Does This Home Have Foundation Issues?

Introduction

When looking for a new home, one of the most important parts is the foundation. A home built on a solid foundation will last much longer and make the house better to live in. On the contrary, a home with questionable or shifting foundations could cause problems in the house in the future. A bad foundation can also be very expensive to repair depending on how long the repair is delayed.

Signs of Foundation Problems

The first step in assessing the state of a foundation is to notice the signs that there are foundation problems in the first place.

The following are signs that there may be foundation issues:

• Sloping floors.

• Cracks in the foundations seen from the interior or exterior.

  • It is possible for there to be cracks inside and not outside and vice versa.

• Doors that get stuck or no longer close as smoothly as before.

• Cracks in walls, usually in the corners of doorways and windows.

• Slanted posts in the crawl space.

It is important to note that none of these issues is an absolute sign that there are foundation issues. A combination of them is usually necessary to make a determination about the state of the foundation.

Sloping Floors

Uneven floors can be caused by a number of different factors. If there are foundation issues, it is highly likely that the floors would be sloped. This is because a portion of the foundation has settled deeper into the ground, or the ground beneath the foundation has heaved, lifting the foundation higher than the adjacent foundations.

The floor can be uneven because of the members supporting the floor itself. In a house with a crawl space or multiple floors, the floors are supported by beams and joists. If the joists or beams were undersized or damaged, it is possible that they deflected and sagged far enough to be noticeable. In this case, the foundations could be in perfect condition.

Ground level floors can be supported by a slab on grade, or concrete poured directly onto the soil. In this circumstance, the foundations do not support the floor, especially between the foundations. Instead, the floor is supported by the soil. If the soil was not compacted well, or the concrete slab on grade was not properly reinforced, cracks and unevenness can be felt when walking around.

Interior and Exterior Concrete Cracks

Cracks found on the interior or exterior sides of the foundations can be signs of foundation failure. There is a common saying in the construction industry, “Concrete cracks”. What is meant by this is that concrete in almost all conditions will eventually crack in its lifetime. Just because it has a crack, does not mean that it is compromised. When concrete is initially poured, it is filled with water. The water reacts with the cement in the concrete to make it harden and then it evaporates. As a result, over the course of its lifetime, concrete shrinks slightly. Steel reinforcement within the concrete can help to prevent it from cracking, but it is not uncommon for small hairline cracks to form in concrete. Small hairline cracks are not an immediate structural concern. They should be sealed and monitored once they are discovered.

The cracks that are of structural concern are going to be:

• Bigger. The general rule of thumb is that if a crack is wider than 3/16” to ¼”, it should be brought to the attention of a structural engineer.

• Associated with other problems in the structure above them. If cracks are paired with cracks in walls above, or slanted floors, they are likely due to foundation movement.

• Uneven in width. A crack that is narrow at one end and wide at the other indicates the concrete is rotating about the cracked area. This attribute can help an engineer to determine how the structure is shifting.

Stuck Doors

Doors are hung so that there is only a small gap between their frames and the floor. A small shift in the floor or walls can cause a door to scrape around its edges. Doors can also start to scrape and get stuck throughout the year because of the seasons, and moisture in the air that causes the structure to shift in shape. A door that scrapes in the summer may be fine in the winter, or vice versa. A door can also scrape because the hinges have come loose. On many occasions, tightening the hinge screws alleviates all scraping.

If these possibilities have been ruled out, the door is most likely scraping because the house has shifted laterally relative to the ground, or the foundations have shifted. In both cases, there are most likely going to be diagonal cracks at the top corners of the door. The nearest foundations and flooring should be investigated further.

Types of Foundations

If any of the signs above are found, there is a chance that there are foundation problems. In order to address them properly, the foundation type must be determined. In many structures multiple types of foundations are used.

There are many different types of foundations, but there are several common types used for residential homes. Generally, in most residential homes in the front range, the garage is constructed on a slab on grade with a perimeter foundation. This means that there is a shallow foundation under all of the exterior walls, and the interior space, where your car is parked, is a 4” thick piece of concrete poured over a vapor barrier and compacted gravel. In most homes, the concrete slab is connected to the perimeter foundation to tie everything together and keep it stable. In the front range, the slab on grade is expected to move so much that it is not connected to the perimeter foundations. It may sound counterintuitive, but by disconnecting the slab on grade from the perimeter foundation, the walls and the rest of the structure won’t move when the slab on grade does.

