Short answer: in Newcastle, Washington’s R-4 and R-6 zones, the code lets you build up to 30 feet tall, 10 feet from the street, 20 feet from the rear line and at least 5 feet from each side line. Roof can cover 35 percent of the lot, and roof plus driveway, walks and patios 40 percent. If the lot has a steep slope, an old coal mine, a stream, a wetland or large trees, those rules usually decide the design before the zone does.

This is the City of Newcastle in King County, between Bellevue, Renton and Issaquah, not Newcastle, Oklahoma or Newcastle upon Tyne. My work here is on my Newcastle architect page; the neighbors are in my Bellevue, Issaquah and Redmond guides.

The city’s code host blocks automated readers, and I did not get around that. Figures come from the city’s own copies of Ordinance 2025-671 (June 17, 2025) and Ordinance 2026-683 (February 17, 2026), its April 8, 2026 fee schedule and city pages, read October 13, 2026; a mirror is labelled. Confirm every number with the city.

Newcastle’s residential zones and the zoning map

Title 18 of the Newcastle Municipal Code (NMC) is the zoning code. R-1, R-4 and R-6 are the single-family zones; R-12 and R-24 are multifamily. Base density is 1 home per acre in R-1, 4 in R-4 and 6 in R-6. An R-1 lot under 15,000 square feet follows the R-4 standards (footnote 7).

Source: NMC 18.12.030(A), Ordinances 2025-671 and 2026-683.

Finding your zone. The code refers to the city’s adopted zoning map (table footnote 4); a mirror of chapter 18.04 says the official copy is on file with the city clerk. The Codes and Plans page links no stand-alone map and I did not confirm a zoning layer in its Maps and Data portal. Ask Community Development to confirm your zone in writing.

Yards, coverage and height by zone

• Side yards total at least 15 feet, with no interior side yard under 5 feet and no street side yard under 10 (footnote 12). With an ADU on the lot, the footnote says side setbacks add to 10 feet for the ADU only; confirm how the city applies that.
• Garage. A garage or carport needs 20 feet of driveway to the street line (footnote 8), though the house can stand 10 feet back.
• Projections (NMC 18.12.160). Eaves reach 18 inches into side and rear yards and 24 into the front. Uncovered decks and patios no higher than 18 inches may reach 15 feet into the rear yard, leaving 5 feet to the line (20 minus 15). Covered porches may reach 5 feet into the front yard, leaving 5 (10 minus 5).

Height is 30 feet in R-1, R-4 and R-6. The city draws the smallest rectangle around the building, averages the ground elevations at the midpoints of its four sides, and measures from that average to a flat roof’s highest point or to the mean height between eaves and ridge on a pitched roof. With midpoints at 108, 96, 102 and 102 feet the average is 102 (408 divided by 4). Eaves 22 feet and a ridge 36 feet above that give a mean of 29 ((22 plus 36) divided by 2), which passes (footnote 23).

How big a house the rules allow: a worked lot

The density table lists floor area ratio as N/A in R-1, R-4 and R-6, so house size comes from three limits. Building coverage is roof area, ignoring eaves of 18 inches or less. Impervious surface is roofs, walkways, patios, driveways and other hard ground; porous and grid pavers count at 50 percent. Hard surface adds permeable pavement and vegetated roofs. Footnote 5 lets impervious surface rise to the hard surface limit only where permeable surfaces are infeasible.

The envelope is 6,175 square feet (65 x 95), but coverage stops the roof at 3,500, and a full 3,500 footprint leaves 500 square feet of impervious surface for everything else. A more usual plan, a 2,600 square foot footprint, a 450 square foot driveway (18 x 25) and 700 square feet of walks and patio, totals 3,750 square feet (37.5 percent), with 250 to spare. Two stories on that footprint is 5,200 square feet above grade (2,600 x 2), plus any basement; zoning sets no cap.

Steep slopes, landslides and coal mine hazards

Critical areas are chapter 18.24, rewritten by Ordinance 2026-683. A site with a critical area, a buffer or a building setback needs a critical area report unless the city waives it (NMC 18.24.110), and you must disclose critical areas within 300 feet (18.24.090). The city says only a qualified professional’s survey confirms one on your lot.

• Steep slopes are 40 percent or steeper with at least 10 feet of vertical change. The city sets the buffer from a geotechnical engineer’s or geologist’s report, never under 10 feet; with no report it is 50 feet. Buffers cannot be averaged, and removing vegetation is prohibited unless part of an approved alteration or temporary at the toe (NMC 18.24.300). Add the 10 foot building setback of 2026 (NMC 18.24.180(B)): at least 20 feet from the slope edge with a report (10 plus 10), 60 without (50 plus 10).
• Landslide hazard areas include land steeper than 15 percent with silt and clay soils and seepage, and ground that has moved since the last ice age. The buffer is 50 feet if no geotechnical report is filed (NMC 18.24.270).
• Coal mine hazard areas. Land over old workings is declassified (typically deeper than 300 feet), moderate (typically 0 to 300 feet) or severe (typically 0 to 150 feet, or where openings and sinkholes exist). Nothing may be altered until the city accepts a hazard assessment by a professional engineer. Moderate areas allow building when structural risk is minimized; severe areas allow a short list, such as a building under 4,000 square feet with no living quarters, unless a mitigation plan supports more (NMC 18.24.200 to 18.24.208).

