Let's reassess. Seattle has made changes since I last studied up. We're on the 2018 Seattle Residential Code (IRC with a few changes). As of 2022, the zone is Neighborhood Residential--NR1 (not SF9600). Also, up to two ADUs are allowed with no additional parking requirements.
Because the building is 76 years old this year, let's look at the property from a developer's POV:
Lot: 10,665 SF. APN: 761120-0125 Legal Description: West 90' of Lot 24, Schroeppel Park Addition as recorded in Volume 35 of Plats, Page 12. King County, Washington
Allowable Footprint: 3,732.75 SF (Includes garage, accessory buildings, balconies, decks over 36" above grade. Only the first 36" of eaves are exempt.)
Allowable Floor Area: The FAR is a flat 0.50, so the total dwelling area for three units is 5,332.5 SF
Required Yards: 20' front, 5' sides, 25' rear. Seattle calls setbacks in NR zones "yards." On the east, we may want to stay with the current 9.5' setback to avoid disturbing the rockery. On the south (canyon) side, we are in a designated Steep Slope zone (part of the Environmentally Critical Area designation) and the city has drawn a map showing a buffer zone around steep slopes. This makes the 25' setback more like 35' in places, but seems pretty loose.
The neighbors to the east are dramatically set back, so the average of west and east is 48' 3". Luckily, it's that or 20', whichever is less.
Allowable Height: The limit is 30' above the average grade as it hits each wall, so we need a design to figure the limit precisely. The lot is basically flat at 260', sloping up to ~266' at the NE corner, ~258' in the SW and, of course, falling off dramatically into the canyon. A pitched roof with a ridge can exceed 30' by 5' and railings can be up to 4' above a flat roof.
Required Parking: Only 1 spot is required, but they want it "as part of the structure." Parking in a yard is okay as long as it's not the front yard. Only one 10' curb cut is allowed on this much frontage.
Climate: I keep forgetting that we are in Zone 4 (Marine), which means:
- Ceiling R-49 (no, R-38 per R402.2.1?)
- Walls R-21
- Floor R-30. Slab R-10, 2 feet depth
- Windows U-Factor 0.30. Skylight U-Factor 0.50
- Frost line depth: 12"
- Winter Design Temperature: 24° F
- Mean Annual Temperature: 52.8° F
- Air Freezing Index: 250
This is the rule I remembered from 2015 that kept the garage from working, assuming that I didn't bring the house forward. But if I do bring the house forward, no problem. Well, no problem with this rule. The other problem is that we get one 10' curb cut, no parking is allowed in the front yard, and the turning radius doesn't work for a 2-car garage at the 20' setback. The garage needs to back away from the street so that the driveway can "Y" out to the 2-car garage. That's just fine with this rule.
Structure Evaluation
Existing 1947 house is 1,082 SF with a 585 SF annex to the west. There is roughly 250 SF basement 4' below grade.
The building is 2x4 stud construction with minimal insulation. The garage workshop is typical of the poor insulation. The floor in the main house sags in places. The hip roof is sagging and the bathroom requires a sewage ejector. Most windows are double-pane, but air infiltration is massive. The 200A electrical system includes a patch panel 10' from the actual panel. The fascia is rotting at 13 corners, and the roof will need to be replaced by 2028. The kitchen layout is awkward and the kitchen sink needs repair.
The gas furnace, electric water heater, and gas tankless water heater are relatively new, but they could be repurposed.
Proposal
Consider building 3 units--a main dwelling and two attached ADUs--on the bones of the existing home. I'm thinking a two-car garage, with occasional driveway or street parking for a third. (SDCI doesn't like parking in the required front yard.)
| Main Dwelling | Up to 2804 SF (based on FAR) |
| ADU-1 | 1000 SF |
| ADU-2 | 1000 SF |
| Garage | 528 SF |
| TOTAL | Up to 5332 SF |
We can leave the existing 34' x 36' foundation but extend the house to the north while demolishing the west annex altogether. If we limit ourselves to the existing footprint, we won't be able to use most of the buildable area of the lot.
It may make sense to remove the 44" diam. Douglas Fir blocking the driveway.
I'd like to create 3 units, only one of which requires stairs. (Aging in place.) Especially if we remove the Doug Fir, we could raise the garage for more positive driveway drainage and have less vertical distance to the house. Drive to street to house should act as a wheelchair ramp.
According to How Much Does it Cost to Build a Home in Seattle? the answer is about $400 per SF. Three units is three kitchens, so maybe more. If we hold the main dwelling to 1200 SF and exclude the garage, that's a $1.28M investment.
An ADU might break down: 150 living, 100 kitchen, 150 bedroom, 120 bedroom, 50 bath, 50 closets, 200 circulation, entry, dining. We could do 2 bedrooms in 820 SF.
So 1100 for Main, 820 for two ADUs, now we're talking about 2740, or $1.1M. We trimmed almost $200K, but it's still a very big number.
