Plain-English Glossary

Every term the county (or your pros) will throw at you, in two sentences or less — and why it matters for your permit.

Jump to: Feasibility · APN · Zoning · Setback · Perc test · Septic · Wells · Survey · Easement · Critical areas · Site plan · Occupancy

Feasibility#

The homework you do before committing to build: can this land legally and physically hold a house, and what will it cost to find out? It usually means a handful of studies — soil, septic, water, survey — done before you pour a dollar into construction.

Why the county cares: the county won't issue a building permit until the feasibility questions (water, septic, soil, access) have documented answers.

APN / Parcel Number#

The unique ID number the county assessor assigns to your piece of land — like a license plate for a parcel. You'll find it on your tax statement, your deed paperwork, or by clicking your land on our parcel map.

Why the county cares: every county form starts with the APN; it's how they pull up your land's zoning, taxes, and history.

Zoning#

The county's rulebook for what each area of land can be used for — houses, farms, shops — and how big or dense it can be. A code like "R-5" or "RR-2.5" usually means residential, with the number hinting at minimum lot size in acres.

Why the county cares: zoning decides whether a house is allowed on your parcel at all, before any other question is asked.

Setback#

The minimum distance your house (or septic, or well) must stay from property lines, roads, streams, and other structures. Think of it as an invisible "no-build" strip around the edges of your land.

Why the county cares: your site plan must show setback distances, and a house drawn too close to a line gets the application sent back.

Geotechnical study#

A licensed engineer digs test pits or borings to learn what your soil is made of and how much weight it can safely carry. The report tells your builder what kind of foundation the ground needs.

Why the county cares: on steep, soft, or hazard-mapped ground, the county requires this report before it will approve your foundation design.

Perc test (percolation)#

A test where holes are dug and filled with water to time how fast the soil drinks it — that's "percolation." It tells you whether your land can absorb wastewater from a septic system, and how big the system must be.

Why the county cares: no acceptable perc result usually means no septic approval, and without septic (or sewer) there's no building permit.

Septic system / OSS#

Your own private sewage treatment setup — a buried tank plus a drain field — used where there's no public sewer line. Counties call it an OSS: "on-site sewage system."

Why the county cares: the health department must approve a septic design (or confirm sewer access) before the building department will touch your permit.

Drain field#

The network of buried, perforated pipes that spreads treated water from your septic tank into the soil. It needs a patch of good soil, plus a reserve area saved in case the first field ever fails.

Why the county cares: the drain field and its reserve area must appear on your site plan, and nothing — driveway, shed, well — may be built on top of them.

Well log#

The official record a driller files with the state when a well is drilled: how deep it goes, what soil and rock it passed through, and how much water it produces. Existing well logs are public — you can look up wells near your parcel before drilling your own.

Why the county cares: it's your proof that the parcel has (or can get) drinkable water, which the county requires before approving a house.

GPM (gallons per minute)#

How fast a well produces water. A typical house needs somewhere in the low single digits sustained — many counties want to see proof of a minimum flow before signing off.

Why the county cares: a well that can't sustain the county's minimum GPM may need a storage tank system, or may not support a permit at all.

Land survey#

A licensed surveyor locates and marks your true property corners and boundaries — which are often not where the fence is. The result is a stamped map you and the county can rely on.

Why the county cares: setbacks are measured from surveyed lines, so an accurate survey is what proves your house sits where your site plan says it does.

Legal description#

The formal written definition of exactly what land you own, using townships, ranges, sections, or plat references instead of a street address. It's on your deed, and it's often a paragraph of dense text.

Why the county cares: permit applications ask for it word-for-word from the deed — a street address isn't legally precise enough.

Easement#

A legal right someone else holds over part of your land — a neighbor's driveway across your corner, a utility line, an access road. You still own the land, but you can't build on or block the easement.

Why the county cares: easements must show on your site plan, and a house or septic placed inside one won't be approved.

AFN (Auditor's File Number)#

The stamp-number the county auditor puts on every recorded document — deeds, easements, surveys — when it's filed. It's how you (or a title company) look up the exact document later.

