Impervious Coverage and FAR – Austin

The rapidly growing city ranks ninth among the most densely populated metro areas in America. With its green spaces, live music concerts, and SXSW music festivals, it is no surprise many people are interested in taking up properties in Austin.

However, calculating building impervious coverage limits for a project in a suburban area in Austin can make anyone’s head spin. From competing regulations to the zoning ordinance, everything related to impervious coverage in mainstream cities like Austin requires in-depth understanding.

People find designing and building homes in Austin cumbersome due to its complicated floor area ratio (FAR) and impervious coverage rules. If you have made up your mind to take up residence in Austin and use hard money, it is important to know and understand key regulations new homes need to comply with.

The given simplified details will help you navigate the requirements of FAR and impervious coverage in Austin.

Impervious Cover and FAR Maximus – All You Need to Know

Before we delve into the discussion of how impervious cover works, it is vital to understand what it is and why it is important.

According to the Land Development Code, impervious is a human-made surface that does not absorb rainfall that includes;

  • Rooftops
  • Sidewalks
  • Some decks
  • Patios
  • Paved/unpaved driveways,
  • Roadways
  • paved/unpaved Parking lots,

What to Consider

Considering building cover is important because Austin has a high impervious cover amount on all new home additions. The city also applies maximums for various building coverage and defines it as an “area covered by roofs or buildings” with a few exceptions.

Know that calculating both building coverage and impervious is of paramount importance to avoid legal issues. You can start calculating the coverage of the building. All you need to is to add conditional sq.ft   of your house’s footprint.

Generally, this calculation includes covered porches/patios of the first floor, roof areas, covered parking areas, and conditioned area of the floor. It is worth mentioning that you d do not need to include ground-level landscaping, balconies, paving, incidental projecting eave, and pools.

How to Estimate Impervious Coverage

You need to include all the extra elements to building coverage when it comes to calculating impervious cover, which means including elements like uncovered floors and driveways. However, estimating impervious cover is easier said than done. That means you cannot calculate it just by adding square footage. You need to include areas various appliances cover, such as AC pad.

 It does not end here; it is also important to calculate the drainage spaces of your uncovered deck located between the planks anywhere over the landscape where rain absorbs. The impervious cover makes half the sq.ft of the deck.  

There is some impervious cover that does not count in the calculation, such as public sidewalks, water surface areas of ground pools, and land’s gravel areas. Plus, if you have roof overhangs of 2 inches, it will not count in impervious cover.

The given chart is the guide for a permit application to calculate impervious cover and building coverage in Austin.

impervious coverage

Floor to Area Ratio Calculation

After the approval of the “McMansion” ordinance in 2006, it has become imperative to consider all maximums related to impervious. The McMansion Ordinance has created a maximum, labeled as a floor-to-area ratio (FAR). The ordinance covers the developments that occurred in the specific neighborhood.  

FAR (floor-to-area ratio) typically is the proportion between the enclosed area and the total area of the landscape. The ordinance has imposed approximately 2,300 sq.ft/40 percent of maximum FAR. That means if your lot is larger than 5,700 sq.ft, it will have .40 sq.ft larger number of the lot. However, a lot that is smaller than 5,700 will have a larger number of 2,300 sq.ft.

Austin’s application of residential permit also contains a comprehensive guide to help you calculate the Total Floor Area. In addition, it tells you about exemptions that are important to consider when you make calculations.

Exemptions in FAR for Parking

You can take advantage of these exemptions implied to FAR’s basic definition. For instance, deduct 450 sq.ft if your building’s parking structure has the following features.

  • It is a rear structure and is 10 ft away from the building’s primary structure.
  • The parking area is detached, excluding open breezeway and is 10 ft away from the building’s primary structure. 
  • Has more than two open sides and does not include any habitable spaces above it

Deduct 200 sq.ft if

  • The parking area is attached to the building but meets the minimum requirements of parking.
  • The parking area is a detached structure and located within the proximity of the primary structure.
  • Parking area within 10 ft. of primary structure and is close to a breezeway.

Getting both exemptions for your building’s parking area is possible. That is to say; you can qualify for the 450 sq.ft exemption and 250 sq.ft exemption with the parking area that does not meet all the requirements of parking.

Exemptions in FAR for Attics, Basements, and Porches

It might sound surprising, but FAR exempts some porches, basements, and attics. For example, it can exempt the ground-floor porch if it is not attached to any driveway or not accessible by the vehicles.  However, you cannot exceed deduction from 200 if your porch is located below a balcony or a habitable space. Therefore, FAR may exempt habitable basements if they;

  • Stick to the first-story footprint
  • Are located below the finished grade
  • Have 50 percent perimeter walls in surroundings

   It exempts habitable attics if:

  • The roof has a 3 to 12 inches slop
  • Make a full roof structure
  • Have one floor
  • Have the highest habitable building portion

Final Verdict – Impervious Coverage

Overall, there is no denying that these FAR rules and restrictions are complex and intertwined and make architects’ job challenging. After that, they need to work out these exemptions to design your house. That is what makes consulting a professional and licensed architect extremely important instead of relying on the information only.  Therefore, the given details will surely help you understand the basics of building impervious cover and FAR limits in Austin. Once you’re ready, contact a hard money lender to finance your new build!

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