Quick answer
ADU framing is the structural skeleton of an accessory dwelling unit: the walls, floor and roof members, usually wood studs, joists and rafters or trusses, that hold the building up and resist wind and earthquakes.
Framing is inspected while it is still open. After that, insulation and drywall hide it for good.
Quick facts
- Most common material
- Wood ("stick framing")
- Model code sections
- 2024 IRC R602 Wood wall framing; R603 Cold-formed steel wall framing 1
- California code in force
- 2025 Title 24, effective 1 January 2026 2
- California licenses
- B general; C-5 framing and rough carpentry 3
- Key inspection
- The framing inspection, before insulation and drywall
Key takeaways
- Framing is the skeleton that holds the ADU up.
- Most ADUs are wood framed; steel and panel systems exist too.
- In earthquake and wind areas, framing includes shear walls, straps and hold-downs.
- The framing inspection happens before walls are covered. It is your last easy look.
- Changes after framing cost more, so settle the layout before it starts.
- Framing is structural work for licensed pros, built to the approved plans.
What it means, in plain English
Picture the ADU with no walls, no roof skin and no drywall. What is left is the frame. It looks like a wooden cage.
Studs are the upright boards in walls. Plates are the flat boards at the top and bottom of a wall. Joists hold up floors and ceilings. Rafters or trusses hold up the roof. A header is the beam over a door or window.
A shear wall is a wall sheathed and nailed in a set pattern so it resists sideways force. That force comes from wind and earthquakes.
The diagram puts those parts around the frame they belong to. Use it to read the framing sheets in your plans.
- Sill plateBolted to the foundation; the frame starts here
- Studs and platesUpright boards between top and bottom plates form each wall
- HeadersBeams that carry the load over doors and windows
- Floor and ceiling joistsHold up floors and ceilings
- Rafters or trussesHold up the roof; factory trusses are never cut on site
- Shear wallsSheathed and nailed to a schedule to resist wind and earthquakes
- Straps and hold-downsTie the frame together and to the foundation
Source: [1]
Why it matters to you
Framing is where the plans become a building you can walk through. It is also the best time to spot layout problems. Is the window where you wanted it? Is the doorway wide enough?
Errors hide fast. Once insulation and drywall go up, missing straps or poor nailing are out of sight.
And framing sets the schedule. Plumbing, wiring and ducts all go in after it. A late framing crew delays every trade after it.
How framing goes up
- The sill plate is bolted to the foundation.
- Floor framing goes in, if the ADU has a raised floor.
- Walls are built, stood up, plumbed and braced.
- Headers go over doors and windows.
- Ceiling joists and rafters, or factory trusses, form the roof.
- Sheathing covers walls and roof. Shear wall nailing follows the plans.
- Straps, hold-downs and anchors are installed.
- Rough plumbing, electrical and ducts go in.
- The inspector checks framing and rough-ins before anything is closed.
Sources: [4]
ADU framing systems
| System | What it is | Where it shows up | Notes |
|---|---|---|---|
| Wood stud framing | Lumber studs, joists and rafters cut on site | Most site-built ADUs | Covered by IRC R602 in the model code |
| Roof trusses | Factory-made triangle frames for the roof | Many site-built and prefab units | Designed by the truss maker; do not cut or alter on site |
| Cold-formed steel | Light steel studs and joists | Some ADUs and prefab units | Covered by IRC R603 in the model code |
| Panelized walls | Wall panels framed in a factory, set on site | Panel and some prefab systems | Faster on site; still inspected locally |
| Modular boxes | Whole sections built and inspected in a factory | Prefab ADUs | Site inspections focus on the set and connections |
Example: a pre-drywall walk-through
A sample walk for a hypothetical one-bedroom detached ADU, done after the framing inspection and before insulation. Bring the plans.
| Room | What to check against the plans |
|---|---|
| Entry | Door opening width; step-free threshold if planned |
| Kitchen | Window and outlet locations; backing for upper cabinets |
| Bathroom | Backing for grab bars if wanted; shower size; fan location |
| Bedroom | Window size for the emergency escape opening the plans show |
| Whole unit | Wall layout matches the floor plan; no missing walls or openings |
Note anything off and raise it with the contractor before insulation. Moving a wall now is far cheaper than after drywall. This walk is for layout only; structure is the inspector's and engineer's job.
