Detached ADUs in East Palo Alto

Detached ADUs in East Palo Alto Stanford Sustainable Urban Systems Initiative, Summer 2017 Derek Ouyang, Lecturer, Sustainable Urban Systems Nikhil Chaudhuri Jacob Waggoner

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Executive Summary In an effort to help guide policymakers and community members around incorporating detached accessory dwelling units into East Palo Alto’s affordable housing strategy, we have prepared this draft report containing both a city-wide ADU suitability analysis and a city-specific ADU design proposal.

The first section, our analytical work, details the suitability of parcels and neighborhoods in the city for ADU development, considering by turns: the physical suitability of parcels (lot capacity, necessity of parking, etc.), the accessibility of basic services by block, and the historical friendliness of blocks to development. Our preliminary findings indicate that central EPA is particularly well positioned for ADU development. The remaining parts of the city, northern and western most notably, also have non-trivial capacity for development, but perform somewhat more poorly in some of our analyses and so merit further examination by policymakers and community members. In consultation with city officials, our we hope to provide this additional scrutiny in a revised edition of this report, incorporating additional analyses as noted in the pages that follow.

In the second section of this draft report, we showcase an ADU design that we’ve created to serve East Palo Alto’s specific development needs for affordability and adaptability.

Our design builds from these needs by focusing on modularity and ease of maneuverability, featuring prefabricated wall, roof, and floor panels manufactured by Lada Cube that can be delivered by truck that can readily be assembled in residential yards with a small team of workers. This panelized design approach, when produced at economies of scale, is more cost effective and less complex to assemble than stick-built construction and crane-delivered shipping container housing modules - the two current approaches to ADU design and construction. Each panelized ADU design consists of three modules - a core (bathroom, kitchen, and mech.), living module, and bed module. The variety of options for each of the three components allow for many different ADU designs, fitting numerous site conditions and allowing for future adaptation in response to code changes. Designed to minimize manufacturing, construction cost, and complexity while maximizing the wide-ranging utility of each design component, the panelized ADU modules (the core in particular) can also be applied to two other affordable housing approaches in EPA (and perhaps all of San Mateo County) - attached ADU garage conversions and R-1 multifamily apartment structures.

Introduction One of the most economically productive and prosperous regions on the globe, it is of no surprise that there is tremendous pressure on its housing market. Scholars have identified a number of factors driving the market, from land scarcity and stunted tax revenues, to high demand and relatively burdensome regulation (Saiz 2010, LAO 2015). The City of East Palo Alto (EPA) has historically resisted these pressures, but it is not immune. Unable to acquire enough water to support new development, the city has approved only a handful of new development permits over the last several years. And what affordable homes or units do exist face mounting pressure from the demand induced by large new employers.

Rents and mortgages rise and the ability of community members to stay in their homes falls. The result? More than ever, tenants, homeowners, and city officials are turning to innovative ways to meet the needs of EPA’s new and longtime residents.

environment in EPA, focusing on what could be done to legalize existing ADUs. And most recently, in the summer of 2017, a local nonprofit called Soup partnered with Abode and members of the East Palo Alto Second Unit Task Force to begin landing prefabricated ADUs in EPA and providing the tenant management services needed to make these units a success.

Drawing from these past efforts, and in consultation with Soup, Abode, and the City of East Palo Alto, Stanford’s Sustainable Urban Systems Initiative has prepared these materials to help decision-makers integrate detached ADUs into an affordable housing strategy for East Palo Alto. The first section briefly details the scope of our work and provides a legal background on ADUs in EPA. The second section is an analytical report documenting the suitability of parcels and neighborhoods in EPA for ADU development. And the third and final section presents and recommends an ADU design template optimized for widespread deployment EPA’s suburban context. Taken together, these three components hope to highlight and maximize the benefits of ADU development in East Palo Alto.

One such innovation, variously called an accessory dwelling unit (ADU), granny flat, or secondary unit, offers a number of unique benefits when deployed as part of a holistic affordable housing strategy; among others, they are typically permitted by right, are amenable to the suburban context, bring greater economic diversity to suburban neighborhoods, and stabilize homeowners on the brink of displacement. Though still relatively new to the housing market, at least as part of an intentional housing strategy, government agencies, community organizations, private enterprises, and academic institutions have begun to take note of these benefits. In 2013, students at Stanford competed in the U.S. Department of Energy’s Solar Decathlon competition and gained experience in prefabrication and panelization techniques in residential architecture. Two years later, students in Stanford’s Energy Transformation Collaborative surveyed the built

Legal Background and Scope In California, ADU development is governed

by Government Code 65852.2, which allows local governments to adopt their own ordinance governing ADU development provided that ordinance complies with 65852.2. At this invitation, EPA adopted Chapter 22.5 of its Municipal Code, Second Dwelling Units, which was most recently amended on January 17th, 2017. Table 1 below outlines some of the main provisions of these legal authorities, distinguishing those for which the state code is the primary authority, and those for which the municipal code is the primary authority.

