Glossary of Foundation Repair and Waterproofing Terms
Understanding foundation and basement terms doesn’t have to be confusing. Use this glossary to learn what common terms like “underpinning,” “sump pump,” and “egress window” really mean. Click on a term below to jump to the definitions for that service.
A
Above-Grade Waterproofing
Surface water management grading, downspout routing, and exterior improvements that keep water from reaching the foundation before pressure builds.
Absolute Humidity
The actual amount of water vapor in a given volume of air.
Absorption
Moisture is being drawn into porous materials like concrete, block, or mortar.
Acidic Soil Reaction
Moisture transporting minerals/salts that can weaken mortar binders and masonry over time.
Active Soils
Near-surface soils that expand when wet and shrink when dry with seasonal moisture swings, contributing to movement and settlement.
B
Backfill
Material placed against a foundation after excavation. Good backfill supports drainage and reduces lateral loading.
Basement
A building level partially or fully below grade.
Basement Waterproofing
Systems that manage water entry through walls and floors using drains, pumps, membranes, and sealing with the goal of relieving pressure and controlling moisture long-term.
Bedrock
Solid rock beneath soil layers can provide reliable support for deep foundation systems.
Below Grade
Any part of the structure below the surrounding ground level.
Black Mold (Moisture-Driven Mold Growth)
A consumer term for dark molds that thrive in damp conditions. The durable fix is moisture control, not cosmetic cleaning.
Bowing Wall
An inward-curving wall caused by sustained lateral soil and/or hydrostatic pressure.
C
Cantilever Soldier Beam
A vertical structural steel I-Beam is installed tightly against a foundation wall to resist inward movement caused by lateral soil pressure. Like a standard soldier beam, it is set into a newly poured concrete footing approximately 18 inches deep; however, unlike a top-braced system, a cantilever soldier beam is not attached to the floor framing above. Instead, it relies on a larger, engineered poured footing at its base to create resistance through embedment and mass. This design allows the beam to counteract soil pressure independently without transferring loads into the home’s framing system. Cantilever soldier beams are structural stabilization solutions intended to halt further wall deflection when properly engineered and installed.
Capillary Action
Wicking of water through porous concrete or masonry, similar to a sponge.
Carbon Fiber Reinforcement
A high-strength structural fabric is bonded to foundation walls with epoxy to restrict crack growth and resist additional inward movement caused by lateral soil pressure. When properly installed over a foundation crack, the system not only reinforces the wall but also seals the crack, preventing water intrusion through that location. Carbon fiber is low-profile, non-corrosive, and designed to provide long-term structural stabilization without the bulk of traditional steel reinforcement systems.
Casement Window
A side-hinged window that swings open, often used for egress due to a large clear opening.
Check Valve
A one-way valve prevents sump discharge water from flowing back into the sump pit.
Cinder Block / Concrete Block (CMU)
Concrete masonry units are used for foundation walls, typically hollow-core and mortared.
Clay Bowl Effect
The clay bowl effect refers to a condition that develops around many homes where excavated foundation walls are backfilled with loose clay soil during construction. Over time, this backfill settles differently than the undisturbed native soil beyond it, creating a shallow “bowl” or depression around the perimeter of the home. Because clay retains water and drains poorly, rainfall and roof runoff tend to collect in this bowl-shaped area rather than draining away. The trapped moisture increases soil saturation directly against the foundation, raising hydrostatic pressure and contributing to seepage, wall movement, and settlement.
Clay Soil
Clay soil is a fine-grained soil composed of very small mineral particles that readily absorb and retain water. When wet, clay expands and increases in volume; when dry, it shrinks and contracts. This repeated swelling and shrinking creates soil movement that can place significant stress on foundations, leading to settlement, heaving, cracking, and wall displacement. Clay soils are highly prevalent throughout the Midwest, including much of Missouri, Illinois, and surrounding states. Seasonal moisture fluctuations — heavy spring rains followed by hot, dry summers — drive ongoing cycles of expansion and contraction. Because many homes in this region are built on or backfilled with clay-based soils, proper drainage, load-bearing evaluation, and structural stabilization are critical for long-term foundation performance.
