ADU Plans for Permit, Detached and Conversion
ADU plans that fit your lot, satisfy local zoning and include every architectural, structural and energy sheet your permit requires.
- Stamped by a PE licensed in your state
- Built to IBC, IRC and local amendments
- Plan-check comments answered
A second home on your lot, permitted the right way
An accessory dwelling unit is a complete, independent home on the same lot as a primary house, with its own place to sleep, cook, eat and bathe. ADU plans have to satisfy two sets of rules at once: the local zoning ordinance, which decides whether an ADU is allowed and how big and where it can be, and the building code, which decides how it is built. Many ADU applications stall because the drawings handle one set of rules well and the other poorly.
We prepare complete ADU permit sets for detached backyard units, attached ADUs, garage conversions, units above garages and basement or interior conversions. A typical set includes the site plan, floor plan, elevations, sections, roof plan, structural sheets, energy compliance and utility information, drawn for your address and, where required, sealed by a Professional Engineer licensed in your state.
ADU rules differ widely across the country. Several states, California among the best known, have passed state ADU laws that limit how far cities can restrict them, while in other states the rules are set entirely by each city or county. We check the ordinance that applies to your parcel before drawing anything, so the unit you design is one you can actually permit.
What you receive
- Site plan with setbacks and utilities
- ADU floor plan and kitchen layout
- Exterior elevations and roof plan
- Building sections and details
- Structural foundation and framing sheets
- Energy compliance and code notes
ADU types we design
The right ADU type depends on your lot, your existing buildings and your local rules, and we can help you compare them.
Detached ADUs
Freestanding backyard cottages built new on their own foundation, designed to meet accessory building setbacks, separation from the main house and any height or size limits.
Garage conversions
Turning an existing attached or detached garage into a legal dwelling, with slab, insulation, window, egress, separation and utility upgrades the conversion requires.
Above-garage ADUs
A new or existing garage with a dwelling unit on the upper floor, including stair access, fire separation from the garage and floor framing over the vehicle bays.
Attached ADUs
An addition to the main house with its own entrance and independent living facilities, separated from the primary dwelling as your jurisdiction requires.
Basement and interior conversions
Converting a basement, attic or wing of the existing house into a separate unit, with egress windows, ceiling height checks and dwelling unit separation.
Junior and efficiency units
Smaller units created within an existing home where local or state rules allow them, such as junior ADUs under California law, with the reduced requirements that apply.
Your Stamped, Permit-Ready Plans Start With One Upload
Send your drawings or describe the project. A licensed engineer reviews it and sends a clear, fixed-fee proposal, often within hours.
- Free and no obligation
- Reviewed by a licensed PE
- Secure file upload
What ADU plans include for permit
Because an ADU is a dwelling, reviewers expect nearly the same information they would for a small new house. A complete ADU permit set usually includes:
- Site plan showing both the primary house and the ADU, setbacks, separation between buildings, lot coverage, parking where required, and utility routes.
- Floor plan with the kitchen, bathroom, sleeping area, egress windows, smoke and carbon monoxide alarms and the location of the water heater and HVAC equipment.
- Elevations and roof plan showing height, roof pitch, materials and window placement, which some cities check against privacy or design standards.
- Sections and details for wall, floor and roof assemblies, insulation, stairs and fire-rated construction.
- Structural sheets covering the foundation, framing, beams and lateral bracing.
- Energy compliance for the new conditioned space, under the IECC or your state’s energy code.
Some jurisdictions also ask for a separate address request, a utility will-serve letter, a sewer capacity review or a fire access plan. We list those items when we quote so nothing is missing at submittal. If the ADU will have its own electric meter or gas service, we note the service size and meter location so the utility and the electrical reviewer see the same design.
Zoning rules that shape ADU plans
Before the first line is drawn, we confirm what your local ordinance allows. The questions that most often decide an ADU design are:
- Whether an ADU is permitted on your parcel and zoning district, and whether more than one is allowed.
- The maximum floor area, which may be a fixed number or a percentage of the main house.
- Setbacks and height limits for accessory dwellings, which are sometimes more generous than for other accessory buildings.
- Parking requirements and whether they are waived near transit or for conversions.
- Owner occupancy, rental and short-term rental restrictions.
- Design standards that require the ADU to match the main house.
In states with ADU laws, such as California, the state sets limits on what local governments can require and often provides a streamlined review timeline for complete applications. Elsewhere, each city writes its own rules, and two neighboring towns can treat the same backyard cottage very differently. Homeowner association rules can also restrict ADUs even where the city allows them, so it is worth checking your covenants early. Getting this research right at the start is the single best way to avoid redesign.
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- Free and no obligation
- Reviewed by a licensed PE
- Secure file upload
Building code requirements for ADU plans
Most ADUs are built under the International Residential Code or a state residential code based on it. The plans need to show habitable room dimensions and ceiling heights, emergency escape openings from every sleeping area, a compliant stair for upper-level units, guards, safety glazing and interconnected smoke and carbon monoxide alarms.
Where your jurisdiction treats an attached ADU as a second dwelling unit, the wall and floor assemblies between the two units must be fire-resistance rated, typically one hour, and penetrations through them must be protected. Above-garage units also need the garage separation the code requires for any dwelling over a garage. We detail these assemblies with listed designs so the inspector can verify them.
