ADU Construction in Playa Vista With a Low-Slope Roof
Playa Vista ADU construction with a low-slope roof: tapered insulation for steady fall, scuppers with an overflow, and stainless or aluminum metal.
The roof we draw for a Playa Vista ADU is close to flat, with a short parapet around it and its water steered to one low edge. Tapered insulation on the deck gives every part of the membrane a steady fall toward a scupper, and a second scupper set a little higher takes over if the first one clogs. From there, a conductor head and downspout carry the water down the wall to a pipe at grade.
Membrane and fall
The code calls for at least 1/4 inch of fall per foot on a roof like this, and the tapered layer is designed to give it everywhere, including behind a skylight curb or an equipment stand, where small crickets split the flow. The membrane itself can be single-ply PVC or TPO, or a self-adhered modified bitumen, turned up the inside of the parapet and capped with metal coping. A light-colored surface reflects sun and keeps the room below cooler. Near the coast, the coping, scupper boxes and fasteners are stainless or aluminum, since salt in the air eats plain steel.
From scupper to the ground
Downspouts from the scuppers drop into a closed pipe sloped toward an area drain, to a dry well where the soil takes water, or to the street through a curb outlet if the city allows one. The overflow scupper empties where its stream can be seen, so a blocked primary shows itself during a storm. LADBS reviews the roof drainage, the parapet and the membrane during plan check. If the parcel is within the coastal zone, the roof height can face coastal review before the building permit issues.
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Anywhere inside the setbacks where the low edge of the roof can face open yard, so scupper water lands on ground we can grade to carry it off. If the yard slopes, turning the low edge downhill keeps the drain pipe short. A parapet close to a lot line also has to meet the fire separation rules for that wall.
For a Playa Vista unit on one level and within 500 square feet, the drawings are part of the package. Its roof plan marks the slope arrows, scuppers and overflow, and LADBS reads it alongside the drainage notes on the site plan. A coastal review fee, where the lot needs one, and construction are priced outside the package.
Tapered insulation and a membrane cost more than shingles on a pitched roof. Parapets add framing and metal coping. Stainless or aluminum fittings raise the hardware line. If the yard slopes, footings step down and take more concrete, and a long drain pipe to the street adds trenching.
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