Zoning Pre-Submission

Now that we know the online SDCI request process works--better than a counter chat, in my opinion--should we seek pre-approval of the basic plan? I think so, but I want to think through the downside.

We're seeking approval for a 20' x 18.5' 370 SF workshop addition and construction of an ADU with bathroom and kitchen in the former garage. The existing bathroom and bedroom from the 1980s was apparently non-permitted, but we'll be studs out for inspection of new work and any old work that remains.

We're providing one-car off-street parking using the existing curb cut and not within the required front yard. Because we're not providing a garage, 23.44.016 F.1.a (garage closer than the house to the street) does not apply. Per 23.54.015 Table B, this space will house a "Medium vehicle, 8' x 16'" because this is a single family residence. The driveway will include an "S" turn with a 24' center radius and 12' width as required by 23.54.03 D.1.e. 

Shifting the practical driveway (not the curb cut) to the east, incidentally, moves vehicular traffic away from the established Douglas Fir.

Zone: NR-1. The new addition respects the 20' front yard and 5' side yard. Actually, the west wall of the addition and ADU is at least 11' from the west property line. There is no construction in the rear yard, which is sensitive due to a steep slope into Carkeek Park.

Lot coverage is limited to 35% of parcel size of 10,600 = 3,710 SF, with an average depth of 117.65'. The existing house and non-permitted ADU is 1,706.5 SF and we're adding 370 SF for a total of 2,076.5 SF, or 19.6% of parcel size.

Our proposal is extremely respectful of neighborhood character.

Workshop addition shown in blue

Approach from the west

Seattle Residential Code

I feel as if I was aware of this, but I was reminded today. The 2021 Seattle Residential Code governs this project. This is the IRC with some changes.

We seem to be in a D₂ Seismic Design Category, per Figure R301.2.2.1(5). Alternate is E, per Figure R301.2.2.1.1(5). Because this becomes important later in the code, I filed a new request (11/25) with SDCI to confirm. I'm also curious if Fatima answers all requests.

Update 26 Nov: Cici Sun answered my request with the following information:

Parcel number: 761120-0125 Address: 817 NW 118th St.
ASCE Design Hazards Report: Risk Category: II, Soil Class: Default, Sds=1.06, Sd1 = 0.81. 
Per SRC Tabel R301.2.2.1.1, the seismic design category is D2. 
 

Per R401, we need to check the soils report or just assume clay, sandy soil with bearing pressure of 1,500. Per R403, 1-story slab-on-grade only requires 12 x 6 footings for 50 psf roof/snow load.

Use details #1 and #4, Figure R403.1.3 (p4-10) because we're in D₂ Seismic Design Category. Per Figure R403.1.7.1, our existing south footing must be 24' from the top of slope (H/3, where H=~72'), and it is. New footings are farther from the top of slope.

Table R602.10.4 PFG=Portal frame at garage. See section R602.10.6.3. Only seems to apply to Seismic A, B, or C (we're D₂).

I thought we might be subject to the Seattle Existing Building Code (and we still might be). There are 3 levels of alterations. Chapter 11 concerns Additions.

• Level 1. Replacement or covering existing materials or equipment with things that serve the same purpose.
• Level 2. Add or delete door or window or installing addl equipment
• Level 3. Work area exceed 50% of the building area. [For this house, work area is 770 SF, 45.1% of 1,706.5. It's close, if "building area" excludes the ADU, we'd be at 59%.]

Alternative

I'm not sure if it would help to show SDCI what their rules allow. If I scrape the house, I could build a solid facade 80' wide and 30' high, with a single-family residence, an attached ADU and a detached ADU, totalling 3,710 SF.