Choosing the type of foundation for a home is a big decision. Much depends on the lay of the land, local Codes, budget, and if you want a crawl space, a full basement, or neither. If you’re wondering what the differences are between a pier and beam vs slab foundation, we’re here to help!
A pier and beam foundation raises the building above the ground and creates a crawl space for storage. It can be built almost anywhere, is less expensive, DIY friendly, and often easier to repair. A slab is usually formed on flat ground, so easier access. It requires more machinery but is quicker to get to the build stage as it includes a solid concrete floor.
In this article, we’ll explain what pier and beam, and slab foundations are, their differences, and the pros and cons of each. We’ll discuss if a pier and beam can be converted to a slab foundation, and also which of the two foundations is better. Our aim is to provide you with the information to make the best choice for your project.
- What is the Pier and Beam Foundation?
- What is the Slab Foundation?
- Pier and Beam vs Slab: Key Points
- What Is the Difference Between Pier and Beam and Slab?
- Pier and Beam Foundation Pros and Cons
- Concrete Slab Foundation Pros and Cons
- Can You Convert Pier and Beam to Slab?
- Is Pier and Beam Better Than Slab?
What is the Pier and Beam Foundation?
Pier and beam foundations are raised foundations that have been around for millennia and are still commonly used today. They use poured or precast concrete, brick, stone, wood, or steel piers or posts dug, drilled, or placed into or onto the ground. They may rest on a rock, a poured concrete pad, gravel, bedrock, or undisturbed dirt.
Beams of wood, steel, or concrete are placed on top to level and connect the piers together, and carry the structural loads. The loads are transferred through the beams to the piers, and then to the underground strata.
The piers are used to raise the structure above the ground and form an easily leveled foundation. They are often used where the ground is uneven, soil strata are unsupportive, the ground is damp, seasonal flooding or storm surges occur, termites are a concern, or to improve views. The foundation typically creates an 18” to 30” open or closed crawlspace under the structure for storage or access to plumbing and utilities.
There are different ways to construct a pier and beam foundation depending on the lay of the land, ground strata strengths, available materials, structural requirements, and local building codes. All involve vertical piers or pillars of a structural material set into or onto the ground to create a supportive level base and raise the structure off the ground. The piers are placed at strategic points around the perimeter and center of the structure based on the building’s footprint and load-bearing needs.
The beams are placed on the piers, leveled, and secured to the pillars. They form a connective framework that supports the building’s floor joists and subfloor platform.
The beams often form supports for perimeter walls as well as the center of the structure, but may also support other structural points too. A pier and beam foundation can provide a strong, level, raised base for residential, commercial, or industrial buildings.
What is the Slab Foundation?
Slab or slab on grade is a relatively modern foundation type that takes advantage of geography and climate conditions. They are typically a reinforced poured concrete pad with a built-in 12” or thicker perimeter ‘footing’.
The slab is usually 4” to 6” thick except at the perimeter or support points, and is often formed and poured directly on the ground. However, the organic material is usually removed, a layer of gravel or sand compacted in its place, and a vapor/moisture barrier added prior to pouring the concrete.
Since the slab is on the ground and there is no basement or crawlspace, all utilities and plumbing connections must be placed prior to the pour. In some situations, several inches of rigid insulation may be placed down and radiant heating lines may also be laid out prior to the pour too. Since the slab is poured near grade level, it needs reasonably flat ground and a warmer, drier climate.
A slab foundation is derived from the blueprints and footprint of the structure it will support. The thicker, reinforced perimeter, along with any central support points, need to provide structural support to the building.
Since it isn’t a deep foundation, it is more susceptible to cold and moisture damage, which is why climate and geography are major factors in its use. Cold can cause frost heaves resulting in cracks, and low ground and heavy rains can result in flooding and erosion.
There are different ways that slab foundations can be formed. The most common is directly on prepared ground, which results in easier ground-level access. Another way is a raised slab foundation that combines a slab with a pier and beam foundation.
It could also be raised using a poured concrete perimeter wall or beam foundation filled with compacted engineered material and the slab floor poured on top. Regardless of type, though, a slab foundation has no crawl or basement space underneath.
