Retaining Walls on Tulsa Hillsides: When One Is About to Fail

Drive through the older hillside neighbourhoods around Tulsa and you will pass hundreds of retaining walls. Railroad tie walls going grey and soft, stacked stone from the nineteen fifties, segmental block from the nineteen nineties, poured concrete of uncertain age. Some are doing their job. A number of them are in the early stages of failing, and the owners have no idea, because a retaining wall gives plenty of warning if you know what you are looking at.

This article covers why there are so many here, the types you will encounter, how they fail, the warning signs, why drainage is nearly always the cause, the ownership question, what repair costs, and what happens when a wall meets a home inspector.

Why this area has so many

The terrain around Tulsa is not flat. The land rolls, breaks toward the river and rises sharply in places, and a great deal of the housing built through the middle of the last century was placed on lots that were cut and filled to produce a level building pad and a usable yard.

Cutting into a slope leaves a face that wants to move. Filling out from a slope creates ground that was never naturally compacted. Both get held back by a wall. Whole streets in the older hillside areas, and particularly on the west side and around Sand Springs, were developed this way, which is one of the themes on our Sand Springs page.

A retaining wall is not landscaping. It is a structure holding back soil, and it is doing that every hour of every day, including when the soil behind it is full of water.

The types you will see

Railroad tie and timber

Extremely common on properties built or landscaped from the nineteen sixties through the nineteen eighties. Cheap, quick, and made of a material with a finite life. Timber walls rot from the back where they sit against wet soil, so a wall that looks acceptable from the front can be substantially gone behind. Treated timber lasts longer than untreated and still does not last forever.

Dry stacked stone

Attractive, common on older properties, and highly variable in quality. A well built dry stone wall with proper batter and drainage can outlive everybody. A decorative stack of stone with soil behind it and no drainage is a wall in name only.

Segmental concrete block

The modular interlocking block systems that became standard from the nineteen nineties onward. When built to the manufacturer specification, with the right base, the right backfill, and geogrid reinforcement where the height calls for it, they perform well. When built by somebody stacking blocks without any of that, they bulge and separate, and the failure is usually visible as a curve in what should be a straight line.

Poured concrete and masonry

Solid when engineered with adequate footings, reinforcement and drainage. Failure is less common but more dramatic when it happens, typically appearing as cracking, rotation at the top, or the wall leaning away from the slope as a unit.

Boulder and gabion

Less common on residential lots and generally more tolerant of movement, since the individual units can shift without the whole structure failing. Still dependent on drainage.

How they actually fail

Very few retaining walls fail because the soil pushed harder than the wall could resist on a dry day. They fail through one of a small number of mechanisms, almost all of which involve water.

• Hydrostatic pressure. Water collects behind the wall and cannot escape. Saturated soil is heavier and exerts far more pressure than dry soil, and the wall was rarely designed for it
• Sliding. The whole wall slides forward at the base because the friction under it cannot resist the load
• Overturning. The wall rotates outward at the top while the base stays put, which is what produces the classic lean
• Bulging. A section deflects outward in the middle while the ends stay in place, common in block and stone walls without reinforcement
• Material failure. Timber rots, mortar deteriorates, concrete spalls, and the wall loses the strength it once had regardless of how it is loaded
• Loss of embedment. Soil in front of the base washes away, and the toe of the wall loses the support it depended on
• Added load. Somebody parks on the ground above, or builds a shed, patio or pool near the top, adding a surcharge the wall was never designed to carry

Signs one is about to fail

Walls announce themselves. Walk yours after heavy rain and look for these.

A wall with any of the first six of these, and any wall over about four feet, warrants an engineer rather than a landscaper. The height matters because the load rises steeply with it and because a taller wall failing has considerably more consequence.

Drainage is nearly always the cause

Behind a properly built wall there should be free draining material, commonly gravel, a way for water to escape through weep holes or a drain pipe, and frequently a filter fabric preventing fine soil from clogging the gravel. That system exists to make sure that water arriving behind the wall leaves rather than accumulating.

When it is absent, or when it silts up over twenty years, water accumulates. Clay soil behind the wall takes it on, swells, and pushes. This is the same mechanism that moves foundations, which our article on drainage and gutters covers, applied to a structure that was often built with even less margin than a house.

Two things make it worse locally. Roof water is frequently directed toward the high side of a lot because that is where the ground falls away, which sends the entire roof discharge into the soil behind the wall. And irrigation on the upper terrace adds water through exactly the dry months when the clay is most able to absorb it.