Cold Joint
A seam between separate concrete pours that can become a leakage path without proper detailing.
Condensation
Water forming on cool surfaces when humid air contacts them (walls, pipes, ducts, slabs).
Control Joint
A groove formed in concrete to encourage cracking along planned lines.
Cove Joint
The wall-to-floor seam is a frequent water entry location.
Crawl Space
A crawl space is a shallow, unfinished area beneath a home that provides access to plumbing, electrical, and HVAC systems. Unlike a basement, it typically does not serve as living space and may be vented or sealed depending on construction type. Because crawl spaces are close to the soil, they are highly susceptible to moisture intrusion, humidity buildup, and temperature fluctuations. Without proper drainage, vapor barriers, and ventilation or dehumidification, excess moisture can lead to wood rot, mold growth, and structural deterioration of floor framing above.
Crawlspace Encapsulation
Crawlspace encapsulation is a moisture-control system that seals the crawl space from ground moisture and outside air. The process typically includes installing a heavy-duty vapor barrier across the soil and up foundation walls, sealing vents and penetrations, and often adding drainage improvements and a dehumidifier. By controlling moisture and humidity, encapsulation helps prevent mold growth, wood rot, insulation deterioration, and structural damage to the floor framing above. Proper encapsulation transforms a damp, vulnerable crawl space into a controlled environment that supports long-term structural health.
Cracked Slab
A floor slab crack caused by shrinkage, settlement, soil movement, or under-slab pressure.
D
Dehumidifier
A device that removes moisture from air; best paired with drainage/water control when intrusion is present.
Differential Settlement
Uneven sinking due to variable soil support, often causing cracking and racking symptoms
Discharge Line
The pipe carries water from the sump pump to an exterior discharge point.
Downspout
A downspout is the vertical pipe attached to a home’s gutter system that carries rainwater from the roof to ground level. Its purpose is to channel roof runoff away from the foundation to reduce soil saturation and hydrostatic pressure. When properly extended and directed away from the home, downspouts play a critical role in protecting the foundation from water intrusion, settlement, and lateral soil stress.
Downspout Extension
A downspout extension is an added length of pipe or flexible tubing attached to the base of a downspout to carry roof runoff farther away from the foundation. Its purpose is to prevent water from discharging directly beside the footing, where it can saturate soil and increase hydrostatic pressure. Properly installed extensions help reduce seepage, settlement risk, and lateral soil stress by directing water to a safe discharge area well away from the structure.
Drain Tile (Perimeter Drain / Weeping Tile)
Perforated pipe (interior or exterior) that collects water and routes it to discharge or a sump basin, typically surrounded by drainage aggregate.
Drain Tile Flush Test
A diagnostic check where water is introduced to confirm drain function and flow.
Driveway Compression
Lateral force on a foundation when expanding slabs push against it due to temperature changes. (See also: Street Creep.)
Dry Well
A subsurface chamber filled with rock or a manufactured unit that disperses stormwater into soil.
E
Efflorescence
White mineral residue left when moisture evaporates from masonry. It signals water movement through the wall.
Egress Window
A code-compliant basement window intended for emergency escape; required for basement sleeping areas.
Epoxy Injection
A structural crack repair method that bonds concrete, used when movement is not ongoing.
Erosion
Soil loss caused by water flow that can alter grade and affect foundation performance.
Expansion Joint
A flexible joint designed to accommodate movement from thermal expansion/contraction.
Expansive Soil
Soil that increases in volume when wet and shrinks when dry, creating movement that can lead to foundation settlement, heaving, and structural cracking.
Exterior Footing Drain
Perimeter drainage is installed outside at the footing level to intercept groundwater.
