Capillary Rise and Why Walls Keep Soaking

Fact: Water can rise through building materials at a rate of up to one inch per hour through capillary action, even without visible flooding.

Water doesn’t need gravity to move downward. Sometimes, it goes up. Capillary rise is the hidden enemy in water-damaged homes—drawing moisture up into walls, framing, and materials long after the original water is gone. Most homeowners and even inexperienced contractors overlook this, assuming that once the floor is dry, the job is done. But the science of capillary action says otherwise. Water moves through porous materials like concrete, drywall, insulation, and wood, climbing vertically through narrow paths created by material density. It’s silent, slow, and destructive.

After a flood damage event, the focus often lands on standing water, soaked flooring, and surface drying. But what happens next is almost invisible. That water, though no longer pooling, is being pulled upward. The tighter the material, the stronger the pull. Wood framing, drywall, and concrete slab edges all act like vertical wicks. And because the moisture creeps slowly, it spreads widely before signs begin to show. Paint starts to bubble, drywall feels soft, and discoloration appears several inches above the original flood line.

A homeowner in Colorado Springs learned this the hard way. After a flood damage cleanup, her team dried the floor but didn’t check beyond the baseboards. A month later, paint began to peel two feet up the wall. Testing showed elevated moisture in the drywall and vertical studs. What was missed? Capillary rise. Moisture had slowly climbed behind the walls, settling in insulation and spreading mold along the framing. The home needed partial demolition, re-drying, and full wall replacement. All of it preventable if the original restoration team had considered capillary behavior.

Capillary rise is strongest in the first 24 to 72 hours after water exposure. During this period, any moisture remaining in the floor or subfloor is drawn upward by materials above it. This includes bottom plates, studs, insulation, and gypsum board. Once the water reaches interior wall structures, it stagnates, and drying becomes extremely difficult without removing the wall or introducing specialized equipment. A simple water pipe break or clogged drain overflow can become a major problem if this invisible movement goes unchecked.

Capillary movement can even bypass barriers. A bathroom sink overflow or kitchen sink overflow, though minor in appearance, can drive water into the base of cabinetry, which then draws that moisture into adjacent walls. The cabinetry itself may dry, but the framing inside the wall continues to wick water upward, often beyond the scope of basic thermal imaging. If left untreated, this turns into slow decay that damages wood integrity and leads to structural restoration needs later.

Capillary action also plays a major role in post-disaster scenarios like storm and wind damage cleanup or roof leaks. When water enters wall cavities from above, it begins to saturate material downward due to gravity. But once it pools near the base of a wall, the moisture reverses direction, climbing back up through internal materials. This moisture migration creates conflicting readings for untrained technicians. They assume the wettest part is near the floor, but in reality, moisture levels spike higher along studs and insulation due to upward movement.

Another concern is flooring. Materials like laminate or engineered wood installed over concrete slabs are especially vulnerable. After a broken water pipe repair, moisture might seem to have dried on the surface. However, the slab below may remain saturated. That moisture begins to rise through the flooring materials due to capillary force. Homeowners are often shocked when floors begin to warp or cup weeks after restoration, despite no new leaks. The water was always there—it was just moving upward.

Even the edges of concrete slabs in basements or crawlspaces can pull moisture upward after water line break events. Concrete, while solid, is highly porous. It acts like a giant sponge. Once water is introduced—especially during a main water line break or emergency water restoration—it doesn’t just sit. It seeps in, then rises. If not treated with vapor barriers or allowed to fully dry, that moisture continues to push into wood framing, drywall, and insulation for days. By then, the visible damage is gone, but hidden damage is just starting.

Capillary rise is particularly dangerous in homes with dense wall insulation or tight building envelopes. These energy-efficient homes are designed to keep heat in and airflow out. But that also means once moisture enters, it gets trapped. If the insulation type—say, cellulose or fiberglass—has already absorbed water from an appliance leak cleanup, it now becomes a vehicle for moisture to rise into upper walls and framing. Since it’s enclosed, the drying process is slowed, and the damage worsens before it’s even detected.

Let’s say you’ve had a plumbing overflow cleanup in a second-story bathroom. Water enters the subfloor, runs to wall cavities, and collects at the base of the interior structure. Within hours, that same water starts to wick upward through vertical studs. It reaches two to three feet high in just a day or two, saturating everything along the way. You dry the floor. You replace the drywall. But unless you cut high enough and checked thoroughly, you’ve likely left behind soaked framing. That’s where smoke damage cleanup or even future fire damage cleanup issues begin—because decaying wood and trapped moisture make perfect conditions for electrical failure or combustibility.

Capillary rise doesn’t stop because you closed the job file. If you’re not seeing upward water spread after a toilet overflow cleanup or shower and tub overflow, it’s likely because you’re not looking close enough. And because capillary action often affects wall studs or sill plates inside sealed wall cavities, detection tools like hygrometers and infrared thermography are essential. Without them, restoration becomes a gamble—and the house is the one paying the price.

What makes capillary rise so frustrating is how little of it is discussed during most water damage restoration work. Technicians may look at where the water touched, but not where it traveled invisibly. Most homeowners aren’t told about the ongoing damage potential. That silence costs them later. After a fire damage restoration, for example, it’s not uncommon for moisture used during suppression to pool at the bottom of walls. Left unchecked, it climbs up, slowly degrading materials meant to be dry.

One restoration firm in Greeley documented a sewage removal & cleanup job where water never reached more than 3 inches up the drywall. Or so it seemed. Their thermal scans revealed a vertical saturation line 24 inches high, thanks to capillary rise. Cutting only the visibly wet section would’ve missed over 80% of the water damage. That’s how secondary mold growth spreads silently through framing and drywall seams. The right cut—made with knowledge—saved the client thousands in long-term repairs.

Capillary rise demands patience, insight, and deep respect for building science. It’s not something you fix with air movers and a few fans. It requires a targeted strategy, proper drying timelines, and complete transparency with the homeowner. Especially in cold or mixed-climate regions like Colorado, where heating systems draw warm air up, that rising heat can actually encourage upward moisture movement. Combine that with poor monitoring, and you’re setting up for disaster.

If your home has faced fire damage cleanup, storm damage restoration, or even something as subtle as a hvac discharge line repair, ask your restoration company if capillary testing was performed. If the answer is no, get a second opinion. Your walls may be silently soaking while you’re trying to move on.

Capillary rise is one of water’s most underestimated behaviors. It climbs when you’re not watching, damages what you can’t see, and ruins materials you thought were untouched. Understanding how and why walls keep soaking is what separates true restoration experts from the amateurs with fans and duct tape. In this business, what goes up must be dried—or you’ll pay for it when it comes back down.