The rest of the home is built on top of a basement wall or on top of a perimeter foundation with a crawl space. When a perimeter foundation and crawl space are used, the home is supported by the perimeter as well as spread foundations interspersed throughout the crawl space. This type of foundation system is relatively cheap to install, but the downside is that the perimeter foundations do not have support from a slab on grade system and they are not coupled with the interior pad footings. Therefore, it is possible for only a portion of the house to settle at a time.

Sometimes a perimeter foundation may actually be grade beams spanning from pile to pile. From within the crawl space, they both look like concrete walls. The difference is that with grade beams and piles, the perimeter foundations are not supported by the soil beneath them. Instead, they are supported by the piles driven much deeper into the ground. This foundation system is common in newer homes in the front range.

In homes with basements, the structure is supported by a large concrete wall as well as some interior columns. In most cases, the perimeter basement walls are deep enough that they do not move in the vertical direction. Most if not all movement is found in the interior columns’ foundations. In some cases, a basement wall will fail by buckling inwards from excessive soil pressure.

Causes of Foundation Failure

The foundations of a home or any structure can fail for a number of reasons. For the purposes of this article, we will only analyze homes with the foundation types described above.  In no particular order, here are the most common reasons that foundations begin to move and shift.

1. Undersized foundations. Every soil only has a certain amount of weight that it can support. The amount that it can support without significant movement is dependent on its contents, water content, and structure. If a foundation does not spread the weight of a structure well enough, it can sink into the soil. Too high pressure from the foundation can break down the soil’s structure and force the air and water out of it.

   
   

2. A pocket of weak soil. Although it is rare, it is possible for foundations to be poured over a particularly weak pocket of soil. Even though the foundations are sized correctly everywhere else, they may not be sized for one particular section. This is nearly unavoidable unless all of the soil is completely excavated and replaced with engineered fill before pouring foundations.

   
   

3. Improper compaction. In many cases, before a home is constructed, the site is leveled. This is accomplished through a combination of cutting away hillsides, or filling them in. Soil that is left after a cut is more compacted and can expand. Where this soil was originally covered by hundreds of pounds of soil, now it is covered by much lighter loads. If it isn’t given time to expand before foundations are installed, it can heave and lift foundations. If soil that was added to a site, is not properly compacted, it can settle and sink after foundations are installed. Sometimes, one end of a structure is on a cut area, and the other end is over a filled in area and the same foundation design will lift in one place and settle in another.

4. Improper foundations. This is usually found in very old structures, where they were built before the builders and engineers knew any better, when an owner builds without the insight from an engineer, or when a builder cut corners on material costs to save money. 

   
   

   In most parts of the country, there is a frost depth. In many older structures, the foundations were not built deep enough to avoid the effects of freezing soil. This causes the foundations to shift seasonally and eventually fall apart.

   
   

   There are many cases where someone without the right knowledge pours a foundation for a DIY structure. Although the foundation seemed adequate at the time, many years later, many times after the installer has moved or passed away, the insufficiencies of the foundation come to light.

5. Excessive water content. Nowadays, it is part of the code that the soil around a home must slope away from it and that the downspouts from the rain gutters should expel water several feet away from the foundations. Water next to foundations poses several issues. First, an excessive amount of water can affect the soil. Depending on the type of soil, an excessive amount of water can cause the soil structure to collapse and settle, or it can be absorbed by the soil causing it to expand and lift the foundation. Another reason to keep water away from foundations is to protect the steel inside of the concrete. Believe it or not, concrete is porous. Water can seep into concrete and make its way to the steel inside and cause it to rust. When it rusts it expands and breaks the concrete from within. This is usually a very slow process and takes years to be discovered. A puddle on a concrete floor for a few days is not an issue. Soil that is continuously saturated for months on end could be an issue.

Foundation Solutions

Now that the types of foundation has been determined and the common causes of foundation are known, we can determine how to address foundation issues. Each option depends on the soil type, information available, and severity.

Option 1: Leave the foundations in place.

