THE ALLEN RESIDENCE: 1125 Maxwell Avenue, Mapleton Hill, Boulder, Colorado

A 1922 Craftsman bungalow and legal, separately metered duplex, with a rare detached 3-car garage and studio, ready as a single-family home, duplex, or triplex.

A Century on Maxwell Avenue

Built in 1922, this Craftsman bungalow was home by the mid-1920s to Mrs. Brilliant Allen, widow of longtime Boulder transfer-business owner W.B. Allen. Mrs. Allen, mother of four daughters and a son, had come to Boulder from Wyoming and called the city home for more than three decades. By 1928 the house had passed to the Browne family, and later to the Pillmore family, who owned it until the current owner took over in 1998. Today the house is recognized as a contributing structure in Boulder’s Mapleton Hill local historic district. It is not individually landmarked, which gives an owner welcome room to update and expand while the home keeps the character that earned it a spot on the historic inventory in the first place.

The current owner has owned the house since 1998, updating every major system along the way: electrical, plumbing, hot water heat, windows, and roof. The original structure holds up just as well. Its poured concrete foundation, brick porch piers, and side-gabled roofline, with the deep overhanging eaves and exposed rafters that define the Craftsman style, are all original to 1922. A Boulder County appraisal card from 1938 rated the construction and framing “good.” Nearly ninety years later, they still are.

The House Today

This property delivers 3,252 sq ft of finished interior living space, 374 sq ft of outdoor living space (covered front porch, patio, and deck), and 732 sq ft of parking and storage between the 3-car garage and tool shed.

Original Douglas fir floors run through the main level, under a classic bungalow floor plan that still reads exactly as it did in 1922: living room, dining room, and bedrooms wrapped around a covered front porch with tapered columns rising off brick piers. Upstairs, a finished attic brings the home into the present day: skylights, a full bath, and open, flexible living space tucked under cozy, low-slung dormers.

Below grade, a fully finished walk-out basement apartment steps straight outside on the east side of the house through its own private entrance, fully separate from the main house. That walk-out access means real windows and natural light instead of a dark basement, plus the kind of true privacy that makes it work well as a rental unit, extended-family suite, or long-term tenant space.

Out back sits the kind of feature you almost never find on this end of Mapleton Hill: a detached 3-car garage, built in 1999, with a studio apartment overhead complete with its own half bath. Under Boulder’s updated accessory-dwelling rules, that studio can be converted into full living space, turning a garage into a genuine third income stream or a private studio for work, guests, or rental.

Single-Family, Duplex, or Triplex: Your Call

The lot is zoned RMX-1 (Residential Mixed-1), and few properties in Boulder offer this much built-in optionality:

• Single-family estate: combine the main house and walk-out basement apartment into one generous residence, and use the garage studio as a home office, gym, or guest house.
• Duplex: live upstairs and rent the finished basement apartment, separately metered for gas and electric (common water), This is known as 1125 ½ Maxwell and has a separate private entrance already in place)
• Triplex: the studio above the garage is currently 612 SF and outfitted with a separate entrance, ½ bath, and can be converted to a full bath. Simply add a kitchenette and optional stackable laundry, to become a self-sufficient legal rental. This space is not separately metered for utilities, it shares metering with the main home. Enjoy 3 income-producing units on one 4,472-square-foot lot: the main house, the walk-out basement apartment, and the garage studio, all subject to Boulder rental licensing.
• Flexibility for income generation: the main house features a lower level area with 1 bedroom, ¾ bath, private exterior entry, private patio, that feels separate from the main home, it was designed so that it can be locked off from the main home, but share the laundry room, this space would need a small kitchenette to be a self sufficient non-conforming apartment for up to 4 separate income producing spaces.

Boulder’s RMX-1 zoning also permits a home occupation, including a licensed cottage food business, giving an owner-operator a rare extra layer of flexibility.

