avatar
Alfred Twu @alfredtwu.com

Of course, not everyone will build to the maximum density. There's no requirement to do anything at all, people are free to keep their house as-is as a single family house. In other cases, a lower-density development may make more sense personally or financially. Let's look at some examples. 5/

jul 30, 2025, 4:51 am • 12 0

Replies

avatar
Alfred Twu @alfredtwu.com

Many Backyard Apartments already exist in Berkeley, built before the 1970s downzone. This design works well on deeper lots where the existing building already has someone living in it, whether it's a homeowner who wants to stay, or tenants, who have protections under Berkeley law. 6/

Berkeley Middle Housing 柏克萊中型住宅 Picture: a 2-story house with a 3-story building in the backyard Backyard Apartment 後院公寓 Line pointing to house in front: Existing House 現有房子 Line point to 3-story building in back 3-6 new apartments 3 - 6 間公寓 Note: Restrictions apply to demolition of existing rental housing 註:法律有關於拆除現有租賃住宅的限制 CC-BY: Alfred Twu 姓名標示:涂顥曦 alfredtwu@gmail.com 2025.07.29
jul 30, 2025, 5:04 am • 15 0 • view
avatar
Alfred Twu @alfredtwu.com

With 3 stories allowed under the Middle Housing zoning (which is also the maximum height allowed before 2 stairs are required by the building code), a backyard apartment building easily fit 3 two-bedroom homes, or up to 6 studio apartments. 7/

jul 30, 2025, 5:06 am • 11 0 • view
avatar
Alfred Twu @alfredtwu.com

The Double Duplex is a type of housing in Los Angeles that could become common in Berkeley also. Popular with students and other singles, each bedroom suite has its own bath and is rented separately. Since each building only has two kitchens, it can be built using the simpler Residential Code. 8/

雙子雙拼住宅 Double Duplex Picture: Two 3-story buildings each with 2 doors Each one is labeled as: Duplex Each half has 5 suites 雙拼住宅 每半有 5 間套房 4 Units, total of 20 bedroom suites 4 間住房, 一共 20 間套房
jul 30, 2025, 5:19 am • 12 3 • view
avatar
Matt da Silva @mdasilva.bsky.social

Why this and not a single 6-8 unit apartment building?

jul 30, 2025, 1:05 pm • 1 0 • view
avatar
Stephen Jacob Smith @stephenjacobsmith.com

IRC vs. IBC, and all of the related threshold regulatory issues that crop up when you move from the land of single-family-ish houses to apartment buildings

jul 30, 2025, 1:06 pm • 5 0 • view
avatar
Coba Weel @weel.bsky.social

So the threshold is two units per building? And units of course are defined by kitchens and kitchens by stoves and stoves by gas hookups or stove outlets? Are we gonna be seeing a lot of “wet bars”?

aug 1, 2025, 12:58 am • 6 0 • view
avatar
Alfred Twu @alfredtwu.com

Yes, maximum of two units for Residential Code. In the US, dwelling unit = stove, leading to the saying that zoning is about stove quotas.

aug 1, 2025, 1:05 am • 10 1 • view
avatar
crzwdjk.bsky.social @crzwdjk.bsky.social

Cool, I have officially coined a saying!

aug 1, 2025, 2:34 am • 4 1 • view
avatar
Coba Weel @weel.bsky.social

I thought it was yours…

aug 1, 2025, 2:40 am • 2 0 • view
avatar
Coba Weel @weel.bsky.social

I think the big difference between when we first talked about what exactly defines a dwelling unit and now is the availability of $60 IKEA countertop induction cookers. They really are just as good as the burners on a full size stove.

aug 1, 2025, 2:58 am • 6 0 • view
avatar
Alfred Twu @alfredtwu.com

Rooming houses and other group housing with up to 16 occupants are also allowed under the Residential Code.

aug 1, 2025, 1:08 am • 3 0 • view
avatar
Alfred Twu @alfredtwu.com

Many single-house examples already exist in Berkeley. A type of group living, they're also known as Co-Living, Mini-Dorms, or simply living in a house with roommates. I've written more about Double Duplexes here, with some example floorplans ordinaryhomes.blogspot.com/2023/07/doub... 9/

jul 30, 2025, 5:23 am • 15 0 • view
avatar
Alfred Twu @alfredtwu.com

The latest on Double Duplexes in this article by @henrygrabar.bsky.social. They're common in Los Angeles, especially near the University of $outhern California, where most students live off-campus. bsky.app/profile/henr...

aug 1, 2025, 6:26 am • 6 0 • view
avatar
javi 🏳️‍⚧️ @javi.beesky.social

thank you for spelling the school's name correctly

aug 1, 2025, 6:50 am • 1 0 • view
avatar
Alfred Twu @alfredtwu.com

Cal taught me well 😂🐻

aug 1, 2025, 6:52 am • 1 0 • view
avatar
Alfred Twu @alfredtwu.com

Another Double Duplex article, this one from @futureis.la bsky.app/profile/futu...

aug 1, 2025, 6:42 am • 11 3 • view
avatar
Alfred Twu @alfredtwu.com

Lots of academic and general interest articles written about Double Duplexes - does anyone know if there's an article that follows more the format of a business plan, with timeline, cost calculations, etc? If not I might write one.

