What Is Gross Floor Area in ENERGY STAR Portfolio Manager?

Gross floor area in ENERGY STAR Portfolio Manager is one of the most important building details owners enter when benchmarking a property.

It is surprisingly, also one of the easiest things to get wrong.

In simple terms, gross floor area is the total square footage associated with a property use in Portfolio Manager. It helps Portfolio Manager calculate energy use intensity, or EUI, which is a building’s annual energy use divided by its floor area.

That means gross floor area directly affects how your building’s energy performance is measured. If the square footage is too low, the building may look less efficient than it really is. If the square footage is too high, the building may look artificially better.

For building owners, property managers, and anyone adding a property in Portfolio Manager, getting gross floor area right is not just a data-entry detail. It can affect benchmarking results, ENERGY STAR scores, compliance records, audit planning, and how a building is compared against similar properties.

Gross Floor Area Is Not Always the Same as Rentable Square Footage

One of the most common mistakes is assuming gross floor area is the same as rentable square footage.

It is not always the same.

Rentable square footage is often used for leasing. It may include tenant areas plus a share of common areas, depending on the lease structure and measurement standard.

Gross floor area for Portfolio Manager is used for energy benchmarking. It should only reflect the building area associated with the energy being reported.

A building owner may have several square footage numbers available:

Rentable square footage
Leasable square footage
Assessor square footage
Conditioned square footage
Gross building area
Gross floor area
Parking area

The best number for Portfolio Manager is usually the one that accurately represents all areas of the building that contribute to its energy, water, and gas usage.

Why Gross Floor Area Matters for EUI

Portfolio Manager calculates EUI by dividing annual energy use by gross floor area. That makes GFA a major input.

For example, imagine two buildings use the same amount of energy in a year.

Building A is 50,000 sq. ft.
Building B is 100,000 sq. ft.

Even with the same annual energy use, Building B will have a lower EUI because that energy is spread across more square footage.

This is why incorrect gross floor area can make a building’s EUI a deceiving statistic.

A small error may not seem like a big deal, but in benchmarking, building performance standards, audit planning, or compliance reporting, the wrong square footage can tell the wrong story.

What Usually Counts Toward Gross Floor Area?

The exact details depend on your building’s property type, but in general, gross floor area usually includes enclosed building space related to the property use.

That can include:

Occupied tenant areas
Vacant tenant areas
Offices
Lobbies
Hallways
Restrooms
Conference rooms
Storage areas
Mechanical rooms
Stairways
Elevator shafts
Interior common areas
Staff areas
Maintenance areas

Portfolio Manager usually wants the full physical space within the building for that property use, not just the space that is occupied, rented, or conditioned.

If the energy meters serve the entire building, the GFA should generally represent the entire building area, not just the occupied units or tenant spaces.

What Usually Does Not Count Toward Gross Floor Area?

Some areas that are not usually included in the main building GFA are:

Outdoor loading docks
Exterior seating areas
Unroofed courtyards
Outdoor parking lots
Open-air areas that are not fully enclosed
Exterior walkways
Outdoor equipment yards
Landscaping areas

Many individuals entering data into Portfolio Manager make the mistake of including every part of the parcel instead of the building. Portfolio Manager is not asking for lot size. It is asking for the floor area of the property use being benchmarked.

Keep in mind, parcel area and building gross floor area are not the same thing.

How to Handle Parking in Portfolio Manager

Parking is one of the biggest sources of confusion.

It’s important to note that, parking should not automatically be included in the main building gross floor area. If parking energy is included in the utility meters, Portfolio Manager generally allows parking to be entered as a separate property use.

For enclosed or partially enclosed garages, parking GFA may include the garage area itself, ramps, storage rooms, mechanical rooms, elevator shafts, stairwells, and other related garage areas.

Open parking lots are handled differently than enclosed parking garages.

The important point is this:

Do not mix parking area into the main building GFA unless Portfolio Manager’s instructions for that property and program require it.

For example, if you are entering an office building with a parking garage, you would typically enter the office GFA under Office and enter the garage under Parking if the garage’s energy is included.

