Room Additions in Altadena, Lapped to Shed Water
Altadena room additions where each wall layer laps shingle-fashion to shed water, with noncombustible siding, county review and an ADU comparison.
Water follows gravity down a wall, so every layer behind the siding of an Altadena addition laps shingle-fashion, with the upper layer over the lower. A single reversed lap can let rain behind the barrier and into the framing. Because mapped fire hazard zones take in a share of Altadena, the same wall also gets noncombustible cladding.
The layers in order
From the framing outward the wall carries sheathing, a water-resistive barrier, flashing at every opening and the cladding. The barrier laps over the flashing at the window head and under it at the sill, so water always runs outward. At the base, a screed lets moisture escape. Fiber cement or stucco meets the noncombustible goal and sheds water well. A drawing that shows each lap direction gives the inspector something to check before cladding hides it. Each lap is photographed before the cladding closes it, giving the file a record of how the wall was built.
Where the old wall meets the new
The joint between existing and new walls is the weak point, since the old barrier may be a different material or missing entirely. We open a strip, read what is there and detail a lapped transition. Altadena is an unincorporated community, so the county building department handles plan review, including any ember-resistance details for vents and eaves. If the lot slopes, drainage at the foot of the wall also gets attention. Where the old wall is framed differently from the new, the transition piece is drawn in detail so the inspector can follow it.
Room Additions in Altadena: common questions
Use decides it. Space that borrows the house kitchen is an addition, and a separate dwelling with a door, kitchen and bath of its own is an attached ADU. Both get laid over your Altadena lot, comparing setbacks, utilities and how each wall assembly handles fire and water.
Altadena is unincorporated, so plans go to the county building department. The set pairs the structural design with the energy forms, and ember-resistance details get reviewed if the parcel sits on a fire hazard map. Field inspections follow the footing, the framing and the finished job. We prepare and file the submittal.
That is a structural question first. An engineer checks whether the footings and walls can carry an added floor, and the height limit is read. A second story adds wall surface that must be flashed and lapped correctly at every level, and in a mapped fire zone its roof and eaves follow ember-resistance rules.
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