Table 1 Detached ADU Development Requirements Relevant Municipal Code

Provision

Principal Authority

Definition of ADU

“a separate dwelling unit providing complete independent living facilities for one or more persons containing living, sleeping, kitchen and sanitation facilities” (see 65852.2(a)(8)(f)(2)(B)(i)(4) for a somewhat more thorough definition)

Section 6426

Municipal code, as in state code

Permit Timeline and Discretion

ADU permit applications are to be reviewed within 120 days. They are ‘ministerial’ permits and are therefore to be granted so long as the proposed ADU meets the requirements set forth in Municipal Code Ch. 22.

Section 6431

Municipal code, as in state code

Zoning Requirement

ADUs are only allowed on lots zoned for single-family or multiple-family residential use, where there is already one (and only one) other building - a single family dwelling (the ‘primary’ or ‘main’ dwelling)

Section 6425(a)

Municipal code, as in state code

Number per Lot

Only one ADU may be constructed per lot

Section 6426

Municipal code, (likely) in compliance with state code

Minimum Lot Size

7,500 square feet

Section 6429(c)

Municipal code, in compliance with state code

Maximum ADU Size

The smaller of: 50% of the living area of existing single family dwelling or 1,000 square feet. (Garages not included in living area)

Section 6429(d)

Municipal code, in compliance with state code

Minimum Open Space on Lot

750 square feet

Section 6429(f)

Municipal code, (likely) in compliance with state code

Minimum Parking Requirements

(for detached units) 1 uncovered off-street parking space unless the unit is located within a half mile of public transit. (Note that a tandem space qualifies as a parking space, and that other exceptions may apply)

Section 6429(g)

State code (municipal code likely out of compliance)

Minimum Setbacks

(for detached) 6ft from rear property line and house, 3ft from side property lines, 12ft from street side property line if a corner lot

Section 6429(m)

Municipal code, in compliance with state code

Utility Connections

(for detached units) new or separate direct utility connection required.

Section 6429(h)(2)

Municipal code, as in state code

In forming our analytical methodology and generating our ADU designs, we placed a number of constraints on ourselves. First, we took the above policies as given, granting particular deference to the zoning, unit size, and minimum setback requirements. Because we felt that we had more value to add to a study of detached units, our analysis is restricted to that subset in this report, though future reports will consider expanding to attached ADUs. We considered only rectangular units as

potential ADU footprints, both for computational tractability and design efficiency, and though not by necessity, we found it useful to think of the possible dimensions of these footprints in terms of two on-the-market options we reviewed and know to be available, along with our own proposed designs. These considered dimensions are indexed in Table 3. Further assumptions and restrictions can be found in the specific report to which they belong.

Analytical Report Cities and the parcels of which they are comprised, though certainly able to accommodate ADUs, were generally not designed with them in mind. It is therefore especially important to understand how well a city can accommodate ADU development - the number, composition, and concentration of units, the proximity of important services, etc - before community organizations and government officials put their resources behind ADUs as an affordable housing strategy. This report aims to fill that need, while also preparing a platform to inform homeowners of the potential of their property - what sizes and shapes are available to them, shortcomings to be shored up, and expected returns.

For each factor, we then designed an independent score that can be used to compare parcels and, in combination, determine parcel viability. As an important note, we’ve taken great care to limit our judgment as regards any form of overall scoring. While we encourage decisionmakers and community members to evaluate the importance of certain factors over others, we’ve avoided any attempt to do so, the one exception being those cases in which parcels come up against cityimposed constraints that disqualify them.

The remainder of this analysis is organized by our three chosen suitability categories.

The factors corresponding to each category can be found in a table at the top of the category’s section, which provides a description of the factor and our scoring.

Toward these ends, we examined three categories of factors, both at the parcel and neighborhood level, that we believe contribute to a given parcel’s suitability for hosting an ADU: physical suitability, accessibility of services, and neighborhood features. Some of the factors in these categories (e.g. land availability) represent a harder constraint that a parcel must generally satisfy for an ADU to be viable, while others (e.g. neighborhood history of noise citations) represent a softer factor that may preference one parcel over another.

