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Re: stone Veneer support

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Here's an analysis of this issue for both the IBC and IRC developed by one of our building code experts:

 

The IBC Chapter on Exterior Wall Coverings states that exterior masonry veneers may be supported on wood construction where installed in compliance with the following: (§1405.5.1 Support)

1. A vertical movement joint is required between the veneer supported by the wood construction and the veneer supported by the foundation. This provision assumes a concrete or masonry foundation. For a permanent wood foundation, refer to §2304.12.

2. Members supporting the masonry veneer shall be attached to wood studs with lag screws. The supporting members could be wood, steel or other approved material. This provision assumes some sort of ledger support, such as at a roof upon which masonry veneer is loaded, with a structural tie provided by lag screws to the adjacent wall system. (See also IRC §RR703.7.2.2.)

3. Horizontal members supporting the masonry veneer shall be designed to limit deflection to 1/600 of the span of the supporting members. The deflection limit is intended to lessen the likelihood of cracking in the masonry veneer.

4. The design of the wood construction shall consider the weight of the veneer plus any other loads. This is merely a restatement that the wood members must be designed to resist all loads and forces.

No limit to the height of masonry veneer is specified in this section. It is assumed that the concrete or masonry foundation will be designed to support the veneer and that the veneer will be adequately anchored to the wall system for lateral support. (See comments below on seismic design categories.)

 

IBC Chapter 23, Wood, states that exterior masonry veneer (brick, concrete or stone) may also be supported by a permanent (treated) wood foundation (PFW). However, when a PWF is used to support the exterior masonry veneer, the height of veneer above the PWF is limited to 30 feet (9144 mm). (§2304.12)

 

The requirements of the IRC are similar to those of the IBC. For example, §RR703.7 states that veneers installed over a backing of wood is generally limited to the first story above grade with exceptions base on the seismic design category where the building is to be constructed:

1.      In Seismic Design Categories (SDC) A and B, exterior masonry veneer may not exceed 30 feet (9144 mm) in height above a noncombustible (concrete or masonry) foundation, with an additional 8 feet (2348 mm) permitted for (gable) ends. (See Figure RR703.7)

2.      In Seismic Design Category C, exterior masonry veneer likewise may not exceed 30 feet (9144 mm) in height above a noncombustible foundation, with an additional 8 feet (2348 mm) permitted for gabled ends. However, in other than the topmost story, the length of bracing is required to be 1.5 times the normally required length of bracing. (See Figure RR703.7)

Figure RR703.7 presents masonry wall details for veneer-clad, wood-frame houses with concrete or masonry foundations.

 

For townhouses in SDC C, veneer height is limited to one story. If braced walls (shear walls) on the first story are increased in length by 1.5 (Section R301.2.2.3), then two stories are permitted. This limitation does not apply to detached one-and two-family dwellings assigned to SDC C, as noted above

 

The code is not explicit with respect to veneers in SDC D.  Because the code is subject to interpretation, there are several opinions on what is required. One interpretation is that the wood and steel frame prescriptive requirements for dwellings does not cover the lateral force resisting system for veneers in SDC D and therefore the framing system must be designed. Another interpretation is that the prescriptive provisions apply to veneers in SDC D, but the veneer height is limited to one-story dwellings. In either case, it needs to be emphasized that masonry veneer is not prohibited on buildings assigned to SDC D in the IRC.

 

An example of seismic provisions for masonry veneers in SDC D is in Section R703.7. The code specifies the same requirements for limiting the support area for veneer ties (R703.7.2) and mechanically fastening the ties to horizontal joint reinforcement (Section R703.7.4.1.2) in SDC D like the CABO Code does for Seismic Zones 3 & 4.

 

[The Brick Institute of America submitted IBC code change proposals in 2001 that revised limitations on veneers in SDC D1 andD2. The revisions permit veneer wall heights for wood frame construction up to 20 feet in height with an additional 8 feet in gabled end walls provided braced wall panels (shear walls) are strengthened. In addition, hold-down connectors at each end of each braced wall panels are required. If the second interpretation above is correct, these changes increased the requirements for masonry veneers in order to satisfy those interested in having adequate seismic requirements in the IRC.]

 

The provisions of IRC generally contemplate support of masonry veneer concrete or masonry foundations. However, when the veneer spans across openings, the code assumes steel angles or wood beams will be used limiting the deflection to 1/600. §RR703.7.2.1 prescribes general support of exterior masonry by steel angles. Table RR703.7.1 provides specific allowable spans for steel lintels supporting masonry veneer. When the masonry veneer is to be supported by wood-fame roof construction, the supporting wood members must be anchored to the adjacent studs with lag screws. The maximum height of masonry veneer above a wood roof and steel angle support is 12 feet, 8 inches (3861 mm). The maximum slope of the roof construction is also limited to 7:12.

 

Further, §RR703.7.2, like IBC §1405.5.1, requires a movement joint between the veneer supported by wood and the veneer supported by the (concrete or masonry) foundation. The method of support for the masonry veneer on wood roof construction shall be constructed in accordance with Figure RR703.7.1 or as approved by the building official.

 

HTH

 

Buddy

 

John "Buddy" Showalter, P.E.
Director, Technical Media
AF&PA/American Wood Council
1111 19th Street, NW, Suite 800
Washington, DC 20036
P: 202-463-2769
F: 202-463-2791
http://www.awc.org

The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AWC develops internationally recognized standards for wood design and construction. Its efforts with building codes and standards, engineering and research, and technology transfer ensure proper application for engineered and traditional wood products.

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The guidance provided herein is not a formal interpretation of any AF&PA standard.  Interpretations of AF&PA standards are only available through a formal process outlined in AF&PA's standards development procedures.

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