Where you will see it
- Framing plans. Floor, wall and roof framing sheets in your plan set.
- Shear wall schedule. A table on the plans with sheathing and nail spacing.
- Truss drawings. From the truss maker, often a deferred submittal.
- A bid. Framing labor and lumber may be separate lines.
- Inspection card. The framing inspection is signed before cover.
Rules: California first, then other states
California. ADU framing must meet Title 24. The 2025 edition took effect on 1 January 2026. Most ADUs follow the California Residential Code, which adds seismic and wildfire rules to the IRC base.
The model code. The 2024 IRC covers wall framing in Chapter 6: R601 General, R602 Wood wall framing and R603 Cold-formed steel wall framing. California numbering can differ.
Licensing. In California, framing is done under a B general license or a C-5 framing and rough carpentry license.
Engineering. Where the design goes beyond the code's simple rules, an engineer designs the structure.
Other states. Most adopt a version of the IRC. See ADU laws by state.
What drives the cost
This page gives cost drivers, not prices. Lumber prices move, so any number dates fast.
The drivers are size, shape, roof style, wall height, the number of openings, the amount of shear wall and hardware, and the labor market. A simple box with a simple roof frames faster than a unit with many corners.
Framing is a hard cost. See ADU cost statistics for measured totals.
Site-framed wood: benefits and limits
Benefits
- Flexible for odd lots and custom layouts
- Many local crews know it
- Easy to add backing or small changes during framing
- Well covered by the code
Limits
- Weather can delay it
- Quality depends on the crew
- Takes longer on site than factory systems
- Lumber prices can swing
Framing compared with related phases
| Phase | What it is | Read more |
|---|---|---|
| Foundation | What the frame sits on | ADU foundation |
| Framing | The structural skeleton | This page |
| Roofing | The weather skin on the roof frame | ADU roofing |
| HVAC | Heating and cooling run through the frame | ADU HVAC |
Common misreadings
- Myth "If it stands up, it is framed right."
- Reality A frame can stand and still lack the straps and nailing that resist earthquakes and wind.
- Myth "Trusses can be trimmed on site."
- Reality Trusses are engineered. Cutting one without the maker's or engineer's approval is not allowed.
- Myth "Prefab skips framing inspection."
- Reality Factory work has its own inspection. The site still gets inspected for the set and connections.
- Myth "Small changes during framing are free."
- Reality Some are simple, but changes can need plan revisions and city approval. Ask first.
What to ask your contractor about framing
- When is the framing inspection? Can I walk the frame after it?
- Are you framing in-house or with a sub? Who holds the license?
- Where are the shear walls and hold-downs on my plans?
- Are trusses ordered, and who designed them?
- Can you add backing for grab bars, TV mounts or cabinets now?
- How will you protect the frame from rain?
- How do changes get approved and priced?
Checklist for your project
- Settle the layout before framing starts.
- Confirm framing licenses on the CSLB site.
- Plan backing for grab bars, shelves and mounts.
- Walk the frame with the plans after inspection.
- Photograph every wall before insulation.
- Get any change in writing before it is built.
- Keep the signed inspection card.
What a framing inspection usually looks at
Each city has its own checklist. These items show up often. The inspector, not the owner, judges them:
- Match to the plans. Walls, openings and beams are where the approved plans put them.
- Shear walls. Sheathing type and nail spacing match the shear wall schedule.
- Hold-downs and straps. Metal connectors are installed where the plans show.
