Repairs: every question answered
209 questions with short answers. Each links to the full, sourced explanation.
Do root barriers and moisture barriers protect foundations?
Buried root and moisture barriers keep roots and seasonal drying away from soil under a foundation. They support other repairs but cannot lift a foundation.
- Why does moisture control matter on clay?
- Oklahoma's expansive clays shrink as they dry and swell as they wet. Uneven moisture around a house — dry under one corner, wet under another — produces uneven movement.
- How do root barriers work?
- A root barrier is a vertical sheet, such as heavy plastic, set in a trench between a tree and the foundation. Its purpose is to stop roots from growing under the slab and drawing water from the clay there.
- How do vertical moisture barriers work?
- A vertical moisture barrier is a deeper buried sheet around the perimeter meant to slow water moving sideways into or out of the soil under the slab edge. This reduces the seasonal wetting and drying that drives perimeter drying settlement and perimeter wetting heave.
- Root and moisture barriers: Should you water around the foundation?
- Watering the soil around a foundation in drought is debated because it can help or hurt. Published maintenance guidance for expansive soils says:
- What landscaping supports moisture control?
- The same maintenance guide recommends:
- What are the limits of barriers and moisture control?
- Barriers and watering do not lift a foundation or repair existing damage; guidance treats maintenance systems as performance aids, not repairs; Barriers can be bypassed by roots and must be deep enough for the root zone; Watering must be kept even, and overwatering can itself cause movement.
- What does a root barrier do for a foundation?
- A root barrier is a vertical sheet set in a trench between a tree and the house. It is meant to keep roots from growing under the foundation and drying the clay there.
- Do root barriers always work?
- No. Research found roots deflected by vertical barriers can grow under them and return toward the surface, and engineering guidance lists removing roots that grow past barriers as a maintenance task.
- Root and moisture barriers: Should I water my foundation during an Oklahoma drought?
- Engineering maintenance guidance says to irrigate soil around the foundation in dry weather where expansive soils occur, keeping moisture uniform, watering at least one to two feet away, and not watering directly into a shrinkage gap.
- Root and moisture barriers: Can watering a foundation cause problems?
- Yes. Uneven or excessive watering can cause swelling and movement, and automatic systems can fail and run continuously, so they need to be maintained.
Does chemical soil stabilization work on Oklahoma clay?
Lime can nearly eliminate swell in some Oklahoma soils but make sulfate-rich soils dramatically worse, so soil testing, especially for sulfates, comes first.
- What is chemical soil stabilization?
- Expansive clay swells when wet and shrinks when dry. Most foundation repair works around it, by placing piers below the moving layer or by controlling water. Chemical stabilization tries to change the clay itself.
- Chemical soil stabilization: What did Oklahoma research find?
- The University of Oklahoma, working for the Oklahoma Department of Transportation, tested lime, fly ash and cement kiln dust on Oklahoma soils after curing:
- Chemical soil stabilization: What is the sulfate problem?
- Ettringite is a calcium-aluminum-sulfate mineral that forms when lime, soluble sulfate (often from gypsum), aluminum from clay and water combine; it can swell up to 250% of its original volume.
- Which Oklahoma soils are candidates?
- Oklahoma State University testing found montmorillonite-dominated clay in western Oklahoma benchmark soils, with Kirkland showing volume change up to 73% and Bethany up to 66%.
- Chemical soil stabilization: What testing is needed before treatment?
- Plasticity index and swell tests on samples from the depth to be treated; see soil testing and lab values; Soluble sulfate content, because of the ettringite reaction; Swell tests on treated and untreated samples, the comparison the Oklahoma studies used.
- What does chemical soil stabilization do?
- It mixes or injects a chemical such as lime into expansive clay to reduce how much the clay swells and shrinks with moisture, treating the soil itself rather than bypassing it with piers.
- Chemical soil stabilization: Does lime work on Oklahoma clay?
- In Oklahoma Department of Transportation research, lime cut swell sharply in Kingfisher soil, from 6.1 percent untreated to a net shrink of 2.8 percent at 9 percent lime. In a high-sulfate Vernon soil, 3 percent lime increased swell by 1,237 percent.
- Chemical soil stabilization: Why do sulfates matter for lime treatment?
- Lime reacts with soluble sulfate, often from gypsum, and with aluminum from clay to form ettringite, a mineral that can swell to as much as 250 percent of its original volume. That reaction caused the 2004 failure of several miles of SH-412 near Woodward.
- Chemical soil stabilization: Do the Oklahoma lab results apply to injection under a house?
- Not directly. The Oklahoma studies tested soils mixed with additives and compacted in the lab for highway subgrades, which is a different process from pressure injection into undisturbed soil under an existing foundation.
How are bowing or cracked basement walls repaired?
Repairs strengthen, brace, anchor or replace the wall, paired with drainage, since soil pressure, swelling clay and trapped water cause the damage.
- Basement wall repair: What does the damage look like?
- Horizontal cracking along a mortar joint or at mid-height of a block wall, with the wall bowing inward (horizontal crack or inward bow); Cracks that let water in, the pattern described for Oklahoma clay; Seepage at cracks or at the joint between wall and floor, or white salt deposits left where water has moved through the masonry and evaporated (water at cove joint or efflorescence).
- What repair methods are used?
- Plain-English definitions of the methods named in repair proposals:
- What water control goes with wall repair?
- Footing drains: required around concrete or masonry walls that retain earth and enclose usable below-grade space, set at or below the top of the footing and discharged by gravity or pump; Drain construction: gravel at least 1 ft beyond the footing and 6 in above it, or perforated pipe on 2 in of washed gravel with 6 in of cover and a filter membrane; Waterproofing: where severe soil-water conditions exist, a waterproofing membrane rather than dampproofing.
- What causes a basement wall to bow inward?
