Accessory Dwelling Units are all the rage right now, ain't they? In this newly retitled Part One I'm going to cover the most common general knowledge ADU questions, like what they are, how big can they be and what licenses or permits you might need.
In the newly published Accessory Dwelling Units Part II I have covered more technical information about the actual drawings required to get your permit.
If you want to skip the reading you can book a free architecture consult with me.
What is an Accessory Dwelling Unit?
An Accessory Dwelling Unit (ADU) is a complete, independent living space on your property or within your house that is separate from your primary residence. Officially known as an Accessory Apartment and sometimes informally known as a Granny Flats or In-Law Suites, an ADU is basically an apartment on your property.
You as the homeowner can live in the house OR in the ADU, but your primary residence must be on the property.
You can only have one ADU on a property.
Is that the same as an Accessory Structure?
Any structure you build on your property that's not your primary residence is an Accessory Structure. This includes garages, studios, sheds, gazebos, etc. If you want your accessory structure to be an actual apartment it has to meet the standards of an Accessory Dwelling Unit. If your goal is to just build a home office in your back yard you will have fewer standards to meet. Send me an email for more details.
Did some laws about ADUs just change?
Yes. As of January 1st, 2020, the minimum 300-foot separation was revoked. Prior to this only one ADU would be licensed within a 300-foot radius. If your next-door neighbor had one then you would not be allowed to have a legally documented ADU. Removing that rule fairly allowed more homeowners to build ADUs as a matter of right. There are still other zoning and technical requirements that you must meet, but these are usually easier to navigate. Read on for more detail.
Do I need a license?
Yes, you will be dealing with multiple government agencies if you want an ADU on your property. The application, inspections and licensing will be handled by the Montgomery County Department of Housing and Community Affairs (DHCA). This is for the ADU only, and your project will still need traditional building permits from the Department of Permitting Services (DPS).
If you are in Takoma Park your actual rental license will be granted by the City of Takoma Park. If you are in an Historic District you will need to go through the Historic Area Work Permit process first. That link goes to another blog that will tell you everything you need to know about that.
CAN an adu BE ATTACHED TO YOUR HOUSE?
Yes. There are two flavors of ADU; Attached and Detached, with some pros and cons to each.
A Detached ADU is an accessory structure out in your back yard, we covered this above. They are completely separate from the house, offer more design freedom and are high on the cool factor. They're also generally more expensive per square foot, are more restrictive in size and they require fire sprinklers and stormwater management, which are big expenses.
An attached ADU is an addition to your house. They are allowed to be bigger, you don't need to add sprinklers, you may be able to avoid drainage requirements (though unlikely if you want to max out your size) and it's generally easier to tie into existing utilities serving your house. You'll pay more in design fees because now you need to coordinate the addition with the entire house and it's sometimes difficult to max out the size and not reconfigure existing spaces you might not have intended to be a part of the project.
Consider a maximum size attached ADU is 1,200 sf…that's a 30′ x 40′ footprint, which is huge and might not fit on your site. You could also do 600 feet on each of two stories, but now we're getting into design, and that's part of the part I get hired to do!
CAN an adu BE ATTACHED TO YOUR HOUSE with a breezeway?
Yes, but not the way you're thinking. An attached ADU must be connected to the house via actual indoor conditioned space. Architecturally referred to as a hyphen, and informally (and somewhat incorrectly) as a breezeway, it is a great design tool which pushes the addition away from the main house, thereby reducing the connection point between the two, making that connection easier from a design and construction standpoint. That connection piece is a great place for a mudroom, laundry, powder room etc, but it is INSIDE space…not just a covered walkway. Check out the Seven Locks project on my home additions page for an example of a hyphen.
Can I just build an ADU and not call it that?
No. An ADU needs to be a fully-functioning apartment, meaning it needs to have a full kitchen. A residential addition or alteration permit, without an accompanying letter from DHCA, will not allow you to add a second kitchen in your house or any kitchen in an accessory structure.
Plans that show a range and cooktop in your basement will get flagged for review at Montgomery County Department of Permitting Services and will be not be approved without the certification from DHCA.
You can add a wet bar and kitchenette to your basement or accessory structure without issue. A new sink, fridge, wine cooler, are all ok. Even a full bathroom is fine, pending unrelated water fixture count requirements.
You are always allowed to rent a ROOM in your house without needing a permit. But this is like having a roommate. You have one front door, one kitchen, one washer/dryer, etc. You can NOT rent a room in your basement and then just lock the door between the basement and the house. And yes, someone asked me this before.
HOW MUCH DO adus cost to build?
Detached, probably at least $250,000. They are expensive per square foot, and the sprinkler piece alone could be $30,000+. Attached, depends on a billion factors, but probably at least $250,000 as well and probably more, though you also get more for your money. It's impossible to say what these things cost until you design them, but these are the prices I've seen on recent projects.
HOW MUCH ARE ARCHITECTURE FEES FOR AN ADU?
I'm going to start in the high teens for a detached ADU and low twenties for an attached ADU, though my proposals always include three tiers depending on how involved you need me to be throughout construction.
I get that is not a small sum of money and might seem like a lot for what might be a small project, but that includes architecture, and structural engineering and civil engineering and coordinating permits with two separate government agencies.
