Jun 20, 2014
Slab, Mono Slab, Crawl Space….It’s all Greek to Me
The new homebuyer experiences several different emotions while moving through the home buying process. One of the emotions they may experience is confusion. Many people in the industry use language that is very common to the business. However, the typical homebuyer does not have that same content knowledge. The expression, “it’s all Greek to me” comes to mind when thinking about the communication exchange between a project manager and those who are not experts in the industry. This blog article (and more to come) is an attempt to assist the homebuyer with the “translation” process between the industry lingo and what it means to them and the purchase of their new home.
In this first article, we will discuss the different types of foundations that are available for a new home and why they are used.
New homes are built on a concrete structure called a foundation. There are several different foundation types and the type used for a particular home depends on many factors.
A concrete slab (sometimes referred to as a mono slab) is used when the developed land is relatively flat. A concrete slab is a layer of concrete that is poured at minimum of 3.5” but 4” is most common thickness for residential applications.
A stem wall foundation is used if the developed land is moderately sloped. The height of a stem wall foundation is dependent upon the degree at which the developed land is sloped. The use of a stem wall foundation may also result in steps leading from the finished grade of the lot to the house and into the house from the garage slab.
When the developed land has a slope that is considered significant then a crawl space foundation is used. This type of foundation consists of a concrete block support structure and a wood floor system made up of floor joists and underlayment. This allows for access to an open area between the floor and the grade. Having this space lets the builder install mechanical systems under the floor. The height of the space under the floor varies due to finished grade.
A basement is used if the developed land has an extreme slope. Basements are more prevalent in some parts of the country than others and allow for more storage space and perhaps additional living space. Basements can be problematic in very humid climates and require a dehumidifier or air conditioner in the summer months to keep the area and any furnishings from becoming moldy.
It’s important for the consumer to recognize the characteristics of concrete.
What? Did you say cracking?!!!
According to the Concrete Foundations Association of North America, some cracking is normal. http://www.cfawalls.org/foundations/cracking.htm
“Cracks can be unsightly but many consumers feel that if a crack develops in their wall or floor that the product has failed. In the case of a wall, if a crack is not structural, is not too wide (the acceptable width of a crack depends on who you ask and ranges from 1/16” to 1/4”) and if it is not leaking water it should be considered acceptable.”
Concrete often cracks because the components: cement, sand and gravel are mixed with water in order to pour the foundation causing it to shrink slightly as it dries. Over time it is often exposed to stress from extreme temperature and humidity fluctuations, which can cause movement leading to additional cracking. Generally expansion joints, sometimes called control joints, are created in concrete foundations when they are poured to control the movement and minimize cracking. Small cracks are normal for any concrete slab or wall and are not a cause for alarm. Cracks over ¼” in width should be inspected by a professional contractor to determine if there is a structural issue or if it is just a surface crack.
While it’s not practical to put a slab foundation on a severely sloped lot, a crawl space foundation can be built on a flat lot if desired, however it is more expensive and will add to the cost of the home. Talk to your contractor if you have questions about what type of foundation is best for your lot and floor plan.