Stucco lath on a wood-framed wall must be corrosion-resistant metal lath fastened with 1-1/2-inch, 11-gage nails or 7/8-inch, 16-gage staples, at no more than 7 inches on center along framing or furring (2021 IRC Section R703.7.1). Cement plaster then goes over it in at least three coats.
Stucco lath is the expanded metal, welded wire or woven wire mesh that gives exterior cement plaster something to grip. It is nailed over the water-resistive barrier on the framed wall, and the stucco layers build on it. This page covers what the 2021 International Residential Code (IRC) requires for the lath and the layers around it, and what the framer has to provide. It does not cover brick veneer, which has its own page on brick ties.
Key facts
- Lath and lath attachments must be corrosion-resistant and comply with ASTM C1063 (2021 IRC Section R703.7.1).
- Lath is fastened with 1-1/2-inch-long, 11-gage nails having a 7/16-inch head, or 7/8-inch-long, 16-gage staples (2021 IRC Section R703.7.1).
- Fastener spacing is not more than 7 inches on center along framing members or furring and not more than 24 inches on center between them, or as otherwise approved (2021 IRC Section R703.7.1).
- Furring, where provided, is spaced not more than 24 inches on center and fastened into the framing members (2021 IRC Section R703.7.1.1).
- A weep screed with a vertical attachment flange of at least 3-1/2 inches is required at or below the foundation plate line on exterior stud walls (2021 IRC Section R703.7.2.1).
- Cement plaster over metal lath or wire lath is at least three coats (2021 IRC Section R703.7.2).
What is a stucco wall assembly?
A stucco wall assembly is the stack of layers from the studs outward: framing, sheathing, water-resistive barrier, lath, and cement plaster, with a weep screed at the bottom to drain trapped water.
Layers of a stucco wall over wood framing, as named in 2021 IRC Section R703.7 and related sections. Listed from inside to outside.
| Layer | What the 2021 IRC says | Section |
|---|---|---|
| Studs and sheathing | Lath fasteners go into framing members or furring. | R703.7.1 |
| Water-resistive barrier | At least one layer over studs or sheathing, with extra requirements under stucco. | R703.2, R703.7.3 |
| Furring (optional) | Wood strips, metal channels or self-furring lath. | R703.7.1.1 |
| Lath | Corrosion-resistant expanded metal, welded wire or woven wire. | R703.7.1 |
| Cement plaster | Three coats over metal lath, with thickness from Table R702.1(1). | R703.7.2 |
| Weep screed | Drains water to the exterior at the base of the wall. | R703.7.2.1 |
The framer's job is the first rows: studs at a spacing the lath can be nailed to, sheathing, and a barrier that can be lapped over the screed. See wall sheathing and stud spacing for those layers.
How is stucco lath attached to wood framing?
Stucco lath is nailed or stapled to wood studs or to furring, never just to sheathing, using the fastener size and spacing in Section R703.7.1.
2021 IRC Section R703.7.1, lath attachment to wood framing members or furring.
| Item | Requirement |
|---|---|
| Nail | 1-1/2 inches long, 11 gage, 7/16-inch head |
| Staple | 7/8 inch long, 16 gage |
| Spacing along framing or furring | Not more than 7 inches on center |
| Spacing between framing or furring | Not more than 24 inches on center |
| Extra fasteners between members | Not prohibited |
The spacings apply "or as otherwise approved". Lath type and weight come from ASTM C1063, which the section cites; the IRC text does not list lath weights.
Three conditions change the attachment:
- Plaster used as wall bracing. Where exterior plaster serves as wall bracing under Table R602.10.4, the lath must be attached directly to framing, not to furring. The bracing rules themselves are in Section R602.10 and are not repeated here.
- Cold-formed steel, masonry, stone or concrete. Attachment to these substrates follows ASTM C1063 instead of the wood-framing nail schedule.
- Foam sheathing. Lath over foam sheathing, or furring over foam sheathing, must also meet Section R703.15, R703.16 or R703.17.
There is one exception: lath is not required over masonry, cast-in-place concrete, precast concrete or stone substrates prepared in accordance with ASTM C1063.
Does stucco lath need furring?
Furring is optional, and where it is used the 2021 IRC sets its size, spacing and attachment in Section R703.7.1.1.
Furring may be wood strips not less than 1 inch by 2 inches, metal channels of at least 3/4 inch, or self-furring lath. It is installed in accordance with ASTM C1063, spaced not more than 24 inches on center, and, over wood or cold-formed steel framing, fastened into the framing members.
Furring is separate from the drainage space that moist and marine climates require behind the barrier (Section R703.7.3.2), covered below.
How does a weep screed work under stucco?
A weep screed is a metal or plastic edge at the base of the wall that ends the stucco and lets water trapped behind it drain out.
Section R703.7.2.1 requires the following:
- A corrosion-resistant or plastic weep screed, at least 0.019 inch (No. 26 galvanized sheet gage) thick.
- A vertical attachment flange of at least 3-1/2 inches.
- Placement at or below the foundation plate line on exterior stud walls, in accordance with ASTM C926.
