ADU Construction in Cerritos, Wrapped for Wind-Driven Rain
Cerritos ADUs with drainable wrap and taped window flashing behind the siding, footings for any grade, and permit drawings that show each layer.
Behind the siding of a Cerritos backyard unit sits a drainable housewrap. Its textured face leaves a thin gap, so water that gets past the cladding in a hard storm drains to the bottom of the wall and weeps out. Windows and doors are flashed with self-adhered tape lapped over that wrap. Inland, dry wind pushes dust into seams, and the same laps keep it out. If the lot slopes, the taller downhill wall catches more wind and gets extra care.
Lapping the wrap and the openings
Wrap goes on from the bottom up, each course overlapping the one below, so water always lands on the outside face. At a window, the sill gets a sloped pan of flashing tape first, then the jambs, and the head tape goes on last over the window's nailing flange, with the wrap above folded down on top of it. A metal head flashing over each opening throws water outward. Vents, pipes and the electrical service each pass through the wall inside a molded boot or a tape collar, because small holes like these admit more water than a whole field of siding.
The base of the wall and the grade
Where the wall meets the foundation, the wrap laps over a metal flashing at the sill plate so water leaving the gap drips clear of the concrete. Soil and paving stay below that line by the clearance the code sets to keep framing dry. On a sloping lot, finished grade has to fall away from the unit on every side, which may take a shallow swale along the uphill wall. The city's plan reviewer reads these layers in the construction details, and the inspector sees the wrap and tape before any siding covers them.
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Most of a level Cerritos yard is open to a unit inside the setbacks. Where the ground does rise or fall, a spot that lets finished grade drop away on all sides, without a tall cut against the uphill wall, saves drainage work and wall height. Candidates are compared on that basis.
Up to 500 square feet on a single floor, a Cerritos unit is drawn for plan check under the package. Its energy forms list the wall insulation and window ratings that sit behind the wrap. Construction carries its own price, and a sloping lot adds an engineering fee, both set after a look at the yard.
Grade in either direction. A rise behind the unit may call for a cut held by a retaining wall, and a drop beneath it for piers or footings that go deeper. A swale along the uphill wall adds digging and pipe. Each is spelled out in the quote, next to the base cost of the wall assembly.
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