Gutters, Grading, and Drainage Moisture in Portland, OR: Moving Rain Away From the House

How much water the roof sends down

The arithmetic is simple. A square foot of roof receiving one inch of rain collects one-twelfth of a cubic foot of water, and a cubic foot holds about 7.48 gallons. That is about 0.623 gallons per square foot per inch. A roof with 1,000 square feet of footprint therefore delivers about 623 gallons for each inch of rain, before any losses to evaporation or splash.

NOAA's 1991 to 2020 normals for Portland International Airport give 36.92 inches of precipitation a year, with 27.32 inches, 74 percent, falling from October through March. Multiplying, a 1,000-square-foot roof footprint sees something like 23,000 gallons a year, most of it in the cool months. A 2,000-square-foot footprint sees about twice that. The number is an upper bound for planning: it ignores losses and measures the roof by its footprint on the ground, not its pitched surface.

All of this water has to go somewhere. If gutters and downspouts carry it away from the house and the ground slopes away, it is a lawn problem. If the gutters overflow, the downspouts end at the foundation, or the ground slopes toward the wall, it becomes a crawl space, basement, or wall problem. The U.S. Department of Energy's crawlspace guide begins its list of exterior moisture sources with roof drainage and grading around the house.

Signs that water is reaching the foundation

Most of these can be seen from outside during or right after rain.

• Water running over the gutter edge, or a gutter that is full of debris or sagging.
• A downspout that ends at the wall or empties onto a path that slopes toward the house.
• Staining, algae, or erosion at the base of a wall below a downspout or a valley.
• Soil, bark mulch, or landscaping built up against siding or the foundation. Portland's downspout page warns that adding bark mulch or changes in landscaping can trap water against building foundations.
• Standing water or soft ground near the house a day after rain.
• Efflorescence (white mineral deposits) on the foundation or basement wall.
• A basement or crawl space that is wet after storms but dry in summer.
• A window well that fills with water or leaks.

Gutters and downspouts

A gutter is only as good as its downspout. The U.S. Department of Energy's crawlspace guide says to inspect the roof's bulk water discharge strategy, including all gutters and downspouts, so that runoff does not collect next to or near the foundation. It adds that downspouts should discharge directly into drains directed to a storm sewer system, retention pond, a daylighted outlet if the topography permits, or yard bubblers that are a minimum of 10 feet away from the foundation.

Maintenance is the usual issue. Leaves and needles clog gutters, the water overflows at the edge, and it falls beside the foundation. Oregon State University Extension's mold checklist says the same: keep rain gutters free of debris and in good repair and make sure drainage directs water away from or around the house. Cleaning twice a year, once after the leaves fall and once before the wet season builds, is a common routine. Gutters that pull away from the fascia, joints that drip, and downspouts that detach in wind are repairs, not cleaning.

Ask where each downspout ends, and walk the line to check that it does not simply drain into a flower bed against the foundation.

Grading, mulch, and the ground next to the house

The ground within about 10 feet of the house matters most. The Department of Energy guide says that ideally the ground slopes a minimum of 5 percent away from the foundation walls for at least the first 10 feet to direct groundwater away from the structure. That is a drop of about 6 inches over 10 feet. If proper slope cannot be established because of the home's elevation and surrounding grade, the guide says a surface drainage system, which it calls a grade gutter, should be installed to collect water and divert it away from the foundation.

Other details follow the same logic. The guide says sprinklers near the foundation must be positioned so they do not subject the foundation or its immediate vicinity to water, and that foundation vents and the access door should be high enough off the grade to keep runoff out. Soil built up above the sill, a patio that slopes toward the wall, and planting beds that hold water all work against the slope. Before any digging, the guide says to identify underground utilities and notify the respective utility companies as required. In Oregon, the Oregon Utility Notification Center takes locate requests by phone at 811 or online, at no charge, and its FAQ says to contact it at least two full business days, and not more than ten, before excavation.

Portland's rules for roof water

The City of Portland's Bureau of Environmental Services has two programs that matter to homeowners. The first is downspout disconnection, which redirects roof runoff from the City's sewer and stormwater pipes onto your property, where it soaks into the ground. The City describes it as a retrofit option for existing buildings and says it helps prevent overflows and backups.

The City's page sets conditions. Do not disconnect downspouts on slopes greater than 10 percent. Do not direct runoff onto a septic system, drain field, or underground oil tank unless it has been decommissioned, or to an area within 10 feet of a retaining wall. Discharge at least 6 feet from a basement and at least 2 feet from a crawl space or slab foundation. The end of the downspout extension must be at least 5 feet from your neighbor's property line, at least 10 feet from structures on adjacent property, and at least 3 feet from the public sidewalk. The City also says disconnected downspouts should not allow roof runoff to drain or pool at the base of a building. These are the City's minimums for a disconnection. The Department of Energy guide asks for 10 feet where the site allows it, which is a reason to talk with a contractor about the right distance for a house with a damp crawl space or basement.