F
Footing
A widened concrete base distributing structural loads to soil; good footing design reduces risk of settlement.
Foundation
The structural base of a building designed to safely transfer the weight of the structure — including walls, floors, roof systems, and live loads — into the underlying soil or load-bearing strata. A properly constructed foundation distributes these loads evenly to prevent excessive settlement, movement, or structural distress. Foundations may consist of poured concrete walls, concrete masonry units (block), slabs-on-grade, footings, piers, or a combination of these elements. Beyond supporting weight, the foundation also resists lateral soil pressure, manages groundwater interaction, and serves as the transition between the structure and the earth. When soil conditions change or loads are not adequately supported, foundation movement can occur — making proper design, evaluation, and stabilization essential for long-term structural performance.
Foundation Movement
Any shift, settlement, or heave that changes the foundation’s original position, driven by soils, drainage, or external influences.
Foundation Repair
Work performed to stabilize and support a structure and preserve structural integrity.
Foundation Settlement
Vertical downward movement from soil compaction, shrinkage, or washout — especially problematic when uneven.
Foundation Wall
A foundation wall is the structural wall that extends from the footing up to the main floor framing of a building. Its primary function is to support the weight of the structure above while transferring those loads safely into the footing and underlying soil or load-bearing strata. In addition to supporting vertical loads, foundation walls must also resist lateral soil pressure and hydrostatic pressure from surrounding soils. They are commonly constructed of poured concrete, concrete block (CMU), or stone. Proper reinforcement, drainage, and stabilization are essential to maintain structural integrity and prevent cracking, bowing, or water intrusion.
French Drain
A gravel-filled trench with perforated pipe that redirects groundwater and reduces hydrostatic pressure.
Freeze–Thaw Cycle
Repeated freezing/thawing of moisture within materials that accelerates cracking and surface breakdown.
G
Gap (Floating Floor Relief Gap)
A perimeter relief space along a slab edge that allows drainage capture and accommodates slab movement.
Grade
The slope of soil around a home; proper grade moves surface water away from the foundation.
Groundwater
Subsurface water can raise the water table and increase pressure against walls and beneath slabs.
Grout
A fluid, cement-based material used to fill voids, bond masonry units, or transfer loads between structural elements. In foundation work, grout is often used to fill block cores, secure anchors, or improve contact between structural components.
H
Heaving
Upward movement caused by expansive soils or frost action.
Helical Pier
A steel shaft with helical plates advanced into stable strata to stabilize (and sometimes lift) settling foundations with minimal disruption.
Helical Tieback (Helical Anchor)
A steel shaft with helical plates advanced into stable strata to hold a foundation wall in place and resist lateral pressure. It attaches to the wall and is tightened to stabilize or straighten the wall. Commonly used for bowed basement walls or retaining walls.
Horizontal Crack
A crack parallel to the ground, often indicating lateral soil pressure and/or hydrostatic pressure.
Humidistat
A sensor/control that cycles dehumidification equipment on/off to maintain a target humidity level.
Humidity
Moisture content of air.
Hydraulic Cement
Fast-setting patch material used to stop minor leaks; best used with proper water management when pressure exists.
Hydrophilic
Describes materials that attract/absorb water.
Hydrostatic Pressure
Water pressure from saturated soil pressing against walls and slabs, driving seepage and contributing to cracking/bowing.
I
I-Beams (Steel Support Beams)
Structural steel beams with a distinctive “I” profile are designed for high strength and stiffness. In foundation applications, I-beams are commonly used as soldier beams to stabilize bowed or leaning basement walls by resisting lateral soil pressure when properly anchored into a concrete footing and braced as required. I-beams are also used as load-bearing support beams in the basement to carry and redistribute loads from the floor framing above. When installed as structural supports, they transfer weight from beams and joists to properly founded columns or footings, restoring proper load paths and correcting sagging or undersized framing.