Pier and Beam vs Slab: Key Points
Pier and beam foundations differ from slabs in many ways. Both foundations have broad usage for different structures, but one may be better than the other in some situations. The Table below compares the two foundation types based on key points.
|Pier and Beam
|Highly durable in specific climate and topographic conditions
|$5 and $12 a square foot for the foundation including labor, but no subfloor
|$4 and $8 per square foot, plus labor and delivery for a finished foundation and floor
|Maintenance and Repair Cost
|Minor repairs between $250 and $1,000, larger problems up to $10,000 or more
|Minor repairs range from $500 to $1,000, extensive repairs up to $30,000 or more
|Risk of Settling
|Risk of settling depends on soil or rock strata quality
|Low risk of settling if built on or near rock strata
|Uneven, flat, or wet ground for all types of structures
|Flat ground for all types of structures
What Is the Difference Between Pier and Beam and Slab?
A slab or slab-on-grade foundation differs from a pier and beam foundation in several unique ways. Not only are they built differently, but they look different and transfer the weight of the structure to the ground differently. In this section, we’ll compare the two foundations based on key decision-making points.
A slab foundation requires relatively flat, well-drained ground. The ground must be made flat and all utility and plumbing connections laid out and readied prior to the slab being poured.
In some situations, the slab may be raised significantly above the surrounding landscape using poured footings and beams or foundation-style walls, piers and beams, retaining walls, or berms. To level the ground and pour a slab foundation requires heavy equipment, greater access, and a team of workers.
A pier and beam foundation can be laid out and built on almost any topography. Utility and plumbing connections can be placed at the same time or added afterward. The most complex part is placing and leveling the piers to meet the structural bearing points of the building.
The piers may lift the building inches off the ground or two or more feet above the surrounding landscape. A pier and beam foundation can be built with locally sourced materials or purchased prefabricated materials easily transported to the site and built by one or more people with regular hand tools.
There are many factors that affect the durability of both pier and beam foundations and slabs. Earthquakes or ground tremors caused by freight trains or large, heavy vehicles can damage even the best construction, as can sinkholes. So, aside from those circumstances, durability depends on materials used, workmanship, load values, and maintenance.
A properly prepared, reinforced, and poured concrete slab should last hundreds of years with minimal cracking. However, freeze-thaw effects or flooding can cause significant damage.
A pier and beam foundation may be all wood, so susceptible to insect and moisture damage. If the piers are made of masonry, concrete materials, or stone, they typically last much longer. There are examples of millennia-old structures with pier and beam foundations still in use today.
The cost factor depends on the size of the project, types of materials used, equipment required, labor needs, and time. In many ways, a slab is a more expensive endeavor as it requires heavy equipment to level the site, gravel or sand trucked in and spread and compacted, trenching for utilities and plumbing, steel reinforcing, vapor barrier, and concrete. Plus, there are the labor factor and delivery charges to do different aspects of the job.
However, the slab can be ready in a short period of time if everything is lined up ahead of time. Expect to pay between $4 and $8 a square foot, plus labor and delivery for a finished foundation and floor.
The cost of a pier and beam foundation depends on the materials used, the size of the structure, equipment, labor, and time too. Poured pads for each pier, pier and beam materials, and fasteners all add to the cost. Today, many contractors trench the perimeter and center of the structure’s footprint so it is easier to pour footings and erect piers, and then backfill and compact the trenches.
Expect to pay between $5 and $12 a square foot for the foundation, including labor. However, if materials can be sourced from the land itself, costs can be zero if doing your own work. It should be noted, though, the joists and subfloor still need to be installed to be in the same building point as a slab.
Maintenance and Repair Cost
The main issues with a slab foundation are cracking due to settling or erosion. Maintenance to prevent erosion commonly involves sloping runoff away from the foundation. Cracks may involve chipping, grinding, and patching depending on the extent and cause.
Settling may require mudjacking – pumping a slurry of water, sand, cement, and soil through holes in the slab to raise it back to level and provide support. Minor repairs may range from $500 to $1,000 while mudjacking or other repairs from $3,000 to $30,000 or more depending on the magnitude of the repair.
Maintaining and repairing a pier and beam foundation depends on the type of materials used, the number of piers, pier location, and load factors involved. Although maintenance depends on the type of materials used, it usually involves moisture and insect protection or repointing.
