Calculating Permitable Density Part 2 of 3 - Density Bonus Law & Form Based Density
In this second installment of the density calculation series, Sibley walks Serena Collins through form-based density—the method used when local zoning does not specify a units-per-acre standard. He explains how developers use Floor Area Ratio (FAR) as the controlling density measure, how to conduct a base density study to convert FAR into a unit count, and how density bonus law then multiplies that count. They discuss the strategic use of multifamily ADUs, the role of the Housing Accountability Act in resolving code conflicts, and the critical distinction between entitlement-stage and building-permit-stage decisions.
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Guest: Serena Collins – Project Manager, Workbench / New Way Homes
Serena has been with Workbench for 5 years managing project development and capital raising. She specializes in brownfield site cleanup and redevelopment funding and grant writing at both the state and federal level.
Key Takeaways
Form-Based Density Explained: When zoning lacks a units-per-acre number, the controlling measure is Floor Area Ratio (FAR), which governs the total building size relative to lot size rather than capping the number of units directly.
Base Density Study Process: Developers must design a code-compliant building on the site—without using density bonus law—to determine the maximum number of units that physically fit. This number becomes the “base density” to which bonus percentages are applied.
Average Unit Size Flexibility: The developer chooses the average unit size in the base density study. Smaller average units yield a higher unit count and therefore a larger absolute bonus. This flexibility is a powerful lever for project feasibility.
Financial Feasibility Not Required: The base density study only needs to comply with code—not be financially feasible. Developers can assume underground parking or other expensive design choices to maximize the unit count on paper.
General Plan vs. Zoning Conflicts: Under the Housing Accountability Act, when the general plan allows a higher FAR than the zoning code, developers using density bonus law may use the higher figure. Height limits may flex to accommodate the full FAR.
Other State Laws Layer In: Transit proximity rules, church-owned lot provisions, and other state laws can increase allowable height or density in the base density study, even before density bonus is applied.
Jurisdiction Must Calculate: State law requires the local jurisdiction to provide its own base density estimate upon request. This can be a useful tool for identifying all applicable rules, even if the developer ultimately produces a more favorable study.
Multifamily ADUs as a Third Layer: After applying density bonus (up to two stacked 50% bonuses), developers can add ADUs equal to 25% of total entitled units. These are ministerial and not subject to the average unit size constraint.
Internal Layout Is Not Part of Entitlement: The entitlement approves the building envelope, not interior walls. This means amenity space labeled in the entitlement application can later be reconfigured into ADU conversions at the building permit stage.
Dramatic Density Outcomes: Through form-based density combined with stacked bonuses and ADU conversions, buildings can reach 3–4 times the height contemplated by local zoning—including examples of 5-story zones yielding 18-story buildings.
Infill Insiders Success Grades
This episode is a technical deep-dive within an ongoing series and does not feature the standalone grading format used in policy-focused episodes (such as the SB 79 and CEQA exemption episodes). However, Sibley Simon’s editorial perspective is consistent with previous episodes:
Concept / Intent of the Law: The form-based density pathway, combined with density bonus law, is a powerful mechanism that can yield far more housing than local zoning appears to allow.
Execution / Complexity: The process is convoluted, requires architectural design work for a building the developer never intends to build, and is poorly understood by most jurisdictions. Complexity remains the core barrier to housing production.
Preview of Part 3 (Episode 6)
In part three, the final installment in our calculating density series, we will cover alternative density calculation methods—additional state law pathways that may yield even more units than either units-per-acre or form-based density, but come with other strings attached. Episode 6 will complete the full picture of how to calculate the density a developer can legally build in California as of 2026.
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00:00:00 - Intro
00:01:01 - Meet Serena Collins: Project Management & Brownfield Expertise
00:03:30 - What Is Form-Based Density?
00:04:44 - Floor Area Ratio (FAR) Explained
00:06:00 - Mixed-Use Zoning and FAR Nuances
00:06:35 - Introducing the Base Density Study
00:07:58 - Average Unit Size: The Developer’s Choice
00:09:12 - Applying the Density Bonus to Form-Based Density
00:09:35 - Why Smaller Units = More Bonus Units
00:10:20 - Local Code Conflicts: Setbacks, Height, and Articulation
00:11:52 - Housing Accountability Act: When FAR Trumps Height Limits
00:13:06 - General Plan vs. Zoning: Using the Higher Density
00:14:01 - Other State Laws That Layer Into Base Density
00:14:25 - Financial Feasibility Is Not Required
00:15:48 - Should the Jurisdiction Do the Calculation?