Physical Suitability In assessing the physical suitability of a parcel for a detached ADU, our analysis focused on the five factors shown in Table 2. We group these factors into four thematic categories - capacity, site location, accessibility, and parking – for organizational purposes.

Table 2 Physical Suitability Factors Description

Capacity Site Location Loading Accessibility Walking Accessibility

Parking

Range of Scores

Summary of Conclusions

The largest ADU that can fit on a property, approximated by a rectangle

-1 if no viable ADU, increasing capacity from 0 to 1

The location (front, side, or backyard) of the largest rectangle that can fit on a property Whether or not the largest rectangle that can fit on a property is accessible via a 15’+ wide path from the street Whether or not the largest rectangle that can fit on a property is accessible via a 3’+ wide path from the street Whether or not the parcel is within a half mile of a transit stop

1 for backyard, 0 for front or sides 1 for accessible, 0 for inaccessible

77% of single family parcels can accommodate an ADU, 62% one of our nine largest models In 53% of parcels, the largest rectangle is in the backyard 47.55% of (all) parcels are accessible by loading truck

1 for accessible, 0 for inaccessible

96.01% of (all) parcels are accessible by foot

1 for exception to requirement, 0 for required parking

100% of single-family residential parcels are exempt from parking requirements

To lay the groundwork for estimating each factor of interest, we began with parcel shapefiles from San Mateo County. Using the assessor parcel number provided with this data, we matched the parcels to assessor data from the private data intermediary Retsly to determine which parcels were zoned single-family residential.

In total, SMC lists 5,078 active parcels in its database for EPA. Retsly separately provides data for 5,039 parcels. We took SMC’s listing to be authoritative, and proceeded to match Retsly’s to SMC’s. Of the 5,078 SMC parcels, we were able to match 4,571 of them, 3,936 of which were zoned “Single Family Residential.” For the 507 that were not matched, we verified by inspection that no more (and possibly fewer) than 36 were zoned as single-family residential. In other words, our matched data is missing assessor data for no more than 36 single family parcels (0.9%).

parcel from Google Maps using its Static Maps API (Map Data, 2017). Specifically, we determined a parcel’s adjacent streets, primary dwelling footprint, and land uncovered by the primary dwelling. This extraction process in depicted in the figures below.

Figures 1 - 5 Parcel Feature Extraction Figure 1 Marked Parcel Vertices

Subsequently, for each of these 3,936 matched parcels, we used an automated process to extract various properties of the

Figure 2

Figure 5

Home Extract

Largest ADU

i. Capacity Our capacity analysis is based primarily on the properties of the largest rectangle that can be fit into a parcel’s boundaries, accounting for the location of the primary dwelling. Importantly, we did not consider certain features of the property that do not appear in Google’s street map imagery, such as plant material, decks, pools, driveways, and existing accessory structures (ADUs, sheds, etc.). We have additionally chosen not to incorporate the open space requirement, which we plan to revisit in future work.

Figure 3 Land Extract

After calculating this largest rectangle for a parcel (see Figure 5 for an example), we shrunk the rectangle to comply with East Palo Alto’s minimum setback requirements (excepting the corner lot requirement) - 3ft setbacks from from the non-rear, non-street property boundaries, 6ft setbacks from the primary building and rear property line.

Because we obseved some inaccuracies in the Google Maps imagery (e.g., with buildings sometimes overlapping property lines) we used a conservative heuristic, subtracting 6ft from the longer side of the rectangle and 12 ft from the shorter side.

This method, though introducing some inaccuracy into the computation, produces a more robust, and relatively conservative, measure. Using these reduced dimensions, we scored the rectangle by the area of the largest of our ADU models that it was able

Figure 4 Streets Extract

to accommodate. We then normalized that score using the square footage of the largest (by area) ADU among our models.

The scoring matrix is shown in Table 3 - the closer the score to 1, the larger the ADU model that the computed rectangle could accommodate. Scores of -1 represent a parcel unable to accommodate even an 8ft by 20ft detached ADU.

As can be seen in Table 4 (which maps to the scores in Table 3) and Figure 6, we estimate a surprising 77.87% (3,065) of the 3,936 single-family residential parcels have the land area to host an ADU footprint, and that nearly 62.06% can accommodate one of our 9 largest models (all at least 9ft by 44ft). We refer to the latter set of 3,065 lots and computed rectangles as ‘viable’ lots.

