Basement Apartment in Denver: Guest Suite and In-Law Guide
A basement apartment in Denver can give visiting family a private place to stay, give an aging parent their own space close by, or give a grown child a first step toward independence. Most Denver Metro homes already have the square footage sitting below the main floor. The question is what it takes to turn that space into a real guest suite or in-law apartment that is comfortable, safe and built to code.
This guide walks through the main pieces of a basement apartment project: bedroom egress, a bathroom, a kitchenette, entrance options, sound and fire separation, and heating and cooling. It also covers the one question we hear most often: can I rent it out?
The short answer on renting: it depends on your city's zoning rules, which vary across the metro.
What makes a basement apartment in Denver different from a finished basement?
A standard finished basement is extra living space for the household: a family room, an office, maybe a guest bedroom. A basement apartment, sometimes called an in-law suite or mother-in-law apartment, is designed so someone can live there with a high degree of independence. That usually means a bedroom, a full bathroom, a place to prepare food and a comfortable living area, all on one level.
That extra independence adds requirements. More plumbing, more electrical circuits, more attention to how the space is heated and cooled, and more thought about privacy between the two households. Planning those systems together from the start is what keeps the project on budget and avoids rework later.
Bedroom egress: the non-negotiable starting point
Any basement bedroom needs an egress opening, which is a window or door large enough for a person to get out and for a firefighter to get in during an emergency. In most basements that means cutting a larger opening in the foundation wall and installing an egress window with a proper window well.
Egress windows are typically about $2,000 to $5,000 per window in the Denver area, including excavation, the window well, installation and finishing. If you plan more than one bedroom, each one needs its own egress. The exact size and placement requirements depend on the building code your city has adopted, and your contractor confirms them during design and through the permit. Our guide to basement egress windows in Denver covers the process in more detail.
Adding a bathroom to a basement in-law suite
A full bathroom is what turns a guest room into a true suite. The biggest cost factor is whether your basement already has plumbing rough-in, the capped drain and supply lines many builders leave for a future bathroom.
With existing rough-in: adding a full bathroom is typically about $8,000 to $12,000 in the Denver area.
Without rough-in: cutting the concrete slab and running new drain lines typically puts it around $15,000 to $25,000 or more.
For an in-law apartment, it is worth thinking about accessibility now. A curbless or low-threshold shower, grab bar blocking in the walls and a wider doorway cost little to plan in and are expensive to add later.
Kitchenette or full kitchen?
Most basement guest suites in the Denver Metro use a kitchenette or wet bar: a sink, a run of cabinets, a small refrigerator, a microwave and some counter space. A kitchenette or wet bar is typically about $8,000 to $20,000 in our area, depending on cabinets, countertops and how far the plumbing has to travel.
A full kitchen with a range and full-size appliances is a larger step. It needs dedicated electrical circuits, ventilation, and sometimes a gas line, and it can affect how your city classifies the space. Our Premium Suite basement package includes a full kitchen with appliances, two egress bedrooms and zoned HVAC for homeowners who want a complete apartment. If you are not sure which level fits, our in-house design team can lay out both options so you can compare.
Separate entrance considerations
A private entrance is one of the features that makes a basement apartment feel like its own home. There are a few common approaches, each with tradeoffs:
Walkout basements often already have an exterior door, which makes this the simplest option.
New exterior stairwell: excavating and building an exterior stair with a door cut into the foundation is a significant structural project and needs drainage planning so water does not end up in the basement.
Shared interior entry: many in-law suites simply use the home's interior stairs, sometimes with a lockable door at the top or bottom for privacy.
Any new opening in a foundation wall is structural work that needs a permit and inspection. It is also one of the items your contractor should evaluate early, since lot grading and the location of utilities can limit where a door can go.
Sound and fire separation between floors
When two households share a house, sound travels. Insulating the ceiling between the basement and main floor, using resilient channels or sound-rated drywall, and sealing gaps around ducts and pipes all make a noticeable difference. Solid-core doors help too.
Fire safety matters just as much. Depending on how the space is used and what your city requires, a basement apartment may need fire-rated assemblies between units, interconnected smoke and carbon monoxide alarms, and specific separation at the furnace and water heater area. These requirements vary by jurisdiction and by whether the space is a guest suite for family or a separate dwelling unit, so we confirm them with the building department during permitting rather than guessing.
HVAC zoning and comfort in a basement guest suite
Basements in Colorado tend to run cooler than the floors above, and a single thermostat upstairs rarely keeps both levels comfortable. For a space someone lives in full time, it is worth looking at:
Zoned HVAC with dampers and a separate thermostat for the basement
A ductless mini-split for independent heating and cooling
Proper return air so the space does not feel stuffy
Bathroom and kitchenette ventilation vented to the outside
Your existing furnace capacity, duct layout and ceiling height all shape which option makes sense. We evaluate them during the onsite consultation.
Can a basement apartment be a rentable ADU?
This is where many homeowners need to slow down. A guest suite used by family is one thing. A rentable accessory dwelling unit (ADU) is a separate legal unit, and whether your basement can become one depends on your city's zoning rules, not just the building code.
Denver, Westminster, Thornton, Arvada and other Denver Metro cities each set their own rules for accessory dwellings, and those rules change over time. They can affect whether a second unit is allowed on your lot at all, and what conditions apply. We do not want you to rely on a blog post for that. As part of planning an ADU project, we verify the current zoning and permit requirements for your address with the city before design is finalized. ADUs are one of the basement services we offer, and you can read more on our basement finishing page.
Planning a basement apartment project?
Basement finishing in the Denver area typically runs about $40 to $90 per square foot, and high-end finishes can run $75,000 to $120,000 or more. A basement apartment usually sits toward the upper end because of the added bathroom, kitchenette, egress and HVAC work. These are typical ranges for the area, not a quote.
Mile High Remodel is a locally owned, licensed and insured design-build remodeler serving Denver, Arvada, Westminster, Thornton, Northglenn, Broomfield and nearby communities. Our in-house design team plans the layout, qualified first-time clients get complimentary 3D renderings, and we pull all required permits and handle inspections. Schedule your free consultation or call (720) 730-7174 to talk through your basement apartment ideas.
Frequently asked questions
Does a basement guest suite need an egress window?
Yes. Any basement room used as a bedroom needs an egress opening for emergency escape and rescue. Each bedroom needs its own.
Can I rent out my basement apartment in Denver?
It depends on your city's zoning rules for accessory dwelling units, which vary across the metro and change over time. We verify the requirements for your address before design is finalized.
How much does a basement apartment cost?
Basement finishing in the Denver area typically runs about $40 to $90 per square foot, and an apartment with a bathroom and kitchenette tends toward the upper end. You get an exact estimate after a free consultation.
Do I need a permit for a basement in-law suite?
Yes. Framing, electrical, plumbing, mechanical and any foundation openings need permits and inspections. Mile High Remodel pulls the permits and coordinates inspections with the city.
Can I live at home during the project?
In most cases, yes. Basement work is largely contained to the lower level, and we explain any temporary disruption, such as water or power shutoffs, before work starts.
