Understanding ASHRAE 90.1's Performance Threshold

When you're using Appendix G to demonstrate code compliance in ASHRAE 90.1-2019, PCIt is the number you need to beat. It's the Performance Cost Index Target, the threshold that determines whether your building is efficient enough to pass.

The formula looks like this:

PCIt = [BBUEC + (BPF × BBREC)] / BBP

That's not particularly illuminating on its own, so let's break down what these terms actually mean and why they're structured this way.

The Components

BBUEC is your baseline building's unregulated energy cost. Unregulated energy is everything the code doesn't directly control: elevators, commercial kitchen equipment, medical devices, datacenter loads, that sort of thing. ASHRAE doesn't care what compressor you spec for a walk-in freezer, but the energy it uses still gets counted in the overall budget.

BBREC is the baseline building's regulated energy cost. This is the stuff ASHRAE does regulate: HVAC systems, lighting, service water heating, and similar building systems. The things the standard was actually written to address.

BBP is baseline building performance, which is just the total annual energy cost of your baseline building design. This is your reference point.

BPF is where it gets interesting. The building performance factor comes from Table 4.2.1.1 and varies by building type and climate zone. A school in climate zone 0A gets a BPF of 0.39. A warehouse in climate zone 8 gets 0.57. The lower the number, the tighter the performance requirement.

This makes sense when you think about it. Schools have relatively predictable schedules and loads, so the standard expects better performance from them. Hospitals run 24/7 with specialized equipment that draws power regardless of how good your envelope is, so they get more leeway. Though "leeway" is relative when we're talking about energy code compliance.

If your building has multiple use types, you calculate an area-weighted average of the BPFs. For anything not explicitly listed in the table, you use "All others," which ranges from 0.50 to 0.57 depending on climate.

Building Performance Factors by Type and Climate

Here's the full BPF table from the standard:

Building Area Type	0A/1A	0B/1B	2A	2B	3A	3B	3C	4A	4B	4C	5A	5B	5C	6A	6B	7	8
Multifamily	0.68	0.70	0.66	0.66	0.69	0.68	0.59	0.74	0.76	0.74	0.70	0.73	0.75	0.68	0.71	0.68	0.72
Healthcare/hospital	0.60	0.60	0.58	0.54	0.56	0.55	0.55	0.55	0.54	0.54	0.57	0.52	0.54	0.57	0.52	0.57	0.57
Hotel/motel	0.55	0.53	0.53	0.52	0.53	0.54	0.54	0.53	0.53	0.52	0.50	0.51	0.51	0.50	0.51	0.50	0.50
Office	0.52	0.57	0.50	0.56	0.53	0.56	0.48	0.51	0.52	0.49	0.51	0.51	0.49	0.52	0.51	0.49	0.51
Restaurant	0.63	0.64	0.60	0.60	0.60	0.61	0.58	0.62	0.57	0.61	0.63	0.60	0.64	0.65	0.62	0.67	0.70
Retail	0.51	0.54	0.49	0.55	0.51	0.55	0.53	0.51	0.55	0.54	0.50	0.54	0.55	0.50	0.51	0.48	0.50
School	0.39	0.47	0.38	0.43	0.38	0.42	0.40	0.37	0.40	0.38	0.36	0.40	0.36	0.36	0.37	0.36	0.37
Warehouse	0.38	0.42	0.40	0.42	0.43	0.44	0.43	0.44	0.43	0.46	0.49	0.47	0.48	0.54	0.51	0.57	0.57
All others	0.56	0.57	0.50	0.52	0.50	0.54	0.53	0.53	0.52	0.54	0.51	0.51	0.50	0.50	0.50	0.50	--

Climate zones run from 0 (hottest) to 8 (coldest), with A/B/C subdivisions for humidity levels. The BPF values are calibrated so compliance represents roughly equivalent effort across these different contexts. A hospital in climate zone 0A and a hospital in climate zone 8 both show BPFs around 0.57 to 0.60, but the actual energy strategies needed to hit those targets look completely different.

You'll notice schools are consistently the tightest, ranging from 0.36 to 0.47. Retail swings from 0.48 to 0.55. Multifamily is generally the most lenient, getting into the 0.68 to 0.76 range in some climate zones.

Those nine categories don't cover everything you'll encounter in practice. What do you do with a vivarium? A sports complex? A manufacturing facility or data center? These don't map cleanly to the table, and "All others" ends up carrying a lot of weight. This matters because getting categorized wrong can shift your compliance threshold significantly.

How It Works

The formula takes your baseline building's unregulated energy cost and adds it to the regulated energy cost multiplied by that building-specific performance factor. Then you divide the whole thing by the baseline building performance to get your target.

Your actual PCI (Performance Cost Index) uses the same formula structure but plugs in your proposed building's performance numbers instead. If your PCI is less than or equal to PCIt, you're in compliance.

There's one complication worth noting. If you're generating more than 5% of your building's energy from on-site renewables (as a fraction of baseline building performance), an additional compliance check kicks in:

PCI + [(PBPnre – PBP)/BBP] – 0.05 < PCIt

This prevents you from solar-paneling your way past mediocre envelope and mechanical design. The standard wants efficient buildings first, renewable energy second. You can't just throw photovoltaics at a poorly designed building and call it done.

Calculating Regulated vs. Unregulated

The standard requires you to calculate regulated energy cost by multiplying total energy cost by the ratio of regulated energy use to total energy use for each fuel type. Unregulated energy cost is just total energy cost minus regulated energy cost.

This gets done separately for electricity, natural gas, and any other fuel sources, then summed up. It's not complicated math, but it does require tracking your energy use by end use and fuel type, which means your energy model needs to be properly detailed from the start.

The BPF gets applied to adjust the regulated HVAC costs, effectively to account for unregulated loads in the calculation. For buildings where ventilation requirements or process loads dominate the energy profile, this adjustment can have significant impacts on your compliance margin.

The Practical Impact

In practice, PCIt determines how much performance headroom you have. A higher BPF means a higher target, which means your proposed building can use more energy and still comply. A lower BPF tightens the requirements.

For projects using the performance path, this is the number that drives design decisions. You're constantly checking your PCI against PCIt as the design develops. Envelope improvements, mechanical system upgrades, lighting strategies all get evaluated based on whether they move your PCI in the right direction relative to this target.

It's worth noting that this whole framework only applies when you're using Appendix G. The prescriptive path (Sections 5 through 10) and the Energy Cost Budget method (Section 11) have their own compliance approaches. But for larger or more complex buildings, Appendix G and its PCIt calculation is often the most practical route.

The BPF values were derived from prototype building models developed by Pacific Northwest National Laboratory. These prototypes are simplified representations intended for large-scale portfolio analysis of building stock performance across different climate zones. The models were built in EnergyPlus and calibrated to represent typical construction and operation patterns for each building type.

The system provides a consistent framework for performance-based compliance that accounts for the reality that buildings in different climates serving different purposes face different challenges. Whether you're working on a school in Phoenix or a hotel in Minneapolis, the BPF adjusts the compliance threshold to reflect what's actually achievable in that context.