Some Homes Need a Foundation That Elevates the Construction
While few people spend little time thinking of the home’s foundation, the simple fact is that it’s one of the most important elements of the home. Like the roof, the foundation – the load-bearing structure that supports the home – is not a popular conversation piece with potential homeowners.
The types of foundations vary – based on factors such as the architectural style, geographical location, climate, soil, and moisture conditions – and the all- important budget for home construction. In addition to the usual options – like full, walkout, or daylight basements; crawlspaces; and concrete slabs – that we are familiar with or at least have heard of and that work across a variety of climates and needs, there are also the out-of-the-ordinary foundations that are particularly significant in coastal, beachfront, shoreline, and flood-prone areas.
Because not every house is built on the same kind of foundation, it is vital to understand the other options. So, let’s focus on a variety of the elevated types like piers, piling, and screw pile foundations.
This 1.5-story, 1619-square-foot Contemporary Coastal style home – built on an elevated floor foundation – features a spacious porch, three bedrooms, two-baths, large windows, and a private bedroom suite on the upper floor. (Plan 116-1085)
Foundations for a Raised House
Whether it is for a practical or aesthetic reason, potential homebuyers are rediscovering the raised-floor foundation. Basically, an elevated foundation is designed to raise the home’s living space off the ground to isolate it from insects and moisture and protect it from heavy rain and storms. Visually, the home’s raised floor foundation works like a pedestal and enhances its curb appeal.
1. Pier or “Stilt” Foundation
Perhaps the most visible of the elevated home foundations is the pier-and-beam – or stilt – foundation commonly found in coastal regions, beachfronts, and mountainous or hilly sites, where it is difficult to install a conventional foundation because of the soil type, periodic water intrusion or flooding, steep slope, and the like. Usually raised about two to ten feet off the ground a raised foundation consists of brick, stone, wood, or concrete piers and wood or steel beams that support the weight of the home. The space below the home is entirely open except for the series of vertical pillars secured to beams that support the structure.
This creates a space beneath the home that allows plenty of natural ventilation. Homeowners also have the option of covering the space with exterior walls or using it for a garage/carport or storage area if it's high enough.
The pier-and-beam – or stilt – foundation is illustrated in this fabulous two-story Beachfront style home. Built on a narrow lot, the home features a total of four bedrooms, including two bedroom suites with walk-in closets on the second floor, and four bathrooms. The open lower level provides plenty of garage, utility, and storage space (Plan #196-1061).
This simple graphic illustrates the way the pier-and-beam foundation is installed: concrete vertical pillars raised above the ground topped by wood beams – providing a built-in crawlspace to place the plumbing and electrical systems (source: Basement Guides).
Advantages of the Pier-and-Beam Foundation
Because they're elevated, homes built on a pier-and-beam foundation are less prone to flooding, eliminating the problem of water reaching and adversely affecting the main residence. There are other benefits.
Easier access to plumbing, wiring, ductwork, and other electrical details
Little or no mildew and rot because of the ventilation beneath the structure
May be more economical than other foundations
Easier and cheaper to repair than slab foundations
May be prone to insect and pest infestation that cause damage to wiring and structural elements. To avoid this, floors must be heavily insulated to be protected from insects
Energy-inefficient – and colder floors in winter – without proper insulation
Squeaking and creaking floorboards possible because the pier-and-beam foundation has less support than floors sitting on a concrete slab
Dampness possible, depending on foundation height, which can be corrected by installing a drain or swale to evacuate water from the foundation perimeter
Significant damage to the entire foundation possible due to minor damage to a post or pier
2. Pile Foundations
Described as a series of columns or long cylinders of a strong material constructed or dug into the ground/soil, a pile foundation acts as a steady support for structures built on top of it. These types of elevated foundations can take higher loads than spread footings. They transfer loads from structures to hard strata, rocks, or soil; and support the structure by remaining solidly placed in the soil.
Pile foundations are particularly useful in areas with unstable upper soils that can be bad for large buildings and are typically installed when the soil conditions are insufficient to carry the design load or when non-vertical loading is expected.
The piling foundation is illustrated in this fabulous three-story Beachfront style home. Built on a narrow lot, the home features a total of six bedrooms, including two master suites on the second floor, five bathrooms, a powder room. The third floor living space features a Great Room overlooking a covered deck. The open lower level provides plenty of garage and storage space (Plan #130-1093).
There are a few types of pile foundations, based on their function and the composition of their materials. The fundamental piles classified according to function:
End Bearing Piles – where the bottom end of the pile rest on a layer of especially strong soil or rock. The bottom end rests on the surface – which acts as the intersection of the weak and strong layer – with the load bypassing the weak layer and is transferred to the strong layer.
Friction Piles – Here the load is transferred to the soil across the full height of the pile … the entire surface of the cylindrical pile works to transfer the weight to the soil. The amount of load a pile can support is directly proportionate to its length.
Batter Piles are driven-inclined to resist inclined loads.
Pile Material and Shape
Piles can be made of wood/timber, concrete, and steel.
This informative sketch shows the various shapes of pile foundations and the materials used to make them (source: School of PE),
Concrete Piles come in two forms. There is precast concrete which is formed into a specific shape at a location other than the building, cured in a casting yard, then transported to the site of work. Cast-at-the-site or poured-in-place means standard concrete is transported to the site, then placed in the required location or into a dumper or pump.
Timber. Because wooden piles are used to support buildings in areas with weak soil, it is necessary to have trees with exceptionally straight and long trunks. The trees must be at least 20 meters long because two tree trunks cannot be joined together to form one pile.
