will add to the R Value of the vented insulation. Cornell Corporation panels are available up to 8” thick, LTTR = 47. If you need more R Value add a separate layer of polyisocyanurate insulation on the roof deck.
Use a separate layer of foam insulation between the roof deck and the vented insulation. This can easily be cut around the conduit, etc. Then install the vented insulation over the foam layer, staggering the joints.
Call Cornell Corporation (888-439-6411 central time) with other technical
questions, design assistance, or autocad downloads on roof insulation or at www.cornellcorporation.com.
Catalogs, detail drawings, draft specifications and installation instructions are available. Call 888-439-6411 or FAX 800-267-8368.
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