Table 3 Area-Normalized Capacity Score Long Dimension

Short Dimension

<20ft

20ft

24ft

28ft

32ft

36

40

44

48

52

<8ft

-1

-1

-1

-1

-1

-1

-1

-1

-1

-1

8ft

-1

0.192

0.192

0.192

0.192

0.192

0.192

0.192

0.192

0.192

9ft

-1

0.192

0.192

0.192

0.192

0.389

0.389

0.389

0.389

0.385

12ft

-1

0.288

0.346

0.404

0.462

0.519

0.577

0.635

0.692

0.750

16ft

-1

0.385

0.462

0.538

0.615

0.692

0.769

0.846

0.923

1.000

Table 4 Percentage of Residential Parcels by Score Long Dimension <20ft

20ft

24ft

28ft

32ft

36

40

44

<8ft

0.05

0.08

0.03

0.78

0.19

2.37

1.21

1.56

8ft

0

0

0

0.00

0.00

0.38

0.30

0.51

0

9ft

0.03

0.22

0.00

0.11

0

0

0.67

2.80

0.97

12ft Short Dimension 16ft

0

0

0

0.27

0

0

0

0

0.27

0.54

0.81

1.43

* 0.00 refers to percentages < 0.01

1.75 8.08

6.25 19.39

48

52

0.40 10.13

1.56 6.65

1.27 3.02 4.17 20.15

Figure 6 ADU Capacity Scores for each Parcel

automate, so we approximated this locational factor by checking our image for any obstructions (namely, a building) every 3ft along the line between the center of the rectangle from i. and the nearest point to it on a road. Using this method, we estimate that 52.29% of all 3,936 of our computed rectangles, and 47.1% of all 3,065 viable computed rectangles were behind the primary dwelling.

ii. Site Location Because we presume a municipal preference for backyard ADUs, and because homeowners themselves might prefer to locate their ADU in the backyard of their property (or at least not the front yard), we included a check for whether or not the largest rectangle found in i. was in the backyard. This is a challenging process to

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Figures 7 - 8 Distribution of Site Location Figure 7: All Single-Family Parcels

Figure 8: Viable Single Family Parcels

Backyard 52%

Backyard

48%

47%

Front or Side Yard

These numbers are larger than we anticipated, and we suspect homeowners will be hesitant to locate an ADU in their front yard, so further work will focus on a more detailed analysis of both 1: properties of the front yard (e.g., location of the driveway), and 2) the largest fitting rectangle in the back or side yards.

Front or Side Yard

To determine whether or not either requirement, accessibility by foot or by loading truck, presents a barrier for ADU development in EPA, we determined the accessibility of the site found in part i from the nearest streetside.

Assuming our method was effective, we should find that nearly all rectangles identified in part i are accessible from the streetside via a 3ft wide path, as the single family dwelling was the primary obstacle we considered and EPA requires a 6ft setback around homes. Indeed, our analysis shows that 96.01% of the 3,065 viable rectangles found in part i can be accessed by a 3ft wide path. We attribute the remainder to parcels like the one marked in Figure 9 below, where the streetside is not visibly accessible from the parcel.

iii. Lot Accessibility Scores As we detail in the Design Brief at the end of this report, there are a number of ways to develop an ADU: through onsite construction (stick-built), acquiring a fully prefabricated ADU (prefabricated), or fitting together prefabricated panels (panelized).

Each comes with its advantages and disadvantages, the most relevant of which, for the purpose of this analysis, is the ease and cost-effectiveness with which the ADU can be delivered to the site. Stick-built and panelized models only require a path to the site wide enough for a person to walk. Fully prefabricated models, by contrast, must be delivered via loading truck, or if the site is not accessible by loading truck, then (expensively) by crane.

53%

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iv. Parking Requirements

Figure 9 Inaccessible Street

As presently written, section 6429(g) of EPA’s ADU ordinance requires that “[a] minimum of one uncovered off-street parking space shall be provided for the accessory unit in addition to the off-street parking spaces required for the main dwelling” unless (among other exceptional circumstances) “[t]he accessory dwelling unit is located within one-quarter mile of a public transit corridor as defined in Health and Safety Code Section 50093.5.”

