Benjamin Hall Design uses masonry walls for Arizona accessory dwelling unit
Local studio Benjamin Hall Design has attached an accessory dwelling unit made of concrete block to an existing house to accommodate a multi-generational family in Phoenix, Arizona, USA.
Known as Moon Valley Residence, the 1,756-square-foot (163-square-metre) dwelling was designed to intentionally contrast the original 1970s suburban main home, set in a golf community that looks eastward to a rock formation called Lookout Mountain.
Completed in 2025, the ADU shares an access door with the main house, but maintains self-sufficiency and privacy both spatially and from the curved wall that shields the dwelling from the cul-de-sac.
Constructed with grey concrete masonry units (CMU) as both the exterior and interior finished material, the accessory dwelling unit (ADU) draws inspiration from studio founder Benjamin Hall's childhood memories of travelling through the Southwest US with his father.
"We explored the ancient Native American ruins called Montezuma Castle – this experience subconsciously embedded itself into my thinking of this project," the founder of Benjamin Hall Design told Dezeen.
"It was used as a reference on scale, stacking forms and how to mitigate the desert's natural heat and light by undulating mass and aperture."
Set lower than the profile of the main house, the ADU is composed of four volumes with apertures strategically carved out to curate views of the surroundings.
"These four rectilinear volumes each identify themselves at different elevations," he said. "On the interior you can feel the scale – compression and release – of each of the volumes and their relationship with the body and program of the space."
This passes to the second volume, containing a living room and kitchen with a view of Lookout Mountain. A glazed interstitial volume leads to the sleeping quarters with a guest suite and a primary suite with another private patio.
The first volume connects the ADU to the main house via a wedge-shaped dining space with sliding glass doors that open to a private patio.
The layout allows a retired couple to age in place privately while directly connected to their children and grandchildren who occupy the main house.
In addition to strategic spans that allowed for self-supporting masonry ceilings, the continuous material of the CMU block required all of the utilities to be contained within built-in millwork.
"The integration of utilities is carefully moulded into the cohesive strategy that embeds itself into the thickness of masonry and the mailability of concrete," Hall said.
"You will notice that no outlets reside in the masonry and the day-to-day haptic experience with the architecture – light switches, door pulls, countertop surface – are embedded into the experience of engaging with the architecture."
Other residential projects recently completed around Phoenix include a weathering steel micro-building by Kendle Design, a Corten cabin designed to act as a telescope by Wendell Burnette Architects and a white ranch house styled after its mid-century modern neighbors by The Ranch Mine.
The photography is by Logan Havens.
Project credits:
Architecture: Benjamin Hall Design
Contractor: Rare Form Builders
Structural Engineering: Structurology
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