00:17:18 - Why You Still Need an Architect for the Base Density Study
00:17:55 - Stacking Two Density Bonuses
00:18:10 - Multifamily ADUs: The Third Density Layer
00:19:55 - How ADU Space Fits in the Actual Building Design
00:20:26 - Dramatic Results: From 5-Story Zoning to 18-Story Buildings
00:21:13 - ADUs Are Outside the Average Unit Size Constraint
00:21:54 - Navigating Jurisdictions on ADU Conversion Strategy
00:23:08 - Internal Layout Is Not Part of the Entitlement
00:24:47 - Preserving Optionality Without Committing
00:25:10 - Wrap-Up & Preview of Part 3: Alternative Density Methods
[00:01:01] Sibley Simon: Serena, what do you work on here at Workbench and on our nonprofit side, New Way Homes?[00:01:14] Serena Collins: Yeah, thanks, Sibley. Glad to be here. I have been with the organization for five years now, which time flies. Really excited about the work that we're currently doing. I help support some of our project management for our New Way Homes funded projects, along with helping raise capital so that those projects can move forward.
[00:01:36] Sibley Simon: And I should say, I know you're being humble. You really do a lot of the project management, not just support it. You really take care of a lot, but also have developed a particular expertise in one additional area. Why don't you mention that?
[00:01:49] Serena Collins: I'm also really excited and have honed in really on getting funding for brownfields. For those of you who don't know, brownfields are sites that have potential contamination due to previously being auto repair, laundromat, things like that.
[00:02:10] Sibley Simon: Car wash—we've got a car wash.
[00:02:10] Serena Collins: Yeah, car wash. And these are not super fun sites, but you want to have those contaminants removed before building housing. A lot of developers tend to steer clear just because it does take a little bit of time and a little extra capital to get those sites cleaned up. We have thousands of sites scattered throughout California that have been sitting vacant for decades. I have honed in and been very fortunate to help get us funding on both the state and federal level to clean up these sites. Right now we actually have a couple of sites that are just about to start that cleanup work, and we have funding to investigate more sites in Oakland. So we're really excited about kicking that off.
[00:02:58] Sibley Simon: So partly I wanted to ask you that question to demonstrate to everyone that while here today I'm going to be telling you and getting your reaction and questions to make sure we can explain things well—something that you may not have dived into as fully. I think it's clear from what you just said, you don't shy away from complicated subjects and complicated parts of development. So we'd love to have you back sometime to talk about just the brownfield part of things, because that's its own whole big world of regulation and process.
[00:03:30] Sibley Simon: Let's get into density on site. As I mentioned, we often call this form-based density when there's not a units-per-acre number. You've probably seen and encountered form-based density. For a long time under California density bonus law, it was unclear and different places might allow different approaches on how to apply this bonus. But that has been very much clarified in state housing law. What you really do is just like with units per acre—you look at your zoning and your general plan. What we did before was say, okay, which one allows the most units per acre? But in this case, we say which one allows the most building within which to put housing. And the controlling element of that is typically FAR—floor area ratio.
[00:04:44] Sibley Simon: This ratio—even though it's called a ratio, it's really just a number. What it's expressing is the ratio of the size of the site in square feet to the square footage of a building you can put on that site. Not the footprint, but the total square footage—if it's three stories, you have square feet on each of three floors. So you might see a floor area ratio of two. That means if you built a building that went to every lot line, you could build a two-story building and use all your FAR. Or if you built on half the lot, you'd use it all with a four-story building. It kind of determines the volume of your building—not literally volume because ceiling heights could be different, but essentially volume.
[00:06:00] Sibley Simon: Some jurisdictions add a wrinkle for mixed-use zoning—a lot of times form-based density is meant for commercial corridors where taller and denser buildings can happen. They may say you have to do first floor as commercial, and then in addition you could do residential at a floor area ratio of two. But in general, you have this floor area ratio.
[00:06:35] Sibley Simon: Still though, how do you get to a point where you can say, "Now I'm doing affordable housing, so I get this bonus density"? There is a procedure for this, and it's called a base density study. What it means is—you can understand that bonus density works in the units-per-acre case. It's like, "How much is allowed under that general plan code? That's your base density." Here we have to do a study to determine what is the base density in number of units.
[00:07:08] Sibley Simon: What you do is design a project—a building on that site, a housing development project that complies with all of the local codes. You don't use concessions and waivers. You have to follow local rules—and local rules as other state laws may amend them. So if you're close to a major transit stop, you might not need as much parking, even if the local rule says you need more. But the point is, if you're not using density bonus law, what is the building you could build and how much housing would be in that?
[00:07:58] Sibley Simon: Conceptually that makes sense, but there's a few tips and tricks. One is—how big are your units? You're trying to get to a number of residential units, which is what the law is now built to do. You get to pick what the average size of those units are. So you're going to make a building, lay it out, and say this building would be legal to build. And the average units I've drawn in it—some are smaller, some are bigger, studio, three-bedroom, whatever—but the average unit, maybe it's 750 square feet. You might draw it differently at 500 square feet. But say the average unit is 750 square feet and 37 units fit. Then you say, my base density is 37 units at an average of 750 square feet. Then you apply bonus density—your first bonus is 50%, so you add 50% to 37 and round up.