Repairs typically are required due to settling or decay issues and may necessitate shimming beams back into level to replacing one or more piers or adding new piers to take the load. The costs are usually less than those required for a slab. Minor repairs may be $250 to $1,000 while larger problems may run from $2,000 to $10,000 or more.
Flood Protection / Water Accumulation
The top or floor of a slab foundation is commonly 6” to 12” above the surrounding ground, so water accumulation and flooding aren’t usually a concern. The house isn’t going to float away, and water shouldn’t cause damage under the foundation. However, deep water flooding or fast-moving water flow can cause damage, so if you live in an area that could happen, you may want to take precautions.
A pier and beam foundation frequently has a crawlspace underneath it, so the structure is better protected from flooding and water accumulation. However, water pooling in the crawlspace can lead to mold and mildew concerns, so it is important to remove and prevent water accumulation. Areas prone to deep flooding or storm surges require that the structure, piers, and beams be securely connected or anchored to prevent the house from floating away.
Risk of Settling
The risk of setting for any type of foundation depends on soil and ground strata, moisture and frost concerns, and if the foundation is properly designed for the loads it must bear and distribute.
Once a foundation begins to settle, it can shift framing out of plumb, making doors and windows difficult to open or close, floors to sag or shift out of level, cracking to appear in walls and ceilings, and even cause it to collapse. The longer it’s allowed to go on, the greater the damage and cost to repair – take the Leaning Tower of Pisa for instance.
A slab on a properly prepared and compacted base on strong soil or bedrock strata won’t shift any more than a pier and beam foundation in a similar situation. The slab technically floats on the ground to uniformly distribute the loads, whereas pier and beam foundations are standing on multiple stilt-like pillars that usually reach down to more solid soil or rock formations.
If built on other types of soil strata, the slab is at greater risk of settling or cracking. There’s always a risk one or more of the stilts will settle in weak support strata and sink or tip out of plumb, which in turn can cause others to shift. However, in the long run, a pier and beam foundation will provide greater structural stability.
Flexible for Uneven Ground
A slab foundation needs to be formed on flat, leveled ground so that it balances and supports the structure properly. The more construction required to create a level surface, the greater the cost and time. A raised slab is an alternative, but also costs more in materials, labor, and time.
Pier and beam foundations are ideal for uneven or level ground since the pier heights can be adjusted to create a level base, which is usually cheaper and easier than leveling the ground. Depending on the topography of the ground and the strength of the load-bearing ground strata, some piers may also need to be deeper in the ground, while others don’t. So, a pier and beam foundation offers greater solutions for uneven ground.
A slab foundation sits directly on a prepared base on the ground. Its solid structure makes it near impossible for pests to penetrate into the structure from below. Plus, the perimeter of the foundation is thicker, so it goes deeper into the ground, offering a greater barrier to pests. However, due to its closeness to the ground, it does offer easier egress to insects, rodents, and reptiles.
A pier and beam foundation typically has an open or closed crawlspace underneath the structure’s floor. If left open, it offers a generous invite to rodents, snakes, porcupines, raccoons, groundhogs, bears, and other visitors. It also can become a safe haven for bees, wasps, ants, and termites too.
A closed-in crawlspace can limit the size of uninvited pests, but unless it is a proper barrier, it won’t. Additionally, if the crawlspace is enclosed, it can lead to mold and mildew growth unless properly vented.
Resale value greatly depends on the age, condition, layout, and style of the house that sits on the foundation, what potential buyers are looking for, and how informed they are. There are pros and cons to both foundation styles too. Selling a house on a slab where storm surges or seasonal floods could or have occurred would likely offer lower resale than one raised up on a pier and beam foundation.
A house on a slab is usually easier to heat and cool and often offers easier access than one on piers. Pier and beam offer extra storage underneath, plus easier access to utilities and plumbing for repairs. It is also easier to add an addition or deck onto a house on piers than one on a slab.
Unless there are obvious issues with the foundation that affect the structure, resale shouldn’t be a concern. However, since many, if not most buyers and realtors know little about foundations, one that sits flat looks safer, so resale on slab foundations is commonly higher.
A slab foundation is best used for areas with flat, dry ground in warm climates. Deep frost can damage the slab, so they are less common in colder climates. They are often used for garages, outbuildings, cabins, homes, barns, stores, malls, warehouses, and even industrial complexes. They are quick and easy to build, and also less expensive than some foundation options.
