Backyard ADU: Framing
Accessory Dwelling Units (ADUs) are popping up everywhere—from backyard cottages to garage conversions—and for good reason. These compact, self-contained living spaces can generate rental income, house aging parents, or provide an affordable home for adult children. But building an ADU is still a serious construction project, and one of the most critical phases is framing.
What Is Framing?
Framing is the skeleton of your ADU. It provides structure and shape and supports everything from insulation to electrical wiring to the roof. There are two main types of framing in residential construction:
- Platform framing (most common today): Each floor is framed independently, with walls sitting on a platform created by the floor joists and subflooring.
- Balloon framing (older method, now rare): Walls extend from the foundation to the roof without interruption.
For ADUs, platform framing is almost always used due to its ease, efficiency, and compatibility with modern building codes.
When Does Framing Happen?
Framing comes after your foundation is poured and cured, and just before major systems like electrical, plumbing, and HVAC are installed. Here’s a rough sequence:
- Site prep and foundation
- Framing (walls, floors, and roof)
- Sheathing and house wrap
- Rough-in systems (electrical, plumbing, etc.)
- Insulation and drywall
Key Components of ADU Framing
Here’s what gets framed in a typical ADU:
1. Floor System
- Built on concrete slab or raised joists (especially in detached ADUs)
- Must be level, square, and properly anchored
- Subfloor (usually plywood) is added to support finished flooring
2. Walls
- Built with vertical studs, usually 2×4 or 2×6 (depending on local energy codes)
- Include rough openings for doors, windows, and mechanical access
- Must be plumb
- (perfectly vertical) and properly braced
3. Roof System
- Roof trusses or rafters form the shape and pitch
- Sheathing (plywood or OSB) is added before roofing material
- Roofs are often designed with low pitches or gables to minimize visual impact
4. Sheathing
- Plywood or OSB sheathing ties the walls together, strengthens the frame, and provides a base for siding
5. Openings and Structural Support
- Headers and beams are used over windows, doors, or load-bearing openings
- Structural elements must meet local codes, especially in seismic or high-wind areas
Considerations for Framing an ADU
1. Code Compliance
Every city has specific building codes, and ADUs often have unique requirements—especially related to fire separation, egress, and energy efficiency.
2. Materials
Using high-quality lumber (such as kiln-dried, straight studs) can save headaches later. Engineered wood products might be necessary for longer spans or special roof designs.
3. Moisture Control
Framing must be protected from moisture both during and after construction. Use pressure-treated lumber near concrete and install proper flashing around openings.
4. Budget and Timeline
Framing typically accounts for 15–20% of an ADU’s construction cost and takes anywhere from a few days to a couple of weeks, depending on complexity, weather, and crew size.
Framing may not be the most glamorous part of building an ADU, but it’s absolutely essential. A solid frame ensures your ADU is safe, durable, and ready for all the systems and finishes that come next. Whether you’re working with a pro or taking a hands-on approach, understanding the framing process helps you make smarter decisions and get the most out of your investment.
MVP Builders is here to help.