- A position not less than 4 inches above earth or 2 inches above paved areas.
- A type that allows trapped water to drain to the exterior of the building.
- The weather-resistant barrier laps the attachment flange, and the exterior lath covers and terminates on the flange.
On wood-frame construction with an on-grade floor slab system, exterior plaster is applied to cover, but not extend below, the lath, paper and screed (Section R703.7.2). That relationship sets what the framer and foundation crew leave exposed. The sill plate page explains the plate line the screed is measured from.
What water-resistive barrier goes behind stucco?
Stucco follows the general barrier rule in Section R703.2 and, over wood-based sheathing, adds the climate-based rules in Section R703.7.3.
2021 IRC Section R703.7.3, water-resistive barrier options under stucco over wood-based sheathing.
| Climate | Option | Requirement |
|---|---|---|
| Dry (B) zones, R703.7.3.1 | 1 | Two layers of 10-minute Grade D paper, or equivalent to two layers of ASTM E2556 Type I, installed as separate continuous planes, with flashing directed between the layers |
| Dry (B) zones, R703.7.3.1 | 2 | 60-minute Grade D paper, or equivalent to one layer of ASTM E2556 Type II, separated from the stucco by foam plastic insulating sheathing, another non-water-absorbing layer, or a designed drainage space |
| Moist (A) or Marine (C) zones, R703.7.3.2 | 1 | The dry-climate rule plus a space or drainage material at least 3/16 inch deep on the exterior side of the barrier |
| Moist (A) or Marine (C) zones, R703.7.3.2 | 2 | The dry-climate Item 2 rule plus drainage on the exterior of the barrier with a drainage efficiency of at least 90 percent, measured under ASTM E2273 or Annex A2 of ASTM E2925 |
Climate zones come from Figure N1101.7, which is not reproduced here. The general rule in Section R703.2 applies on top: No. 15 asphalt felt and ASTM E2556 barriers are lapped horizontally, with the upper layer over the lower by at least 2 inches and joints lapped at least 6 inches. Which option is legal in a given house depends on the climate zone and local amendments, so read your adopted section. For the wall below the barrier, see wall framing basics.
How many coats of stucco, and how long between them?
Cement plaster over metal lath is three coats, and the code sets minimum waiting times between coats.
2021 IRC Sections R703.7.2, R703.7.4 and R703.7.5, coats and timing for cement plaster.
| Situation | Rule |
|---|---|
| Over metal lath or wire lath | At least three coats |
| Over masonry, concrete, pressure-preservative-treated wood, decay-resistant wood (Section R317.1) or gypsum backing | At least two coats |
| Plaster surface fully covered by veneer or other facing, or fully concealed | May be two coats if total thickness meets Table R702.1(1) |
| Moisture between coats | Each coat kept moist at least 48 hours before the next, unless applied under ASTM C926 |
| Three-coat work, second coat | Not sooner than 48 hours after the first coat |
| Three-coat work, finish coat | Not sooner than seven days after the second coat |
| Two-coat work, finish coat | Not sooner than seven days after the first coat |
Total plaster thickness is set by Table R702.1(1) and the aggregate-to-cement proportions by Table R702.1(3); read both in the adopted code. The cement materials allowed are listed in Section R703.7.2 (masonry cement, portland cement, blended hydraulic cement, hydraulic cement and plastic cement, each to the cited ASTM standard).
What does the framer need to provide for stucco?
The framer provides a nailable, flat, correctly spaced backing and leaves room for the barrier and screed to be installed in the right order.
- Framing laid out for the lath. Lath fasteners are spaced not more than 24 inches on center between framing members or furring, so studs or furring have to be laid out to suit.
- A bracing decision made early. If plaster is the bracing method under Table R602.10.4, lath goes directly to the studs, which rules out furring for that wall.
- Sheathing and barrier choice. The barrier option depends on climate zone and sheathing type, so the wall section on the drawings should name it.
- A clear base detail. The screed sits at or below the plate line, 4 inches above earth or 2 inches above paving, and the barrier laps its flange.
- Documented fastening. The nail or staple size and spacing belong in the wall note so the lath crew and inspector read the same thing.
On a framing drawing, the stucco layers appear as a wall section note rather than as members. Framing Plan is a preliminary drawing aid: it draws joist layouts, beams and openings and exports PNG, PDF and DXF. It does not check wall coverings or code sections, and its editor works in millimeters, so the stucco notes above stay in your own wall section detail.
The adopted code edition and local amendments govern every value on this page. Proprietary lath, stucco systems and engineered assemblies follow the manufacturer's instructions. The full model code is at codes.iccsafe.org.
Summary
Stucco lath under the 2021 IRC is corrosion-resistant mesh nailed or stapled at no more than 7 inches on center along framing or furring and 24 inches between. A weep screed at the base drains the wall, a climate-specific water-resistive barrier sits behind the lath, and cement plaster over metal lath is at least three coats with set waiting times between them.
Open the framing studio to lay out the framed structure behind the stucco as a preliminary drawing.