Build a House on Your Land: What to Check Before You Buy

You’ve found the land. You have a price, a closing date and a floor plan you love, and the plan for everything else is simple: buy it, then let a builder say what it takes.

When that’s the plan, the builder is the first person to look hard at the ground, and the money has already moved. Site costs and requirements can show up in the builder’s bid, or after closing, when it’s too late to walk away.

Before you buy land to build a house, start with five things on that parcel: what the zoning allows, whether overlay rules apply, how sewage will be handled, whether a legal road reaches it, and what the slope and ground require, including flood zone and wetlands. Each can change what you can build and what it costs, and each can be checked before you make an offer.

That list is a starting point, not the whole job. The details under it are local and they change from county to county. The examples below come from Oregon, Idaho and Washington on purpose. None of them is your rule. Together they show the kind of thing that can sit on a parcel without showing up in the listing.

Can I build any house I want on land I buy?

No. Owning a lot doesn’t give you the right to put any house on it, because zoning, overlay rules and setbacks decide what can go where.

Zoning is the city or county’s rule for what a piece of land can be used for. An overlay is a second set of rules laid over the zoning, along a river for example. A setback is the minimum distance a building has to sit from a property line or from something like a stream.

Deschutes County, Oregon, shows how an overlay works. Along designated rivers, streams and some roads, the county applies a Landscape Management overlay. Deschutes County Code 18.84.050 says a new structure that needs a building permit inside it also needs site plan approval from the county before construction. If the house won’t be visible from the river, the county’s extra design and setback standards for the overlay may not apply, but the same section keeps the site plan approval step. A listing may not mention any of that. If you’re looking at river frontage or land near it, ask the planning department whether the overlay touches the parcel. If it does, plan for a site plan approval before the building permit, and ask whether the house would be seen from the water, because that decides which design and setback standards apply.

Setbacks take buildable area out of a lot, and water can make them bigger. In Lane County, Oregon, Lane Code 16.290 requires buildings in the RR-2 rural residential zone to sit at least 50 feet from the ordinary high water line of a stream the county’s Rural Comprehensive Plan designates for protection. (The number after RR sets the minimum size for new lots.) The same section generally requires 20 feet from a public road right-of-way and 10 feet from other property lines. Some older lots under 1 acre have a 5 foot setback from side and rear lines instead, so ask the county which numbers apply to yours.

The ordinary high water line is the line on the bank that the stream reaches in a typical year’s high water, not a rare flood. The stream setback is the biggest of the three numbers. On a lot that looks generous on a map, a stream along one edge can take a strip of building area before you’ve drawn a single wall. Confirm with Lane County Land Management whether the stream on your parcel is designated, because different rules apply in a strip around Eugene and Springfield and alternatives can be allowed. The acreage on the listing and the area you can build on are two different numbers, and only the second one matters to your floor plan.

Farmland next door can do the same thing. In unincorporated Benton County, Washington, a house or pool on land zoned RL-5 (Rural Lands Five Acre) has to sit 150 feet from an adjacent orchard, hop field or vineyard of 10 acres or more, whether that’s one parcel or neighboring parcels under the same owner, under Benton County Code 11.11.090. The rule sits in the county’s rural zoning code, and a buyer looking at five acres beside a vineyard may not see it on the listing. Confirm the current standards with Benton County Community Development before you design anything, because the county is updating its zoning code.

What does it cost to build on land you buy?

It depends on what the parcel requires. One example: under Ordinance 2026-002, unincorporated Deschutes County, Oregon, has applied the wildfire hazard mitigation section of the Oregon Residential Specialty Code, known as R327, to new homes since April 1, 2026. The county’s R327 page lists exceptions, such as manufactured homes.

R327 changes how the house is built, so it belongs in your price before you buy. Inside a city, ask the city’s building department, because the standards apply there only where the city has adopted them. We walk through how R327 works, and who decides where it applies, in our post on Oregon’s repealed wildfire map.

There is no honest average cost for what a parcel adds, because the parcel sets the number. The rest of this post shows where the extra cost comes from: a stream setback that shrinks the building area, a septic approval with its own steps, an engineer’s report in Lane County, a permit just to dig in Kootenai County. Each one is tied to the address, not to the floor plan.

A builder’s bid reflects what has been checked. If nobody checks the parcel before you buy, the first full number may arrive after you own it.

Will the lot need a septic system, and what decides that?

A house with no sewer connection needs its own septic system. In unincorporated Canyon County, Idaho, a new home on its own septic system needs a preliminary septic approval before the county will accept the building permit application, according to the county’s building permit checklist. The approval comes from Southwest District Health, the public health district that serves Canyon County and five neighboring counties.

A septic system is a buried tank and drain field that treats your household wastewater on your own land. The county’s checklist accepts a city hookup approval instead of the septic approval, and it doesn’t ask for it when the lot is on community septic, a shared septic system that serves a subdivision. Before it issues a septic permit, the health district does an on-site evaluation, and the applicant arranges a backhoe to dig a ten-foot test hole while the evaluator is there, according to Southwest District Health. The health district’s page publishes no processing time, so ask for current scheduling before you set a closing or build date.

Public sewer can decide what you’re allowed to do with a parcel, not only what it costs. In Deschutes County’s Terrebonne Residential district, known as TeR, the minimum parcel size when land is divided depends on water and sewer. Under Deschutes County Code 18.66.020, with an approved water system but no public sewer, a duplex parcel needs at least 33,000 square feet and a single-family parcel 22,000. With approved water and sewer, a duplex parcel needs 10,000. Public sewer is a sewer system run by a city or district instead of a septic tank on each lot. The county code ties the parcel size to the sewer situation, which a listing may not spell out. If a duplex is part of your plan on an existing lot, ask Deschutes County Planning whether the lot qualifies before you make an offer.

