Stucco Installation and Re-Stucco for Portland Homes

Three-coat stucco

Traditional stucco goes on in three coats. The Northwest Wall & Ceiling Bureau (NWCB) describes three coats of cement, 3/4 to 1 inch thick in all, over an approved metal reinforcement and a weather-resistive barrier (600-102), and its guide specification (600-103) sets out each layer:

1. Scratch coat, 3/8 to 1/2 inch, cross-raked “to provide key for brown coat.”
2. Brown coat, 3/8 to 1/2 inch. The base coats together are at least 3/4 inch (7/8 inch on fire-rated walls), except over concrete block or concrete.
3. Finish coat, 1/8 inch or less, after the brown coat has cured: “Brown coat must cure a minimum 7 days prior to applying finish coat.”

The Oregon code ties exterior plaster to the industry standards: “Installation of exterior plaster shall be in compliance with ASTM C926, ASTM C1063 and the provisions of this code” (2023 ORSC R703.7).

One-coat stucco

One-coat systems are proprietary. NWCB describes them as “a proprietary fiber reinforced polymer cement (usually 3/8” to ½”) applied to a variety of sheathings with a continuous reinforcement”, and notes that they are “alternate materials” that “should have an approved evaluation report and installed per this report.”

On thickness the sources differ, so here are both sides:

• NWCB has “specific up-grade recommendations when considering these systems”, starting with “Minimum plaster thickness should be ½ inch”.
• Manufacturers specify less. Omega’s one-coat systems use “a 3/8-inch minimum thick layer” of base coat embedded in metal lath, and Dryvit’s StucCoat “may be installed as a 1-coat application at a minimum 3/8 inch thickness”, against a 7/8-inch minimum for its conventional scratch-and-brown application.

Ask which system is proposed for your wall, what thickness, and which evaluation report it follows.

What goes under stucco

The stucco is the outer layer; the layers behind it are what let water that gets past it drain out, which is what Oregon’s code asks of every exterior wall. Under the 2023 Oregon Residential Specialty Code (ORSC) and NWCB’s guidance:

• Lath. “All lath shall be self-furred over sheathing. All exterior lath shall be galvanized.” (NWCB 600-103)
• Water-resistive barrier. Over wood sheathing, two layers of 10-minute Grade D paper or the equivalent, each “a separate continuous plane”, or one layer of 60-minute Grade D paper or the equivalent separated from the stucco by foam sheathing, another non-water-absorbing layer or a designed drainage space (R703.7.3.1). NWCB: “Always use two (2) layers of WRB on sheathed walls to receive stucco.”
• Drainage space in the metro counties. In Multnomah, Washington, Clackamas and 15 other listed counties, the barrier also needs a space or drainage material at least 3/16 inch deep on its outside, or 90 percent drainage efficiency with the 60-minute option (R703.7.3.1.1). Oregon’s general rule adds a space of at least 1/8 inch between the barrier and the cladding, formed with furring, drainage mat or drainage board (R703.1.1).
• Weep screed. “The weep screed shall be placed not less than 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building.” (R703.7.2.1) NWCB adds that “the WRB lapping over the flange of the weepscreed” and calls for “a minimum 3 1/2 inch nail flange”.
• Flashing. Oregon requires kick-out flashing “at all wall and roof intersections, such as where a lower roofline terminates against a vertical wall.”
• Joints. NWCB recommends control joints, and ASTM C1063 requires them, but “there are no building code requirements to install control joints in a stucco system.” A control joint handles shrinkage and thermal stress, for movement of less than 1/4 inch in one direction; an expansion joint handles structural or seismic movement beyond that. Neither is a guarantee: “Proper design and installation of control and expansion joints in a portland cement plaster do not guaranty against cracking.”

Re-stucco over an existing wall

When an existing stucco wall is to be re-coated or re-clad, the first question is the condition of what is there. NWCB’s guidance is that “A comprehensive evaluation of the exterior plaster should be conducted by qualified persons prior to making any decisions for final scope of repairs”, and that walls with elastomeric paint “will limit the options of repairs.” If the evaluation finds water damage behind the old stucco, the wall is opened and rebuilt first; that is stucco remediation. If the damage is small and local, a stucco repair may be the answer instead. A stucco inspection sorts out which.

Which code edition applies

The Oregon Building Codes Division says the 2026 ORSC took effect on October 1, 2026 and becomes mandatory on April 1, 2027; until then either the 2023 or the 2026 edition may be used (Chapter 1 excepted). The full 2026 text had not been published when this page was checked on October 19, 2026. The committee that reviewed the 2026 code recommended keeping Oregon’s drainage-plane and kick-out flashing amendments; whether the county list for the 3/16-inch drainage space carries over is not yet published, so this page cites the 2023 text.

Before you sign for new stucco, check the contractor in the Oregon Construction Contractors Board’s license search.