The long-term performance of brick veneer and metal stud wall systems can be significantly enhanced via the incorporation of better insulating measures.
Recent improvements to insulating measures for brick veneer and metal studs (BV/MS) exterior wall assemblies have enhanced the resilience of these systems in colder climates, making them an even more viable option for the creation of sturdy and alluring building exteriors.
The BV/MS assembly system is a form of anchored veneer wall that was first devised in New England during the 1970’s, using anchors or ties to derive lateral support from the backing and the foundation or structural elements to achieve vertical support.
The original design employed gypsum board as both exterior and interior sheathing for the studs, and fibreglass batt as the insulating material within the stud space. A covering of #15h felt was then used to protect the gypsum board sheathing on the exterior from the elements.
The new system rapidly emerged as a popular replacement option for concrete masonry unit (CMU) backup walls because of their compact size and ease of installation. Brick veneer with steel studs became particularly popular for use with medium-scale multi-storey buildings used as schools, office complexes, medical facilities and churches, as they proved highly suited to installation upon the steel or reinforced concrete frames of such structures.
The product was not without shortcomings, however, chief amongst them moisture-induced corrosion that can afflict the masonry ties used the anchor the brick veneers, and is commonly caused by the thermal bridging that takes place in cold weather.
Buildings that typically employed BV/MS systems are particularly vulnerable to this problem, given that the are usually multiple storeys in height and lack the eaves or overhangs more commonly associated with residential buildings, leaving their exteriors highly exposed to the elements.
During cold weather the exterior flange of the studs in BV/MS systems can become exposed to frigid, low-temperature air, while the interior flange remains in contact with the warmer air of the building interior.
This creates a thermal bridge at the juncture between the screw of the masonry ties and the stud units, which in turn permits the accumulation of condensation, and creates associated problems with corrosion and rust.
Within a brief period this corrosion can cause the junctures to weaken or collapse, severely compromising the stability and resilience of the entire wall assembly. Once the brick veneer loosens as a result of failing masonry ties, it can shift and succumb to cracks along its horizontal joints. This undermines the ability of the wall assembly to resist the elements, and facilitates the entry of moisture into building interiors.
Measures and codified requirements have since emerged to remedy this shortcoming of BV/MS assembly systems, primarily involving the use of insulating materials to prevent thermal bridging at the tie and stud junctures.
The “Energy Conservation” section of the 2000 version of the International Building Code (IBC) added the requirement that exterior sheathing of the metal studs employ rigid insulation with a minimum R-value of R-3 to reduce thermal bridging and associated condensation-induced corrosion.
Since the turn of the century it has become commonplace to install insulating materials with even higher R-value to better forestall the possibility of thermal bridging.
A widespread industry standard is the use of 51 mm of XPS insulation board with an R-value of R-10 on the outside face of the stud, as well as the use of a vapour barrier in between the gypsum board and the insulating board to prevent the entry of both air and moisture.
The XPS insulation board must be precisely cut and prepared, ideally using a table circular saw, in order to ensure that the continuous R-value of the wall system isn’t affected by gaps or loose spots around the joints.
Multiple vapour barriers can be used to enhance the thermal-bridging resistance at the joints of the wall assembly, including a liquid air barrier installed on the exterior gypsum board sheathing, or high R-value mineral wool insulation within the metal studs.