Pier and beam foundations are best for uneven or flat ground, areas prone to flooding, poor soil strata, or to raise a structure for better vistas. They are less expensive, so easier on the budget, and more DIY friendly. They are ideally suited for houses, decks, barns, outbuildings, seasonal homes, warehouses, factories, malls, high-density multi-story towers, and most other structures.
Pier and Beam Foundation Pros and Cons
Pier and beam foundations have a long history and are widely used today for all types of structures. The magnitude of the structure and load points determines the number, depth, placement, and size of the piers and beams, and the complexity and cost of the build. The pros and cons identified below may tip the balance in favor of this type of foundation over other choices.
- ideal for uneven ground
- works well for most soil strata, rock formations, marshy areas, and underwater
- elevates the structure above the surrounding ground for better views
- generally, has a useable crawlspace for storage and ease of repairs
- easy access to utilities and plumbing
- less expensive than other foundation types
- DIY friendly
- remote access friendly as heavy equipment usually isn’t necessary
- less expensive than other types of foundations
- reasonably quick and easy to make
- less transfer of ground vibrations
- less disruptive to the surrounding landscape
- offers protection from flooding and termites
- decks and additions can be easily added
- crawlspace may attract insects, rodents, reptiles, or larger critters
- more difficult to heat and cool due to the drafty crawlspace
- if the crawlspace is enclosed, it must be properly vented
- low elevation from the ground may make repairs difficult
- if poorly constructed, the subfloor may be springy, creaky, or not level
Concrete Slab Foundation Pros and Cons
A concrete slab foundation should last a long time if properly built and maintained. The size of the building, the amount of leveling required, and the climate affect the complexity and cost of construction. Like other types of foundations, there are pros and cons to consider.
- a very strong, solid foundation
- reasonably quick to form and pour, and ready to build upon
- no crawl space for unwelcome visitors
- easier to heat and cool than other foundation types
- a solid concrete floor is part of the foundation costs
- low maintenance
- may be less expensive than other types due to built-in floor
- easier ground-level access
- more solid floor for greater finishing options
- mold and mildew shouldn’t be an issue if a moisture barrier installed
- higher resale value
- requires a flat building site
- organic material must be removed prior to construction
- heavy equipment needed, so greater access to the site required
- plumbing and utilities need to be installed prior to pouring, so leaks are difficult to repair
- no extra storage underneath
- deep frost can damage the slab
- concrete can crack, chip, or crackle
- repairs are more expensive than for some foundations
- difficult to connect with additions
- HVAC takes up floor space
- susceptible to flooding and dampness if no moisture barrier
Can You Convert Pier and Beam to Slab?
Converting a pier and beam foundation to a slab depends on numerous factors. If the conversion occurs prior to the construction stage, as in changing the foundation choice on the blueprint, the switch is usually fairly easy. It typically comes down to topography and climate. The cost for conversion would range from $0 to $1,000 depending on the complexity of HVAC and utility hook-ups, and how helpful the architect is.
Converting an existing pier and beam to a slab takes more planning and should be overseen by a Structural Engineer. It also depends on the size and magnitude of the structure, as well as other factors. The existing joist floor could be replaced by a concrete slab with built-in footings, but that means a great deal of work and expense.
An alternative is lifting the house off the pier and beam foundation, removing the foundation, and then installing a slab in its place before lower it and reconnecting everything. The joist floor and structure would then be supported and leveled on the slab. The cost for either conversion would depend on the structure’s size and the work involved but could range between $30K and $60K or more.
Is Pier and Beam Better Than Slab?
There are advantages to both types of foundations, but much depends on the topography, climate, and local HOA or building codes. A slab offers a lower profile and easier access on flat ground and is usually completed in a shorter time. It typically requires more heavy equipment and labor, though, and is better suited for warm dry climates. Plus, it includes a concrete floor, so the building phase can happen sooner.
A pier and beam can be built of more types of materials on sloped, rough, wet, or uneven ground, and is more DIY friendly. It requires less equipment and can be completed by one person, although it’s faster with more helpers.
Once the foundation is built, though, the joists and subfloor still need to be installed before the structure can be erected. A pier and beam foundation offers a greater diversity of location and structural stability in the long run, so is a better choice for more locations and structures. However, personal choice and budget still hold sway over which is best for your build.