What is a DADU and How is it Different From an ADU?
If you've been researching secondary housing units, you've probably run into a confusing alphabet soup of terms — ADU, DADU, JADU, accessory dwelling unit, detached dwelling unit. They're related but not identical, and knowing the difference matters when you're figuring out what your property allows and what you're trying to build.
ADU — Accessory Dwelling Unit
ADU is the broadest term and functions as the umbrella category. An accessory dwelling unit is any secondary, self-contained living space on the same parcel as a primary residence. It has its own entrance, kitchen, bathroom, and sleeping area. The "accessory" part means it's secondary to the main dwelling — smaller, subordinate, but fully functional as an independent living space.
ADU is the term most commonly used in zoning codes, state legislation, and real estate discussions. When Utah's HB 82 opened up secondary unit development across the state, it used ADU as the governing term. If you're talking to a city planning department, ADU is the language they'll use.
DADU — Detached Accessory Dwelling Unit
A DADU is simply an ADU that is physically detached from the primary home — a separate, freestanding structure on the same parcel. It shares the lot but doesn't share any walls with the main house. This is the category that a modular home placement falls into: you have your primary residence, and you add a separate, complete home structure on the same property.
DADUs are generally the most valuable form of ADU because they offer genuine physical separation, are typically larger than attached or interior units, and function most like an independent rental property. They're also what most people picture when they imagine an "ADU" — a backyard cottage, carriage house, or secondary home on the same lot.
JADU — Junior Accessory Dwelling Unit
A JADU is a smaller unit created within the existing footprint of the primary home — typically a converted bedroom, garage, or basement space with its own entrance and basic kitchen facilities. JADUs are generally capped at 500 square feet by most local codes and are designed to be the simplest and lowest-cost ADU option. They don't require new construction and often face the least regulatory friction to permit.
Attached ADU
An attached ADU is connected to the primary home — sharing at least one wall — but has its own separate entrance and full amenities. Think of an addition built onto the side or back of the existing home with a private door. These are common in urban areas where lot size limits a detached structure.
Which type applies to your property?
The answer depends primarily on your lot size and local zoning rules. If you have enough land to accommodate a separate structure with required setbacks, a DADU — the detached version — almost always produces the most value. It's the most rentable, most private, and most flexible option over a long hold period.
If lot size is constrained, a JADU or attached ADU may be the practical option. Either way, the first step is the same: call your city planning department, give them your parcel address, and ask what ADU types are permitted under your current zoning.
The simple version: ADU is the category. DADU is the detached version — a separate structure, the highest-value option, and what a modular home placement creates on your parcel. JADU is the smallest and simplest version, carved out of existing space.
Where modular fits in
When Summit Luxury Dwellings places a home on your property as a secondary unit, it creates a DADU — a fully detached, code-compliant accessory dwelling unit on a permanent foundation. It qualifies for the same permitting and financing as any other detached ADU and is treated identically by local zoning codes. The modular build method simply means it arrives faster and at more predictable cost than a site-built alternative.
Want to add a DADU to your property?
We help property owners across seven western states add detached accessory dwelling units in under 90 days. Fill out our contact form to start the conversation.