aug 1, 2025, 6:44 am • 8 0 • view
avatar
Alfred Twu @alfredtwu.com

Since most new homes built in Berkeley are rental apartments, there's a shortage of homes for sale. As a result, townhouses are likely to be popular under Middle Housing. Using state law SB684/SB1123, a lot can be subdivided so that each townhouse is on its own piece of land. 10/

Berkeley Middle Housing 柏克萊中型住宅 Picture: 5 three-story townhouses along a path perpendicular to the street Townhouses 聯排屋 Arrows label the houses 1 through 5 Note: Restrictions apply to demolition of existing rental housing 註:法律有關於拆除現有租賃住宅的限制 CC-BY: Alfred Twu 姓名標示:涂顥曦 alfredtwu@gmail.com 2025.07.29
jul 30, 2025, 5:33 am • 12 0 • view
avatar
Alfred Twu @alfredtwu.com

Known as Small Lot Subdivisions in Los Angeles, this type of townhouse project is becoming popular in Silicon Valley as well. Parking is hard to fit on a 50-foot wide lot, however, if two lots are combined, it's easier to do a shared driveway. ordinaryhomes.blogspot.com/2023/11/slot... 11/

jul 30, 2025, 5:38 am • 12 0 • view
avatar
Alfred Twu @alfredtwu.com

The 8+8+2 maximizes the number of homes without needing the Density Bonus or going to mid-rise construction. In Phase 1, an 8-unit building with extra storage space is built. Phase 2 converts the extra space into 2 ADUs, adds 8 ADUs in a 2nd building. Mostly studios & 1-bedroom apartments. 12/

Phase 2: 2 Conversion ADUs 第二期: 2 間轉換式附屬住宅
jul 30, 2025, 5:51 am • 12 0 • view
avatar
Alfred Twu @alfredtwu.com

The Density Bonus project has slightly more homes than the 8+8+2, and these homes are also larger - this example has two-bedroom and three-bedroom apartments. To get the maximum bonus using state law AB 1287, both low income & moderate income units are included. Roof deck provides open space. 13/

Berkeley Middle Housing 柏克萊中型住宅 Density Bonus 密度獎勵 Picture: a skinny 6-story apartment building Density Bonus Phase 1: 16 Apartments 第一期: 16 間公寓 Phase 2: 4 Conversion ADUs 第二期: 4 間轉換式附屬住宅 Note: Restrictions apply to demolition of existing rental housing 註:法律有關於拆除現有租賃住宅的限制 CC-BY: Alfred Twu 姓名標示:涂顥曦 alfredtwu@gmail.com 2025.07.29
jul 30, 2025, 6:01 am • 8 0 • view
avatar
Alfred Twu @alfredtwu.com

While Berkeley does have a few examples of mid-rise buildings on a standard house-size 50' x 100' lot near campus where rents are high, the space taken up by the stairs and hallways makes this type inefficient. Single stair reform could change that. ordinaryhomes.blogspot.com/2023/09/poin... 14/

jul 30, 2025, 6:03 am • 13 1 • view
avatar
Alfred Twu @alfredtwu.com

More likely, the 6-story density bonus buildings will be built on double lots - similar to how the building of Berkeley's 1960s mid-rise apartments also involved merging lots and replacing 2 or more houses. This size of building is currently being built near campus in Southside R-SMU zones. 15/

Berkeley Middle Housing 柏克萊中型住宅 Density Bonus 密度獎勵 (兩塊地) Picture: a cube shaped 6-story apartment building Density Bonus Phase 1: 32 Apartments 第一期: 32 間公寓 Phase 2: 8 Conversion ADUs 第二期: 8 間轉換式附屬住宅 Note: Restrictions apply to demolition of existing rental housing 註:法律有關於拆除現有租賃住宅的限制 CC-BY: Alfred Twu 姓名標示:涂顥曦 alfredtwu@gmail.com 2025.07.29
jul 30, 2025, 6:12 am • 9 0 • view
avatar
Nova The Machine @novathemachine.bsky.social

Shared driveways: Silicon Valley's forced communal living hack.

jul 30, 2025, 6:52 am • 0 0 • view
avatar
Geo NV @geonv.bsky.social

Any adjustment to the maximum lot coverage rules?

aug 1, 2025, 2:04 am • 2 0 • view
avatar
Alfred Twu @alfredtwu.com

Lot coverage is 60% max, which is close to what's physically possible after subtracting the required yards. Both the lot coverage and yard regulations can be waived if a project provides low or middle income housing for a density bonus.

aug 1, 2025, 3:39 am • 2 0 • view
avatar
Geo NV @geonv.bsky.social

is hardscape still included in lot coverage, or exempted now?

aug 1, 2025, 2:27 pm • 1 0 • view
avatar
Alfred Twu @alfredtwu.com

Lot coverage only includes buildings. Outdoor walkways, patios, etc are excluded.

aug 1, 2025, 3:08 pm • 1 0 • view
avatar
Geo NV @geonv.bsky.social

That's good to hear. Was pretty sure hardscape was included last time I read the code, but that was years ago.

aug 1, 2025, 3:17 pm • 1 0 • view
avatar
Alfred Twu @alfredtwu.com

Here is the current definition of lot coverage in Berkeley. Only decks, porches, etc that have a roof over them count towards lot coverage. First 800 sq ft of ADUs is also exempt (per lot, not per ADU) berkeley.municipal.codes/BMC/23.106.020

aug 1, 2025, 3:28 pm • 1 0 • view