Performance vs. Prescriptive Energy Code Pathways

We almost always use prescriptive for a simple reason.  Department of Buildings take four to six months for the review process so we submit at the end of Design Development.  To do the performance model we would not be able to submit till near the end of Construction Documents, and this woudl delay start of construction by at least four months.

From our AIA 2030 reporting, we're seeing energy models for about 30% of our projects nationwide and, usually, only because they can't (or won't) comply with a prescriptive requirement (e.g. WWR).  I would like to see more projects do an energy model, but if it doesn't do much good if it's only used for code compliance after the design is complete...

For most states, the energy code itself is a choice between IECC and the corresponding ASHRAE 90.1 version. Both options contain prescriptive and performance pathways but have different implications for design and firstcost. So, choosing between IECC and ASHRAE 90.1 and prescriptive and performance compliance pathways should be an early design collaborative effort on which most project teams should be spending at least a few hours. Ramana Koti LORD AECK SARGENT A KATERRA COMPANY

Prescriptive compliance is almost always easier, if you can meet the requirements.  But we do models on many projects that follow the prescriptive path. The key thing is to run models for design assistance, rather than merely for validation. If you are designing the building, then running a model on that design, you are wasting time and money. 

Design assist models are run early, and used to make decisions. They don't necessarily follow all the requirements a validation model would - you only model what you need to answer the questions at hand - no need to run a code baseline if that is never an option the client would consider.