Say the lease is signed, or about to be. Then a tenant asks about a dog, a second parking spot, who pays the water bill, or whether they can smoke on the patio. The lease doesn't say. That gap is where a lot of landlord headaches start, and a lease addendum is the cleanest fix. It works best when you understand how the full lease agreement fits together first, so the addendum backs up the lease instead of fighting it.

This post is for rental owners in Denver with single-family homes, townhomes, condos, or small multi-family buildings. We'll cover how to add an addendum the right way, then what pet, parking, utility, and smoking addenda each need to say. Colorado put hard caps on pet charges in 2024, so a few real numbers are coming.

In This Guide

What a Lease Addendum Actually Does

An addendum is a signed page that becomes part of the lease. It adds a rule or a cost the main lease doesn't cover. Think of it like a rider on an insurance policy. The base policy stays the same, and the rider spells out one specific thing.

A verbal "sure, bring the dog" is not an addendum. Neither is a text message or an email thread. If it isn't signed and attached to the lease, it's hard to point to later.

You'll find plenty of landlord tips Denver Colorado reddit threads that say "just add a clause." Skip that advice. A good addendum does a few specific things:

• Names the lease: property address, tenant names, and lease date.
• Covers one topic: pets, parking, utilities, or smoking, not all four in a pile.
• Uses plain numbers: exact dollar amounts and exact dates.
• Matches the lease: it never contradicts what the base lease says.

How to Add an Addendum, Step by Step

Here's the order we follow.

1. Decide the rule and the reason. Know what you want and why before a word gets written.
2. Check what already applies. Colorado law, your HOA, and city rules all sit on top of your lease. Denver rental license requirements are worth confirming too, since city rules change. Check the current requirements for your property.
3. Write it in plain language. If a 16-year-old can't follow it, rewrite it.
4. Tie it to the lease. Reference the property address and lease date at the top.
5. Walk the tenant through it. Our leasing agent, Gavin Kelly, goes through addenda with applicants before anyone signs, so nothing in them is a surprise.
6. Sign it electronically. We use DoorLoop, so addenda get signed and stored digitally with the lease. No paper chase.
7. Hand over a copy. It's also a good moment to point tenants to a tenant rights and resources guide so everyone starts from the same facts.

Every adult on the lease signs. That matters a lot in student housing and roommate setups, where one signature isn't enough.

The Pet Addendum

Pets are the addendum we see most. They're also the one with the tightest legal guardrails.

Know the Colorado Caps

Colorado law now caps what a pet addendum can charge:

• Pet deposit: no more than $300, and it must be refundable.
• Monthly pet rent: no more than $35 or 1.5% of the tenant's monthly rent, whichever is greater.

Take our average rent, which runs around $3,000 a month across the properties we manage. The pet rent cap there is $45. On a $1,500 rental, 1.5% is only $22.50, so the $35 floor applies.

Whether the $300 cap applies per pet or per household isn't settled. Check with an attorney before you charge for a second animal.

What Goes in the Addendum

• The animal: type, breed, weight, age, and name.
• Proof of vaccinations: collected before move-in.
• The money: deposit amount and monthly pet rent, within the caps.
• Damage: who pays for scratched floors, chewed trim, and stained carpet.
• Behavior rules: waste cleanup, leashes, noise.
• HOA limits: any breed or weight restrictions your building already has.

Why a Pet Policy With Teeth Beats a Flat Ban

Blanket no-pet rules don't stop pets. They push them underground. Say an owner in Washington Park lets a tenant keep a dog on a handshake, with no deposit, no weight limit, and nothing signed. When the tenant leaves, there's $1,800 in floor and trim damage. The owner has little on paper to back up a claim.

A clear addendum gives you more control than a ban you can't enforce. At our company, the pet policy depends on what each owner wants, and the addendum puts that choice in writing.

Assistance Animals Are a Separate Conversation

The pet caps apply to pets, not to assistance animals covered by a disability accommodation. We always allow ESA animals in Colorado, and we don't run those requests through the pet addendum. They follow a separate accommodation process. Fair housing rules on documentation change, so check current guidance before you answer one.

The Parking Addendum

Parking becomes a real line item fast in dense neighborhoods. In places like LoDo, RiNo, Capitol Hill, and Cherry Creek, off-street or garage parking can add a real monthly cost. That's worth putting on paper.

A good parking addendum covers:

• The space: number, location, and whether it's covered or in a garage.
• The cost: monthly amount and what happens if it changes.
• The vehicle: one registered car, or more?
• Guests: where visitors park and for how long.
• The no-go list: inoperable vehicles, storage, and towing rules.

If the space is optional, keep it a separate charge so the tenant can see what they're choosing. Rules on how required fees are disclosed have been changing, so check current requirements before billing a mandatory add-on.

