Red Clay and Drainage Around Triangle Homes

Anyone who has dug a planting hole in the Triangle knows the soil: dense, sticky, and often bright red or orange a few inches down. That clay is a big reason water management matters so much for Triangle houses. Clay holds water near the surface, sheds rain quickly when it's saturated, and in some parts of the region swells when wet and shrinks when dry. A few inexpensive habits protect foundations, crawl spaces and slabs.

Two kinds of clay trouble

Slow drainage everywhere. Much of the Piedmont around Raleigh, Cary and Chapel Hill weathered into red clay subsoils that let water through slowly. Water that reaches the foundation tends to stay there, feeding damp crawl spaces and pressure on basement walls.

Shrink-swell in the Triassic Basin. Durham County lies in a Triassic rift basin that extends from southern Granville County southwest to northern Moore County. The Durham County Extension Master Gardeners explain that most of the county is underlain by White Store series soils, whose dominant clay mineral, smectite, gives them poor drainage and a high shrink-swell potential. As those soils wet and dry seasonally, they can move foundations, crack slabs and stick doors.

Either way, the fix starts with the same thing: keep water away from the house and keep soil moisture near the foundation as steady as you reasonably can.

Gutters and downspouts

• Clean gutters at least in spring, after pollen and seed drop, and in late fall after leaves. Pine needles clog downspouts quickly.
• Extend downspouts several feet from the foundation, onto splash blocks, into extensions, or into buried pipe that daylights downhill.
• Check buried drains. Downspouts tied into underground pipes can clog or crush. Run a hose into each one and see whether water comes out the other end.
• Size matters. Summer thunderstorms dump a lot of water fast. Larger gutters and downspouts help on big roof areas.

Grading

Soil next to the house should slope away from it. Over time, settling, mulch and landscaping often reverse the slope.

• Rebuild the grade with soil (not mulch) so water runs away.
• Keep mulch and soil a few inches below siding and weep screeds.
• Don't let beds become bowls that trap water against the foundation.
• On sloping lots, a shallow swale above the house can intercept water before it reaches the wall.

Plantings and irrigation

• Keep irrigation heads aimed away from the foundation.
• Avoid planting thirsty trees and large shrubs right against the house; roots and uneven watering add to soil moisture swings.
• On shrink-swell soils, very dry summers can shrink soil away from foundations. Avoid big contrasts between soaked beds and bone-dry soil around the house.

Warning signs to watch

• stair-step cracks in brick or block;
• cracks wider at one end than the other;
• doors and windows that start sticking or won't latch;
• gaps between trim and walls, or floors that start to slope;
• water in the crawl space after storms.

Small, stable hairline cracks are common. Cracks that grow, or several symptoms at once, call for a structural engineer before a repair contractor. An engineer works for you, not for a product.

A once-a-year drainage walk

Pick a heavy rain, put on a raincoat and walk around the house while it's pouring. It's the fastest way to find problems:

• Are any gutters overflowing, especially at inside corners and valleys?
• Is water coming out of every downspout extension, or backing up?
• Where does water pond in the yard, and how close is it to the house?
• Is water running toward the foundation from a driveway, patio or neighbor's yard?
• Are window wells or crawl-space vents taking on water?

Take photos. A drainage contractor or landscaper can work from them, and you'll know whether a fix worked after the next storm.

Before you dig

Regrading, drains and new beds can hit buried utility lines. Call NC 811 before digging so lines are marked.

Building on clay

If you're planning an addition, ask whether the soil warrants a geotechnical evaluation and engineered footings, especially in Durham. See Durham additions and our home additions guide. For crawl-space moisture, see our crawl space guide, and for local context, the Durham page.