The second program is Clean River Rewards, which offers a discount on the stormwater charges of your bill for managing rain on your property so that it does not enter the City's sewer and stormwater pipes. The City says the discount may be up to 35 percent of the total stormwater fee, and that for rain gardens, swales, and similar landscaped areas the ground receiving the water must be at least 10 percent of the area of the roof and paved area. Program rules change, so check the City's current pages. For private property drainage questions the City lists Private Property Drainage Inquiries at the Bureau of Environmental Services.

Connecting a footing drain, sump, or yard drain to a City system is a different matter from disconnecting a downspout. Ask the Bureau of Environmental Services what applies to your property before you change one.

Footing drains, sump pumps, and window wells

A footing drain is a perforated pipe at the base of the foundation that collects groundwater and carries it away. A sump is a pit that collects drain water and a pump that lifts it out. A window well is a metal or plastic liner that holds soil away from a basement window and needs a drain at the bottom.

Where the water goes matters. The City of Portland's guidance on residential non-stormwater discharges lists uncontaminated foundation, footing, and crawlspace drainage as an allowed discharge, and gives Environmental Services pollution prevention at 503-823-5600 as the contact. That page is about water quality. It does not say which outlet a particular property may use, so confirm the right one with the City before installing or moving a sump discharge.

Failure points are predictable. A sump pump runs on electricity, and a power outage during a storm is when it matters most. Pump failure is also a water-category question: sump pump failures are listed among Category 2 sources in the NAU guideline that follows IICRC definitions. The categories and the drying steps are on the water damage page. If a storm brings groundwater or river water into the house, the flood page covers that.

Drains inside a crawl space are a different subject. The ground cover and the water-management plan for that space are on the crawl space page.

How a drainage problem is traced

The way to fix the water is to follow it from the roof to the soil.

1. 1

   Watch it rain

   The best inspection happens during or right after rain. Overflowing gutters, ponding, and downspouts that dump at the wall are visible then.

2. 2

   Walk the perimeter

   Look at each downspout, the ground slope, landscaping, patios, and window wells.

3. 3

   Check inside

   A moisture reading and humidity check in the basement or crawl space show whether the problem is bulk water, vapor from the soil, or both.

4. 4

   Prioritize

   Cheap fixes come first: clean gutters, add extensions, adjust splash blocks, regrade a few feet, clear window wells. Larger systems, such as footing drains and sumps, follow if the cheap fixes do not work.

5. 5

   Confirm

   After storms, check again. Moisture readings should drop; a hygrometer shows the trend.

6. 6

   Clean up what got wet

   Any mold in basements, crawl spaces, or walls is handled on the remediation page.

What affects the price of drainage work

A drainage quote follows how much digging is involved and what the water has to cross.

• Scope Gutter cleaning, downspout extensions, and regrading a flower bed are small. Footing drains and sumps are excavation projects.
• Access Tight side yards, retaining walls, patios, and landscaping increase labor.
• Distance to a discharge point A long run to daylight or a rain garden costs more than a short one.
• Soil and slope Heavy clay, high groundwater, and steep lots change the design.
• Permits and utilities Digging near utilities needs location services, and some work needs permits.
• Electrical A sump pump needs a circuit, and a battery backup is an add-on.
• Restoration Cleaning or replacing wet insulation and materials is a separate scope.

Insurance and ground water

Water that comes in through the ground is usually treated differently from water that falls through the roof, and flood is a separate coverage. Whether your policy covers a specific event is for your insurer to decide. The patterns and what to check are in Does Homeowners Insurance Cover Mold in Oregon?.

Questions to ask a drainage contractor

These help decide whether the proposal solves the water or covers it.

1. Where is the water coming from during a storm, and how did you check?
2. Do the downspouts discharge at least 10 feet from the house, and where does the water go after that?
3. Will the grading slope at least 5 percent for the first 10 feet?
4. If you recommend a sump or footing drain, where does the discharge go, and is that allowed on my property?
5. Is a battery backup included for the pump?
6. Which parts of this can be done in stages?
7. Who repairs landscaping and who handles permits?

Frequently asked questions

Sources

• U.S. DOE Building America, Guide to Closing and Conditioning Ventilated Crawlspaces (sections 2.2.1 to 2.2.6)
• City of Portland, What Is Downspout Disconnection?
• City of Portland, Clean River Rewards
• City of Portland, Non-stormwater Discharges from Residential Properties
• Oregon Utility Notification Center, FAQ
• NOAA NCEI, U.S. Climate Normals 1991 to 2020, Portland International Airport
• Oregon State University Extension, Mold control: Home inspection checklist
• Northern Arizona University, Water Damage Restoration Guideline (adopts IICRC category definitions)

Spotted something out of date? Email info@moldremovalpdx.com and we will check it.