Ottawa office rent is $17.17 a foot. You will pay $35.22.

The number on the listing is the smaller half

Every office listing in Ottawa quotes one number. Colliers puts the weighted average at $17.17 a square foot net for the second quarter, up 0.3% on the quarter with vacancy at 13.2%. Landlords held that number through four straight quarters of rising vacancy, and CBRE, which counts vacancy at 15.0%, says the same thing: net asking rents have not moved.

The same Colliers table has a second column that almost nobody reads. Weighted average asking gross rent: $35.22. The $18.05 between the two columns is additional rent, and it is 51% of what you will actually write a cheque for. In Ottawa office, the rent is the smaller half of the rent.

What sits in the other $18.05

Additional rent is your proportionate share of three things: the building's realty taxes, its operating costs and its insurance. Your share is your suite's area over the building's rentable area. Nothing about it is fixed. The landlord estimates it in January, bills it monthly alongside the net rent, and reconciles it against actual costs after year end. If the estimate was low, the adjustment invoice arrives in the spring.

The tax piece is the line the landlord does not control. Ottawa applies a 2.39 office tax ratio to a value struck on January 1, 2016, which I went through last week. When the province finally reassesses, that line moves, and your lease passes it straight through.

The operating cost piece is where the lease language does the work. Most standard leases add an administration fee, usually 15% of operating costs, on top of the costs themselves. Lease auditors have been writing for years about landlords who also charge a separate management fee for the same work. Whether a new roof or a chiller can be billed through operating costs is decided by the definition in the lease, and the landlord's form is written so it can.

Then HST. Thirteen per cent on net rent and additional rent both. A registrant business gets it back as an input tax credit. A medical practice, which makes exempt supplies, mostly does not, which is one more reason the doctors' buildings price differently.

It is half the cheque everywhere, at every price

Pull the gross and net columns apart across the Colliers table and the share barely moves.

Downtown Class A: $23.58 net, $47.41 gross. Additional rent $23.83, or 50%. Downtown Class B: $16.20 net, $34.71 gross, $18.51 additional, 53%. Downtown Class C: $13.37 net, $26.06 gross, $12.69, 49%. Kanata, all classes: $13.84 net, $28.30 gross, $14.46, 51%. East Ottawa: $16.01 net, $34.44 gross, $18.43, 54%. South Ottawa, the tightest submarket at 8.8% vacancy: $15.06 net, $29.91 gross, $14.85, 50%.

Read that from the tenant's side. A Class C downtown suite is $10 a foot cheaper than a Class A suite in net rent. It is $21 a foot cheaper in gross. The additional rent gap is bigger than the rent gap. When you compare buildings on the quoted number, you are comparing on the number that varies least.

Why it climbs while your rent stands still

Three weeks ago I wrote that the average new Ottawa office lease stretched from 38 months to 61. Your net rent is fixed, or fixed with scheduled steps, for those 61 months. Additional rent is not. It resets every January for five years.

At 15% vacancy there is a second mechanism. Most office leases carry a gross-up clause. If the building is not full, the landlord may calculate variable operating costs as if it were, usually at 95% or 100% occupancy, so the empty floors do not dilute what the paying tenants cover. In a full building the clause does nothing. In a downtown Class B building at 15.8% vacancy, or an Ottawa West Class A building at 20.5%, it moves real money onto the tenants who stayed.

A 3,000 foot suite, five years out

Take a 3,000 square foot suite at the downtown Class B averages. Net rent of $16.20 is $4,050 a month. Additional rent of $18.51 is $4,628 a month. Gross is $8,678 before HST and $9,806 with it. The second line is already the bigger one on day one.

Now let additional rent drift 3% a year, a modest assumption with the tax reassessment unresolved. By year five it is $20.83 a foot. The drift alone costs $17,166 over the term. Compare that to the thing everyone negotiates: a dollar off the net rent is worth $15,000 over the same five years. The drift you did not cap costs more than the dollar you fought for.

At 4% a year it is $23,118. Nobody quotes that number in a proposal, because nobody asks for it.

What to ask for before you sign

Ask for the building's actual additional rent for the last three years, not the estimate for next year. The trend is the tell. A building where additional rent has run 4% a year will keep doing that.

Ask for a cap on the controllable costs. Taxes, utilities and insurance float. Management, cleaning, landscaping and repairs are the landlord's to manage, and a cap of 3% to 5% a year on that bucket is a normal request in a 13% vacancy market. Inducements are what the landlord offers. A cost cap is what you ask for.

Ask for the exclusions in writing: capital replacements, leasing commissions, the cost of fitting out other tenants' suites, an admin fee stacked on a management fee. Ask for the gross-up percentage to be stated and applied only to variable costs, never to realty tax. And ask for an audit right. The Commercial Tenancies Act does not give you one. Only your lease does.

None of this is hostile. A landlord with a well-run building has the statements and will hand them over. The one who will not is telling you something about the next five years of adjustment invoices.

The number to carry into the tour

Gross rent, per month, HST in, for the actual square footage. Rebuild every listing to that before you compare two buildings. On the average Ottawa office deal in 2026, the quoted rent is 49% of the answer.

If you are looking at office space this fall, send me the listing and I will send back what it costs per month, additional rent and HST included, with the last three years of the building's statements if the landlord will release them. 613-262-6545 or fil@613realtor.ca. Or start with what is on the market now.