Downspouts and Your Foundation: Jacksonville’s Cheapest Fix
Walk around almost any Jacksonville house after a summer storm and look at the ground below each downspout. On a lot of them you will find a small crater, bare sand at the bottom, mulch pushed out in a fan, and a dark wet patch against the block. That crater is the beginning of the most expensive problem a gutter can cause, and it is fixable for the price of a few pieces of downspout.
What sand does that clay does not
Most of the country's foundation advice was written for clay. Clay swells when it is wet and shrinks when it dries, and a downspout soaking one corner of a slab causes it to lift and drop. Jacksonville is not clay. Duval County sits on sandy soils with, in the flatwoods neighborhoods, a hardpan layer a couple of feet down that slows drainage. Sand does not swell. It moves.
A downspout delivers a large share of the roof's water to one spot. On a 1,500-square-foot roof, a single 2x3 downspout can be carrying 300 gallons in a hard half-hour storm. That much water landing in the same square foot does two things. On the surface it scours, carrying sand and mulch away and cutting a channel. Below the surface it finds the path of least resistance, which is often the disturbed backfill along the edge of the slab or the stem wall, and it carries fine sand out with it as it goes. Over a few years the fill under the slab edge migrates, the slab corner has less bearing, and the crack shows up inside at the corner of a window.
On the older crawl-space homes in Riverside, Avondale, Springfield and Murray Hill the version is different but the cause is the same. Water dumped at the pier line runs under the house, the crawl space stays damp, and mildew and wood rot follow.
The rule: four feet, onto ground that slopes away
Every downspout should discharge at least four feet from the wall, onto a surface that will not erode and that slopes away from the house. Six feet is better on a flat lot. That is the whole rule. Getting there is a matter of picking the right hardware for the spot.
The options, cheapest first
Rigid extension. A length of downspout on an elbow, laid on the ground, ending on turf. $25–$50 installed. The mower has to go around it and people trip on it, which is why so many end up in the garage.
Hinged extension. Same thing on a hinge so it flips up for mowing. $40–$80. The one we install most.
Splash block. A concrete or plastic trough under the outlet that spreads the water. Fine on a bed that is mulched to hold and slopes away; useless on bare sand, which just washes out around it. $15–$30.
Buried drain to a pop-up emitter. Solid PVC pipe from the downspout, buried a few inches, running 10 to 20 feet to a pop-up that opens under pressure in the yard. $200–$500 per downspout. The right answer on flat lots, on the driveway side, and anywhere an extension would cross a walkway. Do not let anyone use corrugated black pipe for this; it clogs with sand and roots and cannot be cleaned.
Rain barrel. Good for the garden, but a barrel fills in the first five minutes of a Jacksonville storm and then overflows at the base, so it needs its own overflow extension. Not a drainage solution on its own.
Where not to point it
- At a neighbor's lot. In the tighter Southside and Beaches subdivisions the property line is eight feet away, and the water becomes their problem and then yours.
- Onto a walkway or driveway, where it grows algae and ends up in the street.
- Into a screened pool enclosure or against a lanai footing.
- Into a low spot that already holds water after storms; a buried line to the swale at the street is the better route.
- Into the sanitary sewer cleanout. JEA does not allow it and it backs up the house.
Signs it has already been happening
- A crater or channel under the outlet
- Sand splashed a foot up the block or siding
- Pavers or a walkway settling on the house side
- A gap under the stem wall you can push a stick into
- A hairline crack at the corner of a window or door on that side
- A crawl space that smells damp for days after rain
If you see the last three, get a foundation contractor to look, and get the downspout fixed the same week, because nothing they do will hold if the water keeps coming.
What we do on every job
Extensions go on every downspout we touch, on repairs and installs alike. On a first-time install on a house that never had gutters, the downspout layout is the first thing we draw, because on sand the question is not just catching the water but where it can go without cutting a new gully. That planning is described on the first-time gutter installation page. Extensions and buried drains are priced as line items on the cost page, and if you only need the outlets fixed, that is a gutter repair visit, usually $150–$300 for a whole house.
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