- Sideways pressure from the soil behind it. The residential code assigns inorganic clays the highest design soil pressure of the common soil groups, and swelling clay and trapped water add to that load.
- What are the main ways to repair a bowing basement wall?
- Repair methods fall into four groups: strengthening the wall face with bonded carbon fiber straps, bracing it from inside with steel beams, anchoring it to the soil outside with wall anchors or helical tiebacks, and excavating to rebuild it. Each is normally paired with water control.
- Why does basement wall repair include drainage?
- Water in the backfill adds hydrostatic pressure to the soil load and leaks through cracks. The code requires footing drains around below-grade walls that enclose usable space and waterproofing where a high water table is known.
- Can a home inspector tell me how to fix a bowed wall?
- No. Inspection standards require inspectors to report signs of foundation movement and water penetration, but not to provide engineering services or judge the adequacy of structural components.
How are interior slab piers installed by tunneling or coring?
Crews reach soil under the slab interior by tunneling from outside or coring through the floor. Interior piers address settlement only, not a heaved center.
- Interior piers, tunnel or core: How do crews reach the soil?
- Coring means cutting a cylinder out of concrete with a diamond-tipped drill. A tunnel here is a crawl-height excavation under the slab.
- Where do interior piers go?
- Slab foundations can have interior footings under bearing walls, cast with the slab; in Seismic Design Categories D0 to D2 the code requires those footings to extend at least 12 in below the top of the slab.
- Interior piers, tunnel or core: What do Oklahoma install records show?
- Steel push piers rely on the weight above them to drive the pier down. Records from Oklahoma steel push pier installations show a clear difference between piers at the slab and at the perimeter footing:
- What can interior piers not do?
- Interior piers lift or hold up; they cannot pull a slab down.
- How do floating slabs and interior walls affect them?
- Engineering guidance for swelling soils notes that floating slabs are kept isolated from bearing walls, columns, stairs and utilities and that some cracking should be expected.
- Can interior piers be used in post-tensioned slabs?
- Oklahoma's 2024 code adoption requires post-tensioned slabs on grade to carry a label on the electrical panel door. Post-tensioned slabs contain tendons, steel cables stressed after the pour, so the slab type is identified before coring; see post-tensioned slabs.
- What are interior piers?
- They are piers placed under the inside of a slab foundation, beneath interior beams or settled floor areas, rather than along the outside edge. Crews reach the soil either by tunneling under the slab from outside or by cutting a hole through the floor.
- Can interior piers fix a hump in the middle of my floor?
- No. Piers push up; they cannot pull a raised center down. A hump caused by swelling clay or a leak under the middle of the slab is the opposite problem from settlement.
- Do interior piers go as deep as exterior piers?
- In Oklahoma installation records, piers pushed at the slab stopped shallower and at lower pressure than piers at the perimeter footing: about 8 to 11 feet at 4,000 to 5,000 psi, compared with 13 to 17 feet at 7,000 to 8,000 psi.
- Interior piers, tunnel or core: Is there anything special about coring a post-tensioned slab?
- Post-tensioned slabs contain stressed steel tendons. Oklahoma's 2024 code adoption requires post-tensioned slabs on grade to be labeled at the electrical panel door, which identifies the slab type before any cutting.
How are sagging crawl space floors repaired?
Crawl space repair adds supports on proper footings, shims, added beams, reinforced joists and new sill plates, designed to be adjusted as Oklahoma clay moves.
- What gets repaired in a crawl space?
- Adjustable supports are steel posts with a threaded section that lets the height be changed after installation, set on a concrete footing or on a pier.
- Crawl space repair: Why do interior supports move in Oklahoma?
- Seasonal moisture change in clay can extend from 3 to 40 ft deep, and lightly loaded supports in that zone can be lifted when clay swells in the wet season, then lose grip and drop when it shrinks in the dry season.
- Crawl space repair: How are shims, caps and anchor bolts used?
- Shim limits: Oklahoma installation records cap shim stacks at no more than four per support; Manufactured homes: HUD's standard calls for 4 x 6 x 1 in shims used in pairs and driven tight, occupying no more than 1 in of height, with pier caps of solid concrete or masonry at least 4 in thick, lumber at least 2 in nominal, or corrosion-protected steel at least 1/2 in; Sill anchoring: sill plates are held by anchor bolts at least 1/2 in in diameter, no more than 6 ft apart and embedded at least 7 in, with a bolt within 12 in of each end.
- What moisture work goes with structural repair?
- Structural repair in a damp crawl space is paired with moisture work such as: - Removing vegetation and organic debris from the crawl floor, which the code requires. - Covering the ground with a vapor retarder; with a Class I retarder, required vent area drops from 1 sq ft per 150 sq ft to 1 per 1,500. - Correcting grade or adding drainage where groundwater rises within 6 in of the finished floor or surface water drains poorly. - Closing the crawl space as an unvented space under the code's conditions; see crawl space encapsulation.
- Crawl space repair: What access and safety issues apply?
- The code requires crawl space access openings of at least 18 x 24 in through a floor or 16 x 24 in through a wall.
- Why are re-checks needed after repair?
- Because clay keeps cycling with the seasons, adjustable supports are re-checked and re-shimmed as needed. Over-correction after a drought lift is covered under over-lift heave after drought lift, and ongoing readings under the monitoring program.
- How are sagging floors over a crawl space fixed?
- The floor is jacked back toward level and re-supported, usually with new or added supports on proper footings, new shims, added beams under weak spans, or joists reinforced by fastening new lumber alongside them.
- Why do wood shims fail in a crawl space?
- Wood in contact with or near soil or masonry absorbs moisture and is exposed to decay and termites, which is why inspectors report wood-to-soil contact as a defect. Crushed or rotted shims let the beam drop onto the pier.
- Will interior piers keep moving after repair in Oklahoma clay?