Interestingly, EPA’s code appears to be out of compliance with the state statute governing ADU development, which states that “[n]otwithstanding any other law, a local agency, whether or not it has adopted an ordinance governing accessory dwelling units in accordance with subdivision (a) [the primary subdivision governing ADU development], shall not impose parking standards for an accessory dwelling unit in any of the following instances… [t]he accessory dwelling unit is located within one-half mile of public transit.” Public transit, for the purpose of this statute, is described by the CA Department of Housing and Community Development as including bus and train stops (CA HCD, 2016).

For accessibility by loading truck, which we defined as the existence of a continuous, 15ft wide path from the streetside to the center of the ADU site, we found that 47.55% of the parcels accommodated such a path. Importantly, for the remaining 52.45% of parcels, a prefabricated ADU would need to be craned onto the site, thereby incurring an additional $1,500$3,000 in costs on top of the neighborhood disturbance and time costs required by a crane. Assuming that most ADU sites determined by the analysis in part ii to be located in a front or side yard are accessible by loading truck, one implication of this result is that very few backyard sites must be accessible via loading truck. Indeed, we find that only 15.86% (247) of the 1,557 ADUs located in backyards were accessible via loading truck. For the remaining 1,310, we conclude that a prefabricated ADU would have to be craned in.

To examine the need for parking on parcels with the capacity to develop an ADU, we used a 2014 dataset of transit stops from the Metropolitan Transportation Commission (MTC, 2014). Buffering onehalf mile around each stop it provides data for yields the map in Figure 10 below. As can be seen in the figure, every parcel (excepting several non-residential parcels to the East) is within one-half mile of a transit stop. Though dated, the totality of coverage in 2014 suggests much would have to have changed for this to no longer be true.

In summary then, nearly all parcels with viable ADU sites should be able to accommodate panelized ADUs. Most prefabricated ADUs sited in a backyard will need to be placed by crane, but a small few can be placed with a loading truck.

Despite the universal proximity of parcels in EPA to transit, some homeowners may wish to provide parking to those occupying their ADUs. Future work will estimate the availability of parking on a parcel, using a combination of the analyses in parts i and iii.

Figure 10 Parcels Within a Half Mile of Transit

Table 6 Service Accessibility Factors Description Walk Accessibility (5, 10, and 20 minutes) Bike Accessibility (5, 10, and 20 minutes) Driving Accessibility (5, 10, and 20 minutes) Transit Accessibility (5, 10, and 20 minutes)

The percentage of basic services that can be reached within a 5, 10, and 20 minute walk from each block center The percentage of basic services that can be reached within a 5, 10, and 20 minute bike ride from each block center The percentage of basic services that can be reached within a 5, 10, and 20 minute drive from each block center The percentage of basic services that can be reached within 5, 10, and 20 minutes by transit from each block center

Range of Scores

Summary of Conclusions

0% to 100% (or 0 to 1)

5 minute: severe deficit in eastern EPA, moderate deficit in northern and western 10 minute: mild deficit in southwestern EPA 20 minute: no significant deficits

0% to 100% (or 0 to 1)

5 minute: moderate deficit in western, northern, and southeastern regions 10 minute: no significant deficits 20 minute: no significant deficits

0% to 100% (or 0 to 1)

5 minute: scant deficits in western, northern, and southern regions 10 minute: no significant deficits 20 minute: no significant deficits

0% to 100% (or 0 to 1)

5 minute: significant and pervasive deficits 10 minute: severe deficits in eastern region, mild to moderate deficits in all but city center 20 minute: mild deficits in northern and eastern regions

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Access to Services

After computing these travel times, we binned them by whether they were between 0-5 minutes, 5-10, 10-20, or >20, then computed the percentage of these services accessible by each mode of travel within those binned times.

About more than simply providing a roof, affordable housing is a part of the social fabric of a community. For affordable housing to be effective in that capacity, more than the physical structure should be taken into account. Of critical importance is the array of services available to people living in affordable housing - medical services, transit, convenience stores, parks, etc.

Figures 11-18 show several of our results mapped onto EPA, where maps corresponding to a 5+ minute bike ride or drive, and 10+ minute walk are omitted for exhibiting relatively little variation. Taking the below maps together then, three regions emerge: the central-south region, western

To estimate the accessibility of these services, we used the Google Directions and Google Places APIs to compute travel times to various basic services by foot, bike, car, and public transit (Map Data 2017).

Specifically, we considered the 20 services in Table 7 below to meaningfully speak to a parcel’s ability to support residents’ needs, and for each 2010 U.S. Census block in the city, computed the distance from the block’s center to the nearest of each service type.