The Setting

Few addresses in Boulder can match this location for walkability and bikeability, backed by an 87 Walk Score. Nearly everything that makes Boulder Boulder is within easy reach on foot, by bike, or by bus:

• Ideal Market, a short walk or bike ride away
• North Boulder Park, an easy walk from the front door
• The Mount Sanitas trailhead, an easy walk or bike ride
• Downtown Boulder and the Pearl Street Mall, an easy walk or bike ride
• Boulder Creek Path, an easy walk or bike ride
• CU Boulder, an easy bike ride
• An RTD bus route right on the block, for the days you leave the bike at home

The location comes with a design bonus too. Next door sits the Boulder Eye Clinic, designed by acclaimed Boulder architect Charles Haertling, giving the block an architectural pedigree that few Boulder addresses can claim.

Key Facts

Historic Name

The Allen Residence (Boulder Historic Inventory ID 5BL6221)

Year Built

1922, Craftsman Bungalow, 1½ stories

Historic Status

Contributing structure, local historic district (not individually landmarked)

Finished Interior Living Space

3,252 sq ft: the main house (2,640 sq ft across the main floor, upper-level attic, and walk-out basement apartment) plus the 612 sq ft studio above the garage

Outdoor Living Space

374 sq ft: covered front porch, patio, and deck

Parking & Storage

732 sq ft: detached 3-car garage (612 sq ft) and tool shed (120 sq ft)

Bedrooms / Baths

4 bedrooms; 2 full + 1 three-quarter bath in the main house, plus a half bath in the garage studio

Detached Garage / Studio

Built in 1999; studio includes a half bath and is ADU-convertible per current Boulder zoning

Lot Size

4,472 sq ft (0.10 acre)

Zoning

City of Boulder RMX-1 (Residential Mixed-1): permits duplex/triplex use, a detached ADU up to 800 sq ft, and home occupation / cottage food use

Flood Zone

None (Zone X)

Neighborhood

Mapleton Hill / North Boulder Park, Walk Score 87

Complete Feature List

Property Basics

• 1½-story Craftsman bungalow, built in 1922
• Historic name: The Allen Residence (Boulder Historic Inventory ID 5BL6221)
• Contributing structure, Mapleton Hill local historic district (not individually landmarked)
• Lot size: 4,472 sq ft (0.10 acre)
• Zoned RMX-1 (Residential Mixed-1): legal, separately metered duplex, with triplex potential
• No flood zone (Zone X)

Systems & Updates (Since 1998)

• Updated electrical
• Updated plumbing
• Updated to hot water heat
• Updated windows (some original for character)
• Updated roof
• Original poured concrete foundation, brick porch piers, and side-gabled roofline, all in excellent condition for their age

Main House Interior

• 3 bedrooms
• 2 full baths and 1 three-quarter bath
• Original Douglas fir hardwood floors on the main level
• Living room and dining room
• Finished attic with skylights, a full bath, and open, flexible living space under cozy dormers
• Covered front porch with tapered columns on brick piers

Walk-Out Basement (Garden Level) Apartment

• 1 bedroom
• 1 full bath
• Fully finished, with its own private entrance on the east side of the house
• Walk-out access to grade, with real windows and natural light
• Separately metered from the main house
• Ready for a tenant, extended family, or a private guest suite

Detached Garage & Studio

• Detached 3-car garage (612 sq ft), built in 1999
• Studio apartment above the garage (612 sq ft) with a half bath
• ADU-convertible to full living space under current Boulder zoning
• Deck off the studio (66 sq ft)

Outdoor Spaces

• Covered front porch (238 sq ft)
• Patio (70 sq ft)
• Deck (66 sq ft)
• Tool shed (120 sq ft)

Square Footage Summary

• 3,252 sq ft of finished interior living space
• 374 sq ft of outdoor living space
• 732 sq ft of parking and storage

Zoning & Flexible Use

• Legal, separately metered duplex today, with genuine triplex upside
• Detached ADU allowed, up to 800 sq ft
• Home occupation permitted, including a licensed cottage food business
• Rentals subject to Boulder rental licensing

Location & Walkability

• Mapleton Hill / North Boulder Park neighborhood
• 87 Walk Score
• Easy walk or bike ride to Ideal Market, North Boulder Park, the Mount Sanitas trailhead, downtown Boulder and the Pearl Street Mall, Boulder Creek Path, and CU Boulder
• RTD bus route right on the block