Why the county cares: when a permit form asks about your deed, easement, or recorded survey, the AFN is how the county verifies it exists.

Legal lot of record#

Proof that your parcel was created legally — through a proper plat, subdivision, or an old-enough deed — and not by someone informally splitting land. Not every parcel with its own tax number qualifies.

Why the county cares: counties only issue building permits on legal lots; an illegally created parcel may be unbuildable until it's fixed.

Impervious surface#

Any surface rain can't soak through: roofs, driveways, patios, compacted gravel. More impervious surface means more runoff heading somewhere else.

Why the county cares: permit forms ask for your total impervious square footage, and crossing a threshold can trigger stormwater drainage requirements.

Critical areas#

Environmentally sensitive spots the state requires counties to protect: wetlands, streams, steep slopes, flood zones, aquifer recharge areas, and wildlife habitat. If one touches your parcel, extra rules and buffers apply.

Why the county cares: most applications include a critical areas checklist, and a "yes" answer usually means an extra study before approval.

Wetland delineation#

A specialist walks your land and flags the exact edge of any wetland, based on plants, soil, and water signs. Maps only estimate wetlands — delineation is the ground truth.

Why the county cares: building too close to a wetland violates buffer rules, so the county wants the real boundary on paper before approving your site plan.

Shoreline jurisdiction / OHWM#

Land within 200 feet of larger lakes, rivers, and marine water falls under Washington's Shoreline Management Act — a whole extra layer of permitting. The OHWM ("ordinary high water mark") is the line on the bank where the water ordinarily reaches, and the 200 feet is measured from it.

Why the county cares: building inside shoreline jurisdiction usually requires a separate shoreline permit on top of your building permit.

Floodplain#

An area FEMA maps as likely to flood in a big storm year — you'll see labels like "Zone AE" (high risk) or "Zone X" (minimal). Being in one doesn't forbid building, but it changes how and how high you build.

Why the county cares: in a mapped flood zone the county requires a floodplain development permit and often an elevated foundation, and your lender will require flood insurance.

Geologic hazard area#

Ground mapped as prone to landslides, erosion, earthquakes liquefying the soil, or (in some counties) volcanic hazards. Steep slopes are the most common trigger for a residential lot.

Why the county cares: a mapped hazard usually means the county requires a geotechnical study before it will approve your foundation.

Site plan#

A bird's-eye drawing of your parcel showing where everything goes: house, well, septic, driveway, property lines, and the distances between them. It doesn't have to be fancy, but it does have to be accurate and to scale.

Why the county cares: it's the single most-required attachment on a building permit — reviewers check every setback and separation distance against it.

Vicinity map#

A small zoomed-out map showing how to find your parcel from the nearest main roads. Often just an inset box in the corner of your site plan.

Why the county cares: inspectors use it to physically find your land — rural parcels often have no visible address.

Building footprint#

The outline of ground your house actually covers, measured in square feet — the shape it would stamp in the snow. A two-story 2,400 sq ft house might have only a 1,200 sq ft footprint.

Why the county cares: footprint (not total living space) is what's checked against lot coverage limits and drawn on your site plan.

Construction valuation#

The estimated total value of the work you're permitting — labor and materials, even if you do the labor yourself. Counties often calculate it from a standard per-square-foot table rather than your actual contract.

Why the county cares: your permit fee is calculated from this number, so the county checks it against their own valuation tables.

Certificate of Occupancy#

The final document the county issues after your last inspection passes, saying the house is legally safe to live in. It's the finish line of the whole permit process.

Why the county cares: moving in before it's issued is a code violation, and lenders and insurers typically require it.

Letter of availability#

A short letter from a water district, sewer district, or power utility confirming they can serve your parcel. You request it from the utility, usually for a small fee.

Why the county cares: if you're not drilling a well or installing septic, this letter is the county's proof that water or sewer actually reaches your land.

RCW#

The Revised Code of Washington — the state's book of laws. When a county form cites something like "RCW 58.17," it's pointing at the state law behind that requirement.

Why the county cares: counties must enforce state law, so RCW citations on your paperwork are the "because the state says so" behind local rules.