If your property lies anywhere in the Subchapter F area of Austin, the requirements to get a permit become increasingly difficult. Below I want to lay out some key requirements needed to permit an sf3 zoned, home and ADU, in the Subchapter F Overlay.
#1 - F.A.R. or Floor Area Ratio
First you want to locate your property on the map and determine if it falls within the overlay. If it doesn't then you are in luck. The requirements for not being in the overlay area are less stringent, such as not being required to have a licensed architect. Use the picture below to determine if your property falls within the Subchapter F Area.
If you are in the Subchapter F area then the first thing you will want to consider is FAR. FAR stands for Floor Area Ratio and it is the maximum amount of area, under roof, allowed on a lot. FAR is limited to .4 to 1 in relation to lot size or 2300 sqft. whichever is greater. Beyond that if you want to have a home and an ADU ( accessory dwelling unit) on the same lot, then that ADU can only have an FAR of .15 to 1 or 1100 sf, whichever is smaller.
As an example, lets say your lot is 8125sf. You are allowed to have a FAR of .4 to 1, so that would come out to 3250sf. Your ADU can only be .15 to 1 and that comes out to 1232sf. This means your ADU can only be 1100 sf since it is the smaller of the two numbers. In this example 3250 overall FAR - 1100 sf adu = 2150. So your main house will be 2150sf and your ADU will be 1100sf.
#2 - The Tent Diagram
The next big thing that is different about Subchapter F requirements is the required tent diagram.
Above you will see a simplified diagram of what is required. No part of the home other than a dormer, side gable, or a shed roof can protrude from the tent. The tent consists of a 15' tall plane along the property line. At the top of the 15' side plan is another plan that extends at a 45 Degree Angle. This is the roof of the "tent". The roof plane extends until it hits a maximum height of 32' from the ground. This means the maximum height of a building is 32'.
Above is a side view of how the tent diagram should look on an 80+ foot long lot with unlevel ground. The tent is broken up into 40' sections with the rear section being whatever is left under 40'. Each 15' side tent wall is based on the highest ground elevation in each 40' section. You can see in the example above that the middle tent section is higher due to the increase in elevation. On the back of the lot is another 15' wall with a 45 degree plane extending until it hits 32'.
Above is a 3D example to help wrap your head around what this section looks like in real world applications. When you are preparing plans no 3D elevation is required. Just front, side, and rear elevations are required.
#3 - Sidewall Articulation
One Final oddity associated with Subchapter F is the use of sidewall articulation.
Above you can see an example of sidewall articulation in practice. If a building extends more than 36' then a break of no less than 4' deep and 10' wide is required. This is done to prevent long square maximum sqft homes from being built.
#4 - Tips, Tricks, and Things to Look Out For
Keep in mind that FAR includes anything under roof. This means that it includes any covered porches or garages as well. However, there is good news. There are certain exemptions to FAR and I'll list them below:
Up to 450sf of a detached parking area separated from the principal structure not less than 10'; or a parking space that is open on two or more sides if it does not have habitable space above it
Up to 200sf of attached parking if it is used to meet the minimum parking requirement.
A Basement
A habitable portion of an attic if the roof above it is more than 3/12, it is fully contained in the roof, it is the highest habitable part of the building, and 50% or more of the area is less than 7' tall.
Another thing to note is that areas with ceiling heights of 15' or more count DOUBLE against FAR.
One other provision to look out for is neighborhood planning areas (NP). These can add to, or supersede, rules that are in the Subchapter F area. One example is garages. In certain neighborhoods the garage cannot be more than half the size of the habitable part of the home next to it. So, if you had a garage that was 10' wide the rest of the home next to it would have to be 20' wide. This would mean that the overall structure is now 30' wide minimum. This can obviously make it hard to fit garages on small lots. Fortunately there is a workaround in certain areas. If you are within 1/4 mile of a transit stop, the secondary structure is not required to have available parking at all.
Press Start Permitting Services
If the above information seems daunting, you are not alone in thinking this. Fortunately, Press Start offers permitting services for this. Press Start can help you produce plan sets as well as do the permitting required to get your project ready to go.
To procure permitting services, just Press Start!
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