Fire department access matters on deep lots. Some jurisdictions measure the distance from the street to the ADU entrance or require a clear path, and if that distance is too long they may ask for fire sprinklers. We check this early because it can affect where on the lot the unit should go and what the project will cost.
The ADU also needs its own heating and cooling, often a ductless mini-split, and a water heater sized for the unit. We coordinate those with the energy code compliance documents so the envelope and equipment agree.
Converting a garage into an ADU
Garage conversions are often the fastest and least expensive ADU, but the existing building was never designed for living space. The plans have to solve several problems:
- The slab. Garage slabs are usually thin, sloped and lack a vapor retarder. We specify a raised wood floor or a leveling and insulation approach that keeps moisture out and meets ceiling height.
- The garage door opening. The opening is infilled with a framed wall, often with a window or entry door, on a new footing where the existing curb is inadequate.
- The structure. Header, roof and wall bracing are checked, because removing the door and adding windows changes how the walls resist lateral load.
- The envelope. Walls, ceiling and floor are insulated and air sealed to the energy code.
- Separation. An attached garage conversion still adjoins the main house, so the shared wall and openings are detailed for dwelling separation where required.
- Utilities. Plumbing drains are routed through or over the slab, and the electrical service is checked for the added load.
Our garage plans team handles new garages as well, so if you are building a garage now with a future ADU in mind, we can design it to make the later conversion straightforward.
ADU plans are a fit if you want to
- Build a backyard cottage or guest house
- Convert a garage into a rental unit
- Add an apartment above a garage
- Create a basement or in-law suite
- House a family member on your lot
- Legalize an existing unpermitted unit
How it works, start to finish
From your first message to stamped drawings, you work directly with the engineering team.
- 1Share your projectSend the address, scope and any drawings, photos or plan-check comments. Two minutes is enough.
- 2Receive a fixed-fee proposalAn engineer reviews the scope and replies with a firm price and delivery date for your adu plans drawings.
- 3Engineering and draftingWe run the calculations and prepare drawings to the codes your jurisdiction enforces, checked before sealing.
- 4Stamped set deliveredYou receive a sealed PDF set ready to submit, and we answer any plan-check comments within scope.
Codes and rules for ADU plans
ADU plans are prepared to the codes and ordinances your state and local jurisdiction have adopted:
- Your local zoning ordinance and any state ADU law that applies
- International Residential Code (IRC) or your state residential code
- International Energy Conservation Code (IECC) or your state energy code
- ASCE 7 for wind, snow and seismic loads
- Local fire department access and water supply requirements
How licensing works. Engineering drawings must be sealed by a Professional Engineer licensed in the state where your project is located. PE Engineer works with a network of state-licensed PEs, so every set is reviewed and stamped by an engineer with an active license in the state where your project is located. Their name and license number appear on the seal, exactly as your building department requires.
Related services
Garage PlansPermit-ready garage plans for detached, attached and apartment garages, with foundation, framing, fire separation and site plan coordinated in one set.Explore More
Site & Plot PlansScaled site and plot plans showing property lines, setbacks, easements, lot coverage, utilities and drainage for residential and commercial permits.Explore More
Energy Code ComplianceREScheck, COMcheck and Title 24 energy compliance calculations for homes, additions and commercial buildings, prepared to the IECC or ASHRAE 90.1.Explore MoreFrequently asked questions
Can I build an ADU on my property?
That depends on your zoning district, lot size, existing buildings and the local or state ADU rules that apply. Some areas allow ADUs on almost any single-family lot, while others restrict them heavily. Send us your address and we will review the ordinance and tell you what is allowed before you commit to drawings.
Do you have pre-drawn ADU plans?
We draw ADU plans for your specific lot and jurisdiction, because setbacks, utilities, slopes and local rules vary too much for one plan to fit everywhere. If your city offers pre-approved ADU plans, we can also adapt one to your site and prepare the site-specific sheets it still requires.
What is the difference between an ADU and a junior ADU?
A junior ADU is a smaller unit created within an existing home, recognized under some state laws such as California’s. It may share a bathroom with the main house and often has reduced requirements. A standard ADU is a complete independent unit. Whether junior ADUs exist where you live depends on your state and local rules.
Do ADU plans need a structural engineer?
A simple one-story detached ADU may be built from prescriptive residential code provisions, but many jurisdictions still ask for engineering, especially for garage conversions, units over garages, sloped lots, and high wind or seismic areas. We provide structural sheets and calculations with the ADU set when they are needed.
Can you legalize an ADU that was built without a permit?
Often, yes. We document the existing unit with as-built drawings, identify what does not meet code, and prepare plans showing the upgrades needed to bring it into compliance. The building department may require walls to be opened for inspection, and we help you plan for that.
How long does it take to get ADU plans?
Once we confirm the zoning and receive your site information, most ADU permit sets are delivered within a few business days. Projects that need more engineering, such as units over garages or on steep lots, take longer, and we confirm the schedule with your quote. Review time at the building department varies, and some states set timelines for complete ADU applications.
Get your free adu plans proposal
Tell us where the project is and what you need. Attach any drawings, photos or plan-check comments. A licensed engineer reviews every request.
- Upload your filesPlans, sketches, photos or comments
- Get a fixed-fee proposalUsually the same day
- Receive stamped drawingsSealed by a PE licensed in your state