If the foundation movement is small, doors aren’t sticking, cracks are small, and the floor is still close to flat, only minor repairs or corrections are recommended. When there is only a small amount of movement, there are likely simpler and cheaper solutions to the problems being faced. For example, if a framed floor is slightly uneven, this can be fixed by shimming floor joists or changing the heights of posts in the basement or crawl space. If the floor is a slab on grade, it can be leveled using mud-jacking or foam injection under the slab to level it back out.

Often, especially in the front range, columns are adjustable in height. Small amounts of settlement or heaving can be countered by adjusting the height of the column.  Small cracks in the concrete or the walls can be patched and sealed.

If the cracks reappear, it means the structure and foundations are still moving and more drastic measures should be made.

Option 2: Reinforce the existing foundations

If there is more severe movement, or previously repaired cracks have reappeared, it is recommended that the foundation be reinforced. Reinforcement can come in different forms.

• If a portion of the foundation has sunk into the earth more than the foundations around it, it can be bolted to the adjacent foundations, and a new wider and deeper foundation can be poured underneath it. This ties it back to the original foundations and prevents or slows down more settlement. Pouring more concrete and creating a new foundation under an existing foundation is called underpinning. Another form of underpinning uses drilled piers. These are steel poles that are drilled into the ground adjacent to the existing foundation for it to attach to. The poles provide more support in the soil. These are used when the stable soil is too deep to easily pour concrete.

• If a basement wall is starting to buckle inwards, steel can be bolted to the walls to prevent further movement.

Option 3: Replace the existing foundations

In rare cases, the soil has moved and caused the foundations to shift so much that it is not worth the time to reuse the existing concrete. Oftentimes this occurs in older structures where the concrete was not reinforced with the right amount steel reinforcement, or the concrete has deteriorated over time. In one case, the home’s foundation walls had toppled over, and the house was supported by a series of columns balanced on concrete pavers.

In this condition, it is recommended that all damaged foundations be completely removed and replaced with foundations that are up to or exceeding the requirements of today’s code.

Other Considerations

It is always recommended that a geotechnical engineer be hired when dealing with foundations.  A geotechnical engineer will test your soil and explain the strength and characteristics of the soil in an exact location. The information that a geotechnical engineer provides aids the structural engineer is the design of the foundations. The geotechnical engineer will tell the structural engineer the type of foundations to use and the forces that will be exerted on them by the surrounding soil.

By hiring a geotechnical engineer and a structural engineer to diagnose foundation issues, you are ensuring that the actual cause of foundation damage is fully understood and an efficient solution is provided. Hiring both of these professionals may cost several thousand dollars, but they will save you from wasting money on “repairs” that do not work, prevent further damage from occurring, and get you a design that will work for decades to come. In most cases, the initial investment into professional oversight prevents wasted time, wasted money and unnecessary anxiety.

Disclaimer

IMPORTANT: This article is provided for general informational purposes only and is intended to help homebuyers identify potential "red flags." It does not cover every possible structural scenario or foundation type. The information contained herein does not replace the professional judgment of a licensed engineer. Foundation issues are complex and site-specific; therefore, this article should not be used to self-diagnose or attempt to repair structural problems. Always consult with a qualified structural engineer and/or a geotechnical engineer to perform a formal inspection and provide a stamped, site-specific repair design before taking any action.

Glossary of Terms

Deflected / Sagged - When a structural member (like a beam) bends downward under the weight it is carrying.

Grade Beam - A reinforced concrete beam that transmits the load of a wall to spaced foundations (like piles or piers) rather than sitting directly on the soil.

Heave - The upward movement of the ground or a foundation, often caused by expanding soil or frost.

Joists - Horizontal structural members (usually wood, steel, or concrete) used in a repetitive pattern to support a floor or ceiling.

Mud-jacking / Foam Injection - A process where a liquid material (concrete "mud" or expanding foam) is pumped under a sunken slab to lift it back to its original level.

Pile / Pier - A vertical structural element driven or drilled deep into the ground to reach more stable soil or rock layers.

Slab on Grade - A type of foundation where a concrete slab is poured directly onto the ground to serve as both a light foundation and the floor.

Vapor Barrier - A thin layer of impermeable material (typically plastic) placed under a concrete slab to prevent moisture from the ground from seeping through the floor.