And most importantly, I am not the cheap option. I'm the exceptional option! Already have plans or a draftsperson? Check out my plan review service.
What are the technical requirements for an ADU?
There are lots, but for the most part they are very common building requirements that are no different than if you were doing a typical renovation with no ADU. The best place to read the requirements are on the Department of Housing and Community Affairs website. They have an Accessory Dwelling Unit Fact Sheet that you can download. You can also read part two of this post, where I cover drawing requirements for Accessory Dwelling Units.
Here I will cover some of the most common requirements:
ADU Maximum Size
For an attached ADU, i.e. in your basement or rear addition, the ADU can be up to 1,200 sq ft, though it may be larger if the existing basement is already larger than 1,200 sq ft.
A detached ADU is limited to the lesser of 50% of the primary house footprint, 10% of the lot square footage or 1,200 sq ft. Usually the footprint thing is the limiting factor. Actually, property setbacks often become the limiting factor. If an ADU exceeds certain length, width or height limits the required setbacks increase, often restricting the ADU to about 576 square feet. This is very dependent on your property, but is a fairly common constraint for many properties in an R-60 zone, which is a lot of lower Montgomery County.
ADU Entrance and Parking Requirements
The ADU needs its own entrance, either on the side or to the rear of the main house. You need to provide one parking space and a lighted path from the parking to the ADU entrance. If you live within 1 mile of a metro you do not need to provide parking.
ADU Bedroom Size
You need to provide one legal habitable space for sleeping. The requirements here are no different than any other habitable space. It needs to be at least 70 square feet in area, have an egress window and smoke detector and no dimension can be less than 7 feet. If the ADU is in your basement you may need a window well at the egress window. I have a whole other post about Bedroom Size Requirements if you want to learn more.
Quick tangent, “the code” usually refers to the International Residential Code (IRC) and the term Bedroom is not used here. The IRC gives requirements for habitable spaces or sleeping rooms, but having a closet is not one of them. So while a closet is a great idea for a bedroom and most of us would think it weird to not have a closet, this is not actually a requirement. The only time closets come up in a code is when you are on a septic system and need to count bedrooms, but now we’re way off topic.
ADU Ceiling Height and Fire Protection
The minimum ceiling height is 7 feet for bedrooms, hallways and other habitable spaces. In bathrooms and other non-habitable spaces it is 80”, which is 6’ – 8”. A living room is not considered a habitable space.
If there are beams, girders or ducts, the bottom must be 76” from the floor. Any stairs leading up to the first floor might also need the full 80” clear head height.
The ceiling of a basement ADU must also be fire rated to protect the floor above for one hour. This is usually accomplished by adding one or two layers of special gypsum board. The requirement for a fire rating is one of the few things you are required to do for an ADU that is in addition to the typical requirements for a standard renovation project. This is not required if you are just finishing your basement.
If you are building the ADU as an accessory structure it will need fire sprinklers.
Can I turn my garage into an ADU?
Maybe. It's almost guaranteed that your garage does not meet the required setbacks, and though there are some aspects that are grandfathered in, you'll often end up needing a variance. That variance would probably get approved, maybe, but I can't promise that.
What about putting the ADU above my garage?
Also maybe. Same setback issue, plus you'll start getting into the max height issue. Max height on an ADU is 20 feet which can create challenges in creating adequate living space on a second floor and stair clearances and ceiling insulation. People tend to overvalue something that is already there. If you want a detached ADU the best thing might be to build it in a different location on your site or raze the garage and build it there (or close to there, depending on the setbacks.) If you're in a historic district you might not be able to do that.
How do we apply?
Licenses are granted by the Department of Housing and Community Affairs, and they maintain an official Accessory Apartment Class 3 License page.
You can also download the Class 3 Accessory Apartment fact sheet, which covers the Accessory Dwelling Unit application process and a lot of other stuff you need to know.
The first step is to fill out the application. This can be done online or with a hard copy. If you are in Takoma Park the online application might not work for you because technically it is not the jurisdiction of DHCA, so use the paper one. More on that below.
When the application is accepted DHCA will schedule a preliminary inspection. They visit your property to document the existing conditions of the site and the proposed ADU. Then they write you a report that notes the ADU requirements and any deficiencies they may have found. This list of ADU requirements is the same as what is shown in the information sheet, linked above. The important thing about this report is that you need to provide it to DPS when you are submitting drawings for your actual building permits. See FAQ above, but if you try to build an ADU without informing DHCA you will get rejected at DPS. This preliminary report is what they are looking for.
After you are done with the building permit AND construction process, DHCA will inspect again, this time to make sure all the requirements have actually been met.
If you are in Takoma Park, your actual rental license will be issued by the City. They accept the DHCA inspection as their required inspection, but there are some other requirements as well. You can read more about these requirements on the page for the Takoma Park Rental Housing Licensing.
Next Steps
You could check out part two of this post, which includes a more technical list of drawing requirements for Accessory Dwelling Units. You might also visit my friends at Up Craftsmen to learn more about ADUs.
And if you've got more questions or are ready to start designing your own dream home with ADU just send me a message or book a free project startup consult!
