How Failing Gutters Damage an Arizona Foundation

Homeowners in wetter parts of the country worry about gutters because it rains constantly. In Phoenix the risk profile is different, and in some ways worse, because the soil here doesn’t behave the way most drainage advice assumes.

Caliche doesn’t drain

Much of the Valley sits over a caliche hardpan, a cemented calcium carbonate layer that water simply won’t move through at any useful rate. When water pools next to your slab, it doesn’t percolate down and away. It sits. And it moves laterally, along the path of least resistance, which is often the backfill around your foundation.

The soil above it does move

The upper soil layer expands when it takes on water and contracts hard when it dries out, and in Phoenix it dries out fast and completely. That cycle, repeated at one corner of the house where a downspout dumps, is what produces differential settling. Not the whole house moving, one part of it moving.

The symptoms don’t look like water damage

Stair-step cracking in stucco. A door that binds in September but not March. Hairline cracks radiating from window corners. Homeowners attribute these to heat and settling. Frequently the actual cause is a downspout discharging two feet from the slab.

Downspout placement matters more than gutter condition

A gutter in perfect shape that dumps its entire roof plane next to the foundation is doing damage. Extensions should carry water at minimum four to six feet out, further on a two-story, and the grade should fall away from the house.

Irrigation compounds it

Most Valley homes have drip or spray irrigation running near the foundation on a schedule. Add storm overflow to already-saturated soil and you get the worst version of the cycle.

The damage is slow and then sudden

Foundation movement doesn’t announce itself in one storm. It accumulates over five or ten monsoon seasons, and by the time it’s visible the repair is structural, not cosmetic.

Prevention is cheap by comparison

Clear gutters, correct pitch, adequate capacity, and downspouts that discharge well away from the slab. That’s the whole list. Against the cost of foundation work, it isn’t close.