What you ignore at the first site visit is what your client will hate you for after move-in.

We’ve reviewed hundreds of post-move-in surveys, and the message is brutally clear: grading and drainage issues top the list of homeowner frustrations year after year. It’s not trim, it’s not paint—it’s water. Water in garages. Water standing against foundations. Water pooling into backyards. And almost every time? The early warning signs were there on day one.

In this article, we’ll break down:

• The most common residential drainage systems (and when to use them)
• Drainage requirements across western Oregon and Washington
• Site conditions that should immediately trigger drainage planning

Let’s dive in.

Common Residential Drain Types (and When They’re Used)

Understanding drainage solutions is key to avoiding future problems. Here are the big players:

French Drain

• Purpose: Captures and redirects subsurface water away from vulnerable areas.
• How it Works: A perforated pipe is installed in a gravel-filled trench, usually wrapped in a fabric filter to prevent clogging. It collects groundwater and redirects it to a safe discharge point.
• Best Used: In soggy lawns, at the base of slopes, or behind retaining walls where water naturally accumulates below the surface.

Curtain Drain

• Purpose: Intercepts and redirects shallow groundwater before it reaches critical structures.
• How it Works: Similar to a French drain but installed higher and typically shallower. Acts like a “curtain” to shield the foundation or slope.
• Best Used: Along the uphill side of a home site where water migration from higher terrain could threaten structures.

Trench Drain

• Purpose: Collects and redirects surface water flowing across hard surfaces.
• How it Works: A linear channel with a surface grate collects runoff from driveways, patios, or sidewalks.
• Best Used: At the base of driveways, around pool decks, or at garage entries where surface water could enter living spaces.

Perimeter Drain

• Purpose: Protects the foundation from groundwater intrusion.
• How it Works: A subsurface system installed around the footing of a structure, draining water away to a sump, drywell, or daylight discharge.
• Best Used: Required around foundations, especially for basements or crawlspaces in wetter climates.

Rain Drain

• Purpose: Manages roof runoff from downspouts and moves it safely away from the building.
• How it Works: Downspouts tie into underground piping that conveys stormwater to a drywell, swale, curb outlet, or public system.
• Best Used: Required in most jurisdictions where uncontrolled discharge could cause erosion, foundation damage, or neighbor disputes.

Low Point Drain

• Purpose: Removes water from the lowest part of a foundation crawlspace.
• How it Works: Often tied to the rain drain system with a backflow prevention device to keep water moving one way only.
• Best Used: Required by building codes in crawlspaces to prevent water accumulation, especially in high water table areas.

Area Drain

• Purpose: Captures water that pools in localized low spots.
• How it Works: Surface grates connect to underground piping that routes water to an appropriate discharge.
• Best Used: In courtyards, side yards, or any spot where natural flow is insufficient.

Grading and Drainage Code Requirements (Oregon and Washington)

Across Western Oregon and Washington, certain drainage systems are consistently required for residential construction due to wet seasonal climates and stormwater regulations. These include:

• Rain Drains: Almost universally required to manage roof runoff by connecting downspouts to an approved discharge system. Typical in Lane County, Multnomah County, Clark County, and Cowlitz County.
• Perimeter Drains: Required around foundations that retain earth, especially for habitable basements or crawlspaces, to prevent water intrusion.
• Low Point Drains: Required for crawlspaces to ensure the lowest point can be drained, often connected to the rain drain system with a backflow preventer.

Each county or city may have specific engineering design standards or stormwater manuals that add additional requirements, but these three systems (rain drains, perimeter drains, and low point drains) are core expectations across the region.

Bottom Line: Proper planning for these drainage systems isn’t optional—it’s a codified part of responsible site development throughout Western Oregon and Washington.

Where Drainage Problems Start (and How to Spot Them)

Our review of hundreds of new construction homes shows the biggest pain points for drainage issues are:

• Reverse-slope driveways leading to garage flooding
• Water standing against the foundation after heavy rain
• Snowmelt lakes forming in flat backyards
• Neighbor runoff spilling into newly graded lots
• Low areas on flat sites trapping water permanently

These issues don’t appear magically after closing. They’re visible—or preventable—during the first site walk if you know what to look for.

When SiteFacts Flags Drainage Risk

When we evaluate a lot through SiteFacts, here are the scenarios that trigger early drainage planning:

• A home at the toe of a slope without clear runoff paths
• Retaining walls within 10 feet of the building footprint
• A driveway sloping toward the garage or house
• Jurisdiction requirements for low point drains and rain drain connections
• Evidence of seasonal water pooling on site

Ignoring these indicators means passing problems down the line—to your trades, your warranty department, and ultimately, your customer.

Conclusion: Control Water or Pay Later

Grading and drainage issues aren’t cosmetic. They’re structural. They’re emotional. They’re expensive.

And they’re preventable.

The best time to fix a water problem is at the first site evaluation—not after a call from a furious customer standing ankle-deep in their new backyard “lake.”

SiteFacts Reports are designed to surface these hidden risks early—before they cost you time, money, and reputation.

Ready to make smarter, drier decisions?

Visit www.sitefactsreport.com to learn more.