Those recommendations to the Mayor and City Council can be found here:
POLICY+PACKAGE+FOR+COUNCIL-Corrected+2.1.21.pdf (squarespace.com)

The Commission’s first recommendation addressed what has been labeled as:
 “MISSING MIDDLE HOUSING in SINGLE FAMILY NEIGHBORHOODS”
The Commission recommended that single family residential neighborhoods in Edmonds be rezoned to allow for the construction of duplexes or two-unit townhouses on single family parcels.   This proposal was advanced as a way to increase the availability of “affordable”  and “missing middle” housing in Edmonds single family neighborhoods.
The Commission rationalized that:

“Two attached single family homes, otherwise known as duplexes or two-unit town homes, offer an alternative to typical detached single family homes.  They help to address the need for smaller, more affordable housing choices in neighborhoods characterized by single-family homes. Over the past fifty years, the median square footage of new single family units has increased from about 1600 to 3100. This policy would allow two units within the same square footage. ”   (bold added for emphasis)

The Commission further stated:
“Allowing smaller homes in our single family neighborhoods makes them more affordable and accessible to middle income households that are seeking the amenities that we enjoy in Edmonds, i.e. excellent public schools and low crime. (bold added for emphasis)
There is a paucity of empty parcels within Edmonds available to develop the proposed “missing middle”  housing.  By necessity, developers would be required to acquire single family parcels with houses on them. 

In reality, developing either a duplex or two-unit townhouses on existing single family parcels would result in demolishing modest size housing in less affluent single family neighborhoods in Edmonds.  That would result in replacing less expensive residences with more expensive housing units while at the same time transforming those single family residential areas into higher density neighborhoods.
Ironically, the available limited number of modestly priced single family houses remaining in Edmonds would also decline if this policy is implemented, as developers would concentrate their efforts on obtaining smaller and less expensive houses for redevelopment.    
A review of residential sales in Edmonds for the prior one half year reveals the following:

Approximately twenty three detached single family houses on single family residential lots with Edmonds addresses were conveyed for under five hundred thousand dollars. 

Approximately sixty five detached single family homes on single family residential lots with Edmonds addresses were conveyed for between five hundred and six hundred thousand dollars.
In order for a developer to procure a parcel for townhouse or duplex development, that developer will be required to spend at an absolute minimum four to five hundred thousand dollars to acquire a parcel that by necessity would have an existing residence on it.  
And those prices will escalate if this policy is implemented as a result of increased demand for a limited supply of inexpensive single family houses.

With limited availability of housing in the lowest price range, more expensive parcels will be required for redevelopment that would only increase the cost of duplex or townhouse development.
Estimates of construction costs to develop new single family housing in the greater Seattle area range from two hundred fifty dollars to four hundred dollars per square foot.  There are many factors that determine construction costs, such as the quality of the materials utilized for both the exterior and interior of the residence. 

It would be instructive to apply the analysis of both the cost of obtaining the parcel as well as the cost of developing the duplex or two townhouses to determine if the  Commission’s  hypothesis is correct and that their recommended policy would result in ‘affordable” and “missing middle”  housing in single family residential areas.

Example A:

Assuming a developer acquires a single family house for redevelopment at a cost of 500 thousand dollars, incurs construction costs of 250 dollars per square foot, and constructs either a 3100 square foot duplex or two 1550 square foot townhouses, the cost to develop each unit would be as follows:
One half the expense of procuring a half a million dollar parcel (excluding demolition and related costs).  250,000 dollars.
Construction costs – 1550 square feet at 250 dollars a square foot.  
Cost of construction = 387,500 dollars.
Total minimum costs to acquire the parcel and develop each residential unit:

637,500 dollars per unit. 
Each new unit costs at least 137,500 dollars more than the house that each unit replaced if the cost to procure the parcel is 500,000 dollars and construction costs are 250 dollars a foot.

Example B:
Assuming a developer acquires a house with a residential lot for redevelopment at a cost of 500 thousand dollars, incurs construction costs of 300 dollars per square foot, and constructs either a 3100 square foot duplex or two 1550 square foot townhouses, the cost of each unit would be as follows:

One half the expense of procuring a half a million dollar parcel (excluding demolition and other costs).  250,000 dollars.

Construction costs – 1550 square feet at 300 dollars a square foot.   
Cost of construction = 465,000 dollars.
Total minimum costs to acquire the parcel and develop each residential unit:
715,000 dollars cost per unit. 
Each new unit costs at least 215,000 dollars more than the house that each unit replaced if the cost to procure the parcel is 500,000 dollars and construction costs are 300 dollars a foot.
There were more than one hundred and fifty single family houses situated on traditional single family parcels that were acquired for under seven hundred thousand dollars with Edmonds addresses in the past six months.  All those houses were less expensive to purchase than the cost to build residential unit example B at 300 dollars a foot on a parcel that cost 500,000 dollars to procure.  The result will be increased traffic, more vehicles parked on the streets, more noise, more pollution, less tree canopy and vegetation and more dangerous streets without sidewalks for area pedestrians to negotiate.  It is a policy that promotes increased density and the elimination of single family neighborhoods in Edmonds in the name of “affordable” or “missing middle” housing. This proposed policy does nothing to resolve the issue of affordability, and it will acerbate it by replacing less expensive housing with more costly housing.  
The Commission’s proposal also provides the potential to further increase density in those single family neighborhoods.  Once the protection of single family housing zoning is removed, it will only be a matter of time before new demands for increased density will be promoted in the name of “affordability”,  “missing middle” housing or some other rationale that will further encroach upon single family neighborhoods. 
Eric Soll from Edmonds

Reprinted with the Permission of the Author