When shopping for a new home, it&#;s easy to get caught up in the bright and shiny features and add-ons before anything else. New homebuyers should take the time to consider the less exciting (but equally important!) structural elements of their investment. The strong bones of the house will determine its long-term value. A home with stability and longevity will save money in the long run on repairs and play a part in generations of happy memories to follow.
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To increase stability and overall lifespan, a post-tension foundation is an ideal option for single-family homes. It not only functions as a safeguard against cracking in highly-unpredictable soil conditions and wet climates, but it also adds to the home&#;s value.
Because of its unparalleled versatility, a post-tension foundation is compatible with any home type from a sprawling ranch layout to a two-story estate. This type of foundation also uses less steel, which reduces costs. While there are minor drawbacks, the post-tension foundation provides critical support and high-quality structural benefits that any homeowner can enjoy.
What Is A Post-Tension Foundation?
Simply put, a post-tension foundation is a specific type of slab-on-grade foundation. The concrete is reinforced with threaded steel cables that are tensioned after the concrete cures. To allow the cables to slide more easily after the concrete hardens, the steel is encased in plastic sheathing to prevent the cables (tendons) from touching the hardened concrete.
The plastic sheathing is stretched post-pour, which tightens the slab and applies intense force to the concrete system to create a heavily-compressed state. A slab without reinforcement holds a very low tensile strength and is prone to cracking as the soil shifts. However, in a highly compressed state, a post-tension foundation can reduce the potential for breakage.
Post-tension foundations are often compared to standard rebar foundations in which a grid of strong steel is set in the poured slab for reinforcement. There are benefits and costs to both options, but the differentiator is how the rebar is tightened.
Benefits
When considering a post-tension foundation, you will want to consider the qualifies that make it an excellent choice for any new home.
Post-tension foundations are extremely versatile and may be the ideal solution for environments that do not support other types of home builds. Particularly in the Gulf Coast region and tropical areas with largely expansive soils that have a tendency to shift periodically, a post-tension foundation operates as a stiff apparatus to resist cracking. Similar to a boat that rocks back and forth on the waves as one large fixture, the foundation will ride the soil movements as it shrinks and expands with moisture changes.
Compared to the intricate arrangement of rebar that must be laid with precision for a standard conventional slab, the post-tension cables are easier to install. Experts will need to use specific machinery to tighten the cables once the slab hardens.
There are two major benefits to using less steel in the home&#;s foundation. The first one is the structure becomes more lightweight than a conventional rebar foundation; it is also easier for the construction team to pour the concrete due to its placement and extra space for the cables.
Second, there&#;s an economic benefit. In general, a homeowner can expect to spend about $4.50 to $5.00 per square foot on either a post-tension or conventional rebar foundation. However, the total expense relies heavily on steel&#;s current market price. Steel is an expensive material, which translates into savings for the homebuyer.
Fewer cables embedded in the slab than an intricate rebar grid means a simpler and straightforward inspection. Problems can be identified easily and quickly and be repaired before they become significant.
New homes with a post-tension foundation are highly regarded as having inherent strength and structural integrity. Any builder can vouch for the importance of improving the home&#;s stability and longevity with the installation of a post-tension foundation. When it comes time for resale, knowledgeable buyers will recognize the home&#;s long-term value and be willing to pay more for this important structural feature.
Challenges
While there are many wonderful benefits to consider, there are a few minor challenges to keep in mind when choosing a post-tension foundation.
When the foundation is initially poured, there is a vulnerable stage that occurs briefly in which the slab can experience minor cracking at the surface. Prior to tension and after about a week or so of curing, the slab becomes a thick chunk of concrete without tensioned cables to support the bulk of its weight. As a result, the longer ends may sink and allow the middle to buckle. Long, tiny cracks or webs will appear on the surface but do not cause an issue structurally. They may be an aesthetic issue in areas that remain uncovered by tile or wood surface coverings, such as garage flooring.
When post-tension slabs are set, the builder will often include a stamp that warns the homeowner against cutting or drilling into the foundation. Cutting into this type of foundation can be particularly risky for even the most highly-trained construction expert due to the high level of tension suspended in the concrete. If a jackhammer accidentally strikes a cable, it may cause irreparable damage to the home, cause serious injury, and even death.
As previously stated, cutting into post-tension slab foundations can be particularly dangerous and should be avoided. When the bars rip through the slab, they become nearly impossible to repair. Homebuyers should consider any future plans for remodeling, which may prove to be a challenge if it involves adjustments to the foundation.
Phenomenal Foundation Fit
When considering options for building a dream house from scratch, homebuyers should consider the fantastic benefits of a post-tension foundation. Its structural integrity, economic pros, and overall quality makes this a great option in any climate for any home.
Melanie Theriault is a writer, counselor, and lifelong learner. She holds a B.A. in Sociology from Southwestern University, where she discovered her passion for fostering human connection through storytelling.
In , a vacant site in one of the largest cities in the U.S. broke-ground to begin a mixed-use redevelopment project, containing event, hotel, meeting, office, parking, residential, restaurant, and retail space. The new building is planned to be 680 feet tall, encompass 1.5 million gross square feet, and have 49 floors.
GPRS&#; client, a general contractor, was completing fit and finish design plans for a hotel, which will reside on 12 floors. The estimated cost for the hotel build-out is $84.7 million.