Gross Floor Area for Multifamily Buildings

Multifamily properties are another common source of errors.

For Portfolio Manager, multifamily housing generally includes more than just the individual apartment or condo units.

Gross floor area for multifamily should usually include:

Residential living units
Vacant units
Lobbies
Interior common areas
Hallways
Community rooms
Fitness rooms
Common kitchens
Indoor pools
Storage areas
Mechanical rooms
Stairwells
Elevator shafts
Connecting corridors

Owners sometimes enter only the unit square footage multiplied by the number of units. That can understate the building size if the energy meters also serve common areas, corridors, lobbies, elevators, and central systems.

Open-air breezeways and other areas that are not fully enclosed generally should not be included in multifamily GFA.

The best approach is to use the total enclosed building area, then separately identify parking if applicable.

Gross Floor Area for Warehouses

Warehouses can seem simple, but they still require care.

For a non-refrigerated warehouse, GFA should generally include the warehouse floor area plus enclosed supporting spaces such as administrative offices, restrooms, equipment storage, stairways, and elevator shafts.

However, exterior loading docks or outdoor loading bays should not usually be included in the warehouse GFA.

Owners should also pay attention to whether the warehouse has cold storage, refrigeration, manufacturing, office buildout, or other specialized uses. Those details can affect how the building should be entered.

A warehouse with a small office may still be entered primarily as warehouse. A warehouse with a large office component may require more careful separation.

Gross Floor Area for Mixed-Use Buildings

Mixed-use buildings are where confusion is even more prevalent.

A property may include:

Retail
Office
Restaurant
Multifamily
Parking
Warehouse
Medical office
Fitness space
Data center space

Do not force the entire building into one property type if multiple uses are significant.

Portfolio Manager allows owners to create separate property uses when needed. This is especially important when a secondary use is large, eligible for an ENERGY STAR score, has very different operating hours, or affects energy use differently than the main building.

For example, a building with apartments above ground-floor retail may need Multifamily Housing and Retail entered separately.

An office building with a small lobby coffee shop may not need a separate restaurant property use if the space is minor and operates similarly to the building. But a large restaurant, grocery store, data center, or medical office space could need separate treatment.

When in doubt, ask:

Does this use materially affect energy consumption?
Does it represent a large share of the building?
Does it operate on a very different schedule?
Does it have separate meters or equipment?
Would combining it distort the building’s performance?

Common Gross Floor Area Mistakes

Here are the most common GFA mistakes in ENERGY STAR Portfolio Manager:

Using rentable square footage instead of gross floor area
Using parcel size instead of building area
Forgetting common areas in multifamily buildings
Including outdoor loading docks in warehouse GFA
Including parking in the main building GFA
Ignoring mixed-use space
Using an outdated assessor number after a renovation
Entering only occupied space
Failing to update GFA after additions or conversions
Using a temporary estimate and never correcting it

These mistakes can affect EUI, ENERGY STAR scores, compliance submissions, and year-over-year benchmarking trends.

How to Find the Right Gross Floor Area

Building owners can usually find GFA from:

Building plans
BOMA area reports
Assessor records
Prior benchmarking records
Architectural drawings
Property condition reports
Appraisal documents
Owner records
Condo or HOA records
Lease abstracts, with caution
Measured building surveys

If you must enter a temporary estimate, label it internally and replace it once the correct number is confirmed. The worst approach is not using an estimate temporarily.

What Did We Learn?

Gross floor area in ENERGY STAR Portfolio Manager is more than a square footage field.

It affects EUI, benchmarking results, ENERGY STAR scores, compliance reporting, and how owners understand building performance.

The right GFA should reflect the actual building area associated with the energy being reported. That means owners should carefully review what counts, what does not, how parking is handled, and whether mixed-use spaces need to be separated.

Clean benchmarking starts with clean building information.

Before worrying about the score, make sure the foundation is right.

IE Energy helps building owners and property managers review ENERGY STAR Portfolio Manager inputs, confirm building data, resolve benchmarking issues, and prepare accurate energy compliance submissions.