Frequently Asked Questions (FAQs)

Becoming a licensed professional engineer in the state of Texas isn’t easy. In fact, it’s a very difficult feat to achieve. The Texas Board of Professional Engineers and Land Surveyors (TBPELS) governs engineers and land surveyors in Texas. The Board's role in the protection of the public is to license qualified engineers and surveyors, enforce the Texas Engineering and Surveying Practice Acts, and regulate the practice of professional engineering and surveying in Texas. Currently, over 69,000 Professional Engineers and over 2,800 Registered Surveyors offer services in Texas. Earning an Engineering degree from an accredited college is merely the first step in a long process to becoming a registered professional engineer. One must also pass the Fundamentals of Engineering exam and gain at least 4 years applicable and verifiable experience along with 3 character references from active licensed professional engineers. These character references must stem from a personal knowledge about the individual’s character, suitability, reputation and experience. Once the Board has verified all of these accolades, one must pass the Professional Engineering Licensing Exam to become a registered engineer. Pat Sablatura, P.E. graduated from the University of Texas with a Bachelor of Science in Architectural Engineering Degree and aced the engineering licensing exam on his first attempt.

The foundation is one the most important and costly components of your home.  Therefore, hiring someone with an engineering degree and a license that is regulated by a state agency just makes sense.  Sure general contractors can have 20 or 30 years experience, which can be beneficial.  However, they are not regulated by any agencies.  Engineer’s must abide by the Texas Board of Engineers & Land Surveyor’s Rules and Regulations including ethics requirements as well as all applicable building codes.  These factors greatly influence the accendibility of the foundation design engineer. A qualified foundation engineer like 3 Day Design has the ability to run calculations based on soil characteristics to assure the foundation design is adequate to handle the forces exerted on it from the soil below and weight of the structure above based on the loading requirement factors detailed in the applicable building codes.   A house is only as good as the foundation on which it’s built.  Therefore, hiring a qualified foundation design engineer helps to assure that key component is structurally capable of performing its job without breaking the budget.  3 Day Design is the clear leader when it comes to providing a quality design with cost in mind.

Just because an engineer has a ‘P.E.’ after their name does not mean that person is already the best person to do the job. You should consider other factors such as length of experience, knowledge of local foundation construction techniques, and most of all- familiarity with central Texas soil conditions as it’s the soil characteristics that drive the foundation design.  Over the last 25 years, 3 Day Design has successfully completed over 250,000 central Texas foundation designs working closely with contractors and suppliers to ensure 3 Day Design stays on top of the latest foundation construction trends.  3 Day Design is the clear leader when it comes to providing a quality design with cost in mind.  We were born and raised on central Texas soil so we know exactly what we’re talking about.

A slab-on-grade foundation consists of two main components -  concrete and steel reinforcement.  Concrete is strong in compression, while steel is strong in tension.  They work together to keep a slab from differential vertical movement.  A typical central Texas slab-on-grade also has stiffening components called ‘grade beams’ which act to resist the forces from above and beneath the slab giving it rigidity.  These grade beam trenches are dug into the dirt around the perimeter and criss-cross the interior of the foundation area giving the slab a ‘waffle’ look.  Typically, grade beams are 24 to 36 inches deep with a 4 inch thick main surface area of the slab.  Steel reinforcement is then placed down in these trenches along with a ‘grid’ of reinforcement at the top of the slab.  The two types of steel reinforcement are ‘post tension cables’ and standard rebar which are explained in other FAQ’s.

Rebar (short for reinforcement bar or reinforcing bar), is a tension device added into a concrete foundation to form a ‘passively reinforced foundation’ meaning the concrete doesn’t even know the rebar is there until it starts to crack.  Rebar helps concrete structures withstand tensile, bending, torsion, and shearing loads. Since these are areas of weakness for concrete, rebar strengthens concrete structures that would otherwise fall apart under these forces.  Rebar consists of carbon steel bars which significantly increase the tensile strength of the foundation. Rebar surfaces feature a continuous series of ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage. Rebar size is specified by a number such at #4 or #6.  This number divided by 8 is the diameter of the bar in inches.  So a #4 bar is ½ inches in diameter.  The higher the number, the bigger the bar.  It’s just that simple!

