What to check before buying a view home on a steep lot

What “environmentally critical area” means on a Seattle lot

Seattle regulates hillsides, wetlands, creeks and a few other features through its Environmentally Critical Areas code, usually shortened to ECA. On a view lot, the two categories that come up most are steep slope erosion hazard areas and landslide-prone areas. The second is the broader one: it covers ground with a known history of sliding and slopes the city considers likely to move, and it takes in the steep slope areas too.

Parts of Magnolia’s bluff, the west face of Queen Anne, the hillsides above Beach Drive in West Seattle and the slopes of Leschi and Madrona running down to Lake Washington carry one designation or another. So do plenty of quieter streets you’d never think of as cliffside.

A mapping doesn’t mean the house is unsafe. It means the city looks harder at anything you want to build, and that the soils and drainage deserve your attention before you buy. SDCI, the Seattle Department of Construction and Inspections, publishes the critical area maps online, and the permit history for the address often shows earlier geotechnical reports, drainage permits or wall repairs. I read both before we write an offer on a hillside house.

The maps are drawn at neighborhood scale. The line may cut across the backyard while the house sits just outside it, and a slope that feels dramatic from the deck may not be mapped at all. SDCI is the office that can tell you how the code applies to one specific parcel.

Critical areas rules on Mercer Island and the Eastside

Every city in the county has its own critical areas code, because Washington’s Growth Management Act requires cities to protect them. The names and details differ from place to place. Mercer Island regulates geologically hazardous areas, which include landslide, erosion and seismic hazard areas, and sloped ground on the island can fall under those rules. Bellevue has steep slope and geologic hazard rules that matter in hillside neighborhoods such as Somerset. Other Eastside cities have their own versions, and King County writes the rules for unincorporated areas.

Two differences come up often. Some cities restrict clearing and grading on steep slopes during the wet months, which can push a wall repair or a new patio into the dry season. And tree rules on sloped lots tend to be stricter, since roots hold soil. If the view depends on topping a row of firs or thinning your own madronas, ask the city what’s allowed before you count on it.

The planning and permit desks in Mercer Island, Bellevue, Kirkland and Redmond will answer parcel-specific questions, and they’re the right people to confirm with.

Reading the lot: drainage, retaining walls, rockeries and trees

Start at the street below and walk up. Most of what a slope is doing shows up as water or as movement, and both leave marks.

Water first. Follow every downspout. On a well-built hillside lot, roof water goes into tightlines: closed pipes that carry it down to the street or another approved outlet so it never soaks into the bank. Splash blocks at the top of a slope, soggy ground halfway down, a seep at the base of a wall or dark stains running down concrete all tell you water is going somewhere it shouldn’t. Ask the seller where the drains end up and whether anyone has run a camera through them.

Walls next. Board-formed concrete walls, the kind that carry the wood grain of their forms, are usually engineered, which means drawings and permits should exist somewhere. Rockeries, the stacked boulder walls you see all over Seattle and the Eastside, are often older and less formal. A good one can stand for decades. Either kind can be telling you something:

• Diagonal cracks, or cracks that look fresh against older weathered ones
• A wall that leans out or bows in the middle
• Weep holes that are clogged, or ones that run muddy
• Rockery stones that have rotated outward, or soil washing through the gaps
• New fill or bare soil at the top of a wall

Above a certain height, retaining walls generally need an engineer and a permit. The threshold varies by city, so ask before assuming an existing wall was built to code or that a new one will be simple.

Then the trees. A trunk that bends near the ground and then grows straight up can mean the surface soil has been creeping. Big firs and madronas do real work holding a bank together, and removing them changes how the slope drains.

Inside the house, doors that stick, cracks at the corners of window and door openings, a sloping floor or a cracked garage slab aren’t proof of anything on their own. Point them out to your inspector anyway.

When to bring in a geotechnical engineer

A general home inspector will note drainage and wall conditions, but judging whether a slope is stable is a different profession. A geotechnical engineer looks at the soils, the grade, the walls and the water, then tells you what they think is happening and what it might take to address it.

For a purchase, that usually starts with a site visit and a short letter. Booked quickly, it can often happen within an inspection period. A full report with soil borings is a bigger undertaking and rarely fits inside that window, which is why it helps to find out early whether the seller already has one. Many hillside houses were built or remodeled with a geotechnical report, SDCI or the city’s permit records may hold a copy, and the engineer who wrote it may be willing to take a fresh look.

I’d want one involved when the lot is mapped as a critical area, when any wall stands taller than you do, when you see seeps or movement, when the seller has disclosed past slides or repairs, or when you plan to build. If you’re competing for the house and thinking about offering without an inspection contingency, the site visit belongs before the offer. The buying page covers inspections, pre-inspections and review periods in more detail.

How slope rules limit decks, additions and a future ADU

Many hillside houses were permitted under older rules. Today, a deck pushed out toward the view, an addition, a new garage cut into the bank, a taller retaining wall or a backyard cottage may need critical area review, usually backed by a geotechnical report, and a design that keeps its distance from the top or bottom of the slope. Some small projects qualify for exemptions. Others need a formal exception, and some simply aren’t allowed.

Repairing and maintaining what’s already there is generally more straightforward than expanding. That matters when you’re paying for a house partly because of what it could become.

If a backyard cottage is part of the plan, the slope is often the deciding factor more than the zoning. The ADU rules for Seattle and the Eastside open the door on most residential lots, but a mapped slope can close it on yours. Most cities will meet with you before you apply, and a short conversation with permit staff costs far less than a design you can’t build.

Insurance and disclosure questions to ask early

Standard homeowners policies generally exclude earth movement, and landslide damage usually falls under that exclusion. Earthquake coverage is a separate policy and may not respond to a slide that a quake didn’t cause. Ask your insurance agent what a policy on this particular house would and wouldn’t cover, and do it before your inspection period ends.

The seller’s disclosure statement asks about drainage, settling, slides and critical area designations. Read those answers against what you saw on your walk. If the seller mentions a repair, ask for the permit and any engineer’s letter. A wall rebuilt with a permit and an engineer’s sign-off is a very different thing from one patched on a weekend.

Hillside houses often sit on tall cripple walls on the downhill side, the part an earthquake retrofit braces. While you have people looking at the lot, check whether the older house is bolted to its foundation too.