For how septic systems work across the region and what land buyers should know before closing, read our guide to septic systems in the Pacific Northwest.

What do access and slope add?

Access decides whether you can legally and practically reach the building site, and slope affects how much ground work the site needs before anything gets built.

Access means a road you have a legal right to use, that someone maintains, and that actually reaches the lot. An easement is a recorded right to cross someone else’s land, and it’s the paper that makes many rural roads usable. A road that stops at your property line with no recorded right to use it is a problem to solve before closing. Ask who owns the road, whether an easement is recorded, who pays to maintain it, and what the county requires of a driveway or private road for a house.

Steep or unstable ground can put an engineer on the project before a builder lifts a tool. In Lane County, Oregon, the building department requires a geotechnical report for a new home on a site that the county’s Geotech Report Requirement Areas map shows as a hazard area. A geotechnical report is a licensed engineer’s study of the soil and slope under the house. The county describes the map’s hazard areas as liquefaction zones with slopes over 20 percent. Liquefaction is when soil loses its strength in a strong earthquake.

The map is one trigger for a geotechnical report, not the only one. A map check tells you before you buy whether your parcel falls inside a hazard area. A slope next to the foundation can also call for a report. The county’s page carries no revision date, so confirm the current rule with Lane County Building Safety. A report is a cost and a wait. You can plan for both if you know before you buy.

Look up the parcel on FEMA’s Flood Map Service Center. In Zone AE and similar zones, federal rules under 44 CFR 60.3 require a participating community to set a new home’s lowest floor at or above the base flood elevation, or BFE, the water height in a flood with a 1% annual chance. Local rules can be stricter.

SiteFacts’ advice is to have a licensed surveyor provide the elevation certificate, a form that records how high the building sits, and stake BFE on site, so you can see what you’re working with. Getting a house’s finished floor above BFE isn’t just a matter of bringing in dirt to build the house higher. In SiteFacts’ experience, many jurisdictions have stiff rules on importing fill into flood zones. Federal rules in 44 CFR 60.3(d)(3) and (c)(10) restrict fill in an adopted regulatory floodway and in some AE zones. Our flood zone building guide covers the surveyor, elevation certificate and fill steps in order.

Moving dirt can need its own permit. In unincorporated Kootenai County, Idaho, excavating for a house generally needs a site disturbance permit, which is the county’s permit for digging and grading, under the county’s land use code.

The code exempts grading, excavating and fill on a site that meets all three tests: less than 10% slope (a rise or drop of 10 feet over 100 feet of level distance), more than 500 feet from surface water, and less than one-third of the parcel disturbed. It separately exempts sites over the Rathdrum Prairie Aquifer, an underground water supply the code names, that are more than 500 feet from surface water. Surface water in this code can include wetlands and ditches, so the 500 foot test may be broader than it sounds. Even exempt work has to use erosion controls that keep sediment on the property. Slope is one of the tests in the first exemption, so a steeper lot can lose it. Confirm with Kootenai County Community Development how these rules apply to your parcel.

How do I know if a lot is buildable before I make an offer?

Whether a lot is buildable is decided locally, not by the listing. Before you make an offer, check five things with the city or county that issues the permit, and with the health district for septic: zoning, overlays, sewage, access, and slope and ground. Each can change what you can build and what it costs.

Check the five things on the parcel itself: zoning, overlays, sewage, access, and slope and ground. Get the answers before you make an offer.

Start by finding out which city or county would issue the building permit for the lot, because that office decides most of what’s in this post. Ask its planning department what the zoning is, whether any overlay touches the parcel, and what the setbacks are. Ask its building department what standards apply to a new house at that address. Ask the health district or county about septic, and the road authority about the road. Then look at the ground: slope, nearby water, whether the parcel sits in a flood zone or has wetlands on or near it, and whether the county’s maps flag the area.

Utilities need their own calls. SiteScore doesn’t check them, so ask the power and water providers directly what it takes to reach the lot.

Lot lines are a separate question. Setting the lines is a surveyor’s job. A SiteFacts Report pulls the survey records we can find and flags gaps: no survey on record, a survey more than 5 years old, or records that don’t match the assessor’s GIS or tax map boundaries (GIS is the county’s digital parcel map). A flagged gap tells you to hire a surveyor before you rely on the boundaries.

Can I have someone check the lot for me?

Yes. SiteFacts has completed 300+ reports across 140+ jurisdictions in 26 states, and the county examples in this post come out of that research.

Here’s how it works. You enter the lot’s address. SiteScore screens the Big 5: zoning with setbacks, floodplains, wetlands, access and slope. That is a different list from the five things above. It comes back in 2 business days. For the lot you’re serious about, a full SiteFacts Report typically returns in 7 to 10 business days. Screen with SiteScore before you make an offer, and order the full SiteFacts Report early in your contract’s investigation period, if it has one, so the answers come back before the deadline. On our website, SiteScore is $99 and a SiteFacts Report is $899. Neither one replaces your own calls to the utility providers, and neither replaces a surveyor.

We don’t cover every county, so confirm your parcel’s jurisdiction is covered before you order.

You can do a lot of this checking yourself, and the free Land Buyer’s Field Guide is built for that. It has a one-page checklist and 15 free checks to run from home, a decoder for 12 listing phrases like “utilities available” and “buildable,” five call scripts with the good answer and the red flag for each, four real cases, and a cost worksheet. It fits you if you’re about to make an offer and want your own answers in hand before the builder conversation starts.

Download the free Land Buyer’s Field Guide and work through it on the lot before you make an offer.