- They can. Shallow pads under interior supports sit in clay that shrinks and swells with the seasons, so adjustable supports and periodic re-checks are part of many crawl space repairs.
- Crawl space repair: How many shims can be stacked on one support?
- Oklahoma installation records cap shim stacks at four per support. For manufactured homes, HUD's installation standard calls for 4 by 6 by 1 inch shims used in pairs, taking up no more than 1 inch.
How are under-slab plumbing leaks found and repaired?
Supply leaks are found with a water-meter check and drain leaks with a hydrostatic test and camera; in Oklahoma the repair is licensed plumbing work.
- Why do plumbing leaks matter for foundations?
- Most Oklahoma homes built on a slab have water supply pipes and sewer drains running in the soil under the concrete. When one leaks, it wets the clay in one area.
- How are supply leaks detected?
- Pressurized water lines leak constantly, so the water meter is the first check.
- How are drain and sewer leaks tested?
- Drain lines are not under pressure, so they do not move the meter. A hydrostatic test is used instead:
- Under-slab plumbing leaks: What are the repair options?
- Once a leak is located, the plumber's options range from repairing a single section through the slab, to rerouting a line around the slab, to lining or replacing longer runs of pipe. The choice depends on the pipe material, its age and how many leaks the testing finds.
- Who may repair leaks in Oklahoma?
- Oklahoma's plumbing rules state that no person or firm may perform plumbing work without first obtaining the appropriate license or registration.
- Under-slab plumbing leaks: What ongoing checks help?
- A foundation maintenance guide suggests checking for dripping faucets, air-conditioner condensate drips (especially from the overflow line) and stoppages, and fixing local moisture sources as soon as possible.
- Under-slab plumbing leaks: How can I tell if I have a water supply leak?
- Read the water meter, use no water for two hours, then read it again. EPA says any change in the reading during that time probably means a leak.
- Under-slab plumbing leaks: What is a hydrostatic test on a sewer line?
- The main drain is plugged at a cleanout, the under-slab drain system is filled with water to slab level, and the level is watched for about 15 minutes. A drop in the water level suggests a leak, which is then located with a camera and isolation testing.
- Can a plumbing leak cause foundation movement?
- Yes. Water leaking under a slab on expansive clay changes the soil moisture, which can make the soil swell and cause uneven movement and stress in the foundation, according to engineering research.
- Do I need a licensed plumber in Oklahoma to repair a leak under my slab?
- Oklahoma's plumbing rules say no person or firm may perform plumbing work without the appropriate license or registration from the Construction Industries Board.
How do drilled bell-bottom piers work on expansive clay?
A drilled bell-bottom pier is a reinforced concrete column with a widened base set below the active clay and anchored to minimize uplift from swelling clay.
- Drilled bell-bottom piers: How does the system work?
- Trade words used on this page: - Auger: a large drill that bores a round shaft into the ground. - Under-reaming (belling): widening the bottom of the shaft with a special tool to form the bell. - Rebar cage: a bundle of steel reinforcing bars lowered into the shaft before concrete is placed. - Pier cap: the top of the pier, on which a beam or footing rests. - Active zone: the depth of soil whose moisture, and therefore volume, changes with the seasons.
- Why do depth and the bell matter?
- Engineering guidance for swelling soils calls for piers to extend well below the zone of seasonal moisture change and to be anchored in non-swelling soil against uplift, using belled bottoms, grooved pier holes or greater depth.
- Where are drilled piers used?
- New construction on swelling soil: drilled piers with a grade beam are generally recommended for moderately to highly swelling soils, with a 3 to 6 in gap between the soil and the beam.
- What can go wrong with drilled piers?
- When piers move after construction or repair, the mechanism is described in pier uplift or movement after repair.
- Drilled bell-bottom piers: What practical considerations apply?
- Design input: depth and bell size come from a site soil investigation, and swelling-soil guidance calls for the foundation to be designed by an engineer who specializes in soil and foundation engineering; depth to rock from borings summarizes Oklahoma boring data; Engineering: drilled piers are an engineered system; how homeowners work with an engineer is covered in working with engineers.
- What is a drilled bell-bottom pier?
- It is a reinforced concrete pier cast in an augered hole, with the bottom of the hole widened into a bell shape. The pier carries load down below the clay that swells and shrinks, and the bell anchors it against being pulled up.
- Why does a pier need a bell in expansive clay?
- Swelling clay grips the upper part of a pier and can lift it. Engineering guidance calls for piers on swelling soil to be anchored in non-swelling soil by belled bottoms, grooved holes or greater depth.
- How deep do drilled piers need to go?
- Well below the zone of seasonal moisture change, which researchers report can extend from 3 to 40 feet deep. The design depth comes from a geotechnical investigation for the site.
- Have drilled piers been studied in Oklahoma?
- Yes. An Oklahoma Department of Transportation study published in 2024 built and load-tested eight drilled shafts socketed in weak rock at two Oklahoma sites to improve design methods.
How do helical piers support a foundation?
A steel shaft with screw plates is turned into the ground and bracketed to the foundation. It installs without building weight, suiting light loads and uplift.
- How does a helical pier work?
- Trade words used on this page: - Shaft: a square steel bar or round steel pipe, added in sections as it goes deeper. - Helix (helical plate): a round steel plate formed into one turn of a screw, welded near the lead end; a pier may have one or several. - Torque: the turning force the motor applies, read from a calibrated gauge during installation. - Bracket: the steel seat that connects the pier to the footing, slab edge or beam. - Tension capacity: the ability to resist being pulled upward.
- Helical piers: Why is torque recorded?
- Turning resistance is used as a measure of soil strength in federal rules: HUD's manufactured home installation standard uses a torque probe, a small screw-tipped rod turned into the soil, to classify soil strength: readings over 550 inch-pounds indicate class 2 soils such as gravel and dense sand, while readings under 175 indicate class 5 soils: uncompacted fill, peat and organic clays.