Infiltration
Unintended entry of water, vapor, or air into a structure.
IRC Code Requirements
International Residential Code rules for egress window size, sill height, and accessibility for emergency escape.
Iron Ochre
Orange/slimy residue caused by bacteria in iron-rich water that can clog drains and foul sump systems.
Interior Footer Drain
An interior perimeter drain installed at/near footing level to capture water and relieve under-slab pressure.
L
Lateral Pressure
Horizontal force from soil acting on foundation walls; a major driver of bowing and horizontal cracking.
Load-Bearing Capacity
The maximum amount of weight that soil or rock can safely support without excessive settlement, shear failure, or long-term instability. In foundation repair and structural design, load-bearing capacity determines whether existing soils can reliably support a structure or whether loads must be transferred deeper to more competent strata. Proper evaluation of load-bearing capacity is essential to preventing settlement, structural cracking, and progressive foundation movement.
Load-Bearing Strata
Dense, stable soil or rock capable of supporting structural loads without significant settlement is the target for underpinning systems.
M
Membrane (Waterproofing Membrane)
A flexible exterior barrier used to reduce water penetration through foundation walls.
Mildew
Surface-level fungal growth in damp environments.
Monolithic Slab
A monolithic slab is a foundation system in which the concrete slab and the footing are poured at the same time, forming one continuous structural unit. The slab thickens around the perimeter and load-bearing areas to serve as both the foundation and the floor. Because the slab and footing act together as a single component, soil preparation and compaction are critical. Movement in underlying soils can lead to cracking or elevation changes across the slab, making proper drainage and stable load-bearing support essential for long-term performance.
Mortar Joint
The bonded seam between masonry units; joint failure can allow seepage.
Mold / Mold Remediation
Mold growth and the process of addressing it. Permanent results require correcting the moisture source.
N
Negative Hydrostatic Pressure
Water pressure pushing from outside toward the inside surface; one reason interior coatings alone often fail.
P
Piering
A foundation repair method that stabilizes or lifts a settling structure by installing vertical structural elements (piers) beneath the existing footing. The piers transfer the building load from weak or shifting surface soils to deeper, more stable load-bearing soil or bedrock.
Pilaster
A thickened wall section designed to increase stiffness or carry concentrated loads.
Plate Anchors (Wall Anchors)
Plate anchors are structural stabilization systems used to stop and, in many cases, gradually correct inward movement of bowed basement walls caused by lateral soil pressure. The system consists of a steel interior wall plate connected by a threaded rod to an exterior anchor plate embedded in stable soil away from the foundation. Once installed, the rod is tightened to counteract soil pressure and stabilize the wall. Over time, controlled adjustments may allow for partial wall realignment, depending on soil conditions and the degree of displacement. Plate anchors are most effective when installed in non-expansive soils with sufficient distance from the foundation to develop proper resistance.
Polyurethane Injection (Urethane Injection)
A flexible crack-sealing method intended to stop water intrusion while tolerating minor movement.
Poured Concrete Foundation
A poured concrete foundation is constructed by placing liquid concrete into temporary wall forms that contain reinforcing steel (rebar). Once cured, the forms are removed, leaving a solid, monolithic concrete wall. This type of foundation provides high compressive strength and uniform load distribution. However, like all concrete, it can develop cracks from settlement, shrinkage, or soil pressure. Proper reinforcement, drainage, and water management are essential to ensure long-term structural performance and prevent moisture intrusion.
Pressure Relief System
A drainage approach designed to intercept under-slab water and relieve hydrostatic pressure.
Push Pier (Resistance Pier)
A steel foundation pier hydraulically driven into the ground using the weight of the structure as the reaction force. The pier is advanced until it reaches load-bearing soil or bedrock. Once installed, hydraulic jacks can be used to attempt lifting or stabilizing the structure before permanently locking the pier in place.
