Building an Addition in DC? Here’s 5 Things You Need to Know


With a surge of new Class A commercial office buildings entering the DC market, existing property owners are considering how best to upgrade their buildings to attract and retain top tenants. High-visibility rooftop amenity spaces and two-story glass lobbies are renovation musts, especially in light of recent changes to DC zoning laws which favor occupiable rooftops. However, adding multiple areas of fenestration isn’t as easy as it used to be in a town with a new emphasis and outlook on green building.

Cost-friendly monolithic glass additions are often chosen due to ease of construction – before you decide to add a rooftop amenity space or new glass vestibule to your property, here are 5 things you need to know:


1. The DC Green Code Requires Strict Adherence to the IECC & ASHRAE 90.1

Any building addition in DC must comply with the requirements of ASHRAE 90.1 or the IECC. If these additions have more than roughly 50% glass by area, it becomes extremely difficult to adhere to the energy code without an energy model and making improvements to your building outside of the Addition’s scope of work.


2.  Additions Can Be Energy-Consuming & Decrease Overall Building Efficiency

Additional square footage in the building, coupled with an all- or mostly-glass façade, has the ability to negatively impact your property’s overall efficiency. Heating and cooling this additional space could require significant overhauls to the building’s HVAC systems – a cost frequently not considered by owners embarking on a quick facelift.


3. Energy Modeling Can Help Simulate the Whole Building’s Consumption

Many of the scenarios encountered in DC cannot simply be addressed by the Prescriptive or Comcheck Tradeoff approach. They each require an experienced energy modeler to analyze the options, run the model iterations, provide recommendations, and create the supporting documentation to prove code compliance to DCRA.


 4. Changes Elsewhere Can Offset Your New Addition

 GHT has helped many owners and architects offset the energy consumed by a new addition through the following sample strategies:

  • Including a retrofit in the Scope of Work that you’ve been meaning to do for a while. Replacing 30-year old lighting in a below-grade garage can easily offset the inefficiency of a new 2-story all-glass vestibule.
  • Removing old 2” insulated ballast roof and replacing it with an R-30 continuously insulated high SRI roofing system can support a rooftop amenity space with floor-to-ceiling glass.
  • Providing a new Variable Refrigerant System for ground floor retail tenants could allow installation of new 10’ tall storefront windows to entice tenants and retail customers.


5. Documentation from Energy Modeling Can Ensure DCRA Compliance During Permitting

On a new Class A upgrade, the GHT team was able to use a detailed energy model to prove code compliance and receive permitting approval from DCRA. The Owner wanted to build a new 2-story all-glass entry lobby to command additional street presence.  However, the space was small enough that there were no options to trade off façade inefficiency with lighting or HVAC improvements.  As such, the team was able to replace glazing and make changes to the perimeter HVAC system type on the office floors to offset the increased glass in the new entry lobby – resulting in permitting approval from DCRA.


As experienced energy modeler’s, we specialize in helping owners successfully navigate this process to avoid complications and stay code complaint with DCRA. GHT completes these tasks for numerous renovation projects in the DC area, and we will happily work with your team to make your vision a reality.

For specifics on the methodology and options for energy code compliance, call or email us today. To learn more about this process, schedule a lunch ‘n learn with us by emailing

James Hansen, PE, BEMP, LEED AP is a Principal and Senior Mechanical Engineer with over 20 years of experience. He provides engineering design, energy modeling and project management support for a wide range of projects in the Building Systems, Interiors and OES Studios. James has extensive experience with the US Department of Energy’s building modeling engine (DOE-2.1E) using multiple interfaces, including DOE-Plus and eQuest. He is also familiar with CONTAMW, the building pressurization/smoke control modeling software that is becoming the accepted method for verification of stair pressurization design in the Washington, DC area. James is a Professional Engineer registered in three states and the District of Columbia.