What is a common area factor (CAF)? How it affects your rent

When searching for commercial space, most tenants focus on location, size, and the advertised rent per square foot. However, one often-overlooked factor can significantly change the real cost of a lease: the Common Area Factor (CAF). Without understanding how CAF works, it can be difficult to compare properties or estimate your true occupancy costs. This guide explains what a Common Area Factor is and why it plays a crucial role in the rent you pay.

A Common Area Factor (CAF), sometimes called a load factor or add-on factor, is the percentage of shared building space that is added to your private office space to determine how much rent you pay. In commercial buildings, tenants don’t just pay for the space inside their own office or shop; they also contribute to the cost of maintaining the areas everyone uses.

These shared areas typically include lobbies, hallways, lifts, stairwells, shared bathrooms, reception zones, and sometimes amenities such as meeting rooms or kitchens. Because all tenants benefit from these spaces, landlords spread the cost across everyone in the building through the CAF.

In simple terms, CAF explains the difference between usable square footage and rentable square footage. Your rentable area equals your usable space plus a portion of the common areas. This means even if two offices have the same usable size, the one in a building with more shared facilities may have a larger rentable size and therefore higher rent.

When leasing commercial space, one of the most important concepts to understand is the difference between usable square footage (USF) and rentable square footage (RSF), because your rent is based on the latter, not the former.

Usable area

Usable area (USF) refers to the space your business actually occupies and uses every day. This includes your private office, workstations, meeting rooms, storage areas and internal corridors within your suite. In short, it’s the area your team can physically work in and control.

Rentable area

Rentable area (RSF), on the other hand, is the number used to calculate your rent. It includes your usable space plus a portion of the building’s shared areas. These shared spaces can include the lobby, lifts, stairwells, shared bathrooms, corridors, and other amenities that all tenants rely on.

This is where the Common Area Factor comes into play. Landlords distribute the cost of maintaining and operating shared spaces across all tenants by adding a percentage (the CAF) to each tenant’s usable space. As a result, the rentable area is always larger than the usable area.

The basic formula is: Rentable Area (RSF) = Usable Area (USF) × (1 + CAF)

Imagine your business needs 1,000 sq ft of usable space and the building has a 15% CAF:
– Convert the percentage to a decimal -> 15% = 0.15
– Apply the formula -> 1,000 × (1 + 0.15)
– Your rentable area becomes 1,150 sq ft

The Common Area Factor has a direct impact on how much you actually pay for a commercial lease, often more than tenants expect. This is because rent is calculated using rentable square footage (RSF), not the usable space your business physically occupies.

You pay for more space than you use

For example, if the lease rate is $40 per sq ft and your usable office is 1,000 sq ft:
– With a 10% CAF -> you pay for 1,100 sq ft
– With a 20% CAF -> you pay for 1,200 sq ft

That difference alone can add thousands of dollars to your annual rent.

Amenities can increase the CAF

Buildings with premium facilities often have higher CAFs because there is more shared space to maintain, such as:
– Large reception areas and lobbies
– Fitness centres or shared meeting rooms
– Wide corridors and multiple lifts

While these features can improve the workplace experience, they also increase the rentable area and therefore the rent.

CAF makes comparing properties more difficult

Without understanding the CAF, tenants may assume two offices are similarly priced when they are not. A lower rent per square foot does not always mean a better deal if the building has a high common area factor. In short, the CAF directly influences your true occupancy cost, making it a critical number to review before signing any lease.