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Underlayments, membranes and WRBs · Lesson 2 of 4

Underlayments, membranes and WRBs: materials, standards and design constraints

Felt and its ASTM types, synthetics and evaluation reports, self-adhering membranes and their heat ratings, compatibility and exposure limits, the code rows by slope and wind, the ice barrier rule, and the wall WRB.

You will be able to: Identify felt, synthetic and self-adhering underlayments by their standards, read product heat, compatibility and exposure limits, and apply the code rows for slope, wind design, ice barrier and wall WRB.

14 min · 12 slides · 12 questions

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Slide 1 of 12

Asphalt felt

ASTM D226/D226M-25 covers asphalt-saturated organic felt used in roofing and waterproofing.

Its Type I is commonly called No. 15 felt.

Its Type II is commonly called No. 30 felt.

Code texts also list ASTM D4869: Hopkins, Minnesota includes D226 Type I and D4869 Type I; New Orleans names D226 Type II or D4869 Type III or IV.

Sources

Videos for this lesson

What this video shows: Thad Barnette on underlayment types, which suits standing seam metal, and basic installation tips; its description says Sheffield Metals recommends following the manufacturer's instructions.

Video: Roof Underlayment Types for Standing Seam Metal Installs by The Metal Roofing Channel, on YouTube. AFS checked its description against this lesson.

Glossary

No. 15 and No. 30 felt
The common names for ASTM D226 Type I and Type II asphalt-saturated organic felt.
Synthetic underlayment
A mechanically attached polymeric sheet underlayment, accepted product by product through ICC-ES acceptance criteria and evaluation reports; ASTM D8257 is its specification (Keeler, 2021).
Evaluation report (ESR)
An ICC-ES report recognizing a named product as a code alternative, only within the conditions of use it states.
High-temperature (HT) underlayment
A self-adhering underlayment rated for heat under metal roofs. Each maker gives its own rating, for example Grace Ice & Water Shield HT 260 F and Malarkey Secure Start HT 250 F.
Wind-design area
An area where the code requires wind design; Charleston County's 2021 form calls for two underlayment layers there, or an ASTM D1970 self-adhering alternative.