Steel Piles are heavy columns made of steel instead of concrete and are designed to handle heavy structures like skyscrapers, highway bridges and vertical towers. Steel’s strength and durability enables the piles to be driven further into the ground and past dense layer of hard gravel.
Advantages of a Pile Foundation
Let's start with the precast process that pre-prepares the piles according to desired/required length, which reduces completion time.
The foundation is suitable for all property sizes and can be installed over a large area and exceptionally long lengths.
Piles can be used in a place where drilling is not required.
The piles are very neat and clean.
Disadvantages of a Pile Foundation
Here are a few disadvantages to consider:
Prone to damage when being driven through stones and boulders, as well as attacks by marine borers
Difficult to know the actual required length in advance
Vibrations common – and affects neighboring structures – when piles are being driven down the soil
Requires heavy machinery to operate
Do not have low drainage
3. Screw Pile Foundation
This foundation – also known as helical piles, screw cylinder anchors, and helical foundations – was introduced in 1836. Discovered, developed, and patented in 1833 by the blind Irish engineer Alexander Mitchell, screw piles were utilized as successful foundations for lighthouses, bridges, and piers.
Mitchell achieved fame by building the first screw-pile lighthouse – the Maplin Sands Lighthouse at the mouth of the Thames River. Construction on the lighthouse began in 1838 and was first lit in 1841. A screw-pile lighthouse stands on piles that are screwed into sandy or muddy sea or river bottoms.
Screw piles are a steel screw-in piling and ground anchoring system used for building deep foundations. They are described as “galvanized iron pipes with helical fins” that are installed deep into the ground to solidly support the structure.
Screw pile foundations are common in tiny houses, vacation homes, decks, and small backyard structures.
A rendering of the first screw pile lighthouse – the Maplin Sands Lighthouse on the River Thames – shows the steel pipes that anchor the structure (image credit: Public Domain).
Top: A very cozy 456-square-foot Contemporary style home with one bedroom, one bath, a fireplace in the living area, and a covered front porch with wood stove is an ideal model for a small residential design where a screw pile foundation is an attractive option. Bottom: The floor plan shows location of the screw piles and beams anchoring the structure. As we can see, the foundation is small and compact and allows easy additions and expansions to the home (Plan #116-1013).
Advantages of a Screw Pile Foundation
A top reason why industries use screw pile foundations is cost efficiency. A screw pile foundation is an economical alternative compared to traditional deep foundation techniques. Other benefits:
Versatile and offers many possibilities
Shorter project times
Ease of installation – and flexibility of being done year-round
Ease of access
Reduced carbon footprint/reduced environmental impact. Driving the screw piles in the ground means less soil displacement. Excess soil then does not need to be transported from the site, saving on transportation costs, and reducing the carbon footprint of the project.
Ease of removal when the foundations are no longer required
Reduced risk to the workforce
Minimal noise and vibration disruption to adjacent structures
Top: This 2318-square-foot Coastal / Beachfront home supports 5 bedrooms, including two master suites, four bathrooms, a powder room, and a large open living space with fireplace using a piling foundation. Bottom: The floor plan of the ground level shows the positions where supporting screw piles would be placed using square boxes with Xs in them. Note the space where 3 cars may be placed, along with storage and a bedroom and bath for someone who might not want to or can’t climb stairs easily (Plan #130-1045)
Disadvantages of a Screw Pile Foundation
On the other side of the coin, here are some drawbacks of a screw pile foundation.
Minimal noise and vibration disruption to adjacent structures
Difficult to penetrate extremely hard bearing layers
Damage to helixes possible during installation through strata (like rocky solid layers)
Manufacturing lead time required
Additional expenses possible related to sub-par and difficult to predict soil conditions.
4. Stem Wall Foundation
Quite common in California, Texas, the Northwest, the South, and in areas prone to earthquakes and flooding, a stem wall is the supporting structure that connects the foundation of a building to the vertical walls constructed atop the foundation. The stem wall is short – about the height of a crawlspace – and transmits the load of the structure to the footing, which distributes the weight over a wider area. In addition, this foundation provides a raised platform for the walls.
How are stem walls built? A footer is poured at the ground level, then cement blocks are laid to create a wall that rises above the slab elevation. They are sometimes called “two-pour foundations” in reference to the first pouring for the footing and then for the walls themselves.
Often built with masonry – cinder blocks – or of concrete, stem walls can also be made with preservative-treated wood (known as “pony walls”). Concrete stem walls are stronger and are necessary in flood zones and in areas with high winds.
With the concrete slab in place, the stem wall is ready to be constructed around it. Steel is often used to attach the wall to the foundations.
This charming two-story, 2,401-square-foot Traditional-style home with Coastal influences features an elevated foundation that enhances its curb appeal. The lovely residence has an open floor design and includes four bedrooms, 3.5 baths, a covered front porch, patio, sunroom, kitchen with a breakfast nook (Plan #168-1113).
Advantages of a Stem Wall Foundation
It is not surprising that the stem wall foundation is popular since it provides options to build a basement or a crawlspace. Other advantages…
Solid and durable foundation that transmits the load from the house to the footing and distributes the weight over a larger area.
The raised foundation protects the floor from flooding and the elements.
Allows easy access to plumbing, wiring and mechanical systems.
Suitability to most soil conditions
The elevated foundation adds to the aesthetic of the home.
Disadvantages of a Stem Wall Foundation
The cons include greater effort and expense and additional visits from inspectors, high frost levels that can cause issues, and the need for proper insulation to improve energy-efficiency and protection from pests.
Since foundations are not a “one-size-fits-all” proposition, think of the exciting task before you – as you spend the time considering – and understanding - the options that best fit your house design, lifestyle style, your needs, geographical area, climate, and budget.