What does the ADU plans package include?

Permit drawings for a qualifying single-story unit within the size limit shown on this page. Bigger or two-level units get their own quote.

Do ADUs in fire hazard zones have extra rules?

Yes. The exterior must meet the wildfire code, and some areas add access or sprinkler requirements. We check them for your address before design starts.

Can I build an ADU while I rebuild my house?

It can be. Building both on one permit path can save time. We check whether your lot and your rebuild route allow it.

Can the ADU match the look of the main house?

It can. We match the stucco texture, the window frames and the trim where you want them matched, as long as each material still meets the exterior standard in the scope. Where an existing finish cannot meet it, we name a rated material that comes close and show you samples before anything is ordered.

ADUs Built with a Wildfire-Rated Exterior

Fernhill designs and builds detached ADUs, attached units and garage conversions with the shell of a hardened house: rated vents, tempered glazing and noncombustible walls, each named in a written scope.

Call the office Request a written scope

An ADU is a second house to protect

A detached unit can sit close to fences, slopes or the property line. That makes its exterior just as important. We design ADUs with noncombustible cladding, rated vents and tempered glazing from the first drawing.

Plans, permits and utilities

The plans package covers the drawings needed for permit on a qualifying one-story ADU. We coordinate the structural, energy and fire-area requirements and file with the department that covers your lot. Utility connections and any fire sprinkler or access questions are worked out before the build starts.

Garage conversions

Turning a garage into a unit means new insulation, windows, a door and sometimes a new slab or foundation work. It is also a chance to replace an old garage door opening with a rated wall and glazing. We tell you what the existing structure can keep.

What we check on the lot first

Before any drawing, we walk the spot where the unit would go. We note what stands within reach of its walls: fences, sheds, woodpiles, trees and the slope of the ground. We check how a crew, and later a fire engine, would reach it, and where the utilities would run. Those findings decide where the unit sits and how its exterior is built.

The ADU shell, assembly by assembly

The scope for an ADU reads like the scope for a hardened house. Walls are listed layer by layer, in stucco or fiber cement. Vents are named with the mesh or baffle that stops embers. Windows and the entry door carry their glass type. Under the eaves, the soffit is closed. If the unit has a deck or a landing, its surface and framing are listed too.

Roof edge, attic and gutters on the unit

A small unit puts its roof edge low, close to fences, plants and whatever is stored in the yard. We draw that edge with care. The roof covering is specified as a Class A assembly, and the gap where the covering meets the fascia is closed with a bird stop or metal flashing so embers cannot lodge under the first course. Gutters get a metal cover, or are left off where the drawings allow it. If the unit has an attic, it breathes through ember-resistant vents named in the scope, or it is built as an unvented assembly with insulation at the roof deck. A low-slope roof gets a membrane and edge metal detailed on the drawings. Each of these choices sits on its own line in the scope, with the reason written beside it.

ADU Construction: questions

Permit drawings for a qualifying single-story unit within the size limit shown on this page. Bigger or two-level units get their own quote.
Yes. The exterior must meet the wildfire code, and some areas add access or sprinkler requirements. We check them for your address before design starts.
It can be. Building both on one permit path can save time. We check whether your lot and your rebuild route allow it.
It can. We match the stucco texture, the window frames and the trim where you want them matched, as long as each material still meets the exterior standard in the scope. Where an existing finish cannot meet it, we name a rated material that comes close and show you samples before anything is ordered.

Cities with a ADU Construction page

Ask about an ADU on your lot

(626) 463-5662 Book a hardening walk-through