- How deep must helical piers go in clay?
- Expansive soils swell with added moisture and can lift a structure, and shrink with moisture loss and let it settle; Seasonal moisture change in clay can reach from 3 to 40 ft deep, and the upper part of a pier can lose contact with shrinking soil; Engineering guidance for swelling soils calls for piers to extend well below the zone of seasonal moisture change and to be anchored in non-swelling soil against uplift.
- What are the limits of helical piers?
- Plates that end inside the active zone do not provide reliable anchorage, which depends on soil below the zone of seasonal moisture change; Corner piers on swelling soil can be lifted in wet seasons, then lose skin friction as the soil shrinks in dry seasons and drop; The design depth depends on site soil data; soil survey reports are the minimum resource for locating expansive soils.
- How do helical piers compare to other piers?
- Helical piers, steel push piers, pressed concrete piles and drilled piers are compared side by side in the method selection matrix.
- What is a helical pier?
- A helical pier is a steel shaft with one or more screw-shaped plates welded near the tip. A hydraulic motor turns it into the ground like a screw, and a bracket connects the top to the foundation.
- Why is installation torque recorded on helical piers?
- The resistance to turning rises in firmer soil, so the torque reading at the end of installation is used as an indicator of the soil the plates are bearing in. Federal manufactured housing rules use torque-probe readings in the same way to classify soil strength.
- When are helical piers used instead of push piers?
- Helical piers do not rely on the weight of the building to drive them, so they are used for light structures such as porches, additions and manufactured homes, and where resistance to upward pull is needed.
- Can helical piers resist heave from swelling clay?
- Engineering guidance for swelling soils calls for piers to be anchored in non-swelling soil below the zone of seasonal moisture change to resist uplift. A helical plate set below that zone provides that anchorage, while plates within it move with the clay.
How do mudjacking and polyurethane foam lift a sunken slab?
Both pump material under a slab, cement slurry or expanding foam, to fill gaps and lift it, but they rest on the same soil and do not stop clay movement.
- Mudjacking and foam lifting: What are the two methods?
- Mudjacking pressure-injects a slurry of sand, fly ash or topsoil mixed with cement between the slab and the soil. The slurry fills empty spaces and, as more is pumped in, raises the slab.
- Mudjacking and foam lifting: Where are these methods used?
- Driveways, sidewalks, patios, garage slabs and pool decks — see heaved or settled flatwork and flatwork and exterior slabs; Filling voids under slabs after erosion or leak washout — see erosion, undermining and washout voids; Interior slab areas that have settled over loose fill, rather than heaved.
- Mudjacking and foam lifting: Why don't they fix clay movement?
- Expansive clay swells when wet and shrinks when dry, and its shrinkage cracks do not close up perfectly on rewetting. A slab lifted with grout or foam still sits on that soil.
- What are the risks during lifting?
- The same review lists installation problems for both methods:
- What should be checked before lifting?
- Plumbing. Grout and foam can enter cracked or broken pipes and plug them, so under-slab drains are often checked before lifting. A hydrostatic test plugs the main drain, fills the under-slab system to slab level and watches for a drop in water level for up to 15 minutes.
- Mudjacking and foam lifting: Can they be combined with other repairs?
- Foam or grout is sometimes used together with piers: piers carry the foundation beam, and foam fills voids or supports the slab between beams. Cost depends mainly on slab area, how much material is needed and access.
- What is the difference between mudjacking and polyurethane foam lifting?
- Mudjacking pumps a slurry of cement mixed with sand, fly ash or soil under the slab. Polyurethane lifting injects a two-part foam that expands under the slab; the slab then rests on the cured foam.
- Will mudjacking or foam stop my foundation from moving again?
- No. Both are shallow repairs that sit on the same soil, and engineering reviews list changing soil moisture, plumbing leaks, trees and poor drainage as causes of movement after these repairs.
- Why test the plumbing before slab lifting?
- Grout or foam can flow into cracked or broken drain lines and plug them, and leaks change soil moisture under the slab. A hydrostatic drain test is one way to check under-slab drain lines.
- Can slab lifting crack the concrete?
- Yes. Injecting too much material or using too much pressure can make the slab bulge, crack or blow out, so lifting is done gradually.
How do pressed concrete piles work and what are their limits?
Short precast concrete cylinders are jacked into the ground until they stop. Refusal does not prove stable soil, and they generally do not resist uplift.
- Pressed concrete piles: How does the system work?
- A pile (or pier) is a column that carries a building's load down to firmer soil. Underpinning means adding piles under an existing foundation. With pressed concrete piles:
- Pressed concrete piles: What are the installation steps?
- Dig an access hole at the foundation beam; Press the first segment and keep adding segments under the jack; Continue to refusal and record the depth and driving force or pressure.
- Pressed concrete piles: What spacing does published guidance show?
- For lightly loaded homes, one engineering guideline gives prescriptive maximum spacing:
- Pressed concrete piles: What are the limitations?
- Refusal only shows the jack could not push further at that moment. Guidelines note that piles that do not reach stable soil below the active zone — the depth where soil moisture changes with the seasons — may not resist shrink or swell movement.
- Pressed concrete piles: How do they compare with steel push piers?
- Steel push piers are installed the same way but use steel pipe, which can often be driven deeper. Oklahoma installation records for steel push piers at one large Tulsa site logged a median depth of about 12 feet, with the middle half between 9 and 14 feet.
- What is a pressed concrete pile?
- It is a column of short precast concrete cylinders pushed into the ground one at a time with a hydraulic jack that uses the weight of the house as its reaction. Pressing stops at refusal, when the driving force exceeds the load the pile must carry.
