The Seattle Department of Construction and Inspection (SDCI) made an initiative to pre-approve drawings for a few Detached Accessory Dwelling Units (DADU’s), also known as backyard cottages and mother-in-law houses. These are secondary homes on a property that are detached from the main house, and they are limited to 1000 square feet, have lower height limits, and have relaxed property line setback limitations. These are not to be confused with AADU’s (Attached Accessory Dwelling Units) which are the same thing as a DADU but they are contained within the primary residence. A lot is allowed to have one AADU and one DADU (or two AADU’s).
You can see the drawings that Josh Architects submitted to the building department here:
https://www.seattle.gov/Documents/Departments/OPCD/OngoingInitiatives/EncouragingBackyardCottages/DADU_Submission001.pdf
https://www.seattle.gov/Documents/Departments/OPCD/OngoingInitiatives/EncouragingBackyardCottages/DADU_Submission002.pdf
https://www.seattle.gov/Documents/Departments/OPCD/OngoingInitiatives/EncouragingBackyardCottages/DADU_Submission003.pdf
https://www.seattle.gov/Documents/Departments/OPCD/OngoingInitiatives/EncouragingBackyardCottages/DADU_Submission004.pdf
Our design solutions are the first entries to appear after the ones pre-approved by the city, but they are not actually pre-approved. To be honest, we like the idea of pre-approved structures, but this is a bit far-fetched for Seattle’s thick bureaucratic permitting system. Here’s why pre-approved DADU plans rarely work in the most common neighborhood residential zones of Seattle:
Lot Size: for a DADU to be allowed, your lot must be at least 3200 square feet (and min 25’ wide and min 70’ long). Not all lots are big enough to allow them.
Lot coverage: the percentage of a lot that is allowed to be covered with structures has a limit, so selecting a pre-approved DADU rarely works in our experience since most don’t fit within the remaining percentage of the land that is still allowed to be developed.
Setbacks: DADU’s are required to be spaced a certain distance from each property line, from the main residence, and also from any other structure. It is pretty rare that a pre-approved DADU happens to be the exact size required to magically fit on a property without violating the setback requirements (and also without exceeding the percentage limit in #2 above).
Trees: trees are good, but Seattle likes its trees more than you and more than the housing problem. Removal of trees to make way for a DADU is regulated, and commonly, many trees are not allowed to be removed since they exceed the size threshold to get permission to remove them. Consequently, the required setbacks from protected trees commonly do not leave enough space for a pre-approved DADU to fit on the remaining property. There is a way to relax property line setbacks in this scenario, but it rarely helps.
Topography: there’s usually something about the slope of Seattle lots that causes the foundations of any structure to require special custom design considerations. Consequently, the pre-approved structure needs to be re-evaluated, so there’s really not much about the design that is truly “pre-approved” (if it even happens to fit on your lot based on the previous points). It is common that the topography will be a catalyst for a custom designed DADU.
As you can see, there are many factors that cause the pre-approved plans to not work on many lots. We have never seen one that actually fits outright without some sort of modification. There’s even more reasons than the ones listed above, but another common reason they don’t work is because of a homeowner’s specific needs. They may want the entry door to face a certain direction, or they may not want the DADU’s living room window to be facing the master bathroom window of their main house.
Once a pre-approved DADU doesn’t fit for one of the reasons above, or if a homeowner wants to make a change to it, a redesign happens, and the pre-approval is no longer effective. This almost makes the pre-approval a little scammy. It gets homeowners’ hopes up that they can pick a plan and just expect things to flow smoothly, but the building department doesn’t make anything easy. The redesigns required for most of these situations make the system of pre-approvals nearly pointless.
The moral of the story is not to rely on buying a pre-approved plan because there’s a really really really good chance you will be wasting your money on something that won’t be allowed. It would be best to use the pre-approved plans for inspiration, and to contact an architect that you like, so they may design something for you that will actually fit on your lot that also meets your wants and needs. That would be a much smarter investment and result in no compromise. After all, a DADU is an actual house in your backyard, so it makes sense to spend the money to do it right rather than compromising and selecting something that doesn’t meet all your needs.
If you’d like to learn more about our design process, visit www.josharch.com/process, and if you’d like to get us started on your project with a feasibility report, please visit www.josharch.com/help