Choosing to use block centers rather than parcels, while obscuring some variation at the parcel level, was a necessary heuristic for reducing the computational expense of the analysis and one we thought justified; a back-of-the-envelope calculation suggests that no single family residential parcel is more than one-seventh of a mile from its nearest block center (~2.7 minutes of walking at an average human pace 3.1mph).

region, and northern-eastern region. For all modes of transit, the central region performs relatively well, which is encouraging given the concentration of parcels with strong viability scores in that part of the city. The western region, another region with strong physical viability scores, performs somewhat less well, particularly for manual transportation (walking and biking), while the northern and eastern parts of the city perform relatively poorly. The underperformance of the latter is concerning given the number of parcels with strong physical viability scores in the centraleastern part of EPA, but the northern and south-eastern parts of the city present fewer opportunities for site development so are of perhaps secondary concern. We recommend, on the basis of this analysis, that a parcel-level transit accessibility study be performed on the eastern, particularly central-eastern, region of the city in 5 minute increments from 0 to 30 minutes.

Table 7 Compilation of Basic Services Bus Station

Subway Station

Train Station

Convenience Store

Hair Care

Fire Station

Bike Store

Transit Station

Bar

Atm

Gym

Pharmacy

Park

Doctor

Dentist

University

Cafe

Hospital

Bank

Restaurant

Figures 11 - 18 Percentage of Basic Services Available

Figure 11: Within 10 Walking Minutes

Figure 12: Within 20 Walking Minutes

Figure 13: Within 5 Biking Minutes

Figure 14: Within 10 Biking Minutes

Figure 15: Within 5 Driving Minutes

Figure 16: Within 10 Driving Minutes

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Figure 17: Within 10 Transit Minutes

Figure 18: Within 20 Transit Minutes

Table 8 Neighborhood Friendliness Factors

(per block) # of All Permits Issued (1, 3, 7 years)

(per block) # of Building Permits Issued (1, 3, 7 years)

(per block) # of All Violations Issued (1, 3, 7 years)

(per block) # of Building Violations Issued (1, 3, 7 years)

(per block) # of Parking Violations Issued (1, 3, 7 years) (per block) # of Noise Violations Issued (1, 3, 7 years)

Description # issued over a 1, 3, and 7 year horizon, normalized by the number of parcels in the block

Score Range +/- 0.5 for each std. dev. above or below city average

See above

See above

See above

See above

See above

See above

See above

See above

See above

See above

Summary of Conclusions 1 year: Low variation 3 year: Low variation 7 year: High variation Some blocks with sustained frequent development or high permit compliance rates 1 year: Conc’n in pockets 3 year: Conc’n in pockets 7 year: Conc’n in pockets Some blocks with sustained frequent development or high permit compliance rates 1 year: Conc’n in W. EPA 3 year: Conc’n in W. EPA 7 year: No significant conc’n Alarming rates of violations – avg of one per parcel on some blocks over the 3 year horizon 1 year: Conc’n in W. EPA 3 year: Conc’n in W, N, Central EPA 7 year: Conc’n in W, N, Central EPA Visually, some correlation with issuance of all violations Too infrequently issued to draw meaningful conclusions Too infrequently issued to draw meaningful conclusions

Neighborhood Friendliness

given the overlap in ‘hot’ parcels between the seven-year and three-year maps, one plausible explanation is that projects requiring permitting have generally slowed, excepting in the few neighborhoods that exhibit relatively reliable development.

Though building permits make up only a fraction of the total permits meted out by the city, the stability of their issuance period-toperiod seems to support this explanation.

Regardless, the stability of the latter is interesting in its own right, suggesting that some neighborhoods are consistently either building significantly more than average or complying with permitting requirements at significantly higher rates.

ADUs are often lauded as an affordable housing strategy for their ability to sidestep NIMBY-inspired intervention; they are generally less obtrusive than multifamily developments and are typically permitted by-right, rather than through a process requiring the discretion of city officials.

Despite these advantages, ADUs are not fully insulated from the neighborhoods in which they are built. ADU development may affect the neighborhood’s property values, traffic patterns, and the need for police and fire services, among other neighborhood qualities.

As an exploratory neighborhood-level analysis, we considered two other such qualities: the number of city permits and number of code violations handed out in a given 2010 US Census block (our approximation of a neighborhood) between July 2017 and July 2016, July 2017 and July 2014, and July 2017 and January 2010.

Within these two categories, permits and violations, we additionally considered several subcategories: building permits, building violations, and noise violations as respective proxies for homeowners’ interest in permitted development and a neighborhood’s record of substandard construction or prohibitive noise. All of our data came from a city records request, and was parsed using an automated pdf reader.

