Chapter 3: Foundation
Foundation is the most critical component in a building. It’s also the root cause of many issues in other components. When a problem occurs in foundation, if not repaired immediately, it’ll cause severe damages to the entire building structure and other systems, which will result in financial loss to the home owner.
Below are general descriptions of foundation. It’s designed to help readers identify foundation problems as quickly as possible so that it can be repaired before the entire building structure is damaged, in order to reduce or lower financial cost. This article will address foundation in two perspectives: from construction engineer’s point of view and professional inspector’s point of view.
Building foundation is categorized into pier/pile foundation, deep foundation and shallow foundation. Shallow foundation is the simplest in both structure and field construction. In the South, most foundations adopt shallow foundation, because its frost line depth is close to zero. For instance, most buildings in Austin and San Antonio metro area adopt shallow foundation.
There are three common shallow foundation configurations in terms of the relationship between supporting concrete slab and foundation wall:
- Floating slab, supported by the ground, independent of perimeter foundations.
- Partially supported slabs, the floor slab is partially supported by the foundation wall.
- Monolithic, the slab is an integral part of the footing. This is the best configuration.
The type of soils pays a key role in foundation stability. Common soil types and their maximum loads are:
- Rock (12,000 pounds/sqft)
- Sedimentary and foliated rock (4,000 pounds/sqft)
- Sandy gravel (3,000 pounds/sqft)
- Silty sand ((2,000 pounds/sqft)
- Clay (1,500 pounds/sqft)
In Austin and San Antonio metro area, most soils are silty sand, clay or the mixture of silty sand and clay. When a building foundation is clay, due to its weak bear loading and high swell coefficient, foundation may become extremely unstable, exhibiting the symptoms of uneven settlements.
Foundation settlement after a building has been constructed is common. The most serious issue is uneven settlement causing increased overload on some parts of the structure. When the load exceeds its tolerable limit, construction materials will break or rupture. Other systems such as electrical and plumbing system will be also severely affected causing fire and flooding hazard.
From a professional inspector’s perspective, foundation inspection is the most important item during inspection. Many deficiencies in a building are caused by foundation problems. An experienced home inspector will find the root cause in structure and foundation through observing and analyzing deficiencies. Therefore an ideal home inspector should possess construction knowledge and hand-on experience, be familiar with construction materials, construction methods and building codes as well as local construction specifications.
Cracks are most commonly seen in a building. Cracks often appear in ceilings, walls and floors. They have different shapes. The cause of cracks varies. Some cracks are caused by shrinking materials due to moisture loss. Irregular cracks on concrete floors might be caused by inadequate hydration during the curing process of concrete. This is a cosmetic issue, does not affect foundation. Some cracks are however caused by uneven settlement of foundation. It’s an extremely complicated process to identify the cause of cracks. An experienced home inspector will evaluate foundation performance based on observations on foundation and other systems. I will describe in more details in upcoming articles.
Tip for this issue: To better protect foundation, connect a 5-foot long extension pipe at the end of downspouts to guide the storm water from gutters to at least 5 feet away from the foundation so that the soil moisture remains even around the foundation. This will prevent foundation problems due to increased pressure in part of the foundation that may eventually damage the entire building.
Per suggestions from readers, I have started a blog. Please visit http://www.abtinspections.com/home-inspection-blog/ to upload pictures and questions.
Published in the July 2013 edition of Texas Capital News