ADU Construction in Winnetka, Sealed from the Roof Down
Backyard units in Winnetka built with a sealed, vent-free roof, cement plaster walls and tempered glass, drawn and permitted by Fernhill Builders.
Closed-cell foam sprayed against the underside of the roof deck lets a Winnetka backyard unit do without attic vents altogether. With no openings under the eaves, wind-carried sparks have no gap to slip through, and the dust that dry inland gusts drive into a vented attic stays outside. The foam also keeps hard afternoon sun from turning the space above the ceiling into an oven, which matters in a unit small enough that every room sits right under that roof.
A roof with nothing to breach
The foam goes on in layers until it reaches the depth the energy calculations call for, and it bonds to the sheathing so the roof deck, rafters and insulation act as one tight layer. Above the deck we lay a Class A covering, either standing-seam steel or a rated shingle, with metal flashing at every edge. The eaves are closed with fiber cement soffit board, so the underside of the overhang offers no wood for a spark to find. Ductwork for the heat pump can then run through the conditioned space above the ceiling, where it loses very little.
Walls and glass to match
Cement plaster over a drainage layer covers the walls, because stucco gives a stray ember nothing to ignite and stands up to the knocks a narrow side yard hands out. Each window pairs a tempered outer pane with an insulating inner one, and that pairing holds together under radiant heat far longer than plain annealed glass. Wherever foam stays exposed in the space above the ceiling, an ignition barrier coating goes over it as the code requires. Bark mulch is kept off the plaster by a band of gravel or poured concrete at the foot of each wall.
ADU Construction in Winnetka: common questions
Whether the code demands it comes down to the fire hazard mapping for the specific parcel, which LADBS can look up for any Winnetka address. Our drawings carry the same hardened shell in either case, with noncombustible walls, a roof that has no open vents and tempered glazing, since sparks from a brush fire can drift well past any mapped boundary.
On a Winnetka unit with a sealed roof, the energy compliance forms are read with care, since the foam depth and the conditioned attic are recorded there, along with the site plan that fixes where the unit stands. What the package draws is a qualifying single-story unit, and a larger design is scoped on its own.
It can work, provided the house is going back up under its own permit and the lot leaves room for both. LADBS decides whether the two travel through review together or one after the other. Building them side by side lets a single trench carry utilities to both and keeps one staging area on the lot, so the yard is torn up for one stretch of work.
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