Who owns the wall

This question causes more trouble than the engineering. A wall on or near a boundary may be wholly on one property, straddling the line, or on one property while retaining the soil of another. Who is responsible for maintaining and repairing it depends on where it sits, on any recorded easements or agreements, on how it came to be built, and on facts specific to the situation.

We are not going to give you an answer on that, because there is not a general one and getting it wrong is expensive. What we would say is this.

• Find out where the boundary actually is before assuming. A current survey, not the fence line, not what a neighbour says
• Check the abstract and the title work for recorded easements or maintenance agreements. Our article on reading your abstract covers what is in there
• Take legal advice early rather than after the wall has failed and somebody's driveway has moved
• Put any agreement with a neighbour in writing. A verbal understanding about a shared wall does not survive either party selling

Permits and engineering

Most jurisdictions require a permit for a retaining wall above a certain height, and frequently require engineered drawings above that height or where there is a surcharge such as a driveway or structure above the wall. The trigger height varies between the City of Tulsa and the surrounding municipalities and counties, and it changes, so ask the relevant building department rather than relying on what a contractor tells you.

This matters at sale. A wall built without a required permit is unpermitted work, with all of the complications that carries, which we cover in unpermitted work. If you are having a wall built now, keep the permit, the engineering and the invoices, because they are worth real money to you later.

What repair actually costs

Figures move and vary enormously with height, length, access and material, so treat these as ranges rather than quotes and get several written bids.

• Clearing and reinstating drainage behind an otherwise sound wall is the cheapest intervention and can be a few hundred to a few thousand dollars
• Rebuilding a short timber wall is typically a low four figure to mid four figure job
• Rebuilding a segmental block wall properly, with base, backfill, drainage and geogrid, commonly runs into five figures on any meaningful length
• An engineered wall with a surcharge above it, or one requiring machine access down a difficult slope, can run considerably higher again
• Engineering fees sit on top and are worth paying, because the alternative is buying a contractor's opinion about their own work

The pattern worth noticing is that repairing drainage early is cheap and rebuilding a collapsed wall is not. A wall in the early stages of failing is the moment where money makes the most difference.

Disclosure and the sale

Oklahoma places disclosure obligations on residential sellers regarding known defects, and a retaining wall that you know is failing is a known condition. Our article on seller disclosure requirements covers the general position, and specifics are a question for a real estate attorney.

Practically, hiding it does not work. A leaning wall is visible from the street, it is one of the first exterior items an inspector photographs, and a buyer who discovers it after closing has a grievance you do not want.

What lenders, insurers and appraisers do

Reactions vary and depend on severity and on the loan product. Government backed loan programmes generally take a stricter view of anything presenting a safety or structural concern, and an appraiser who flags a wall as a condition issue can trigger a requirement for repair before closing or a reinspection afterwards.

Insurance is a separate question. Retaining walls are frequently excluded or limited under standard homeowner policies, particularly for earth movement, so an owner assuming the policy covers a collapse may find otherwise. Check the policy rather than assume, and read our note on denied claims for the general shape of that problem.

The effect at sale is a narrowed buyer pool. A house with an obviously failing wall attracts fewer financed buyers, more repair requests, and more renegotiation after inspection.

Where we come in

We buy houses in Tulsa and the surrounding towns as they are, including hillside properties with retaining walls that have moved, bulged or partly collapsed.

The honest position is the same one we take on foundations. If the wall is early in its failure and the fix is drainage, that is a comparatively small amount of money and it protects a much larger asset, and you should do it and keep the house. Where selling makes more sense is when a full rebuild is quoted at a number you cannot fund, when the wall is one item on a long list, or when a boundary dispute over a shared wall has become the thing standing between you and moving on.

We price the wall into the offer rather than asking you to rebuild it first, we close on Oklahoma title company timelines, and our offer process is free with no obligation.

The short version

• Hillside lots around Tulsa were cut and filled to create building pads, which is why retaining walls are everywhere here
• A retaining wall is a structure, not landscaping, and it is loaded every day
• Nearly all failure is water related, through hydrostatic pressure behind a wall that cannot drain
• The warning signs are a lean, a bulge, separation, cracking, soil spilling through, sinking ground above and seepage through the face
• Photograph the wall annually from the same spot. It is the cheapest monitoring there is
• Timber walls rot from the back, so the front tells you very little
• Anything over roughly four feet, or showing movement, needs an engineer rather than a landscaper
• Ownership of a boundary wall is fact specific. Get a survey and legal advice rather than assuming
• Permit requirements vary by jurisdiction, and an unpermitted wall becomes a sale problem later
• Fixing drainage early is cheap. Rebuilding a collapsed wall is not