More on the Denver Green Roof Initiative that passed in November and that we blogged on earlier this month. As we track the progress of the Review Task Force, Group14 anticipates modifications that will allow design teams to achieve equivalent environmental benefits through other approaches.
The task force is looking at Seattle’s Green Building Standard and Chicago’s Green Permit Program. Both programs offer permit incentives and require green building certification, such as LEED. The task force also heard from the Denver Building Department that they are considering the International Green Construction Code (IgCC) as a stretch code.
Denver also has the opportunity to leverage incentives from Xcel Energy and Denver Water with these alternative approaches. Group14 has been a consultant for Xcel’s Energy Design Assistance program (EDA) for ten years now. Xcel’s EDA program has goals of 15% electricity demand savings and 15% natural gas savings.
Group14 performs energy modeling and guides teams on the most cost-effective energy efficiency solutions. On average, the projects Group14 works on to realize a 20% energy cost savings under 2015 International Energy Conservation Code (IECC). The energy modeling can also be used to demonstrate compliance with the 2015 IECC.
Using our Front Range projects as case studies, we estimated the associated cost for the area of the green roof required under the initiative. Using $25/sf as the cost estimate for a green roof (recognizing this depends on the application) the first cost for a green roof is estimated at $3-$5/sf of conditioned building area. However, K-12 schools may see double these costs due to the larger average roof area.
For comparison, the annual energy cost savings Group14 predicted for these projects is about 1/10th the cost of the green roof. The energy savings are not related to green roofs; they are the energy savings primarily from better glazing, efficient lighting design, and high-performance mechanical systems. The obvious question is how much do the energy efficiency improvements cost? Simply stated, we typically see an 8-12 year payback on the upgrades and shorter still by installing LED lighting. Depending on the goals of a project, the investment in energy efficiency can be within the same price range as the cost of a green roof.
Group14 is a strong proponent for the City of Denver allowing alternative approaches to achieving equivalent environmental benefits of a green roof under the initiative. Our first pass on comparing the cost of a green roof with that of energy efficiency improvements, or green certification, is that the costs are the same order of magnitude. While the realized environment benefits differ with each approach, a design team should pursue what makes the most sense for the project.