The Utility Addendum

A lot of the older housing stock around here, including single-family homes and older multi-family buildings, was never built with separate meters for each unit. So who pays for what gets fuzzy quickly.

The addendum should name every utility and say who pays. A simple list works:

• Gas and electric: whose name is on the account.
• Water and sewer: paid by the tenant, or billed back some way.
• Trash: who arranges and pays for service.
• Internet and cable: tenant's choice and tenant's cost.

If you bill utilities back through a flat fee or a ratio system, spell out exactly how you calculate the amount. Say a duplex has one water meter. You'd state the split and the formula in writing, not just show up with a number each month. A utility charge that looks like a disguised rent increase invites a fight. Rules on utility billing and disclosure are in motion, so check the current rule first.

The Smoking Addendum

Most templated leases handle smoking with one line about tobacco. That's a gap.

Say a landlord adds a no-smoking clause that only mentions cigarettes. The tenant smokes marijuana on the back porch, or vapes in the bedroom. Technically it isn't tobacco, and the landlord has no written ground to act on.

Address each one separately:

• Tobacco
• Marijuana
• Vaping

Then name the places. Inside the unit, balcony, patio, yard, and garage might each get a different answer.

Here's our honest take. The smoking addendum isn't really about smoking. It's about remediation costs. Smoke settles into carpet, drywall, and ductwork, and cleaning it out can get expensive. The addendum, paired with move-in photos, gives you a documented basis if you ever need to claim those costs.

When an HOA or Property Type Changes the Answer

Your addendum has to fit the rules stacked above it. That's especially true for condos and townhomes.

Picture an owner with a LoDo condo who wants to allow a dog. The building's HOA prohibits pets over 25 pounds. If the pet addendum doesn't mirror that limit, the owner has approved an animal the building will eventually reject. Now there's a conflict in the middle of a tenancy with nothing in writing to resolve it.

We manage single-family homes, multi-family buildings, townhomes and condos, and student housing, and each one needs different addendum language. Check the HOA documents first. Then write the addendum to match them.

Adding an Addendum at Renewal or Mid-Lease

The easiest time to add one is before move-in. The second easiest is at renewal, when you're already updating terms and the tenant expects a conversation. Our lease renewal fee is 10% of one month's rent, disclosed up front, so on a $3,000 rental that's $300. Reviewing the addendum then costs nothing extra in effort.

Mid-lease is different. An addendum changes the deal, so the tenant has to agree, and rules about notice and fees can apply. Don't spring new fees on someone partway through a lease. Check the current Colorado rules or talk to an attorney first.

One owner who had us find a tenant for a townhome described the process as "very honest and transparent," with "accurate and timely communication, collaboration, and fair compromise." That's how addenda should work too. Explain them, hear the tenant out, and settle on terms both sides can live with.

Where Owners Get Tripped Up

The rental property owner questions Denver Colorado landlords ask us most tend to come back to the same few misses:

• Using a generic template: it skips marijuana, HOA limits, and local parking costs.
• Charging over the pet caps: it puts you on the wrong side of Colorado law.
• Relying on verbal approval: it vanishes when you need it.
• Skipping signatures: every adult on the lease needs to sign.
• Never revisiting it: a clause that fit two years ago might not fit today.

We've been managing rentals for 15 years and currently handle 60 properties. We keep our own fee schedule to one page, and we hold lease paperwork to the same standard. If an addendum is hard to read, it's not done.

If pets, parking, utilities, or smoking feel harder to put in writing than they should, Denver Leasing and Property Management is open to a conversation.

FAQ

Can I add an addendum after the lease is signed?

An addendum changes the agreement, so the tenant generally has to agree and sign. Rules on notice and new fees can apply mid-lease, so check the current Colorado rules or ask an attorney first.

How much can I charge for a pet deposit and pet rent in Colorado?

The pet deposit can't exceed $300 and must be refundable. Monthly pet rent can't exceed $35 or 1.5% of the tenant's monthly rent, whichever is greater.

Do emotional support animals pay pet rent or a pet deposit?

The pet caps apply to pets, not to assistance animals covered by a disability accommodation. We treat those requests separately from the pet addendum, and fair housing guidance on documentation changes, so check it before you respond.

Does every tenant on the lease need to sign the addendum?

Yes, every adult on the lease should sign. That matters most with roommates and student housing, where one signature leaves the others unbound.

Can I charge separately for parking?

If the space is optional, a separate monthly charge in a parking addendum is clear and common. If the charge is mandatory, check the current rules on how required fees must be disclosed.

Should I just use a free template?

A template is a starting point, not a finish line. Most skip marijuana and vaping, HOA limits, and your property's actual parking and utility setup.