A Close Look at Stucco

Flashing details frequently involve the interaction of two trades. Here, for example, the stucco crew members responsible for installing the building paper had to remove and reinsert a gable vent installed by the framers so that they could run building paper under the vent flange.

Integrating building papers with window flashings can be a challenge on site. In California, where this crew works, stucco contractors aren't typically licensed to install windows, so the paper crew must work with the existing flashing. Here, the window crew left the window perimeter protected by strips of flashing, with side strips lapped over the bottom strip and the head strip lapped over the side strips and the window flange. The paper installer lifts the bottom flap and runs paper under it.

The installer seals the flashing to the paper with adhesive membrane.

He lays paper under the side window flashings and staples the flashing down before applying membrane to this joint as well.

Paper-backed lath then butts directly to the window flange, but water that gets behind the stucco at the window sill and jamb will be handled by the membrane, the flashing, and the first layer of paper.

Less than ten years old, this building had been repaired twice previously with surface-sealing methods that did not work. The author's crew first stripped the stucco. At this window corner, badly detailed flashing and paper let water soak the sheathing and framing, leading to rot.

After pulling out the window, the author's crew repapered the wall with Tyvek StuccoWrap, then applied membrane and Tyvek FlexWrap to the rough sill to protect the wood structure even if the window leaks.

The crew then replaced the window.

The crew slid the top flange under the Tyvek and sealed the flange to the Tyvek all around the window.

The crew applied a second protective layer of Grade D building paper.

Roof-to-wall intersections create particular problems. This bad detail held up the work: The rafter placed tight to the building wall does not allow paper to slip behind it, and the flashing left by the roofers will direct water behind the stucco and into the wall if used as configured.

A water diverter (kick flashing) was installed by the author's crew in a retrofit job: This design will lead water out away from the wall and dump it off the roof's drip-edge rather than into the wall. Papers installed on the main wall can readily integrate with the membrane and flashing between roof and wall at the rafter tail.

A wall-and-roof intersection built without the correct flashing detail shows discoloration and staining after a few years in service; the author typically finds significant rot in buildings with this detail, even though the wall surfaces may show only minor traces of trouble.

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