Tucked behind a pretty porte cochere in a Bethesda, Md., neighborhood, this backyard accessory unit started out as a detached garage. But then it evolved. Once the framing was up and the owners could visualize its relationship to the main house and pool, they opted to make it a guest cottage and entertainment pavilion instead. (It also has an underground basement lair for their son, who plays drums.)

Functionality notwithstanding, the beauty of this charming little outbuilding lies in its resourcefulness. Although it was a custom job for builders Mel Silicki and Jamie Maloney, most of its finishes are made of leftover materials from the recent construction of the main house. Those include tile remnants in the bathroom, vintage lanterns in the kitchen, quirky furnishings from the owners’ stash of antiques, and lots of surplus wood.

Residual walnut planks were predictably used for flooring in the upstairs bedroom, but they also make an unorthodox appearance on the cottage’s main level, where finish carpenters combined them with two sets of reclaimed armoire doors to create a storage space that hides pool equipment and supplies. “We couldn’t put a ceiling on the storage area due to sprinkler requirements, so it’s really just an open space behind a wall partition,” Silicki explains.

There are a lot of eclectic parts in the design mix, and thoughtful execution is what ties them all together. The top of the pool storage partition is aligned with a perpendicular header adorned with vintage pots and skillets. The kitchen floor is a herringbone brick that matches the driveway. And the same retractable Clopay cedar garage door that provides ingress from the street side is repeated on the back side of the accessory dwelling, where it opens onto a generous pool patio.

As in the main house, the guest cottage is an artful blending of old and new. A horseshoe plaque on the wall hides structured wiring for an eventual flat-screen TV, and an old farmhouse table on casters rolls away easily to free up space for parties. The centerpiece of the space is a vintage, brass-knobbed Lacanche stove that was headed for auction until the clients got it on a tip (and for a steal).

“The design was definitely a process,” Silicki says. “The owners do a lot of traveling, so we would get e-mails from all over the country (and the world), saying, ‘Hey, we found this cool thing and we’re bringing it back. How can we incorporate it?’ It was fun.”