- Anchor bolts. The sill plate is tied to the foundation as detailed.
- Headers and beams. Sizes match the plans over doors and windows.
- Fireblocking. Gaps that would let fire spread inside walls are closed.
- Notches and holes. Cuts made for pipes and wires stay within code limits.
- Truss paperwork. Truss drawings are on site where trusses are used.
Weather, moisture and the framing schedule
A wood frame can take some rain. Long soaking is the problem. Wet wood can shrink as it dries, which can crack drywall or pop nails later.
Good crews dry in fast. That means getting the roof sheathing and underlayment on, then windows and wrap. Ask how your crew plans for the rainy season.
Framing also sets the pace for later trades. Plumbers, electricians and HVAC installers all work inside the open frame. They can only start when framing is far enough along. A slip in framing pushes every trade after it.
Before insulation, many inspectors ask for the frame to be dry enough. If the frame got wet, ask the contractor how they will check it.
Framing for attached and above-garage units
Detached units stand alone. Attached units and units above a garage tie into an existing building. That changes the framing work.
An attached ADU shares a wall or roof with the house. The new frame must connect to the old one, and the wall between them may need a fire rating the plans call for.
A unit over a garage puts new weight on old walls and footings. An engineer checks whether the garage can carry it. Often the answer is new posts, beams or footings.
Questions about adu framing
What is framing in ADU construction?
Framing is the structural skeleton: wall studs, floor joists and roof rafters or trusses. It carries the weight of the building and resists wind and earthquakes. Everything else attaches to it.
What material is used to frame an ADU?
Most ADUs are framed with wood. Some use light-gauge steel, factory panels or modular boxes. The plans and the building code set what is allowed.
When does framing happen in an ADU build?
After the foundation and before plumbing, electrical and HVAC rough-ins. Insulation and drywall come after the framing inspection.
What is a framing inspection?
A city inspection of the structure before walls are covered. The inspector checks the frame, shear walls, straps and connections against the approved plans.
What is a shear wall in an ADU?
A wall sheathed and nailed in a set pattern so it resists sideways force from wind or earthquakes. The plans show where each one goes and how it is nailed.
Who can frame an ADU in California?
A contractor with a CSLB B general building license or a C-5 framing and rough carpentry license. Check the license number on the CSLB website.
Can I change the layout during framing?
Sometimes, but changes may need plan revisions and city approval. Settle the layout before framing starts, and get any change in writing first.
What code covers ADU framing?
In California, Title 24, mostly the California Residential Code (2025 edition, effective 1 January 2026). The 2024 IRC covers wood wall framing in R602 and steel in R603.
Should I walk through the framing before drywall?
Yes, if the contractor allows it. It is the last easy chance to check door widths, window places and backing. Leave structural checks to the inspector.
Can I frame my own ADU?
This page does not give DIY steps. Framing is structural and is inspected for safety. Use licensed pros who follow the approved plans.
What does a framing inspector check?
Usually that walls, beams and openings match the plans, shear wall nailing, hold-downs, anchor bolts, fireblocking, and cuts for pipes and wires. Each city has its own checklist.
Can ADU framing get wet in the rain?
Some rain is normal during framing. Long soaking can cause shrinkage and drywall cracks later. Crews aim to get the roof and wrap on quickly, and the frame should be dry before insulation.
Sources
- International Code Council, 2024 International Residential Code, Chapter 6 Wall Construction, retrieved .
- California Building Standards Commission, California Building Standards Code (Title 24), retrieved .
- Contractors State License Board, License Classifications, retrieved .
- International Code Council, 2024 International Residential Code, Chapter 4 Foundations, retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: The 2024 IRC Chapter 6 section list (R601 to R603) and Chapter 4 were opened on codes.iccsafe.org; CBSC Title 24 edition page and CSLB classifications on 8 October 2026. No prices or member sizes are given.
Suggest a correction. We fix errors and say what changed.