We likewise illustrate the results of our code violation analysis in the figures below. Again the geographical variation is insightful among all violations issued, showing some amount of concentration in the western region of the city. More concerning are the numerous blocks that have received, on average, nearly one violation per parcel in the last three years. The building-specific violations do not add significantly to this analysis, except to say that they make up a large share of all violations issued by the city (34.7% for the 1 year history, 28.4% and 14.9% for the 3 and 7 year histories), so the correlation between the pairs of images is not surprising. Parking and noise violations, by contrast, make up relatively small shares of all issued violations (roughly 1% and 2% respectively). These rates are low enough as to render their geographic distribution and magnitude relatively inconsequential, though taken together with the building and total violation maps, perhaps elevate the western region of the city to a level of concern worthy of further analysis.

The results of our permit analysis are shown in the table of figures below. Taken together, it appears that permits have been distributed fairly evenly on a per (single family) parcel basis for at least the past three years. The seven-year map, by contrast, shows significant variation. It is hard to explain this change over time, but

Figures 19 - 24 All Permits

Building Permits

Figure 19: 7 Year History

Figure 20: 7 Year History

Figure 21: 3 Year History

Figure 22: 3 Year History

Figure 23: 1 Year History

Figure 24: 1 Year History

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Figures 25 - 30 All Violations

Building Violations

Figure 25: 7 Year History

Figure 26: 7 Year History

Figure 27: 3 Year History

Figure 28: 3 Year History

Figure 29: 1 Year History

Figure 30: 1 Year History

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Figures 31 - 36 Parking Violations

Noise Violations

Figure 31: 7 Year History

Figure 32: 7 Year History

Figure 33: 3 Year History

Figure 34: 3 Year History

Figure 35: 1 Year History

Figure 36: 1 Year History

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Panelized ADU Brief There are currently two polarized approaches to constructing ADUs. The first, on-site stick-built construction, is relatively inefficient, has higher on-site construction costs, longer timelines, and greater human error. The second, crane delivery of completely prefabricated housing modules, is very costly and demands technical experties, especially in EPA’s tight residential neighborhoods. We have developed a new design-build approach falling conceptually in between the two existing extremes: a partially prefabricated approach using panelized wall, floor, and roof segments.

two gypsum board boundaries with insulation in between. These panels are structurally similar to shear walls, and so only require additional support for long spans. Though several SIP manufacturers exist, we’ve been in conversation with one based in Colorado whose SIP panels have the added advantage of built-in cam locks.

These allow the panels to be swiftly connected on-site with a small team of workers and simple tools. Finally, because they are much smaller than a fully prefabricated ADU, these panels can be easily manouevred through EPA’s narrow side yards.

There are many benefits to this panelized approach – benefits both inherent in the properties of the panels, and also benefits realized through the holistic design of the ADU that these panels allow. The prefabricated panels are known as SIPs (structurally insulated panels) and consist of

In creating a template of panelized ADU designs, we considered the best spatial strategies for maximizing both resident living and the unique utility and potential of cam locking panels. Our designs are thus based on the principles outlined in Table 9. below.

Table 9 Design Principle Minimize the Number of Panel Types Minimize the Total Number of Panels Condense Mechanical Systems Maximize Modularity of Rooms and Layouts

Maximize the Number of 4ft Wide Panels Maxmize Re-use and Hybridity of Design Elements

Explanation of Principle Fewer panel types correlates to fewer assembly processes, and hence cheaper and swifter panel manufacturing Fewer total panels means fewer joints to assemble on-site, and hence faster construction time Restricting plumbing, HVAC, etc. to one wall or floor panel per ADU reduces the number of panels that have to be retrofitted with ducts and outlets, significantly reducing manufacturing and construction time and complexity There are a variety of site conditions in EPA, and many (sometimes changing) zoning codes governing development. Modularity allows one design template to meet many different site parameters, from yard width and allowable area to maximum occupancy and setback requirements.

Lada Cube’s default panel width is 4’. Using 4’ wide panels allows us to utilize full-sized panels off the assembly line without an additional cut, avoiding both added cost and material waste.

Designing elements that can be used with many different site constraints and housing types speeds development and is an efficient use of resources and production systems

Considering the above principles, we developed our ADU designs around three module types, described in Table 10 and shown in Figures 37 and 38 below. We provide the full set of combinations between modules in Table 11.

