Roof, wall and foundation transitions · Lesson 2 of 4

Roof, wall and foundation transitions: materials, standards and design constraints

The code text on flashing, parapets and overflow, the sidewall and cricket rules, the heights and laps different documents set, base-of-wall clearances and grade, the metals that suit masonry, flood-zone materials and the ASTM wall guide.

You will be able to: Identify the code sections, publisher values and material limits that govern roof-to-wall, eave-to-sidewall and wall-base transitions, say which datum and which document each number belongs to, and recognise what the code leaves to the detail.

11 min · 12 slides · 7 questions

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Slide 1 of 12

The code duty to flash

Section 1503.2 says flashing shall prevent water entering the wall and roof through joints in copings and at intersections with parapet walls.

Section 1503.2.1 requires flashing at wall and roof intersections and, where it is metal, a corrosion-resistant thickness of not less than 0.019 inch.

Example text: the 2021 Seattle Building Code (IBC-based); your adopted edition governs.

Sources

2021 Seattle Building Code, Chapter 15 Roof Assemblies and Rooftop Structures (2021 IBC as amended) - City of Seattle, SDCI

Glossary

Positive drainage: Drainage that actually carries water off a surface; the 2021 Seattle Building Code (IBC-based) section 1503.3 says the top surface of a parapet wall shall provide it.
Cricket or saddle: A small sloped piece built on the ridge side of a chimney or wide roof penetration to shed water around it; the IRC-based Seattle code requires one where the chimney or penetration is more than 30 inches wide.
Weep screed: A stucco accessory at the bottom of the plaster that lets trapped water out; the IRC-based Seattle code places it not less than 4 inches above earth or 2 inches above paved areas.
Finished ground: The final ground surface beside a wall, from which base-of-wall flashing and weep heights are measured; BIA says flashing and weeps should be no more than 10 in above it.
Base flood elevation (BFE): The flood level FEMA uses as the reference for flood damage-resistant materials; materials below it in Special Flood Hazard Areas must be flood damage resistant.
Through-wall flashing: Flashing that runs through a masonry wall from the backing across the cavity and out to the exterior to collect water and send it out; BIA does not recommend galvanized steel for it.