Approximately 12,500 sq. ft. of reinforced concrete foundations were poured for each floor of the high-rise. The GC had the challenge of planning and coordinating the MEP and HVAC connections between the hotel guest rooms after the concrete was poured. This required precise planning and engineering of the mechanical, electrical, plumbing, and fire protection designs.
The post tension cable system created many obstructions to work through for below-grade MEP and HVAC installation. That&#;s why the general contractor hired GPRS to locate and mark the full post tension cable layout, so they could design the building fit-out, resolve clash detections, and coordinate a trade schedule.
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The post tension cable system created many obstructions to work through for below-grade MEP and HVAC installation.&#;
The best way to determine post tension cable location and depth is with ground penetrating radar (GPR) and 3D laser scanning technology.
Contact us to discuss your requirements of post tension anchor. Our experienced sales team can help you identify the options that best suit your needs.
GPR technology is a non-destructive concrete scanning detection and imaging method that sends a radio wave from a receiver into a concrete structure. The wave will &#;bounce&#; off any material it encounters. Those bounces are then displayed in a reading as a hyperbola, and a professional concrete scanning technician can interpret that data to tell you what was found and exactly where it is located. Post tension cable layouts must be traced in short distances to reveal the slope.
3D laser scanning captures an accurate map of the site pre-pour and after field markings are complete, in the form of a point cloud, where every point of the scan is converted to a pixel with a known x, y, and z coordinate.
GPRS had a comprehensive plan to capture the post tension cable system layout for the general contractor. A team of GPRS Project Managers 3D laser scanned the slabs pre-pour to document the post tension cable system in the form of a point cloud. The concrete was poured for each floor. Then, the team located and marked the post-tension cable system with GPR technology, including the location, number of cables, and depth directly on the slab and ceiling. 3D laser scanning was completed a second time to collect the concrete field markings on the slab.
From the scan data, the GPRS Mapping and Modeling team created 2D plan sheets and 2D floor elevation contour maps to add more accuracy to the depth of cover that was field marked. The data was also used to create a 3D BIM model and virtual tour of the site pre and post-pour.
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GPRS located and marked the post-tension cable system, including the location, number of cables, and depth directly on the slab.
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The 2D CAD drawings and 3D BIM model provided the general contractor with precise data for virtual design and construction. This permanent record of the post-tension cable system layout was used to complete fit and finish design plans for the building.
Accurate post tension layout will ensure safe cutting, coring, and drilling during the MEP and HVAC installations. Mapping the support grid in concrete slabs facilitates design and minimizes the risk of injuries and delays.
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Post-tensioned systems consist of a series of high-strength steel cables embedded within concrete slabs that, once stressed, support the loads imposed on the slabs. The cables are commonly called &#;tendons.&#;
Post-tensioned cable systems reinforce concrete, allowing structures to require fewer beams, longer clear spans, more slender elements, and thinner slabs. This helps to reduce the amount of concrete required for construction, also reducing the weight and height of the building. Lower building weight and height can contribute to savings in terms of facade and mechanical system costs. There will also be a lesser load on the foundation.
Post tension cable location, spacing, and depth are determined by an engineer, and are specific to each project.
Drilling, cutting, or coring into a post-tension slab can be dangerous. It is important to avoid hitting the cables when cutting or drilling for construction or renovation. Each tendon pulls 24,000 to 33,000 lbs. of pressure. Damaging a cable when cutting, coring, or drilling into a slab can cause a tendon to burst with enough force to cause severe injury or death, and impact the structural integrity of the slab.
This is why it is important to locate post-tension cable systems when finishing or repairing buildings or structures. An accurate layout of post-tension cables protects tendons from damage, prevents injury and mistakes, and protects the integrity of the building.
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An accurate layout of post-tension cables protects tendons from damage, prevents injury and mistakes, and protects the integrity of the building.&#;
Each member of GPRS&#; elite team of over 500 Project Managers has completed the industry-leading Subsurface Investigation Methodology (SIM) program. This program defines protocols for concrete scanning that far exceed the industry norm.
The SIM program consists of 80 hours of hands-on classroom training and 320 hours of mentorship in the field to ensure Project Managers&#; competence in utilizing GPR equipment, EM locators, and 3D laser scanners.
SIM allows GPRS Project Managers to clear dozens of cutting/coring areas daily with an exemplary level of accuracy. GPRS is so confident in our SIM-trained Project Managers that we provide a Green Box Guarantee, which states that when GPRS places a Green Box within a layout before the crew anchors or cores concrete, we guarantee that the area will be free of obstructions.
GPRS is the nation&#;s leading provider of utility locating, concrete scanning and imaging, 3D laser scanning, video pipe inspection, leak detection, drone photogrammetry, and mapping & modeling services for the construction, architecture, and engineering industries. Since , GPRS has led the industry, providing accurate data and outstanding service to improve planning and communication and mitigate risk for your team.
What can we help you visualize?
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A 3D BIM model provided the general contractor with precise data for virtual design and construction.&#;
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Core drilling creates holes in concrete that make it easy for pipes, utility lines, and other objects to pass through to the other side, a common practice for plumbing, electrical, and HVAC contractors.
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Replacing a single post-tension cable costs $10,000 - $20,000.
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HVAC is an acronym that stands for Heating, Ventilation, and Air Conditioning. The term HVAC is used to describe a complete comfort system that can be used to heat and cool your building, as well as provide improved indoor air quality.
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