Roofing for ADUs and backyard cottages in Vancouver, WA

Accessory dwelling units come in a few common shapes here: a new detached cottage in the backyard, a garage converted to living space, or a unit built above a garage. Many use a simple shed roof sloping one way, or a low-slope roof to keep the building height down. Those designs look clean, but they put the waterproofing under more stress than a standard pitched roof on a house.

We roof ADUs as their own job, separate from whole new homes. The details are different: tight side-yard access for materials, roofs that sit close to fences, neighbors and big trees, and drainage that has to go somewhere other than a neighbor's yard. For garage conversions, the old roof was often built for a car, not a bedroom, so we check what is under it before anything new goes on.

Roof types that suit small backyard buildings

Shed roofs are the most common ADU shape we work on. With one slope, all the water runs to one edge, so that gutter and downspout have to handle a lot of flow. If the slope is steep enough, standing seam metal is a strong choice: it sheds needles well, looks modern, and has few seams for water to find. At lower slopes, a single-ply membrane like TPO is usually the better fit.

Gable and hip roofs on cottages are often roofed to match the main house, with the same shingle color and profile so the two buildings read as one property. Most shingle makers set a minimum slope for their products, so very low pitches need a membrane instead. Garage conversions sometimes have a mix: a pitched main roof with a flat section over a new bump-out or entry, which needs careful flashing where they meet.

Details we plan for on an ADU roof

Small roofs leave less room for mistakes. A single bad penetration on a 400 square foot roof is a big share of the surface, and living space sits right under it. We go over every vent, skylight and wall joint before the job starts so the flashing order is set, and we plan where the water goes once it leaves the roof.

• Bath fan, dryer and plumbing vent penetrations
• Skylights and sun tunnels over small rooms
• Roof-to-wall flashing on units attached to a garage
• Gutters and downspouts that drain away from neighbors
• Ventilation or insulation details for living space
• Overhangs near fences and property lines

Converting a garage roof for living space

Detached garages from the mid-century era often have thin roof decking, no underlayment worth keeping and rafters sized for light loads. When a garage becomes a living unit, the roof suddenly needs insulation, ventilation or an unvented assembly, and a clean dry deck. We open the roof, check the framing and sheathing, and tell you what has to change before the new roofing goes on.

Many owners also want a skylight, a dormer or a raised section to make the room feel bigger. Those changes need framing work that may involve your builder or a designer, and they affect how the roof is flashed. We work with your general contractor if you have one, or handle the roofing scope directly, and we time our work so the interior stays dry while the conversion moves ahead.

Permits, rules and working with your builder

ADU rules on height, setbacks, roof pitch and materials are set locally and change from time to time, so we do not assume anything. Confirm the current requirements with the City of Vancouver, Clark County or your Oregon city before final design, and expect us to check with the building department and pull roofing permits where they are required. If an HOA covers your lot, its color and material guidelines apply to the ADU too.