ADUs can vary in both shape and size, but there are some general building code limitations to the sizes of certain rooms. Read on to learn more about how the rooms in your ADU build up to a full unit.
Updated Feb 07, 2022
Breaking Down Your ADU
As a custom ADU builder that constructs your new accessory dwelling unit from the ground up, Cottage is able to design the ADU unit that fits your needs and use cases.
One common question we often get from homeowners is—”How big or small can my ADU unit be in order to have one, two, or even three bedrooms (or bathrooms?” While your ADU can be infinitely flexible in its use cases and our design team can plan your ADU that works for your property, there are some basic building code limitations—not to mention comfort-level minimums—that lead to a few common patterns in ADU size and orientation.
Most ADUs can be broken up into three sections:
Living Room, Dining Room, and Kitchen Space
Let’s dive deeper into each of these sections for the full breakdown of your potential ADU floor plan.
Living Room, Dining Room, and Kitchen Space
One key benefit of designing your ADU from the ground up is that the Cottage team can help you optimize your living space for the intended use case.
If you’re looking to host dinner parties and guests in your ADU space, you may want to consider an open floor plan. By combining the living, dining, and kitchen spaces, you create an open concept feeling that facilitates hang-outs among family and friends.
For example, this popular Cottage open concept floor-plan devotes half of the space to a combined kitchen-dining-living room area. Combined with two sets of French doors, the space is perfect for hosting guests. The trade-off, however, is that the space takes up over 300 square feet of floor plan space.
On the flip-side, if you’re looking for more privacy or building your ADU unit primarily for rental income, you may choose to minimize the dining and living space in favor of larger (or more) bedrooms, and even an extra bathroom squeezed in to maximize the potential monthly rent.
In this floor plan example below, the homeowner could have either had a larger 510 sq.ft. studio or a smaller 1 bedroom unit. In the end, adding the additional wall to create the 1 bedroom unit would lead to a higher rental income without significantly impacting the cost. However, the trade-off here was a smaller dining-living room space instead of an open studio floor plan.
Regardless of what you choose, your ADU will require at least a kitchenette space and some form of living/dining room area. For most homeowners and ADU layouts, this will require anywhere from 200-400 sq.ft. of space for these dedicated areas.
Bedrooms in Your ADU
For a room to be called a bedroom in your ADU, it typically needs to be at least 70 sq.ft. and have at least one “ingress or egress” window, which is a fancier term for a window large enough to climb out of in the case of a fire.
Realistically, most homeowners choose to have bedrooms larger than 70 sq.ft., and these typically range from 90 sq.ft. for small rental bedrooms or mini-den/office spaces to 200 sq.ft. for the largest master bedrooms.
Looking at the same floor plan example as just above again, you can see why most homeowners choose to build larger than the minimum:
At 109 square feet, this ADU bedroom is a comfortable size, and has a full wall in-room closet as well. The overall sizing allows for a full queen bed with bedside tables to fit into the room comfortably while allowing the inward-swinging bedroom door to pivot fully. Most homeowners choose for their bedroom(s) to be roughly this size in order to provide the full flexibility of a full-sized bedroom.
On the other end of the spectrum, homeowners with enough space (and budget) to build a much larger ADU to house family members have the option of larger bedroom sizes for their ADU. Check out this example 1200 sq.ft. ADU floor plan:
The master bedroom in the bottom left of the design is a full 213 sq.ft. and connects to a full master bathroom with two closets. The design allows for full privacy and a large amount of open space for the residents—two important considerations for the homeowners, as multiple family members were planning to move into the unit at once.
On the other side of the ADU at the top of the floor plan, you can see that the secondary bedroom, while much smaller than the master, is still a comfortable 107 sq.ft., and comes with a separate in-suite bathroom and dedicated closet.
Some Cottage homeowners needing extra space choose to add an extra smaller “bedroom.” Functionally, the space might be used as a home office, gym, or hobby space—however, the title report and permits will show an additional bedroom, adding to the future sale value for the property with the ADU.
Here’s a classic example of this: the property owner sought to add as many bedrooms as possible, and settled on a design that has a third flex bedroom that has the full ingress/egress window to designate it as a legal bedroom space, but is small enough to be used as a different space if desired:
Regardless of what you choose, Cottage is here to help you make the right decision for your ADU space based on your needs.
Bathrooms in Your ADU
By law, every ADU must have access to at least one bathroom. Whether it’s a studio, 1-bedroom, or 2+-bedroom ADU space, smart bathroom placement and design is pivotal for your floor plan.
If your budget and property allows, it is often in your best interests to have as many bathrooms as possible. And you may be able to squeeze in more than you think!
For example, adding an extra half bathroom on the same plumbing wall as the full bathroom helps save on both cost and space. Half bathrooms consist of just a sink and a toilet, while full bathrooms include a bathtub and/or shower space:
Check out this example 2 bedroom, 1.5 bathroom ADU that has both types of bathrooms:
By pairing a washer and dryer closet with the second half bathroom, along with a pocket door instead of a swing door in that bathroom, the Cottage design team was able to squeeze in the 1.5 bathrooms in a 664 sq.ft. ADU space. That may not sound like much, but imagine being able to tell your tenants that each bedroom gets its own bathroom, or even that there is one bathroom accessible by the entire unit, and one that is completely private.
Small design decisions like these can add significant value to your project without breaking the bank.
A small ADU footprint doesn’t have to mean a small ADU bathroom either. This garage conversion ADU is only 364 sq.ft. However, it sports a full bathroom with a panel shower, as well as an in-unit washer and dryer. In a hot rental market like Oakland, CA where the ADU is located, having those extra amenities is important—and Cottage’s design team is happy to help you make the best choices for your ADU unit.
Designing the Right ADU Space for You
At Cottage, we believe in designing your custom, stick-built ADU in a cost-effective and smart way to give you the best bang for your buck while matching your needs, budget, and use case(s) for your ADU unit. That requires attention to detail for each design decision for your project, which Cottage’s in-house team of architectural designers are standing by to assist with.
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