Metal Stud Wall System Anatomy

The Brick Industry Association (BIA) has issued a revised Technical Note #28B that describes in detail Brick Veneer/Steel Stud Wall Construction.  The following is an abbreviated summary of their minimum recommendations:

• The allowable out-of-plane deflection of the studs due to service level loads should be restricted to L/600 to L/700.
• The minimum air space should be increased to 2 inches.
• Ties must be spaced closer. There should be one tie for each 2 sq ft (0.18 sq m) of wall area.
• Sheathing should be upgraded. Possible choices include: closed-cell rigid insulation meeting ASTM C 578 or C 1289 at a minimum of 1/2" thick; exterior grade gypsum sheathing, OSB or glass fiber mat-faced sheathing or cement board at a minimum of 1/2" thick.
• A water-resistant barrier should be installed over sheathing.

Brick veneer with metal stud backup is typically a vented wall system.  This is to provide a way out for any moisture that enters the wall system through the brick joints or other openings.  A vented cavity also allows for pressure equalization of external pressures caused by wind loads. Venting is accomplished by providing weeps or vents immediately above the wall flashing. Open head joint weeps are recommended with a spacing of no more than 24 inches on center. BIA recommends that wick or tube weeps, when used, be spaced no more than 16 inches on center.

BIA recommends four types of adjustable masonry anchor assemblies for brick veneer/metal stud systems. Each of these is connected to the studs with metal screws. Due to thermal bridging at the stud, condensation can form on the inside face of the stud’s outside flange during long term cold conditions if a thermal break is not provided.  When using XPS as part of the exterior system, brick ties that connect directly to the framing must not rely on the compressive resistance of the exterior sheathing material to transfer positive wind loads to the steel studs.  This will eliminate the thermal bridge issue at brick ties.  All anchors must be embedded at least 1 1/2 inches into the brick veneer with a minimum mortar cover of 5/8 inch to the outside face of the wall.