The short answer: The Florida Building Code (FBC) does not provide prescriptive requirements but does, through a circuitous route, point to ASTM C 926 and ASTM C 1063 regarding the installation of exterior stucco on frame construction.

The not so short answer: Starting with the current Florida Building Code (2007 w/ 2009 revisions), Chapter 14 governs exterior walls. Within Chapter 14, Section 1405.14 covers cement plaster. This section points the reader to Chapter 25 which deals with gypsum board and plaster. Within Chapter 25, Section 2510.3 covers the installation of lathing and furring for stucco. This section dictates that installations must comply with the code adopted versions of ASTM C 926 and ASTM C 1063.

FBC Chapter 14 | Section 1405 Installation of Wall Coverings
1405.14 Cement Plaster. Cement plaster applied to exterior walls shall conform to the requirements specified in Chapter 25.

FBC Chapter 25 | Section 2510 Lathing And Furring For Cement Plaster (Stucco)
2510.3 Installation. Installation of these materials shall be in compliance with ASTM C 926 and ASTM C 1063.

ASTM C 926 is titled Specification for Application of Portland Cement-Based Plaster and ASTM C 1063 is titled Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. ASTM C 1063 is the standard that addresses the attachment of lath to wood framing, and is the standard that we will focus on.

Section 6.7.1 of ASTM C 1063 is the first section that we come across that discusses method of attachment:

ASTM C 1063 | 6.7.1 Nails -
For attaching metal plaster bases to wood supports, 11 gauge diameter, 7/16-inch head, barbed, galvanized roofing nails or galvanized common nails.

Then, in Section 7.9, Spacing of Attachments for Metal Plaster Bases we read:

ASTM C 1063 | 7.9 Spacing of Attachments for Metal Plaster Bases -
Attachments for securing metal plaster bases to framing members shall be not more than 7 in. apart for diamond mesh and flat rib laths and at each rib for 3/8 in. rib lath.

Furthermore, Section 7.10.2 Attachment for Metal Plaster Bases to Wood Framing Members states:

ASTM C 1063 | 7.10.2 Attachment for Metal Plaster Bases to Wood Framing Members:
7.10.2.1 Lath shall be attached to framing members with attachments spaced not more than 7 in. on centers along supports.
7.10.2.2 Diamond-mesh, expanded metal lath, flat-rib expanded metal lath, and wire lath shall be attached to horizontal wood framing members with 1-1/2 in. roofing nails driven flush with the plaster base and attached to vertical wood framing members with 6d common nails or 1 in. roofing nails driven to a penetration of not less than 3/4 in., or 1-in wire staples wire staples driven flush with the plaster base. Staples shall have crowns not less than 3/4 in. and shall not engage less than three strands of lath and penetrate the wood framing less than 3/4 in. When metal lath is applied over sheathing, use fasteners that will penetrate the structural members not less than 3/4 in.
7.10.2.3 Expanded 3/8 in. rib lath shall be attached to horizontal and vertical wood framing members with nails or staples to provide not less than 1-3/4 in. penetration into horizontal wood framing members and 3/4 in. penetration into vertical wood framing members.
7.10.2.4 Common nails shall be bent over to engage not less than three strands of lath, or be bent over a rib when a rib lath is installed.

According to these standards, a proper installation will utilize 11 gauge galvanized roofing nails or galvanized common nails, barbed, with a 7/16" diameter head to hold the lath. The fasteners will be nailed into the wall framing members and the fasteners will not be more than 7" apart. The fasteners will penetrate the framing member a minimum of 3/4". If the structure has sheathing on it, the fasteners still need to penetrate the framing member a minimum of 3/4". Therefore, you will need longer fasteners than what is recommended within the standard to ensure proper installation.

It should be noted that ASTM C 1063 does not have a specification on the spacing or the placement of any fasteners that are not along the framing members. However, the 2007 Florida Building Code with 2009 revisions does state in Chapter 25, Section 2516 that:

FBC Chapter 25 | Section 2516 | 2516.2 Stucco on walls other than concrete or masonry.
2516.2.3.4 Fastenings into wood sheathing or wood framing shall be by galvanized nails, with heads not less than 3/8 inch in diameter, driven to full penetration, using a minimum of two nails per square foot, or by approved staples having equal resistance to withdrawal.

However, this provision is found only in Section 2516 titled, High-Velocity Hurricane Zones – Stucco and therefore only appies to structures located in a High Velocity Hurricane Zone (HVHZ).

In conclusion, if a 24" square stucco sample is taken from a wall, there should be a line of fasteners that were installed along the framing members and none, or a minimal amount of fasteners within the field of the wall. As long as the sample is not taken between two wall studs, or between horizontal framing members, you should see fasteners in a line, and less than 7" on center if the stucco was installed properly according to the Florida Building Code.

If you have any questions regarding stucco attachment or other code issues, please contact William Bracken at wbracken@brackenengineering.com.

Every 20 minutes, a child is diagnosed with autism. The goal of Autism Speaks is to change the future for all who struggle with autism spectrum disorders. Walk now for Autism Speaks raises funds to support research into the causes, prevention, treatments, and cure; raise public awareness and its effects on individuals, families and society; and bring hope to all who deal with the hardships of the disorder.

Bracken Engineering is proud to help the fight for Autism Awareness and to assist in raising money for research of the disorder. When our company walks on Saturday, May 1st we will be walking for the 2,000 families that will be newly affected by Autism this month, and every month until a prevention, treatment and cure is found.

While we are well on our way to reaching our goal, support from our friends is always appreciated. If you would like to support us, you can make a donation online using the link below. Donations are tax deductible. Thank you for taking an important step in the fight against autism.

http://www.walknowforautismspeaks.org/tampabay/brackenengineering.