Technical Bulletin #20
current as of july 2016
In an asphalt shingle roof system, various eave protection and underlayment materials may be specified. Underlayments are recommended for various reasons (See CASMA Bulletin # 3) and are also referenced in almost all building codes.
When reviewing any test standard the correct specification should be selected for the appropriate application of the product. There is occasional confusion in roofing specifications since they are often written for multiple applications and uses.
The eave protection or underlayment materials will typically conform to one of the following standards, which will be shown on the product packaging:
CSA A123.3-05 (R2010): Asphalt Saturated Organic Roofing Felt
As with most long-established felt standards, this specification was originally intended to address heavier perforated felts used in built-up roof construction. Non-perforated grades were added to reflect the needs for shingle and wood shake underlayments.
CSA A123.22-08: Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing Underlayment for Ice Dam Protection
This CSA standard is a Canadian adaptation of the ASTM D 1970 standard.
CGSB CAN2-51.32-M77: Sheathing, Membrane, Breather Type
This standard covers saturated Kraft paper, which is most often used as a water resistant “house wrap” membrane beneath wall cladding materials. Because the product is water-resistant and asphalt saturated, it has occasionally been used in roofing. Various weights and grades of saturated sheathing membrane are manufactured – generally only the heavier grades are suitable for use beneath asphalt shingles.
Various weights and grades of saturated sheathing membrane are manufactured but according to the National Building Code only grades of at least 125g/m2 are suitable.
ASTM D 226-09: Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing
This standard is similar to the CSA A123.3 standard, in that it applies to both built-up roofing felts and other uses of felts such as underlayment in shingle roof assemblies.
The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.
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