Have you ever wondered what part of a building is the most important? The truth is the type of foundation used to erect a structure determines the holding capacity or strength of that structure. This article talks about the best kind of foundation for your home.
“Which type of foundation is better for home construction; a poured slab type at ground level, or a raised foundation with walls and a crawlspace or basement?” The answer is that both types have advantages and disadvantages, it just depends upon your particular needs and preferences, and it depends upon what types of home construction are available in your area.
First, the basic components of a foundation system. Although the base structure below a home is often called a foundation, it is really a system of several integrated parts, divided into three groups:
Footing: This is the base, the lowest point of the structure, designed to carry the weight of the building to the ground. The footing is usually wider than the wall, column, or foundation edge that it supports. And since the footing must rest upon solid soil for stability, and be well below any frost levels, it is usually not visible without digging into the dirt.
Foundation Walls or Slab: These are the partially visible sections which carry the loads from the floor and wall structure above, to the base or footing below. These sections typically use poured concrete, masonry blocks, or other rigid materials. Concrete is the most widely used material for the outer perimeter, with wood and steel used for internal columns and support structures, often called post and piers. Installed correctly, all of these materials are acceptable per today’s building codes.
Internal Structures and Materials: This refers to items like the concrete, its mix of cement, aggregate (sand and stones) and water. Also of equal or greater importance, within most concrete foundations or slabs you will also find steel mesh, rebar, or solid steel beams; all encased within the concrete like the skeleton and ribs of a human body.
If we were to take this analogy of a human body a bit further, and apply the components of home construction from above, the footing would be like a persons feet, thus providing a platform which holds up the rest.
Then we have the walls or slab, which act like a body standing upright if a wall, or lying horizontal if a slab, but both have steel intertwined like a skeleton and ribs within them.
And then we have the strength of the concrete, okay maybe that would be the muscles that wrap and/or attach to the skeleton? Like many other systems around us, the foundation is also a system, whose primary purpose is to carry weight from the structure above, through a strong and continuous framework, it must carry this weight to a stable footing below.
So, which foundation type is better, slab on ground or raised walls with a crawlspace?
Until after WWII almost all homes were built using concrete footing pads, outer raised foundation walls, with additional post and pier type inner supports usually constructed of wood. The advantages were that the concrete could be limited to footings and the outer perimeter location (as transport of large amounts of concrete was not common back then), and once the raised walls were in place, then the wood floor beams and joists could be added later.
This construction method also allowed a functional area known as the crawlspace (12-36 inch area between the ground and the floor above), or a full basement 6-foot or greater clearance from finished floor to ceiling. This cavity between the ground and floor allowed access, and it provided a convenient place to put the plumbing, fuel lines, heating systems and so on. In colder climates, basements were common, often the location to store fuel for heating the home during the wintertime. In more temperate climates (no need for deep walls to avoid frost) the area below the flooring reduced to only a space large enough to allow a person to enter, and a place to run necessary utilities.
One of the advantages to having a crawlspace was that a person could return as often as desired, to work on the plumbing if it sprang a leak, or yes, should a home inspector need access to check the condition of the columns and walls for cracks or other structural problems. Another advantage was that the house was raised up from the street level, slightly above the noise and visual distractions from the street outside. On the downside, this usually meant there were stairs to all access points, and since the floor structure was raised (and often constructed out of wood members) this type of flooring was prone to squeaks and minor movements. Often over time, these wood flooring systems also had some uneven surfaces due to settlement within the supporting structures below.
Now fast-forward through the sixties and beyond; with free love, rock music, and the advent of cheep concrete. All kidding aside, it was the inexpensive concrete mix, and ease of transportation methods, that led to the boom in poured concrete slab construction.
Also the abundance of steel re-enforcing rebar, which made the horizontal concrete structures stronger, all led to the use of slab construction as the most practical method for new home foundation systems. A huge, and I mean huge, benefit to slab construction was the speed within which a home could be built. Within days of clearing the soil and preparing the concrete forms, a contractor could pour the slab, and days later, could begin building the walls, roof and so on.
Developments known as tract-housing literally sprang up seemingly over night, as row after row of homes could be built, and built quickly. The only downside to the early slab construction was that homes were low to the ground level, and therefore easily prone to flooding, pest intrusion, etc. Also, since the slab on ground had no access to the underside, the buried items like galvanized steel water lines and cast iron waste plumbing; these could not be repaired without cutting away sections of concrete flooring.
Newer construction methods of today, with copper water lines and plastic ABS waste lines, have greatly reduced the “trapped piping” concerns of older slabs. And with high-quality concrete and steel, almost all homes are now built using the poured slab construction. Slab construction is here to stay.
New or old, slab construction does poses a problem for home inspectors and buyer alike, as we no longer have access to visually inspect the structure and systems below the slab. But that said, home inspectors still have an arsenal of tools at their disposal. Visual inspections of the outer perimeter for cracks are always the first step, plus looking for cracks within the wall structures above can also be used for indications of movement.
For example, if there are cracks within the stucco or masonry wall coverings, this may indicate that a smaller section of the slab could have broken away from the larger slab itself. From there, inspectors can visually check flooring surfaces within a home for uneven surface (indications of cracks or separations), and water-leveling techniques can even determine if a section has sloped to one side or to one corner. Now if a slab has been poured upon good soil, poured to proper depths with quality concrete mixes, over a skeleton of rebar steel, a concrete slab can provide years and years and years of solid support for your home. And did we mention “squeak-free” first floor construction?!
As you can see, both types of foundation systems have their advantages and disadvantages, so there is no need to choose a home simply based upon which type of foundation exists. What really matters is whether or not the foundation structure is in a good condition, free from structural defects, and built to sufficient size and strength to support the structure above. Bringing in a qualified home inspector can be your “first level of detection,” thus letting all parties know if a potential problem exists within the foundation system.
The home inspector may be able to provide indications as to the route cause or causes of any problems; if it appeared there might be soil movement, or possible water leakage, or poor construction practices, etc. The inspector may also be able to provide guidance to other testing services or local agencies for further analysis.
Foundation problems can be serious and costly concerns, but the home inspector can help make the process of detection and analysis a little less of a concern.