Selecting thermal clips for building envelope remediations

Example of thermal clips used for exterior insulated wall assemblies.

Improving a healthcare facility
A recent project involved a challenging building envelope remediation for a healthcare facility. This building had a history of envelope failures due to air and water leakage. Originally, it was constructed with insulation between the steel framing. To increase the thermal performance of the exterior walls and to enhance the airtightness of the building, the design team decided to have the air barrier/vapour retarder (also the weather barrier layer) and the insulation layer outside the sheathing.

During the demolition phase, the deterioration to the existing steel framing and interior components were found to be worse than expected. Due to the condition of the existing sheathing, studs, and interior wall components, it was necessary to remove all wall components down to the framing.

Another challenge was to properly scaffold and weather-protect the building during demolition, as this is a hospital setting. Since the building was required to remain operational during construction, strict infection-control procedures were needed to safeguard patients and staff. The exterior walls and scaffolding area were fully enclosed, and the interior of the building was pressurized to prevent any contamination of the occupied space. This pressure was monitored at all times, and air quality testing was performed before, during, and after construction.

The new wall design incorporated engineered wall cladding assemblies to allow for drying and drainage, while reducing thermal bridging with fibreglass clips to reduce heat transfer.

The layer of exterior insulation behind the Z-girts, which are secured to the fibreglass thermal clips.

The new wall assembly comprised:

  • fibreglass-faced gypsum sheathing installed over the
    steel framing;
  • a new self-adhered air barrier/vapour retarder (also the weather barrier layer) membrane installed onto the sheathing; and
  • new fibreglass thermal clips connecting the cladding to the sheathing to reduce thermal bridging through the semi-rigid insulation layer.

The cladding types utilized for this remediation project were fibre-cement panels and horizontal corrugated metal panels.

Challenges during design and construction included providing proper structural support at all the joints in the new fibre-cement panels, and at transitions between wall cladding types. This required careful planning prior to installation of the fibreglass thermal clips and Z-girts. One of the disadvantages of this particular thermal clip is the lack of possible adjustment—both laterally (i.e. side to side) and front to back—to allow for construction tolerances. Therefore, the clip must be shimmed if the exterior wall sheathing is not plumb.

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