R
Radon Gas
A naturally occurring radioactive gas that can enter through cracks/openings below grade.
Rebar Pop
A rebar pop is a small surface crack or chip in concrete caused by corrosion of reinforcing steel located too close to the surface. As moisture reaches the steel, it begins to rust and expand, creating internal pressure that forces the concrete outward. While often appearing minor at first, a rebar pop indicates moisture intrusion and active steel corrosion. If left unaddressed, it can progress into larger cracking and spalling, compromising the durability of the concrete.
Relative Humidity (RH)
A measurement of moisture in air compared to the maximum the air can hold at that temperature. Sustained RH above ~60% in basements increases the risk of condensation, mold, and odor issues.
Rust (Oxidation)
Corrosion of steel caused by moisture and oxygen; can contribute to cracking and spalling as corrosion expands.
S
Seepage
Slow water migration through masonry or slab surfaces rather than a fast flow.
Settlement Crack
Cracking caused by foundation movement, often tied to differential settlement.
Sill (Sill Plate)
The horizontal wood member that sits directly on top of the foundation wall and serves as the base for the home’s framing system. The sill plate transfers structural loads from the framing above into the foundation and is typically anchored to the concrete with bolts. Because it rests at the critical transition between masonry and wood, the sill plate is vulnerable to moisture intrusion if water enters at the top of the foundation wall. Proper sealing, flashing, and drainage are essential to prevent rot, deterioration, and structural weakening at this connection point.
Silt
Fine soil particles can clog drainage systems and reduce drain performance.
Slab-on-Grade
A type of foundation where a concrete floor slab is poured directly at ground level, typically over compacted soil and a gravel base, without a basement or crawl space. The slab serves as both the structural foundation and the finished floor surface. Because slab-on-grade foundations rely entirely on the supporting soils beneath them, proper soil preparation and drainage are critical. Movement in underlying soils — such as settlement, shrinkage, or expansion — can lead to cracking, floor elevation changes, and structural distress within the home.
Soil Pressure
The force soil exerts on foundation walls and footings. When soils swell or are over-saturated, pressure increases — driving bowing, cracking, and wall movement. (See also: Lateral Pressure.)
Soldier Beam (Steel Wall Reinforcement Beam)
A vertical structural steel I-Beam installed tight against a foundation wall to resist inward movement caused by lateral soil pressure. The beam is set into a newly poured concrete footing approximately 18 inches deep and braced at the top to the floor framing system above. By anchoring at the base and transferring load into the framing at the top, a soldier beam creates a rigid support system that stabilizes bowed or leaning walls and helps prevent further deflection. Proper spacing, footing size, and structural attachment are critical to ensuring long-term performance.
Solid-Filled Block Wall
Block wall with cavities filled; reduces internal water storage but does not eliminate joint/crack leakage.
Spalling
Concrete surface breaking/flaking caused by freeze-thaw action or expansion from corroding embedded steel.
Stair-Step Crack / Step Crack
A stepped crack following mortar joints, typically related to settlement or lateral movement.
Steel Wall Braces (Steel Restraints)
Vertical steel supports used to resist continued inward wall movement.
Stone Backfill
Clean aggregate used to promote drainage and reduce settlement compared to native clay backfill.
Stone Foundation
A foundation constructed from stacked natural stones bonded together with mortar, commonly found in older homes. Because stone sizes and shapes vary, these foundations often have irregular surfaces and numerous mortar joints. Over time, mortar deterioration and moisture migration can allow water intrusion and reduce structural integrity. Stone foundations typically require specialized repair and waterproofing approaches due to their porous nature and uneven exterior surfaces.
Strata
Layers of soil or rock that exist beneath the ground surface, each with distinct physical properties such as density, composition, and load-bearing capacity. In foundation engineering, understanding subsurface strata is critical because structural performance depends on how loads are transferred through these layers. Effective underpinning and deep foundation systems are designed to bypass unstable upper soils and transfer weight to competent, load-bearing strata capable of long-term support without excessive settlement.
