Principles and precepts
While this kind of overcladding is an extensive project, it offers several attractive benefits. For instance, thermal performance and air tightness are significantly improved, which helps eliminate moisture and condensation issues. Further, overcladding can boost desirable acoustic isolation and attenuation. Properly executed, overcladding can also optimize the use of a masonry enclosure’s thermal mass. It can add decades to the structure’s service life expectancy without decreasing room sizes, as with interior facade stabilization and insulating options.
Specific considerations for facade overcladding approaches are like those for any enclosure assemblies retrofit that are predominantly masonry, including bearing walls and brick veneer. Design goals include:
- Increasing thermal performance.
- Providing an air and water barrier.
- Providing fire/smoke containment to enhance building resilience.
- Modest costs in addition to short design and construction schedules.
- Allowing the building to be largely occupied and accessible during construction.
- Limiting the amount of disturbance to occupant or tenant operations.
Another critical consideration is the retrofit approach should allow the limiting of overcladding system weight to stay below structural framing load capacities. Typical limits for steel-framed, masonry veneer systems, for example, would be about five per cent of the dead load threshold for steel structural members, and 10 per cent of building lateral loads.
Done well, overcladding will improve building esthetics with relatively minimal impacts to occupants during installation. Green retrofit projects and building rehabilitations should be designed to tighten up the building envelope for better thermal efficiencies, not to mention dramatically reduced air and moisture infiltration. Overcladding options include energy-efficient insulated wall systems, silicone sealant and gaskets for glazed areas, new air and vapour barriers transitioning into window openings, and the sealing of all window-wall interfaces.
So where does one start? For example, how much insulation is required, and where should the vapour barrier be located? What are the benefits and disadvantages of overcladding for masonry assemblies? These are good questions, and the project team should start with the basics, as a pioneering enclosure guru, the late Wagdy Anis, would say: heat, air, and moisture, or HAM.
Heat (and cold)
Overcladding, as with all enclosure design opportunities, hinges on climate. The climate zone will dictate many of the design choices, such as the location of air and vapour barriers. The building configuration, orientation, and the local site’s topography, prevailing winds, external shadowing, and direct sunlight will determine what the enclosure needs during heating and cooling seasons. In all climates, ci is important—the insulating layer should not be interrupted by structural members or thermal bridges, such as metal elements that extend from the building interior through the insulation layer to the exterior. Thermal breaks at window frames, for example, ensure effective ci.
Project teams can use building information modelling (BIM) or U-value calculations to determine enclosure properties. Another option is the simplified building energy model (SBEM), a standard used to determine the energy efficiency of commercial properties. The methods allow project teams to evaluate heat flows and the overcladding design’s impact on energy performance. Variables include window-wall rations (WWRs), insulation levels, and barrier types, uses, and location. For projects in Canada, the team should ensure compliance with the National Energy Code of Canada for Buildings (NECB), Part 8.