- Does refusal prove a pressed pile has enough capacity?
- Not by itself. Engineering guidance notes that piles that stop before reaching stable soil below the active zone may not resist shrink and swell movement, and shallow piles can lose skin friction during drought.
- Do pressed concrete piles stop a slab from heaving?
- No. Guidelines state these piles generally do not resist uplift, so they will not stop swelling clay from lifting a foundation that rests on it.
- Should pressed piles have a cable or rebar through the center?
- Reinforcement through the center hole is optional in published guidelines. A committee review lists unreinforced segments shifting sideways as one possible cause of problems after repair.
How do steel push piers fix a settling foundation in Oklahoma?
Steel pipe is driven down with a hydraulic ram, using the house's weight, until it reaches soil or rock that resists the load. Pressure is recorded per pier.
- Steel push piers: How does the system work?
- A pier is a column that carries a building's load down to firmer ground. A push pier (also called a resistance pier) is driven rather than drilled:
- How deep do push piers go in Oklahoma?
- Oklahoma installation records for 396 steel push piers at a large Tulsa site (2025) show:
- What do push piers address?
- Push piers are used where the foundation has settled — moved down — and firmer soil lies below the zone causing the movement. Typical cases include perimeter drying settlement, tree-root desiccation settlement, fill consolidation settlement and soft alluvial soils.
- Steel push piers: What are the limitations?
- The recorded pressure shows how hard the pier resisted at the time it was driven. Engineering reviews of post-repair performance list two related problems with steel pipe piles: piles not driven deep enough, and loss of skin friction (side grip) at shallow depths during drought.
- Steel push piers: What records and follow-up are kept?
- Each pier's depth and final pressure are recorded, and gauge pressure is converted to load using the ram area and calibrated gauges.
- How deep do steel push piers go in Tulsa?
- Oklahoma installation records from one large Tulsa site logged a median depth of about 12 feet, with the middle half of piers stopping between 9 and 14 feet and a full range of 2 to 40 feet.
- Steel push piers: Does the installation pressure prove each pier's capacity?
- The recorded drive force shows the resistance at the time of installation, which is a field check on every pier. It is not a static load test, and engineering reviews note that skin friction at shallow depths can be lost in drought.
- Can steel push piers stop a foundation from heaving?
- No. Push piers resist downward load, and piers will not prevent uplift from swelling soil unless they are designed to do so. Heave is addressed by controlling the water source first.
- Can push piers be used on a light structure?
- Push piers need enough building weight to push against while they are driven. Light structures may not provide enough reaction, which is one reason helical piers are used in some cases.
How does grouting fill voids under a foundation?
Cement-based grout is pumped under pressure to fill voids or densify loose soil; larger voids, fill or sinkholes are normally grouted to an engineer's design.
- What kinds of grouting are there?
- These descriptions are general terms used in ground improvement. Which type fits a site depends on what the investigation finds.
- Where do voids come from?
- Erosion and leaks. Running water from leaking pipes, downspouts or poor drainage can carry soil away from under a slab edge; see erosion, undermining and washout voids and exposed slab edge or void under footing; Loose or decaying fill.
- Void and compaction grouting: Where do sinkholes and karst occur in Oklahoma?
- A sinkhole is a ground depression with no surface drainage outlet, where water drains underground. USGS describes two common types:
- How are voids found before grouting?
- Engineering guidance describes several ways to locate voids under a slab:
- Void and compaction grouting: What are the risks and limits?
- Pressure grouting under a slab carries the same installation risks reported for mudjacking: too much material can bulge or crack the slab, excessive pressure can cause blowouts, and grout can enter and plug cracked utility lines.
- What is the difference between void filling and compaction grouting?
- Void filling pumps grout into empty spaces under a slab or footing. Compaction grouting injects a stiff grout under pressure that pushes surrounding loose soil aside and densifies it, and is normally an engineered ground-improvement method.
- How are voids under a slab found?
- Engineering test methods include ground penetrating radar, hammer sounding of the slab, impact-echo testing, electrical resistivity surveys, test openings and soil borings. Each has limits, so results are usually checked against borings or openings.
- Void and compaction grouting: Does Oklahoma have sinkholes?
- Yes. The Oklahoma Geological Survey reports karst in limestone and dolomite mainly in the Ozarks, the Arbuckle Mountains and the Limestone Hills north of the Wichita Mountains, and gypsum and shallow salt in many areas of western Oklahoma.
- Can grouting damage a foundation?
- Yes. Uncontrolled grout pressure or volume can lift or crack a slab, cause blowouts, or flow into and plug damaged utility lines.
How is a foundation protected from slope creep and creek erosion?
By combining grading and drainage, erosion protection, engineered retaining walls and, in some cases, supports designed for sideways load.
- Slope and erosion stabilization: What problems does this address?
- Slope creep is slow, downslope movement of soil. Expansive clay swells when wet and shrinks and cracks when dry, and these cycles are not fully reversible, which helps loosen and move soil on a slope over time.
- Slope and erosion stabilization: Why does investigation come first?
- A recommended practice for geotechnical work states that on sloped lots where the foundation is closer than four times the slope height to the toe of an embankment, borings should extend at least twice the slope height, and that reports should recommend earthwork stabilization and slope stability requirements.
- What stabilization methods are used?
- Controlling water is the base of most slope work. Drainage guidelines note that:
- Slope and erosion stabilization: What are the limitations?
- Usually requires an engineer's design and may require permits; Cost is driven by wall height and length, access for equipment, the extent of bank protection and engineering and permitting needs.
- What is slope creep?
- Creep is slow downhill movement of soil on a slope. In clay it is pushed along by repeated wetting and drying, and it can tilt fences, retaining walls and trees and pull at the downhill side of a foundation.
- Slope and erosion stabilization: Do I need a permit for a retaining wall?
