The "High Pour" Trap: Why Concrete Against Vents is a Major Defect

The Dilemma

A homeowner recently asked:

My contractor poured a new concrete path that nearly covers my foundation vents, but he says it's common and not an issue. Is this a defect?

The GardenOwl Diagnosis

The Scenario

You hire a contractor to pour a simple concrete path. You come home to find the fresh slab looks great, except for one nagging detail: it is sitting incredibly high against the wall, almost covering your foundation vents. When you ask the contractor, he waves a hand and says, "Don't worry, that's common practice. The slope handles the water".

Do not write that check.

This is a textbook case of The Occluded Cavity Syndrome. While your contractor might be good at smoothing cement, he has just committed a cardinal sin of building physics: he has bridged the Damp Proof Course (DPC).

The Trap: The "Hard Sponge" Effect

The most dangerous myth in hardscaping is that concrete is waterproof. It isn't. Concrete is essentially a hard sponge. It absorbs moisture from the ground and holds it.

When a wet slab is poured directly against your masonry wall above the DPC line (the waterproof barrier built into your house), you create a highway for moisture. Through a process called capillary action, water wicks from the wet concrete directly into your dry wall structure. This leads to rising damp, salt damp, and eventually, peeling plaster and mold inside your living room.

Furthermore, those vents are the "lungs" of your home. They are designed to create cross-ventilation under your subfloor to keep your timber joists dry. By blocking them, you are creating a stagnant, humid incubator for rot. And if you live in a termite-prone area, this setup is catastrophic. You have obscured the inspection zone, effectively rolling out the red carpet for termites to enter your framing undetected.

The Solution: The Strategic Air Gap

If the concrete is already dry, you don't necessarily need to jackhammer the whole thing up, but you absolutely cannot leave it touching the house. You need to create a Mechanical Isolation Zone.

1. The Saw Cut (The "Moat")

Since the grade is already too high, we need to physically separate the materials. Have the contractor use a concrete saw to cut a strip—typically 4 to 6 inches wide—parallel to the foundation wall. Remove this strip of concrete entirely.

2. Excavate and Expose

Once the concrete strip is removed, dig out the soil in that gap. You need to go deep enough to expose the bottom of the air vents and, ideally, see the DPC line on your bricks. The goal is to ensure that rain splashing off the concrete hits this trench, not your vents.

3. The Drainage Backfill

Do not fill this gap with mulch! As we discuss in our guide on Rotten Siding and Low Slabs, organic material against a house is a recipe for disaster. Instead, line the trench with a permeable landscape fabric and fill it with clean, washed 1-inch river rock or crushed granite. This acts as a splash guard and ensures rapid drainage.

4. Check the Lawn Grade

If your concrete is this high, your lawn might be too. Ensure the grass slopes away from the new concrete edge. You never want your lawn higher than your hardscape, or you risk the Accretion Dam Syndrome where turf traps water on the patio.

The Diagnostic and Visualizing Safety Net

Hardscape mistakes like this are incredibly expensive to fix once the cement truck leaves. This is why planning is non-negotiable. GardenDream acts as your project safety net. By uploading a photo of your site before you start, our AI scans for constraints—like vent heights, weep screeds, and drainage patterns—that a casual contractor might ignore.

It allows you to visualize where the hardscape should stop and helps you spot these "constructibility" issues before a single bag of cement is mixed. Upload a photo to our Exterior Design App to verify your layout and protect your home's envelope.