A Guide to Accessory Dwelling Units


On April 17, 2018 the City of San Marcos adopted a new zoning code that expands the ability for owner occupied, single family properties to construct accessory dwelling units.

JUNE 2018

Contents Definition and Benefits......................................... 3 WHAT IS AN ACCESSORY DWELLING UNIT (ADU)? 3 WHAT ARE THE BENEFITS? 3 Ownership and Location .................................... 4 WHO CAN BUILD AN ADU? 4 WHAT IF I HAVE AN ADU AND MOVE OUT? 4 WHERE IS AN ADU ALLOWED? 4 Building Standards............................................... 6 SIZE RESTRICTIONS 6 HEIGHT RESTRICTIONS 6 Permit Process....................................................... 7 WHAT PERMITS DO I NEED? 7 HOW TO APPLY 7 DO I NEED A CONTRACTOR? 7 PERMIT COSTS 7 Additional Information......................................... 8 CONTACT 8 CREDITS 8 Site Requirements ................................................ 5 LOT SIZE 5

A dwelling unit contains a kitchen and bath and is suitable for occupancy by a family.


WHAT IS AN ACCESSORY DWELLING UNIT (ADU)? The City’s zoning ordinance defines an accessory dwelling unit as, “ A secondary living space which shares ownership and utility connections, and which is on-site with a primary living space that may be contained within the same structure as is the primary living space, or may be contained in a separate structure. ” A dwelling unit is defined as “A room or suite or set of rooms occupied and suitable for occupancy as a family residence and having a kitchen, and bath and sanitary facilities, together with appropriate appurtenances to that occupancy.” WHAT ARE THE BENEFITS? A dditional I ncome S ource An accessory dwelling can be rented as an individual dwelling, providing the homeowner with additional income. The homeowner would have the option of renting either the primary home or the ADU. The unit may be rented on a long-term or short-term basis when registered and compliant with the City’s Short Term Rental Ordinance. C ommunity B enefits Accessory dwelling units benefit the community by contributing to the diversification of housing types and sizes. Accessory dwellings also increase the supply of affordable housing and offer more housing choices to accommodate the varying needs of San Marcos residents. E xtended F amily and A ging -I n -P lace B enefits Accessory dwellings provide families with the means to care for extended family members - both young and old - by enabling them to maintain their independence and avoid costly housing alternatives.

An ADU may be attached to the primary home or a separate structure on the same lot.

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City of San Marcos Planning and Development Services Department


WHO CAN BUILD AN ADU? A homeowner living on single-family property may build an ADU. Proof of owner occupancy is established with a homestead exemption on the property. Alternatively, owner occupancy may be established with a deed and proof of residency, including at least two of the following: • Motor vehicle registration, • Driver’s license, • Texas State identification card, • Voter registration, • Tax documents, or • Utility bill. WHAT IF I HAVE AN ADU AND MOVE OUT? If your single-family property has an existing ADU, and you no longer live on the property, you may only enter into one lease. An ADU and primary building may not be leased to two separate families. WHERE IS AN ADU ALLOWED? ADU’s are allowed in all single-family areas of the city. If your property is zoned for something other than single-family, you can view the zoning ordinance here for regulations specific to your property. In order to check the zoning of your property you can view the city zoning map here.

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City of San Marcos Planning and Development Services Departmen t


An ADU must fit within the setbacks of your zoning district






LOT SIZE There is no minimum lot size requirement for building an ADU as long as your project meets the requirements of the San Marcos Development Code. Parking Your lot must be sized and configured so that one additional off- street parking space can exist in the third layer of the lot. Parking areas must be constructed from an all-weather surface. M aximum impervious cover The allowable impervious cover on a Single-Family - 6 lot may not exceed 50%. E asements or deed restrictions Be sure to check your property records to locate any utility, drainage, access or floodplain easements that may exist. No structures may be placed within an easement. It is the property owner’s responsibility to ensure compliance with all deed restrictions. S etbacks Your ADU must meet the required setbacks for an accessory structure identified by your zoning district. Single-Family - 6(SF-6) lots require:

Impervious Cover

Impervious cover percentage is the percent of lot area made up of impermeable surfaces such as pavement or rooftops which prevent the infiltration of water into the soil.



Property Line

Parking Location

One additional parking space is required on-site and must be placed in the third layer.


3rd Layer


Primary Street Setback: 25’ min. Secondary Street Setback: 15’ min.

2nd Layer

Property Line

1st Layer



2nd & 3rd


No ADU Parking

Side Setback: 5’ min. Rear Setback: 5’ min.

1 Additional Parking Space

1st Layer


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City of San Marcos Planning and Development Services Department


SIZE RESTRICTIONS The maximum square footage of the habitable area of an ADU is limited to either one half (1/2) the habitable area of the primary building, or one thousand (1,000) square feet, whichever is smaller. HEIGHT RESTRICTIONS The maximum height of a detached ADU is determined by the zoning district. An ADU located on a single-family zoned property must not exceed a height of twenty four (24’) feet. M easuring height Building height is measured from the average grade to the mean height level between the eaves and ridge of a gable, hip, mansard, or gambrel roof, or to the highest point of the surface of a flat roof. A verage G rade Average grade is determined by calculating the average of the highest and lowest elevation along the front of the building, parallel to the primary street setback.

Average Grade Maximum 24’ Maximum size of half the main house or 1,000 sq. ft. whichever is smaller

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City of San Marcos Planning and Development Services Departmen t


WHAT PERMITS DO I NEED? ADU construction only requires a building permit. When submitting your building permit application, you must include the following information with your application: • Proof of ownership and residency • A site plan • An engineered foundation • Building plans in compliance with the 2015 International Residential Building Code (IRC). HOW DO I APPLY? You may apply for a building permit online by visiting www. mygovernmentonline.org . This website will allow you to apply, upload necessary paperwork, pay, schedule inspections, and track the progress of your project. If you have any questions during the process, you can email permitinfo@sanmarcostx.gov or call (512)805-2630 for assistance. DO I NEED A CONTRACTOR? A licensed contractor is encouraged but not required when your property is homesteaded. Compliance with all applicable building codes will be verified during plan review and on-site inspections by a City building inspector. HOW MUCH DOES A PERMIT COST? The fee for a residential building permit is 46 cents per square foot. In order to encourage property owners to improve their property, the City of San Marcos waives all permit fees for homesteaded properties with completion of a homeowner’s affidavit when the homeowner is applying for a permit.

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City of San Marcos Planning and Development Services Department


CONTACT P lanning and D evelopment S ervices 630 E. Hopkins San Marcos, TX 78666 Main Phone Number: (512) 393-8230 Email: planninginfo@sanmarcostx.gov

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City of San Marcos Planning and Development Services Departmen t

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