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Here are examples of the density, shown in units per acre, of local known buildings in Humboldt County and specific buildings outside of our area.

If there are buildings you’d like to see added here, please contact me and I’ll look up the units per acre and put it into this article.

Net units per acre vs. Gross units per acre

The common figure used is Gross dwelling units per acre.

Gross units per acre is a simple equation:  The number of dwelling units divided by the overall area of the parcel.

In looking at the Net units per acre, we subtract out those portions of the parcel that could not be built on. Unbuildable portions of the parcel can include environmentally sensitive areas and the area put aside for privately-owned publicly-accessed open space. In a new subdivision, the new roads to be built would be considered unbuildable area.

Here in Arcata, in the Gateway area, one clear example of an unbuildable area is in the car wash parcel, a full city block between 9th and 10th and K and L Streets. Other Gateway opportunity parcels are subject to reduction in buildable area because of environmental concern as well.

The full parcel is 1.44 acres. Jolly Giant Creek runs diagonally through the property and currently about half has been daylighted, with all of it slated to be daylighted before any new construction on the site were to occur.

When the daylighting is complete, the area left to build might be half of the full parcel, or about 0.72 acres. If, as a hypothetical example, a 50-unit apartment complex were to be built on the un-daylighted portion, the Net units per acre would be 50 ÷ 0.72, or 69.4 units per acre. If we look at the Gross units per acre, that would be 50 ÷ 1.44, or 34.7 units per acre.

Privately-owned publicly-accessed open space reduces the area of what can be built on

The privately-owned publicly-accessed open space situation is more thoroughly discussed here on Arcata1.com at The Myth of “Privately-Owned Publicly-Accessible” Open Spaces. If a developer is required to give up 12.5% or 15% of the parcel as unbuildable property, that’s a good-sized hit on the amount of land that can be built on.

“Dwelling Units per Acre” is a terrible way of measuring housing

Let’s say a developer wants to put up a family-oriented apartment complex on a parcel that’s 0.7 acres in size — that’s the size of Sorrel Place on 7th Street, or about half of a city block. The apartments are a blend of some 800 square feet two-bedroom units, mostly 1,000 sq.ft. three-bedrooms, and a smaller number of 1,400 sq.ft. four-bedroom units. The overall average size is 1,100 sq.ft. for the apartments, and the total area of the living space is about 36,000 square feet. 

If the average size of the apartments there were to be 1,100 square feet, there’d be 33 apartments total. The density figure would be 48 units per acre.

If the developer instead made a blend of one, two, and three-bedroom units, with an average size of 824 sq.ft., which is what Sorrel Place actually is, then the density figure would be 64 units per acre.

And if the developer wanted to make the entire building consist of 394 sq.ft. one-bedroom apartments — as is being done at the Westwood Garden Apartments, as approved in January, 2023 — then there’d be 90 or so units, with a density figure of over 130 units per acre. Making 300 sq.ft. studios yields 120 units, which shows a density of over 170 units per acre.

Or make the apartments filled with 236 square foot studios — the size of the studios at the Strombeck Properties “Parkway” apartments on Union Street near the Arcata Sports Complex, which, by the way, are referred to on the Strombeck website as “Top of the Line Studios.” More details on these studio units here below. With 236 sq.ft. units, you’ve got a density of over 200 units per acre.

So from 32 units per acre to 200 units per acre, all on the same parcel — depending on whether the developer wants family-type groups (or just group housing in general, including student-oriented housing) or individual renters.

The number of bedrooms or “doors” is far more important for our housing needs

The “family-oriented” apartment complex example, with 33 apartments, would house about 120 people. The 100% one-bedroom example, with 90 apartments, would house about 135 people (with half of the one-bedroom units occupied with two people). In other words, both fill close to the same level of housing needs — just for different types of persons in our community. 

In the building trades, the term “door” is used as a means of describing the size of the apartment unit in terms of how many bedrooms it is.

For more on this, see:  “Dwelling Units per Acre” – Another terrible way of measuring housing — with over 600 views now — and “Housing Units” and “Housing Density” – Why these are terrible ways to measure housing success.

Examples of buildings and their densities

Sorrel Place. 7th Street, between I and J Street. Four stories, flat roof. 44 units, 83 bedrooms. Average unit size 824 square feet. 0.69 acres, about half of the city block. Completed in January 2022. More details below.
Density is 64 units per acre or 121 bedrooms per acre.

Plaza Point. 8th and I Streets. Three stories, peaked roof, as tall as a four-story building. Commercial storefronts on the ground floor.  0.52 acres for the building and parking lot. 29 units, average 884 square feet. Completed in 2012.
This project was set up as an air-space condominium, with 10 separate legal parcels: 5 on  the ground floor, one each for floors 2 and 3, and 3 parcels for as common and exclusive use of the parking area.
Density is 54 units per acre. Number of bedrooms unknown.

Other Cities

“Mio” apartments, Seattle. Four stories plus elevator houses for roof access. 41 studio and one-bedroom apartments, 401 to 599 square feet. Small parcel of just 0.20 acres elevates the density per acre figure. See articles on the “Mio” apartments here and at Visualizing Compatible Density.
Density is 205 units per acre or 205 bedrooms per acre.

Links and details for these apartment buildings

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Sorrel Place

Link to the City’s website page for Sorrel Place, here. Includes meetings and staff reports. Note: This page is from 2019 and may be removed in the future.

Plans for Sorrel Place. 14 pages. When viewing, you can use the + and – keys to enlarge or reduce the image size, and use the horizontal scroll bar at the bottom of the viewer to move the image left and right.

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Strombeck “Parkway” Top of the Line studio apartment, 236 square feet

View a larger version of this image on the Strombeck properties website, here.
The Stombeck properties website here.