Use as an Air and Vapor Barrier

Technical Letter 2

GCP’s self-adhered underlayments (Grace Ice & Water Shield® , Grace Ice & Water Shield® HT, Grace Ultra™, Grace Select™, Grace Basik® and Grace Roof Detail Membrane™) are excellent air and vapor barriers. When used in full roof coverage applications, adequate ventilation must be provided in the roof design to avoid condensation problems within the roof structure or the attic space. Ventilation is necessary in all climates and is critical in warm, humid areas.

Proper roof ventilation and insulation design should be left to a qualified design professional and care should be taken to comply with local building codes. However, standard roofing practice is to use 1 ft2 (0.093 m2) of net free ventilation area per 150 ft2 (14 m2) of attic space, split evenly between the ridge and soffit vents. Soffit, ridge, gable or roof deck vents may be used alone or in combination depending on the specific roof design. Soffit and ridge vents used together provide the most complete ventilation and is the preferred ventilation configuration. Gable vents are sometimes used but are not usually as effective as ridge vents.

Failure to properly vent roof structures can cause water vapor from building interiors to condense within the roof structure or in the attic. This occurs most readily in warm, humid climates. Condensation can wet the insulation reducing its effectiveness, dampen wooden structural components, and can actually cause the roof to appear as though it is leaking even when there is no precipitation. In the worst case, neglecting ventilation issues can cause premature failure of structural components and can void various building component warranties.

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We hope the information here will be helpful. It is based on data and knowledge considered to be true and accurate, and is offered for consideration, investigation and verification by the user, but we do not warrant the results to be obtained. Please read all statements, recommendations, and suggestions in conjunction with our conditions of sale, which apply to all goods supplied by us. No statement, recommendation, or suggestion is intended for any use that would infringe any patent, copyright, or other third party right.

Ice & Water Shield, Grace Basik, Grace Ultra, Grace Select and Grace Roof Detail Membrane are trademarks, which may be registered in the United States and/or other countries, of GCP Applied Technologies Inc. This trademark list has been compiled using available published information as of the publication date and may not accurately reflect current trademark ownership or status.

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All rights reserved. GCP Applied Technologies Inc., 62 Whittemore Avenue, Cambridge, MA 02140 USA.

In Canada, GCP Canada, Inc., 294 Clements Road, West, Ajax, Ontario, Canada L1S 3C6.

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Last Updated: 2018-12-12

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