[00:09:12] Sibley Simon: But that 750 square feet still applies. You can't, when you apply bonus density, make your units bigger. You can just say, I get that many more units under bonus density, as long as the average unit is still no more than the average was before the bonus. Your bonus units can't be really big four-bedroom units.
[00:09:35] Serena Collins: So the developer, whoever's working on the project, they get to determine how big the units are. So if I say 500, because I know that I'm going to need more units to actually make this project pencil—that lives in our court.
[00:09:52] Sibley Simon: That's right. You can do a larger number of smaller units or a smaller number of larger units. That's the point of form-based density—to not say there's a maximum number of units, just a maximum size of the building. Then grossing those up by the bonuses, you still get that similar percentage of additional units to pay for the affordable units.
[00:10:20] Sibley Simon: A couple more important details. You have to follow all those regulations—setbacks, articulation, upper-story setbacks, parking. But here's a nuance: it's not unusual that there's all these restrictions in the code, and one of them is height. You may find that if you follow the setbacks, articulation, upper-story setbacks, and height limit—and build as much as possible—you don't actually get all your floor area ratio.
[00:11:06] Sibley Simon: The reason it comes up is the general plan may say floor area ratio of two, but the specific zone might say 1.5 and then have setbacks. You get to use that FAR from the general plan—let's say 2.0. But if you follow all the other rules and can't get 2.0, the Housing Accountability Act says you can build that whole FAR. Something has to give—usually that's height. So you would say, I can go taller, because that's the only way to get the FAR, which is the controlling measure of density.
[00:12:13] Sibley Simon: Some zoning codes, like Los Angeles's new code, don't have a height limit—just the FAR limit. But plenty of others do create this conflict.
[00:12:33] Serena Collins: Okay. But I'm not using a concession for that?
[00:12:36] Sibley Simon: We haven't even gotten to concessions yet. We're still doing the base density study.
[00:12:41] Serena Collins: We're just doing base density, but I'm still allowed my FAR? So if general plan is two and local code is one and a half, I'm still allowed to get to two?
[00:13:06] Sibley Simon: Because that's the version of state law that says if the density is not the same between zoning and general plan, and you're using bonus density, you get to use the more dense one. So you can run into that conflict. And for base density, you get to use the more dense of the two. That might mean you don't follow the height limit—even in your base density study.
[00:13:30] Sibley Simon: The other thing is to look out for other state laws that also might change the height or density. Major transit stop proximity is a very common one, but there are also church-owned lot provisions and others that may increase height or density. Those override local rules, so if you weren't using density bonus law, you'd still get those benefits—and you can use them in your base density study.
[00:14:25] Sibley Simon: The other important thing: all you have to do in this base density study is follow code, including building code and health and safety code. It doesn't have to be financially feasible. So something we would typically do is say, well, under local and state law we have to have this much parking—we'll put all the parking underground. Underground doesn't count toward your FAR. Of course, we wouldn't be able to afford to do that on our type of projects. But it doesn't matter—it's a density study. It says we can follow all the rules.
[00:15:20] Sibley Simon: You can do different things—don't worry about whether the underground amenity space might still count as FAR. The point is you can do some things you wouldn't do financially in order to meet the various limits that you have. You may need to follow height limits if you're still getting your whole FAR, so then you may want to put stuff underground. That's the other trick.
[00:15:48] Sibley Simon: You as a developer don't have to do the base density study. When you go to a jurisdiction and submit your pre-application or bonus density application, state law says the city or county has to do their own calculation. Their calculation is an estimate, but we get to use it as a base density. The problem is we haven't seen a jurisdiction that would really be puzzling this out to find the largest number of units that legitimately fit. But sometimes that's still useful—they're required to do it. Have them do it, because there may be rules you don't know about. There can be overlay districts with different rules. Parts of the code can be very hard to follow.
[00:16:44] Sibley Simon: It can be maddening trying to figure out and prove the negative that there's no rules I've missed. So sometimes, and we have done this, we've asked the jurisdiction—you're required to do this, can you do the calculation, give it to us. Then we can point out ways they were wrong, but at least we understand all the rules we have to follow. At the end of the day, we end up doing a base density study generally to get a base density we think is correct and apply for a project using that.
[00:17:18] Sibley Simon: All this to say—from an efficiency standpoint, we literally will have somebody on the architecture team laying out a building that we're never going to build, have no intention to build. But it is very important, because if I just chicken-scratch it, it's not going to be legally defensible or come out with the most units. You have to have somebody on a design team really lay out a building to get a base density.
