The race to modernize office buildings is in full swing, with owners and architects transforming underused spaces into vibrant rooftop terraces, loggias, and outdoor gathering spaces. But modifying a building’s façade isn’t just about aesthetics – it requires compliance with the energy code which could impact the project scope and cost.
Here’s what you need to know before making changes to the building envelope (walls, windows, and roofs):
1. Energy Code Compliance is Mandatory
If you’re adding to or modifying the building envelope, the new design must meet energy code requirements. This may get complicated, as there are multiple energy code options among our local jurisdictions (IECC, ASHRAE 90.1, and local code amendments) and multiple paths for compliance within each of those code options. In most jurisdictions, the three available compliance paths are:
Prescriptive: Each component of the new facade must comply with the prescriptive requirements listed in the applicable energy code.
Tradeoff: Use a simplified modeling tool (like Comcheck) to offset slight “deficiencies” in a particular construction type by improving efficiency in other construction types. Example: Using windows with a solar heat gain coefficient that exceeds the prescriptive requirement of the energy code to compensate for a roof insulation that does not meet the minimum requirements.
Performance: Use an energy modeling program to prove your proposed building (with modifications) is more efficient than a baseline building in terms of overall annual energy consumption or cost. The model includes everything from the building facade to HVAC systems, lighting, plug loads, miscellaneous equipment, and renewable energy systems, and it incrementally calculates the energy consumed by these systems across the year. In our example above, instead of improving window performance to offset deficient roof insulation, we could improve the efficiency of the HVAC central plant or design a higher efficiency interior lighting system and achieve the same result.
It is important to note that some compliance paths are only allowed under certain conditions. For example, in DC, if the facade more than 40% glass, the project will likely need to pursue the performance path (energy model) to demonstrate compliance with the energy code. Virginia and Maryland have similar rules, with varying glass percentage triggers.
2. Plan Early to Avoid Surprises
If a project involves a facade modification, the design team should calculate the window-to-wall ratio of the new facade and the building as a whole early in the project. If either ratio is lower than the threshold triggering the performance path (40% in DC), then the project can comply relatively easily by specifying a new facade that complies with the prescriptive requirements in the code. However, most commercial office buildings in the DC area have window-to-wall ratios higher than the thresholds triggering the performance path. In these cases, architects and owners should engage their MEP engineer early in the project to assess options for code compliance. An energy model will likely be required, which will take time to develop and could produce results showing that additional design scope is required for code compliance, such as upgraded lighting, HVAC, or insulation. If these upgrades are required, that scope will need to be included in the same permit set as the façade modifications.
Initiating this process early will help identify any cost implications and potential impacts to the project schedule. This applies to any project that consists of an addition or modifications to the building envelope. GHT has guided numerous projects through this process, including 1250 Eye Street, NW, 1101 Connecticut Avenue, NW, and the upcoming transformation at 1275 K Street, NW.