- Model building codes require a permit for retaining walls over 4 feet tall, measured from the bottom of the footing to the top of the wall, and for any wall that supports a surcharge such as a building. Local rules can differ.
- Slope and erosion stabilization: Can foundation piers stop a house from sliding downhill?
- Standard push piers provide vertical support only. Sideways soil movement calls for a design that addresses lateral load, such as engineered walls, tiebacks or other lateral supports.
- Slope and erosion stabilization: Where in Oklahoma are landslides most common?
- The Oklahoma Geological Survey reports that most landslides occur in the eastern third of the state, where the climate is wetter and the terrain is steeper.
How is foundation movement monitored in Oklahoma?
Repeat elevation surveys, crack gauges and soil-moisture records taken over at least a year show whether a foundation is still moving or has stabilized.
- What is a monitoring program?
- Monitoring is observation, not a repair. It combines three kinds of records taken on a schedule:
- Why does monitoring matter on Oklahoma clay?
- Expansive clay swells when wet and shrinks when dry. The depth where this seasonal moisture change happens is called the active zone.
- Foundation monitoring: How are the measurements taken?
- Readings are taken about every 30 to 100 square feet, including room corners and near heavy loads such as masonry fireplaces; The instrument should read to about 1/8 inch or better; a spirit or carpenter's level is not considered accurate enough; Each survey uses the same points and the same reference point so that a "time-change" plan (later reading minus earlier reading) can be drawn.
- Foundation monitoring: How often are readings taken and when is movement stable?
- Guidelines from a Texas engineering group working on similar expansive clays set out these points:
- What are the limitations of monitoring?
- Monitoring takes at least a year and only shows whether movement has stopped; it does not stop movement itself; Results depend on repeating the same points, the same reference and comparable instruments; Newly built foundations commonly go through a 12- to 24-month adjustment period, which can look like movement.
- How long should a foundation be monitored before deciding on repair?
- Engineering guidelines call for at least one year of monitoring, with at least three elevation surveys and the first and last taken in the same season, so seasonal swings can be separated from ongoing movement.
- Foundation monitoring: Can I use a carpenter's level to check my floors over time?
- No. Published guidelines say a spirit or carpenter's level is not accurate enough for an elevation survey; a manometer-style or other floor-level instrument reading to about 1/8 inch is used instead.
- Foundation monitoring: What does it mean if a crack closes in spring and opens again in summer?
- A crack that opens and closes with the seasons is moving with soil moisture. It indicates cyclical movement, which is typical of expansive clay, not that the problem fixed itself.
- Foundation monitoring: How can I check soil moisture conditions where I live in Oklahoma?
- The Oklahoma Mesonet publishes daily soil moisture readings at depths from 2 to 24 inches at most of its stations, including the Fractional Water Index on a 0-to-1 scale.
Should I remove a tree near my foundation in Oklahoma?
Trees dry clay under foundations and can cause settling, but removing a large tree on expansive clay can let soil rewet and swell for years afterward.
- How do trees affect clay under a house?
- Trees draw water from the soil to replace water lost through their leaves. In clay, that drying makes the soil shrink, and if the shrinkage reaches beneath a foundation, the foundation can subside.
- Trees near the foundation: How close is too close?
- Published rules of thumb differ:
- Trees near the foundation: Which tree species use the most water?
- UK building guidance lists oak, poplar and eucalyptus among high-water-demand trees and notes that hardwoods have broad, spreading roots while conifers have a more local effect.
- Trees near the foundation: What are the tree management options?
- Reducing a tree's crown cuts its leaf area and so its water use. A foundation maintenance guide recommends a pruning program where a tree is too close, with a reasonable interval of every two to three years.
- Trees near the foundation: What are the limits of tree management?
- Removal on clay can cause years of heave; Pruning must be repeated as the tree regrows; These steps do not raise a foundation that has already settled.
- How close is too close for a tree near my house?
- One engineering maintenance guide says broadleaf trees should not be closer to the foundation than their height. OSU Extension advises planting at least half the tree's mature width from a building, noting roots can extend two to three times beyond the canopy width.
- Will cutting down a tree near my foundation fix settlement?
- Not necessarily. When a large tree is removed from clay soil, the ground slowly rewets and can swell, lifting the foundation; guidance notes this heave tends to occur during the first few years and its duration is hard to predict.
- How often should a tree near the house be pruned to reduce its water use?
- A foundation maintenance guide suggests a pruning program for trees that are too close, with a reasonable interval of every two to three years.
- Do some trees cause more foundation problems than others?
- Building guidance commonly lists oak and poplar as high water demand, and larger trees with more leaf area generally take up more water. Researchers have also argued rooting habit matters as much as species water use.
What drainage fixes protect a foundation on Oklahoma clay?
Grading, gutters, buried downspout lines and other drainage work move water away and keep clay at a steady moisture level rather than bone dry.
- Foundation drainage solutions: Why does water control matter on clay?
- Expansive clay swells when it takes on water and shrinks when it dries. Lawn watering, leaking pipes and pools can create the moisture differences that damage foundations, and engineering guidance calls for positive surface drainage away from all sides of a foundation.
- Foundation drainage solutions: What are the code minimums?
- Grade: the ground must fall at least 6 in within the first 10 ft from the foundation (IRC R401.3); When that is not possible: drains or swales carry water away instead.
- What drainage methods are used?
- Perched water is a temporary saturated layer that sits on top of tighter clay or rock after heavy rain; it is explained in groundwater and perched water.
- Foundation drainage solutions: Why should Oklahoma clay stay consistently moist, not dry?
- Colorado State University Extension notes that both overwatering and underwatering near foundations can damage structures, and that drip irrigation near a foundation can be acceptable if well maintained.
- What signs point to drainage work?