Table 11 Module Combinations Core Modules Width (ft)

Figure 37 Example Module Combination

Length (ft)

Area (sf)

Core - Standard 12

12

12

144

Core - Standard 16

16

8

128

Core - Deluxe 16

16

12

192

Living Modules Width (ft)

Length (ft)

Area (sf)

Size 1

12/16

8

96/128

Size 2

12/16

12

144/192

Size 3

12/16

16

192/256

Bed Modules Width (ft)

Length (ft)

Area (sf)

Single + Double

12/16

20

240/320

3 Singles

12/16

24

288/384

Double

12/16

12

144/192

2 Singles

12/16

16/12

192

Single

12/16

8

96/128

Studio - Double

12/16

8

96/128

Studio - Single

12/16

4

48/64

Figure 38 Example Module Combination

This final kit of parts used to construct the modules in Table 11 consists of 12 wall panel types, 3 door panel types, 1 window panel type, 8 floor panel types, and 8 roof panel types, all shown in Figure 39. Of these 30 or so different panel types, 4â&#x20AC;&#x2122; wide panels are the most common.

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Figure 39 Complete Kit of Parts

around 16â&#x20AC;&#x2122;, the same width as most of the CORE module options used in the ADU designs. The CORE could thus be readily delivered by truck and slid into garage door openings with minimal trimming around the edges.

Figure 40 Example Detached ADU

Additional Uses Although detached ADUs have been the primary focus of the viability analysis and the design process, the panelized ADU modules were also designed with other housing applications in mind. Through spatial iterations and dimensional tweaking, we also developed the living mods, bed mods, and particularly the core mods as feasible design components for attached ADU garage conversions.

Figure 41 Example Attached ADU

As parking needs decrease and housing demands increase, many residents of EPA will have the opportunity to convert their garages into accessory dwelling units to increase housing density and benefit from additional revenue. Because retrofitting these garage units with bathroom and kitchen facilities is one of the most intensive aspects of the conversion process, we have adapted the CORE module and Lada Cube panels as, respectively, a garage attachment that can be prefabricated off-site and divider walls for delineating different living spaces in the garage. Conveniently, the standard garage door width in EPA is

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Further Work Figure 42 Example Multifamily Structure Build from ADUs

Several components of our analysis and design process are ongoing and are scheduled for future release as a revision of this report. Specifically, we’d like to build out our suitability study, add an ‘outcome’ and ‘policy’ study, and broaden the use cases of our ADU designs.

In our suitability study, we plan to incorporate three new components to the physical suitability analysis: EPA’s open space constraint, its corner and rear setback requirements, and parcel parking capacity. We would also like to add a ‘motivational’ analysis to the suitability study, which would measure demographic factors (average age and assessed property value) that might lead to higher uptake of ADUs in a given neighborhood.

An outcome study would extrapolate from a random sample of parcels with an existing ADU to estimate the number of ADUs that might actually be produced citywide under several different buildout scenarios. Using this estimate, we could estimate expected increases in assessed value and city revenues. We can also use a national survey of households to estimate energy usage of homes in EPA, and so could consider the feasibility of a city program subsidizing ADUs in exchange for retrofitting the primary dwelling and ADU to be more energy efficient.

Our policy study, meanwhile, will look at how changing the requirements in Table 1 would impact the results of our suitability and outcome studies. It also considers the ADU ordinances of several other jurisdictions to consider policy levers not currently present in EPA’s code. Using these new results and case studies, we would be able to recommend, on the basis of our generated evidence, updates to EPA’s existing code.

Finally, we will consider how our panelized ADU designs might be applied to different settings. For example, Figure 42 shows a simple design for a multi-family apartment structure that could be built on empty R-1 size plots. Depending on the plot’s allowable FAR and general dimensions, up to 7-8 adaptable apartment designs using the same modules as the detached ADUs could be easily stacked (two levels) and arranged on either side of an open circulation/social space. The same design principles considered in the ADUs apply to these apartments and function well with their multifamily organization. Most of the fenestration is on the plot edges, allowing more natural light and maintaining privacy from the shared circulation/social space. The mechanical closets from each of the apartment’s COREs can combine to create central two-story mechanical rooms and continuous wet walls.

References CA HCD (2016). Accessory Dwelling Unit Memorandum: December 2016. Prepared by the California Department of Housing and Community Development. Sacramento, CA. Map Data (2017). Google Maps API. Mountain View, CA. MTC (2014). Transit Stops. Prepared by the Metropolitan Transportation Commission. San Francisco, CA.

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