A GUIDE TO BUILDING IN THE HILLS OF LOS ANGELES
Article #5: RFA & Slope Band Analysis (Baseline Hillside Ordinance)
We are working through the Baseline Hillside Ordinance to determine what we can build at the fictional property, 809 Higgins St. in the Hollywood Hills. Today we will look at Residential Floor Area (RFA) & Slope Band Analysis. As always, the ordinances are intended to preserve general intents and exceptions may be approved in individual cases.
Maximum Residential Floor Area (RFA)
This is the Baseline Hillside Ordinance’s number one weapon to discourage overbuilding and to make sure that the scale of existing neighborhoods is preserved.
Residential Floor Area (RFA) is the total area in square feet measured from the inside of the walls of the building. Stairs are counted only on one level. Porches, exterior walkways, etc. are not counted in the RFA calculation. 400 square feet of parking and basements are not counted either.
Page 8 of the Baseline Hillside Ordinance gives a more nuanced definition of Residential Floor Area, including conditions and exceptions. Some of them are quantified such as excluding up to 250 SF of covered porches, patios, and breezeways from the RFA calculations.
There are two ways to determine the maximum RFA that is permitted for your property: One is with a Slope Band Analysis and the other is to utilize the Guaranteed Minimum Residential Floor Area provision of the code.
- Slope Band Analysis
The Slope Band Analysis combines three regulatory elements in one:
- Zoning
- Land Survey – specifically, topographical contour maps
- Floor Area Calculations (RFA & FAR – Floor Area Ratio)
The purpose of the Slope Band Analysis is to quantify the floor area density of a site according to the severity of the slope. A key feature of this provision is the bonus options that award 20% additional RFA depending on which limiting design options are exercised.
2. Guaranteed Minimum Residential Floor Area
The Guaranteed Minimum Residential Floor Area provision guarantees at least 1,000 square feet of allowable floor area regardless of the slope band calculations. If you use this provision, then you qualify for a 30% bonus by exercising one of the 7 design options given.
The reason for this provision is to allow a reasonable RFA on properties that, under the slope band analysis, might not give you enough floor area to build.
At 809 Higgins Street, what is our RFA? First, we have already established that per Setbacks, our maximum buildable area is 1360 SF.
But now we need to determine the maximum RFA allowed within this buildable area. We have two ways to determine this:
- Decide if an area that is 25% of the lot size, or that is 1000 SF, is enough to satisfy the program requirements. Don’t forget you can add the RFA Bonus of 30% by utilizing one of the 7 given design options. (Guaranteed Minimum RFA)
or
- Do a preliminary, back-of-the-napkin slope band analysis study. (Slope Band Analysis)
1) Guaranteed Minimum Residential Floor Area
Decide if an area that is 25% of the lot size, or that is 1000 SF, is enough to satisfy the program requirements. Remember that Stairs are only counted on one level. Porches, exterior walkways, etc. are not counted in the RFA calculation. 400 square feet of parking and basements are not counted either. If the percentage of lot size corresponding to zoning, as outlined in Table 4, is greater than 1,000 SF then you can use that number. In our case, at R1 zoning our Guaranteed Minimum Residential Floor Area is 25% of our lot size. Don’t forget you can add the RFA Bonus of 30% by utilizing one of the 7 given design options. So if you use the 1,000 SF minimum, with a 30% bonus you have a total RFA of 1,300 SF
|
TABLE 4 |
Guaranteed Minimum Residential Floor Area
|
Zone |
Percentage of Lot Size |
|
R1 |
25% |
2) Slope Band Analysis
Do a preliminary, back-of-the-napkin slope band analysis study. In some cases, it is enough to draw a section or two through the site to find out the prevailing slope and do ballpark calculations. If it is obvious that the allowable area per the topographical map would be less than the minimum 1000 SF, then it makes sense to skip the formal slope band analysis and exercise the Guaranteed Minimum Residential Floor Area option. Otherwise, your land surveyor will prepare a formal slope analysis map that you can use for the permitting process.
At 809 Higgins Street, part of the site is flat from the previous home, and the other part is a steep slope held back by an existing retaining wall. A rough section drawn through the site gives you a few different slope bands.
The slope bands are a measurement of the percentage of a slope’s inclination – not the actual angle of the slope. For example, if the distance across a lot is 65 feet, a vertical increase of 65 feet from one end of the lot to the other would mean a 100% slope. If, however, the vertical increase is 41 feet, then the percentage increase in height is 63% (41′ divided by 65′ = 63%). Using basic trigonometry, we can determine that the actual angle of the slope is 32 degrees ((tan-1(41’/65′) = 32)). The slope band % in this case is 63%, whereas the angle of the actual slope is 32 degrees.
How does the Slope Band Analysis work?