- Water standing near the foundation after rain; see water ponding near foundation; Flatwork that no longer slopes at least 2% away from the house; Erosion, washed-out soil under slab edges, or sediment fans below downspouts.
- Foundation drainage solutions: How much should the ground slope away from my house?
- The residential code requires the grade to fall at least 6 inches within the first 10 feet from the foundation. Where lot lines or slopes make that impossible, swales or drains are used, and paved surfaces within 10 feet must slope at least 2 percent away.
- How far should downspouts discharge from the foundation?
- Guidance for expansive soils ranges from at least 5 feet, in Colorado State University Extension advice, to at least 10 feet in Colorado Geological Survey guidance. Either way, the aim is to release roof water away from the foundation edge.
- Can drainage work make clay foundation problems worse?
- Guidance for expansive soils warns that both overwatering and underwatering near a foundation can cause damage. The goal is to remove concentrated water while keeping moisture under the edges of the foundation as even as possible.
- Foundation drainage solutions: What is a French drain?
- It is a gravel-filled trench with a perforated pipe, usually wrapped in filter fabric, that collects water below the surface and carries it to a lower outlet or sump.
What is crawl space encapsulation and what does code require?
Encapsulation covers the ground with a sealed vapor retarder, seals vents, insulates walls and dries the air. Code allows it as an unvented crawl space.
- How do vented and unvented crawl spaces differ?
- The residential code (IRC Section R408) allows two approaches:
- What does encapsulation typically include?
- Removing debris, vegetation and organic material from the crawl floor, which the code requires in any crawl space; A sealed ground liner, lapped and taped at seams and attached and sealed to the stem wall; Sealing vents and the rim area to outside air.
- Crawl space encapsulation: Why must water problems be fixed first?
- Encapsulation does not fix bulk water. The code's crawl space section calls for raising the under-floor grade or adding a drainage system where groundwater may rise to within 6 in of the finished floor at the perimeter or where surface water does not drain readily.
- How does encapsulation apply to manufactured homes?
- For manufactured homes, HUD's installation standard requires a vapor retarder of at least 6-mil polyethylene covering the ground whenever the space under the home is skirted or enclosed, with joints overlapped at least 12 in and tears repaired, unless the home is in an arid region with dry soil.
- How does encapsulation relate to structural repair?
- Encapsulation protects new or repaired framing from moisture but does not re-support a sagging floor. Rot, failed shims and settled piers are addressed under crawl space repair, and the moisture mechanism is described in crawl space moisture and wood decay.
- What is crawl space encapsulation?
- It turns a vented crawl space into a closed, unvented one: the ground is covered with a sealed vapor retarder, vents are closed, walls are usually insulated, and the air is dried or conditioned.
- What does the code require for an unvented crawl space?
- A continuous Class I vapor retarder over all exposed earth with seams lapped at least 6 inches and sealed, the retarder carried at least 6 inches up the stem wall, and one of several air-control methods such as continuous exhaust, conditioned supply air or dehumidification.
- Does encapsulation stop water from coming into a crawl space?
- No. A vapor retarder controls moisture rising from the soil and humid air, but standing water from poor grading or a high water table is handled with grading and drainage, which the code addresses separately.
- Crawl space encapsulation: Do manufactured homes need a vapor barrier under them?
- HUD's installation standard requires a ground-cover vapor retarder of at least 6-mil polyethylene when the space under the home is skirted or enclosed, unless the home is in an arid region with dry soil.
When is cosmetic crack repair enough?
When cracks come from something other than foundation movement, or movement has stopped. If soil is still moving the house, cosmetic repairs reopen.
- When is cosmetic repair the whole answer?
- Not every crack means the foundation is moving. Several common causes of cracking leave the foundation sound:
- Cosmetic repair only: Why does the movement trend decide?
- Expansive soils, usually clays, can cause excessive cracking of floors, walls and foundations as they shrink and swell. In clay, moisture change follows wet and dry seasons and can reach from 3 to 40 ft deep.
- What does cosmetic repair include?
- Drywall crack repair and re-taping; Brick and mortar repair (repointing) and sealing of veneer cracks; Trim, baseboard and crown molding adjustment.
- When is cosmetic repair a supporting step?
- Cosmetic work also follows structural repair. After movement from center heave, a leak or settlement has been stopped, finishes are repaired as the last step. Finishing first and stopping movement later risks repeating the work, since cracks reopen while the mechanism is active.
- Cosmetic repair only: Can I just patch cracks without fixing the foundation?
- Patching finishes is the full repair when the cracks come from causes other than ongoing foundation movement, such as concrete shrinkage, or when movement has stopped. If an active soil mechanism is still moving the house, patched cracks tend to reopen.
- Cosmetic repair only: How do I know if foundation movement has stopped?
- Repeated floor elevation readings over wet and dry seasons show whether the house is still moving. Clay soil moisture changes with the seasons, so one set of readings cannot separate seasonal movement from steady movement.
- Cosmetic repair only: Are hairline cracks in new concrete normal?
- Concrete shrinks as it dries, and extra mixing water increases shrinkage. Engineering guidance for slabs on swelling soil states that some cracking of floating slabs should be expected.
- Do cracks that open and close with the seasons need structural repair?
- Not always. Seasonal opening and closing points to clay shrinking and swelling with moisture. Whether that calls for structural work depends on how large the movement is and whether it trends in one direction over time.
When is foundation or slab replacement needed?
Replacement is the most disruptive repair, used when piers, lifting and moisture control cannot restore the foundation, and it follows an engineered design.
- When is replacement considered?
- Replacement is generally a last resort for severe cases, such as:
- Slab or foundation replacement: Why do soil conditions drive the design?
- Clay with a linear extensibility (an NRCS measure of shrink-swell) of more than 3% can shrink and swell enough to damage buildings, and special design is often needed.
- What replacement foundation options exist?