A reasonable use exception exists if the rules would deny all reasonable economic use of the lot; the 2026 fee is $8,058. See my sloped lot guide.

Streams, wetlands, Lake Boren and the shoreline

The 2026 update set stream buffers, measured from the ordinary high water mark, at 200 feet for Type S, 150 for Type F, 100 for Type Np and Type Ns, and 110 for Lake Boren. The old table had 100, 50 and 25 for F, Np and Ns, so a seasonal Ns stream went from 25 feet to 100. With the 10 foot setback, an Ns stream puts the house 110 feet back (100 plus 10) and Lake Boren, on the stream table’s number, puts it 120 feet from the water (110 plus 10). The same ordinance says Lake Boren is a wetland rated by city consultants and tells owners to ask the city for its category and buffer widths, so get that in writing. Wetland buffers depend on category, habitat score and land use intensity, set by a qualified wetland professional (NMC 18.24.315).

Lake Washington. Nothing I read shows Lake Washington frontage in Newcastle, and the waterfront chapter, 18.17, covers docks and piers on Lake Boren only (mirror copy). Lake Boren covers 16.20 acres per the Washington Department of Fish and Wildlife, and the state Shoreline Management Act leaves out shorelines on lakes under 20 acres (RCW 90.58.030(2)(e)(iii)). I found no Newcastle shoreline program for it, so the city’s buffer and dock rules appear to govern; confirm with the city. For lakefront sites see my waterfront architect page.

Trees and clearing

Tree retention in chapter 18.16 applies to new development: a change of occupancy or a substantial improvement, meaning work costing 50 percent or more of the structure’s market value. As I read it, a rebuild is over that line. At a $750,000 budget the line is crossed on any structure with a market value of $1,500,000 or less (750,000 divided by 0.5).

• Retention. Keep 25 percent of the mature trees in the lot interior, outside critical areas and buffers. A mature tree is 8 inches across for evergreens or 12 for deciduous trees, measured 4 feet above grade. With 20 mature trees you keep 5 (20 x 0.25). A certified arborist prepares the retention plan with the building permit, and a 6 foot fence goes 2 feet outside the drip line (NMC 18.16.130 to 18.16.160).
• Replacement. If the required trees cannot be kept, or 10 or more significant trees come out, removed trees are replaced at 2 inches of new trunk for each inch removed, in 2 inch trees, at least 70 percent conifer: a 10 inch tree means 20 inches, or ten trees (NMC 18.16.170).
• Clearing permit. Clearing 2,500 square feet or removing 10 or more significant trees needs a clearing and grading permit (NMC 17.07.040). The city says up to 9 can come out of private property not under permit review, but not from critical areas.

Remodel, rebuild or tear down

As far as I can read, Newcastle uses no remodel cost percentage to end a nonconforming house’s protection, unlike Clyde Hill or Bellevue; see when a remodel counts as a new house. Its 50 percent test applies to damage and demolition. Two rules matter.

• Zoning nonconformance (chapter 18.32, read on a mirror that already shows Ordinance 2026-689, which I did not read). You may modify a nonconforming improvement if the change does not increase its area, height or degree of nonconformity. A damaged or demolished one can be rebuilt only if the nonconformance does not grow, the permit application comes within 12 months, and the loss stays under 50 percent of assessed or appraised value, with an exception for fire or natural disaster. That suggests a teardown of a house sitting in a yard brings a new house under today’s rules, but it rests on the mirror alone, so confirm with the city.
• Critical areas (NMC 18.24.055, new in 2026). An addition to or voluntary replacement of a nonconforming house must go outside the critical area and buffer where possible. For stream and wetland buffers a house may go up, with a one-time footprint addition of up to 500 square feet in an already improved area, reaching no closer to the water than today. The old exemption for 250 square feet on a house built before incorporation was struck, and for steep slopes I found no addition allowance, so ask early. An administrative variance (fee $3,168) cannot cut the setback below 5 feet.

ADUs and middle housing

NMC 18.31.030, as adopted in June 2025, allows up to two ADUs with a house, attached or detached, of 300 to 1,000 square feet (the director may allow more for one on a single floor), at up to 30 feet attached or 24 detached, with one parking space each except within half a mile of a major transit stop. See my Washington ADU guide. Chapter 18.19 also allows two units per lot by right on lots zoned mainly for housing, including duplexes and cottage housing, with standards no stricter than for a detached house, but not on critical area portions or lots created by splitting a single residential lot.

The building permit: who reviews it, where you apply, what the city charges

Community Development’s Building division reviews permits and inspects projects, and the building code is Title 15 of the NMC. The Permit Center page now sends applicants to the city’s OpenGov portal, where single-family permits moved from MyBuildingPermit.com in June 2026.

Who reviews. City staff do. You also reimburse the city for consultants it hires when staff cannot do the review, structural engineering among them, with a deposit and a 10 percent overhead charge. I found no published review time for house permits, so I quote none.

The building permit fee itself sits in NMC 15.05.109 on the blocked code host, so I have not calculated it. If the per bedroom parks fee applies to a house, a four bedroom replacement is $19,122 in transportation and parks fees (11,046 plus 4 x 2,019) before any credit for the house you remove; I could not read Title 16 to confirm either point, so ask. The schedule also lists 4.0 percent fees for MyBuildingPermit.com and card payments; ask whether the first still applies after the move to OpenGov. Energy rules are in my energy code guide and teardown steps in my demolition guide.

Questions