With a topographical contour map of the property in hand, we can through each slope band one by one to determine which of the 6 major slope categories it falls under. Then we measure the area of that slope band and multiply it by a ratio given in the code. The ratio is called Floor Area Ratio (FAR) and it is given in Table 2 of the Baseline Hillside Ordinance.
Lets go through the Slope Band Analysis step by step for 809 Higgins Street.
- Determine the Zoning – our zoning is R1-1.
- Obtain a topographical map
Note: If you are only doing a rough back-of-the-napkin analysis and do not have ready access to a topographical map of your property, then you can visit www.navigatela.com, input the lot’s APN number, and turn on the level curves layer. This will give you the topographical contours of the site.
3. Determine the degree of slope for each slope band based on the zoning classification (R1-1). Color each slope band with the corresponding color from the key.
- The slope is considered in increments up to 45 degrees. This gives us 6 categories of slopes:
1) 0° to 8.5° = 0% – 14.99% (lowest slope band)
2) 8.5° to 16.7° = 15% – 29.99%
3) 16.7° to 24.2° = 30% – 44.99%
4) 24.2° to 31° = 45% – 59.99%
5) 31° to 45° = 60% – 99.99% (highest slope band feasible for building)
6) 45° and greater = 100% and greater (since the multiplication is Zero for all zonings of this category, no RFA can be built on these slopes anyway)
4. Add the total area of each slope category and tabulate the results next to the slope band analysis map.
5. Multiply the total area of each slope category by the Floor Area Ratio (FAR) given in Table 2 of the Baseline Hillside Ordinance. We use the property’s zoning to determine which FARs to use. For R1 zoning:
|
TABLE 2 |
Single-Family Zone Hillside Area Residential Floor Area Ratios (FAR)
|
Slope Bands (%) |
R1 Zoning |
|
0-14.99 |
0.50 |
|
15-29.99 |
0.45 |
|
30-44.99 |
0.35 |
|
40-59.99 |
0.35 |
|
60-99.99 |
0.30 |
|
100+ |
0.00 |
Table 2 of the Baseline Hillside Ordinance gives multiplications for each slope band category based on the zoning. The multiplications are called Floor Area Ratios (FAR). To obtain the RFA of each slope band, we take the area of that slope band and multiply it by the FAR in Table 2.
6. The maximum RFA per the Slope Analysis analysis is 1017.15 SF.
Now a decision must be made. We are allowed two alternative routes to determine the maximum RFA for our site.
- Slope Analysis + 20% Bonus
or
- Minimum Guaranteed RFA of 1000 SF + 30% Bonus
In our case, since we have already completed the slope band analysis, we will stay with the slope band analysis and go for the 20% additional RFA bonus.
After a review of the 7 bonus options available to us, we will obtain a 20% additional RFA bonus for exercising one of the following:
- Proportional Stories Option
- Front Façade Setback Option
- Green Building Option
The 7 different options for the bonuses range from the Proportional Stories Option (to encourage designs that stagger volumes rather than mass them) to the Green Building Option (must satisfy Tier 1 or higher of the LA Green Building Code). Only one bonus per property can be used. We will use the proportional stories option.
So, here is the run-down for 809 Higgins Street:
– Maximum Residential Floor Area per Slope Analysis Map = 1017.15 square feet
– 20% Residential Area Bonus = 203.43 square feet
– TOTAL Residential Floor Area including 20% bonus = 1,220.58 square feet
The total of 1,220.58 square feet is easily within the 1,360 square feet Buildable Area limited by the Setback Requirement. The 1,220.58 square feet can be used anywhere within the Buildable Area – subject to the Lot Coverage requirement (see Article 7 of this Series).
If we needed more square footage, we could have used the Minimum Guaranteed RFA of 1000 SF plus 30% bonus for a total of 1300 square feet. However the total of 1,220.58 square feet is sufficient for our program requirements.
Note: The Residential Floor Area value is different from areas calculated for obtaining construction permits or used by real estate agents for the sale of homes.
Note: The Hillside Neighborhood Overlay may supersede the requirements for Maximum Residential Floor Area.
Note: If your property is subject to the Northeast Los Angeles Hillside Ordinance No. 180,403, it is exempt from the Maximum RFA provision of the Baseline Hillside Ordinance.
Note: If your property is subject to the Oaks Hillside Ordinance No. 181.136, it is exempt from the Maximum RFA provision of the Baseline Hillside Ordinance.
Note: The content in this article is for information only and it represents our interpretation of Los Angeles Zoning & Building codes. Current Los Angeles Zoning & Building Codes should be consulted for an in-depth understanding of the legal text contained in them, and building officials should be consulted as their interpretation of the Los Angeles Zoning and Building Codes may differ from ours.