Zoning envelope

Trees House is zoned SF9600 (single-family homes only, minimum lot size 9,600 SF). The following information is based on Seattle Development and Planning Department (DPD) Tip #220. The lot size is important, because lot coverage is a consideration. Unlike most parcels, we won't know the precise boundary dimensions until the survey is prepared--it's just not clear from the available public records.

Setbacks

Standard setbacks apply: 20' front, 25' rear (see below), 5' on sides, and the existing house has a margin all around--we can extend the house in any direction.

I can't remember a project where the existing house didn't touch at least one setback.

Front: The living room can be at least 9' closer to the street. The garage can be 17' 6" closer to the street. (Pending confirmation by the survey)

Sides: The NW and NE corners are apparently not 90 degrees. The north boundary bears at N 88-27-02 W, and the west boundary at N 0-55-11 W, so the NW corner is 87.5309 degrees.

Rear: The garage can extend at least 20' to the south. The main house can move at least 28' south. The normal 25' setback is already reduced to 24' (20% of average lot depth), but an odd rule about not counting portions of parcels less than 10' wide might apply to the SE corner where the parcel makes an acute angle.

Keith Cross, the soils engineer, warned against proposing construction in the rear, for fear of Carkeek entanglements, so it is ironic that being in an Environmentally Critical Area (ECA) could reduce the setback requirement by 5'. That would effectively allow us to build right to the top of slope (pending confirmation by the surveyor). For the ECA reduction, see Seattle 23.44.014D15.

Height Limit

The height is limited to 30' about average grade, with several possible exceptions.

The average grade can be calculated by one of several methods (see Seattle Director's Rule 9-2011), but it will likely work out to about 3' below the main floor level (the grade is about 6' below at the SW corner of BR3).

Exceptions. The ridge on a gable or hip roof can be 35' from the average grade, but flat and shed roofs must stay under the 30' limit. Exceptions are made for railings and chimneys up to 4' above a flat roof. Clerestories can be up to 4' above a flat roof, but the raised area must be less than 30% of the roof area.

We have been using +263.0 as the finish floor of the main house, so the base height limit is +290. We can do two floors with a 10' ceiling downstairs and a 14' ceiling and a flat roof upstairs. Three stories would be hard to sell in this neighborhood of mostly one-story homes.

Garage Frontage

We would like to move a 20' wide garage to the front setback, but a special Seattle rule applies, designed to de-emphasize garages along a streetfront. First, the garage is limited to 50% of the structure width (currently 68' 1"), so we're good there.

Second, the garage may not be closer to the street than 80% of the walls that are not the garage. Currently, the 20' 3" garage is set back from the 47' 10" house, except for the 13' 8" breezeway, which is 28.57%. We are currently non-compliant, which is a potential exception for us--hey, it works for side setbacks.

Seattle wants to discourage this sort of thing

Lot Coverage

The lot coverage is limited to 35% of the parcel size, with several exceptions, none of which apply. The "footprint" is supposed to include things like bay windows, even if they don't touch the ground, but not ordinary roof eaves. The existing house, including the front porch and the greenhouse, is 1895.082 SF. The current coverage is either 17.9% (10,589) or 17.5% (10,800).

The limit is either 3,706.15 SF (10,589) or 3,780 SF (10,800), which we are unlikely to approach.

Parcel Size

We know the parcel is 90 feet wide (from the legal description--it's the westernmost 90' of lot 24), and the lot size is either 10,589 or 10,800 square feet. Not sure where the first number came from, but the King County Parcel Viewer database says it's the latter. Because the lot is a simple trapezoid, we can calculate the average depth of the lot. 90' wide at the street, sides parallel, means that the average depth is 120' becase 90 x 120 = 10,800. Because we know the angle of the boundary with Carkeek Park, we can calculate the lengths of the two sides.

The property line to the west is 102.06' and to the east is 137.94'--these are my calculations, based on the angle of the south line, pending confirmation by the surveyor. Even if my angle of 68.27 degrees is found to be mistaken, the lot area is still 10,800. (If the lot is really 10,589 SF, the average depth is 117.65'.)