Addressing Unusual Steel Lintel Configurations (Inverted C-Channels)
By: Jimmy Monahan
Lintel replacement is commonly performed as part of façade restoration projects. A lintel is a horizontal support member, comprised of stone, masonry, timber, concrete or steel, that’s installed across the top of a door, window or other opening to support the load above the opening, and transfer the load down to the bottom of the wall. This article will focus primarily on steel lintels, particularly, inverted C-channel lintels.
It’s essential that Building Envelope Consultants carefully inspect lintels to ensure they are in good condition, and properly support the loads above. Common signs of deterioration range from rust jacking at the ends, improper bearing lengths, shifted masonry, and excessive deflection with cracked mortar joints.
An inverted C-channel lintel can be recognized by the exposed face of the outward flange at the façade, and the presenceof these channels can create complications when lintel replacement is necessary. The function of a lintel is to span the entire width of a wall opening and support all masonry above the opening. Typically, C-channels must span and support 2 or 3 wythes of brick. Therefore, it’s important that replacement structural steel lintels are accurately designed to properly support this additional masonry above the openings. This scope of work might require the installation of larger or additional steel angles, along with additional waterproofing and brick masonry installation. If substantial lintel replacement is required as part of a façade restoration, this increased scope can negatively impact allocated allowances and the project budget.
Masonry above an inverted C-channel lintel is more apt to destabilize over time. Due to an inverted C-channel’s vertical flanges, it’s difficult to install brick flush above the lintel. In some cases, a thick bed of mortar is installed over the steel channel to create a flat surface for the brick masonry installation. This mortar bed will eventually crack and deteriorate due to moisture accumulation. The inverted C-channels will then trap moisture in the wall, especially if there’s no proper means of mitigating water such as: waterproofing, weep vents, or holes drilled into the exterior flange of the steel. As the mortar bed deteriorates, the masonry above will bear on the flanges of the channel. Over time, the brick masonry will destabilize due to this increased stress. And as mentioned previously, this unstable brick is always 2 or 3 wythes deep. Due to this increased amount of deteriorated and failing brick associated with the replacement of inverted C-channellintels, more brick installationwill berequired as part of a restoration effort.
During any facade restoration effort, it is absolutely crucial that the exterior wall is stabilized during demolition activities. Temporary shoring during demolition is an absolute must when performing brick and lintel replacement; however, as previously stated, the increased brick replacement and larger lintel replacement common in C-channel lintel replacement requires additional shoring for wall stabilization. During demolition, the Contractor and Engineer must be prudent and systematic to ensure each wythe of masonry is supported. The execution of multi-wythe shoring must be particularly strategic when replacing lintels that are near, or next to each other. Each demolition location should be addressed independently to minimize the amount of disturbed masonry and concurrent shoring that will be required. This type of shoring demands additional material, time and planning, which ultimately equates to increased costs.
A final concern for Building Envelope Consultants is addressing the aesthetic look of the brick installed above the new lintels. When a steel angle is installed to replace an inverted C-channel, it can disrupt the bond pattern of the brick masonry. Rather than installing large beds of mortar, contractors will often have to cut the brick masonry to keep the masonry and mortar joints aligned and uniform. When addressing the aesthetics of this type of lintel replacement, the mason’s skillset is key factor.
As discussed in this article, it’s extremely important to identify these types of lintel configurations early in the design phase of any façade restoration project. By retaining a Building Envelope Consultant, problems and increased costs associated with their replacement can be addressed and accounted for prior to the start of a project.