Protect Your Basis: Square Footage Due Diligence Before You Close

To verify a building’s square footage before purchase, do three things. Confirm which measurement standard produced the stated RSF and when, documented in a report or spreadsheet rather than asserted. Reconcile the rent roll’s suite RSF against the source measurement records. Field-verify the building independently rather than relying on the seller’s documents.

Most diligence checklists stop at step one. The value is in steps two and three.

Every dollar of your pro forma is priced per square foot of rentable area you haven’t independently confirmed. Here’s how to make that number yours instead of the seller’s.

Why Is Stated RSF a Risk at Acquisition?

Because the stated rentable is usually inherited, not verified. It came from a prior owner, who may have gotten it from a prior owner, who may have derived it from scaled drawings that describe what was designed rather than what was built.

Along the way, the building lived: buildouts, demising changes, corridor reconfigurations, amenity additions. And the standard itself moved — BOMA’s 2024 revision changed what counts as rentable. A stated RSF can be off in either direction, and both directions cost you.

If the building measures smaller than stated, you’re overpaying on day one and inheriting future tenant disputes.

If it measures larger, the seller is handing you upside they haven’t priced — but only if you know before close. Found area discovered after closing is nice. Found area confirmed before closing is negotiating room.

At acquisition pricing, 3% on a $200M asset is real money in either direction.

What Should Measurement Due Diligence Cover?

Five questions, in rising order of effort.

1. Which standard, what version? BOMA 2024, 2017, 2010, or older? Measured when, by whom? If this can’t be answered, treat the stated RSF as an estimate.

2. Was it field-verified? A number calculated from drawings, especially paper drawings, is an estimate. Field measurement confirms what’s physically built: demising walls, tenant improvements, common area configurations.

3. Do the leases reconcile? Pull suite areas from the leases and compare them to the rent roll and to the measurement report, if one exists. Interior improvement permits create a common gap here: the interior architect’s suite calculation gets used for city permits, that number often lands in the lease, and it was produced suite by suite with no view of the whole building. Lease, rent roll, and building totals that don’t reconcile are telling you something.

4. How were load factors derived? Load factors are frequently market-driven rather than grounded in the building’s actual measurement. Current load factors should trace back to measured areas.

5. What would the building measure under BOMA 2024? This is the upside question. Outdoor amenity areas, tenant-dedicated shafts, and other 2024 changes often mean an asset generates a larger rentable under the current standard than under the one it was last measured by.

What Does Independent Verification Catch That Document Review Misses?

The gap between paper and building. In 40 years of field verification work we see the same patterns: common areas classified in ways that understate rentable area, vertical penetrations applied inconsistently from floor to floor, suites measured to boundaries the walls don’t match, and whole categories of space — storage, terraces, shafts — that the old standard couldn’t count.

None of this is visible in a data room. All of it is visible in the building.

“We’re often the only company that field-verifies what’s actually built. Most available information tells you what the seller believes. Field verification tells you what you’re actually buying.”

The deliverable matters too. An independent, third-party measurement to the current BOMA standard, performed by the firm whose team co-authors that standard, gives you a rentable number you can take to your investment committee, your lender, and eventually your buyer. Lenders in particular respond to defensible area numbers; their underwriting rests on the same NOI yours does.

When in the Deal Should Measurement Happen?

Inside the diligence window, as early as possible. A whole-building verification is fast relative to environmental and structural workstreams, and its findings feed everything downstream: the Argus model, the financing package, the price conversation.

Two timing notes from the field:

• Buy side: verification before close protects basis and arms negotiation. After close, it still finds the area, but the pricing conversation is over.
• Sell side: the same engagement run pre-disposition lets you price found area into the exit. Sellers who skip it donate their unrecognized rentable area to the buyer.

What This Protects

A 3% variance on a $200M asset moves your basis by roughly $6M, and it moves in either direction. Understated RSF is upside the seller hasn’t priced. Overstated RSF is an overpayment plus the tenant disputes that come with it. Three things, in rising order of effort.

Ask the five questions during document review. Standard, vintage, verification, lease reconciliation, load factor derivation. It costs nothing, and it tells you whether you have a problem worth sizing.

Field-verify independently inside the diligence window. It sequences fast against environmental and structural, and the findings feed the Argus model, the financing package, and the price conversation while all three are still open.

Do it before close, not after. After close it’s still found area. Before close it’s negotiating room.

Whichever direction the number moves, it moves once — into your basis, at signing. Everything after that is you living with someone else’s measurement.

Frequently Asked Questions

How do I verify a building’s square footage before buying it?

Confirm the measurement standard and version behind the stated RSF, reconcile leases and rent roll against source measurement records, and commission an independent field verification to the current BOMA standard.

What is RSF verification?

An independent, third-party measurement that confirms or corrects a building’s stated rentable area. It’s designed for buyers whose target’s RSF was inherited, estimated from drawings, or never field-verified.

How long does measurement due diligence take?

It fits comfortably inside a customary 30-to-90-day diligence window, and SSI typically sequences it early so findings can inform pricing.

What if the building measures bigger than stated?

That’s found rentable area: recurring revenue the seller hasn’t priced. Confirmed before close, it’s upside you bought without paying for.