What is slab engineering and why do I need it?
Updated: Jul 13, 2022
When you build a new custom home, your expectation is for it to last a long time. Starting with an engineered foundation is one of the first critical steps!
When the big day arrives to pour the foundation of your new home, there's more involved in the design and construction than you may first realize. After you have settled on the design (size/layout) of your new home with an architect or home designer, the next step is for your builder to have the slab designed by a state-licensed "professional engineer." Professional Engineers are a type of Civil Engineer, which is a professional that has special education, experience, and training along with have meeting state-requirements that help to ensure your foundation will stand the test of time.
In addition to concrete, there are several other elements that are part of your slab, including: base material, rebar, vapor barriers and additional design features including shower drops, drops & slopes for porches and garages. Even the type, strength and chemical balance of the concrete for your slab is determined by the engineer. The engineer is responsible for determining how much and what type of these materials will be required to make sure your foundation has the strength to support your home. The engineer will also consider the type of soil you are building on: primarily considering what is known as the Plasticity Index (PI) rating of the soil in your build area.
In addition the the engineering design of your foundation, the engineer will also need to perform a site inspection before your slab is poured with concrete. This on site inspection is performed to make sure the elements of the engineer's designs were followed by the foundation sub contractor. Inspected elements include making sure the correct rebar was used, the correct spacing for beams has been achieved, and the vapor barrier has been properly installed. These are just some of the items the engineer will check during their site inspection.
Once the inspection is complete, the engineer will issue a letter called a 'Pre-Pour Inspection (PPI)' that will include their approval (or disapproval) for the slab to be poured. Approval letters should include the engineer's seal as well.
Typically, if your homes slab has been both designed and inspected by a Professional Engineer, then your home will be covered by a 50 years warranty by the engineer. Therefore getting your home's foundation engineered and inspected is a critical component of the construction for your new home.
The two most common types of slab design in the Texas Hill Country are: 1) Monolithic Convention Slab or 2) Post Tension. Builders tend to have their personal preference as to which slab type they prefer, but my preference is for the conventional slab design.
Given the highly technical nature of the slab design, its important for you to have a basic understanding of this process, but your builder will work to make sure these important steps are followed through from start to finish.