Street Creep
The gradual expansion and forward movement of exterior concrete pavement — typically streets and driveways — caused by repeated thermal expansion. As concrete expands during temperature increases, it has nowhere to relieve pressure and slowly pushes against adjoining structures. Over time, this horizontal force can transfer into the home’s foundation, leading to cracking, interior slab movement, misaligned doors, or garage wall displacement. Proper expansion joints and isolation detailing are critical to preventing street creep from impacting structural components.
Sump Pit (Sump Basin)
A sump pit, or sump basin, is a below-floor container installed at the lowest point of a basement or crawl space to collect groundwater from perimeter drains or pressure-relief systems. Typically made of durable plastic or fiberglass, the basin houses the sump pump and allows water to accumulate safely until it is discharged away from the foundation. A properly sized and sealed sump basin helps prevent debris from entering the pump system, reduces moisture vapor release into the basement, and supports reliable long-term groundwater management.
Sump Pump System
A sump pump system removes groundwater collected in a sump basin and discharges it safely away from the foundation. The primary pump activates automatically when water reaches a set level, providing the first line of defense against basement flooding. A backup pump offers added protection if the primary unit fails or cannot keep up during heavy water events. For additional security, a battery backup system allows the pump to operate during power outages — a critical safeguard during severe storms when flooding risk is highest.
Sump Pump Discharge Pipe
The pipe that carries groundwater from the sump pump basin to a safe exterior discharge location away from the foundation. Typically constructed of PVC or ABS piping, the discharge pipe is connected directly to the pump outlet and routed through the basement wall or rim joist to the exterior. Proper sizing, slope, and termination location are critical. The discharge line should direct water well away from the foundation to prevent recycling water back into the perimeter drainage system. In colder climates, exterior routing must also be designed to minimize freezing risk, which can obstruct flow and compromise system performance. A check valve is commonly installed on the vertical section of the discharge line to prevent backflow into the sump basin after the pump shuts off.
Support Column
A vertical structural member designed to carry and transfer loads from beams, floors, or framing above down to the footing, slab, or underlying load-bearing strata. In basement environments, support columns may be fixed, adjustable, or helical-based depending on the structural need. Properly installed columns help correct sagging floors, reinforce weakened framing, and restore load paths to stable bearing conditions. Structural support columns are engineered solutions, not temporary jacks, and must be properly sized, aligned, and founded to provide long-term performance.
T
Tempered Glass
Safety glass that fractures into small, rounded pieces; commonly required for below-grade windows.
Tensile Strength
A material’s resistance to pulling forces.
Thermal Movement
Expansion and contraction caused by temperature swings.
Tie Rods (Form Ties)
Steel connectors used in poured wall forms; tie locations can become leak points if not properly sealed.
Tuckpointing
Removing and replacing failing mortar in masonry joints.
U
Underpinning
Strengthening a foundation by extending support down to stable, load-bearing strata — commonly using piers or piles.
V
Vapor Barrier
A sheet material is installed to block moisture vapor from entering finished spaces and insulation.
Vertical Crack
A crack is typically tied to shrinkage or settlement; significance depends on width, displacement, and water entry.
W
Wall Anchors
Steel plates connected by rods installed to stabilize and gradually straighten bowed walls. (See also: Plate Anchors.)
Wall Deflection
Measured the inward movement of a foundation wall.
Wall Drainage Board
An interior drainage panel that channels wall moisture into a perimeter drain system.
Water Infiltration / Penetration
Active water entry through cracks, joints, seams, or porous materials.
Water Table
The subsurface level where soil is fully saturated; higher levels increase hydrostatic pressure.
Weep Holes
Openings that allow trapped water within block cores/cavities to drain into a managed drainage path.
Window Well
An excavated area around a basement window designed to hold back soil and often paired with drainage.