- An engineering committee comparison of foundation systems on expansive clay describes the following:
- Slab or foundation replacement: What are void spaces and why are they used?
- A void space is a deliberate gap between swelling soil and a suspended slab or beam. It is formed with cardboard (corrugated paper) forms that hold up the wet concrete and later break down, or with plastic or metal forms.
- Slab or foundation replacement: What are the limitations?
- Highest disruption of any repair, since floors, plumbing and finishes over the replaced area are removed and rebuilt; Requires engineered design, permits and inspection — see codes and permits and working with engineers; Cost is driven by the area replaced, pier count and depth, access, and the restoration of plumbing and finishes.
- When is a foundation replaced instead of repaired?
- Replacement is generally reserved for severe cases, such as major original construction defects or badly damaged post-tensioned slabs, where piers, lifting and moisture control cannot restore acceptable performance. The decision rests on an engineer's evaluation.
- What is a structural slab with a void space?
- It is a concrete floor that spans between grade beams carried on deep piers, cast over corrugated paper forms that later degrade, or over plastic or metal forms. The forms leave a gap of about 1 to 24 inches so swelling clay can rise without pushing on the slab.
- Is a crawl space better than a slab on expansive clay?
- An engineering design review describes a raised wood floor over a crawl space on deep foundations as usually the highest-cost option; it reduces vertical movement from expansive soil if enough crawl space is maintained, and it needs ventilation and drainage.
- What information does an engineer need to design a replacement foundation?
- A geotechnical report with soil borings, lab tests and an estimate of how much the ground could rise or fall, including the void height needed for a suspended slab.
Which foundation pier type is right for an Oklahoma home?
Pressed concrete, steel push, helical and drilled piers differ in installation and bearing; on clay, the key is reaching below soil that swells and shrinks.
- How do the pier types compare?
- Trade words: underpinning means adding support under an existing foundation; refusal is the point where a pier will not go deeper under the applied force; reaction is the weight a hydraulic jack pushes against.
- Pier type comparison: What does Oklahoma installation data show?
- Oklahoma steel push pier installation records give these working figures: - Typical depth 8 to 16 ft at exterior footings and 5 to 13 ft at interior locations. - At one large Tulsa site, 396 piers reached a median depth of 12 ft, with the middle half between 9 and 14 ft and a full range of 2 to 40 ft, at a median of about 9,000 psi. - Field standard of 6,000 psi minimum, with 8,000 to 10,000 psi as the target range. - Spacing usually about 7 ft between piers. - Pressed concrete piles in the same records usually stopped at 5 to 12 ft.
- Pier type comparison: Why does depth matter on clay?
- Seasonal moisture change can extend from 3 to 40 ft deep. Engineering guidance calls for piers on swelling soil to extend well below that zone and to be anchored against uplift.
- Pier type comparison: What questions guide the decision?
- Heave or settlement? Piers hold up settling areas; heave calls for other methods. See heave vs settlement; Is a water source still active? Grading, gutters and leaks are addressed first; the code calls for grade to fall at least 6 in within 10 ft of the foundation.
- What non-pier methods are used?
- Every mechanism is matched to these methods in the mechanism-method matrix.
- What is the difference between push piers and helical piers?
- Steel push piers are driven down in sections using the weight of the building as the reaction, and the hydraulic pressure is recorded at each pier. Helical piers are screwed in with a torque motor, do not need building weight, and the final torque is recorded.
- How deep do foundation piers go in Tulsa?
- In Oklahoma steel push pier installation records, exterior piers typically reached 8 to 16 feet. Across 396 piers at one large Tulsa site, the median depth was 12 feet, with the middle half between 9 and 14 feet and a full range of 2 to 40 feet.
- Why does pier depth matter on clay?
- Piers that stop inside the zone where clay swells and shrinks with the seasons can move with the clay. Research describes six-foot piers that handled normal annual fluctuations but did not appear adequate over a two-year drought followed by an extremely wet year.
- Pier type comparison: What decides which repair method fits a house?
- The main factors are whether the house is settling or heaving, whether a water source is still active, the weight of the structure, the depth to firm bearing, the need to resist upward pull, and access around and under the house.
Which foundation repair method fits each cause of movement?
Each repair method only works for some causes. Piers can hold up settlement, but they cannot fix heave or water problems.
- Repair method by cause: How do you read the table?
- Primary: the method acts on the cause or carries the load the cause has taken away; Supporting: the method helps, protects the main repair, or controls part of the cause, but is not enough alone; Not suitable: the method works against the cause, cannot act on it, or treats a symptom while the cause continues.
- Repair method by cause: What is the physical logic behind the table?
- Settlement vs. heave: swelling clay lifts lightly loaded foundations, and corners tend to rise relative to the center of a slab.
- Which methods fit which causes?
- A mimic is a crack pattern that looks like foundation movement but comes from something else, such as roof framing or concrete shrinkage; see cosmetic repair only. Whether a house is settling or heaving is worked out in heave vs settlement.
- Why does the cause of movement decide the repair method?
- Different causes move a foundation in different directions. Piers hold up settling foundations, but they cannot pull down a foundation lifted by swelling clay, and they do nothing about a water source or a plumbing leak.
- Are piers the right repair for every foundation problem?
- No. Piers are a primary method for settlement, but heave, leaks, crawl space moisture and basement wall pressure are addressed with other methods such as drainage, leak repair, moisture control and wall repair.
- What does a supporting method mean in this table?
- A supporting method helps control the cause or protect the main repair but is not enough on its own, such as drainage alongside perimeter piers on clay that dries and shrinks.
- Repair method by cause: Why is lime stabilization marked with caution in sulfate soils?
- Oklahoma highway research found that lime added to a high-sulfate soil formed ettringite and increased swell by more than 1,200 percent, so sulfate testing comes before lime treatment.