Post tension cables or tendons are tension devices added into concrete a foundation to form an ‘actively reinforced foundation’ putting the entire slab in compression 24/7.  Post tension cables are basically high strength steel strands coupled together and encased in a plastic sheathing.  These cables are usually ½” in diameter and positioned in a foundation system similar to standard rebar.  Once the concrete slab is placed and cures to sufficient strength, these cables are pulled in tension and secured such that the resulting cable is in tension pressing the concrete into compression.  Think of post tension cables like a group of thin steel strands inside a greased garden hose that get stretched like huge steel rubber bands.

We at 3 Day Design get asked this question a lot.  Take a poll of 10 people and half of them will have a horror story about a rebar slab that has cracked into pieces and had major up and down movements while the other half will have the same horror stories about a post-tension slab.  Both foundation reinforcement systems utilize steel in tension to aid the concrete in compression and, designed correctly, a rebar foundation and post-tension act just the same.  They are equally capable of handling the required loading.

Typically, a post-tension slab contains less reinforcement than a comparable rebar slab.  That is not to say it’s less strong.  It’s just a slightly different mathematical design concept.  Besides a reduced cost of reinforcement, less material means less labor cost to install typically resulting in a quicker foundation installation. All things considered, a post tension foundation isn’t THAT much cheaper or quicker install than a rebar foundation, but in construction, every penny counts.  We at 3 Day Design understand how important costs are so we create quality designs with cost in mind.

The number one factor utilized in designing a slab-on-grade is characteristics of the soil beneath it.  Namely, the amount of clay that soil contains.  Clays act like sponges to expand when wet and shrink when dry.  The higher the clay content, the greater this spongelike activity and therefore the more forces the foundation must resist to remain flat which means an expansive clay soil foundation design requires deeper grade beams, more steel reinforcement, and more interior grade beams.  Conversely, a foundation design on soil with low clay content can have shallower grade beams, less steel reinforcement, and fewer interior grade beams. Thus, the underslsab soil characteristics drive the foundation design and ultimately the cost of the foundation installation.  We understand the high cost of the foundation so 3 Day Design never over-engineers their foundations.

All concrete cracks.  The two basic types of cracks are curing cracks and movement cracks.  Curing cracks are the most common cracks and stem from the curing or strengthening process concrete undergoes as it ages.  Usually, these cracks are microscopic and imperceptible to the human eye, but sometimes the forces get together and create a larger crack which is easily visible.  Once concrete is mixed, it immediately starts to cure and gain strength.  The curing process releases water which evaporates and induces tensile forces resulting in cracks.  The second basic type of cracks are caused by the soil beneath a slab heaving (lifting) or settling (dropping).  When one part of a slab moves up or down in relation to the other part of the slab movement cracks can occur. Steel reinforcement is the structural glue that holds concrete together once it cracks.

All concrete cracks.  Curing cracks are a result of the strengthening or ‘curing’ procedure concrete undergoes once it is mixed.  The curing process occurs very rapidly during the first 24 hours and decreases over time so it’s the early stages of this process which are the must susceptible to crack remediation techniques.  The easiest way to potentially reduce the amount of curing cracks is to pour the concrete early in the morning when the air temperature is low and wind speeds are minimal.  These two factors help to decrease the rate of hydration associated with the curing process which usually means less curing cracks will form. However, it is important to note that just because the foundation is poured before dawn in the morning doesn’t mean it will not crack.

No, not necessarily.  Cracks are often merely cosmetic aberrations which do not detract from the concrete slab’s structural integrity. In fact, if concrete did not crack, then there would be no need for steel reinforcement because before a crack forms, the concrete doesn’t even know the steel reinforcement is there.  However, once a crack does form, it’s immediately the job of the steel reinforcement to mitigate the length, depth, and width of the inevitable cracks associated with a concrete slab on grade foundation.  Just because a slab cracks, does not necessarily mean it has undergone a structural failure.