[00:17:55] Sibley Simon: Okay, so we've got a base density. We can apply the 50% bonus, and if you had an odd number of units you round up. Then another 50% bonus if you use the second density bonus.
[00:18:10] Sibley Simon: As we ended on last time: in addition to those density bonuses, there are the multifamily ADUs. You can make room in a building—even a new building—to create space that's undesignated: amenity space or storage space. Eventually we'll do a full ADU episode. The point here is you can have space in the building and then later, when you're going for your building permit or even after construction, you can get permits to convert that space into additional units—up to 25% of the total units. If density bonus got you to 100 units total, you could do another 25 units within the building.
[00:19:07] Sibley Simon: In this form-based density, how does that work? The whole reason to do this study to get a number of units is that you just use that number with your multiplier for density bonus and don't worry about the rest of the building. Your building with the density bonus units might be more than twice the size of your base density study, because you didn't have to have a lot of amenity space—just what's legally required. Then you naturally want actual amenities, so you add those in your larger building, and you could add space that you might convert to multifamily ADUs.
[00:20:10] Sibley Simon: So your actual design building is often significantly more than twice the size of your base density study building.
[00:20:26] Sibley Simon: That convoluted process can be quite dramatic. We haven't built high-rises ourselves—that's a more expensive building type—but we have seen properties where the form-based zoning was five stories and you could end up with an 18-story building. In theory, you could do mass timber or steel and concrete construction, still having your average unit size not more than it was in the base density study, and you might add commercial space back in.
[00:21:13] Sibley Simon: Last thing I want to say on the ADUs: they're a ministerial separate thing, they're not part of the entitlements, so the average unit size doesn't apply to them. If your average unit size in your building was 500 square feet, you could build in enough amenity space to have a few three-bedroom ADU units if you wanted that in your unit mix.
[00:21:54] Serena Collins: Going back to the ADUs—looking at base density, we've already figured out what our base density is, but we've set aside some amenity space that we know will be converted to ADUs. How do you typically deal with jurisdictions when you're coming from a standpoint of doing form-based density? What's the typical approach?
[00:22:29] Sibley Simon: There are some judgment calls. We don't hide it, but we also are not guaranteeing it. What we're doing is preserving the option to do it. And the option to do it is in state law. It's just not relevant to the process of getting the project approved.
[00:22:57] Sibley Simon: Here's another useful point: when you're getting entitlement for an apartment building in California, the internal layout is not actually relevant. What you're getting the right to build is a building of that size—with that look on the outside, shape, location on the property, the site plan, entrance and egress, fire truck turnaround. That's what you're getting an entitlement to build.
[00:23:29] Sibley Simon: Internal walls can totally change. You're getting the right to build a certain number of units within that building, perhaps a certain maximum average square footage in the case of form-based density. But you could have a whole floor of amenity space in your project application, and when you're going for your building permit, you can mix that all around.
[00:24:00] Sibley Simon: We remind folks in the entitlement processes: internal dividing walls, how the units are laid out, are the bathrooms big enough—it's just not relevant. And if we're straight up asked, "Are you going to put multifamily ADUs in this?" we'll say, we have the option to do that under state law. We have not made a decision or committed one way or the other. And that's just not relevant to the entitlement decision that's here today, because it isn't.
[00:24:47] Sibley Simon
Better to stick with that. And it's true—until you've submitted an application, you haven't done anything and you don't have to do it. You might get partway through and say, I want that space to be something else, or I might do fewer ADUs or more, within the limit.
[00:25:10] Sibley Simon
Cool. I think we'll wrap up there. Next episode, we're going to come back—now we've done units per acre from your general plan and zoning, and form-based density. What we're going to come back to next time is the third way: sometimes there may be a whole other way to calculate density that might be preferable, that gets you more units but comes with other strings attached. There's a bunch of different ways under state law that apply in some places and at some times. We're going to cover all those in the next episode. Then you'll have the whole picture—as of here in 2026—of how you calculate density that you know you have a right to do, that you can get approved on a project on a site in California.
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Who Are The Infill Insiders?
The Infill Insiders break down the highly complex process of infill housing development in California. Host and principal developer, Sibley Simon, shares Workbench's experience to teach developers and land owners how to use the many state housing laws to successfully develop infill housing, while showing jurisdictions what makes the process more efficient, and encouraging elected officials and anyone interested to face the big challenges that still remain in housing creation. Join us and become more effective at creating infill housing.Hosted by
Sibley Simon
Principal & Impact Development Executive, WorkbenchSibley leads the Workbench development team's impact focused projects geared towards creating more affordable housing without public subsidy. With years of experience driving legislative progress, he’s forged strong alliances with leaders dedicated to tackling California’s housing equity challenges. Before joining Workbench, Sibley founded numerous companies and created an impact investment fund to spur new workforce and affordable housing development.
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