Why New Construction in Union County Floods
There is a particular call we get more than any other, and it goes like this: the house is four years old, it is well built, nothing is obviously wrong with it, and there is water against the foundation every time it rains hard. The owner assumes they have been unlucky or badly built. Usually neither is true. What has happened is a sequence that is entirely normal and entirely predictable.
What happens to a lot before you ever see it
Building a house on a Piedmont lot involves stripping the topsoil, running tracked machinery across the subsoil for months, digging a hole for the foundation, and then putting the spoil back around it. Every one of those steps changes how the ground handles water.
The subsoil gets compacted
Clay that has had a loaded machine driven over it repeatedly does not behave like clay in a field. Its ability to take water in drops sharply, and it does not recover on its own in any timeframe you care about. The lawn goes on top and looks fine. The ground underneath is closer to a paved surface than to soil.
The backfill settles
The soil put back around a foundation is loose and it consolidates over the following years. As it settles, the ground that was graded away from the house at handover quietly becomes level, and then quietly becomes a channel running back toward the wall. Nobody does anything wrong. Physics does it.
This is why the problem so often appears in year three or four rather than year one, and why the settlement ring around the foundation is one of the most reliable things to look for.
The finish grade was set for the day it was inspected
Residential building code requires the ground to fall a minimum of six inches within the first ten feet away from the foundation — that is a five percent slope — and requires paving within ten feet to fall at least two percent. Where lot lines or slopes make that impossible, the code requires drains or swales to carry water away instead.
A new house meets that on the day it is checked. Then beds get built up, mulch is added every spring and never removed, an irrigation trench is backfilled loose, somebody installs a patio. Six years of small decisions, none of them unreasonable, and the grade is gone.
The impervious area went up and the outlet did not
Roof, driveway, walks, patio. All of it sheds water instead of absorbing it, all of it arrives somewhere, and on a tight lot there is often nowhere for it to go that is not the neighbour or the low corner.
What to check on a house between three and eight years old
Grade, all the way round. Four-foot level and a tape. Six inches of drop in the first ten feet. Flat is a problem; sloping back toward the house is a bigger one.
A settlement trench or ring following the foundation line. That is the backfill consolidating.
Mulch and bed height against the siding. Beds should sit below the siding line and below any weep holes.
Where every downspout actually lets go. If it discharges within a few feet of the wall, that is 300-odd gallons per downspout in a one-inch rain landing on the settled backfill.
Whether the builder's swale is still there. Many lots were handed over with a shallow swale along a side or rear boundary. Several years of mowing, mulching and a new fence line and it is frequently gone.
The order to fix things in
This matters more than which fix you choose. Water leaves the roof and follows a path: gutter, downspout, discharge point, grade, route away, outlet. Each stage protects the next. Regrading the first ten feet while a downspout still dumps at the corner achieves very little, and people do it constantly.
Get the roof water away from the house first. Cheapest, fastest, biggest effect.
Restore the grade second.
Only then consider excavation.
The Outside-the-House Water Calendar lays that whole sequence out with a twelve-month schedule attached, and it is written for exactly this house.
One thing worth saying about builders
Very little of this is a defect in the ordinary sense. Compaction is unavoidable when you build. Backfill settles. Codes are written around the condition at completion. If you are inside a warranty period it is absolutely worth asking the question, but the honest expectation is that this is now a maintenance matter rather than a claim, and the sooner it is treated as one the cheaper it stays.
If this is your yard
Newer house, water against the foundation, nothing obviously wrong — that is the most common thing we look at. We work in Waxhaw, Weddington, Marvin, Wesley Chapel, Indian Trail, Matthews, Monroe, Mint Hill, Stallings and south Charlotte. Call 980-280-7638 or use the drainage page to ask for a look.
Every guide we have written is sorted by symptom on the Start Here page.
Who wrote this. Alex Purdy owns Carolina Terrain LLC in Waxhaw and holds North Carolina Landscape Contractor Licence CL.1872, the NCSU Stormwater Control Measure Inspection and Maintenance Certification (#5970), and NDS Certified Drainage Contractor status. He is not a Professional Engineer and not a Registered Landscape Architect. Nothing here is an engineered design, a legal opinion, or a substitute for either.
Sources
IRC R401.3, Drainage — grade falls a minimum of 6 inches within the first 10 feet; impervious surfaces within 10 feet fall at least 2 percent; drains or swales required where lot lines or slopes prohibit it
Roof runoff arithmetic — 0.623 gallons per square foot per inch of rain; a 2,000 sq ft roof sheds about 1,247 gallons in a one-inch storm
Rules and published figures change. Everything here was checked when this was written. Before you rely on any of it for a permit, a purchase or a build, confirm it with the agency that issues it.
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