If you own a home in Summerville, SC and you have been thinking about an accessory dwelling unit (ADU), you are not alone. A backyard cottage, a garage apartment or a mother-in-law suite can give aging parents a place nearby, give a grown child a first home, or simply add flexible living space. Before you sketch a floor plan, though, it helps to know what the Town of Summerville’s Unified Development Ordinance (UDO) actually allows. This guide walks through the ADU rules in plain English, based on the current UDO (adopted October 10, 2019, last amended July 9, 2026).
What counts as an ADU in Summerville, SC?
The UDO defines an accessory dwelling unit as an auxiliary dwelling unit that is either attached to a primary home or located in an accessory structure on the same lot. The Town specifically lists guest houses, carriage houses, pool houses and units above or beside a garage as examples. In other words, an ADU can be a detached backyard cottage, an apartment over a detached garage, or an attached in-law suite, as long as it is a separate dwelling unit that serves the main home on the lot.
Which Summerville zoning districts allow ADUs?
The UDO’s Table of Permitted Uses (Section 3.3) allows ADUs in many of the Town’s districts, but not all of them, and the rules depend on the district:
- Conditional use (C): N-R, N-MX, GR-2, GR-3, GR-5, MF-R and MH-R. These include most of Summerville’s residential neighborhoods. “Conditional” here means the ADU is allowed by right, as long as it meets the extra standards in Section 3.4.2.B described below.
- Permitted use (P): D-MX, UC-MX, N-B, G-B and AC.
- Not allowed: the L-I and H-I industrial districts and PL.
Your first step is to find your property’s zoning district. The Town’s FAQ notes that its regulations apply only inside Town limits and offers an online property lookup tool so you can confirm your jurisdiction and zoning.
The 9 conditions for an ADU in Summerville’s residential districts
For the residential districts listed above, Section 3.4.2.B of the UDO sets these standards:
- Public water and sewer. The lot must be served by public water and sewer. A lot on a well or septic system does not qualify.
- Number of ADUs. One ADU per lot, or up to two in the N-R, N-MX and GR-2 districts.
- Owner occupancy. The main home must be owner-occupied, and the ADU must have the same ownership as the main home. You cannot sell the ADU off separately.
- Placement. The ADU must sit to the rear or side of the main residence, not in front of it.
- Bedrooms. A maximum of two bedrooms.
- Size. No more than 50% of the gross floor area of the primary building. For example, if your home has 2,000 square feet of gross floor area, the ADU can be up to 1,000 square feet.
- Residents. No more than two adults (people over 18) may live in the ADU.
- Parking. A maximum of two off-street parking spaces per ADU. Separately, the UDO’s parking table (Section 7.4.1) sets a minimum of one space per ADU.
- Matching exterior. The ADU’s exterior must be compatible with the main house in color, siding, roof pitch, window detailing, roofing materials and foundation appearance.
That last rule matters more than many homeowners expect. A prefab shed-style unit with a different roofline or siding may not meet it, so design and materials should be planned together with the main house in mind.
Planning a mother-in-law suite or backyard cottage in Summerville
Put together, these rules point to a few practical questions to answer early:
- Attached or detached? An attached mother-in-law suite can share a wall and roofline with the house, which can make the matching-exterior rule easier to meet. A detached backyard cottage gives more privacy but needs its own utility runs to public water and sewer.
- How big can it be? Start from your home’s gross floor area and work down from the 50% limit, keeping in mind setbacks and the rest of the lot.
- Who will live there? The two-adult limit and two-bedroom cap work well for one or two aging parents or a young adult, but not for a larger household.
- Where will cars go? Plan at least one off-street space for the ADU and no more than two.
These are zoning standards only. Building permits, inspections and HOA covenants are separate, so confirm those with the Town and your HOA before you commit to a design.
ADU rules outside Summerville town limits
Many addresses with a Summerville mailing address are actually outside Town limits, and the Town of Summerville itself sits in parts of Dorchester, Berkeley and Charleston counties. If your property is in unincorporated Dorchester County or in another town, the Summerville UDO does not apply and different rules will. Homeowners looking at an accessory dwelling unit in North Charleston, an ADU builder in Goose Creek, or a mother-in-law suite in Ladson should check with that city or county’s planning department first. The same goes for a backyard cottage in Mount Pleasant or an ADU in Charleston, West Ashley or James Island, where the City of Charleston or Charleston County sets the rules.
Frequently asked questions
Can I build an ADU in my backyard in Summerville, SC?
In most of the Town’s residential districts, yes, as long as the lot has public water and sewer, the main home is owner-occupied, and the ADU meets the size, bedroom, placement, parking and design standards in UDO Section 3.4.2.B. Check your zoning district first.
How big can an ADU be in Summerville?
Up to 50% of the gross floor area of the primary home, with a maximum of two bedrooms and no more than two adult residents.
Looking for an ADU builder near me in Summerville?
Intelligent Home Services is based in Summerville and designs and builds ADUs, mother-in-law suites and backyard cottages across the Lowcountry. Learn more about our Lowcountry ADU services.
Plan your Summerville ADU with a local builder
Zoning rules are only the first step. Intelligent Home Services can help you check your lot, plan a layout that fits the UDO, and design an ADU that matches your home. See how we approach ADU design and construction in the Lowcountry, then schedule a consultation or call us at (843) 376-9730.
Areas we serve: Summerville, Charleston, North Charleston, Goose Creek, Hanahan, Ladson, Ridgeville, Moncks Corner, Mount Pleasant, James Island and West Ashley.
Sources: Town of Summerville Unified Development Ordinance (last amended July 9, 2026), Sections 3.2.1, 3.3, 3.4.2.B, 7.4.1 and the definitions chapter; Town of Summerville jurisdiction FAQ. This article is general information, not legal advice. Rules change, so confirm current requirements with the Town of Summerville Planning Department before you build.