Can you put a modular home on a cement slab?

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Putting a modular home on a cement slab is a common practice since this type of permanent foundation is quite affordable and fast to build. Cement slabs are referred to as concrete slabs and are built as a thick block of reinforced concrete, usually about 4 to 6 inches (10 to 15 cm) [1], that lays on a bed of gravel to prevent groundwater from reaching the slab [2]. Just as any other type of permanent foundation, a cement slab is designed to offer a solid base to the modular home, though not every house will benefit from this type of foundation. 

Modular homes that highly benefit from being built on a concrete slab:

  • Modular homes based in hot-dry climates
  • Modular homes built on flat lands
  • Modular homes built on hard lands that are difficult to excavate

Used in the right setting, concrete slabs have several advantages over other types of permanent foundations. However, in some circumstances, it will fail to provide the solid base the modular home requires.

When to put a modular home on a concrete slab?

A great number of modular homes can be built on a concrete slab, though there are only a few circumstances where modular homes will take advantage of the benefits granted by this type of foundation.

Houses based in hot-dry climates

These types of climates are characterized by the lack of humidity and frost, which allows the structure to perform in its most effective way without being damaged or cracked. Therefore, the simplest approach to a concrete slab is sufficient in this situation, assuring that the cheapest and easiest form of a permanent foundation offers a long-lasting base for the house. 

Houses built on flat lands

A concrete slab is a type of shallow foundation that requires a bed of leveled, horizontal soil; and it is placed pretty much on the surface of the ground. Therefore, when built on flat land, the excavation works required to install a concrete slab are minimal. In these circumstances, concrete slabs are a highly cost-effective type of foundation.

Houses built on hard lands that are difficult to excavate

The composition of the soil is a very important aspect to consider when choosing the best foundation solution to build a modular home. Most foundations require excavation work but a concrete slab doesn’t, which makes concrete slabs the ideal type of foundation to use in plots where the soil is rocky or very hard since any excavation work will be difficult and very expensive. 

When not to choose a concrete slab foundation for a modular home

There are some situations where using a concrete slab foundation for a modular home is highly discouraged since it won’t offer a solid base or will fail to protect the house from the weather conditions to which it is often exposed. Below, are described those situations where a modular home should never be put on a concrete slab; as well as those cases, where this type of foundation could only perform properly if modified to adapt to the environment. 

  • Hurricane or flood-prone areas: A modular home built in an area where floods and/or hurricanes are common, shouldn’t be put on a concrete slab foundation. The foundation built in these circumstances should elevate the house above the ground to enable the water to freely run underneath the house without causing any damage to the living space [3]. 
  • Weak or damp soil at the surface: The foundation should offer a solid base for the modular home and soils with a weak or damp surface can’t provide it. Therefore, in these situations, it is essential to build a foundation that is buried deep down to reach lower layers of solid ground [4]. 
  • Very cold weather (unless properly treated): In areas where the land freezes, a concrete slab can easily get damaged and crack, so other types of foundations are more commonly used in these types of climates. However, it is still possible to use a highly engineered concrete slab that is properly insulated and even heated  [5].

References:

  1. Vanderwerf, P. (2007, July 23) Concrete floor slabs Concrete Construction https://www.concreteconstruction.net/how-to/construction/concrete-floor-slabs_o
  2. Slabs-on-grade Trenchlesspedia https://www.trenchlesspedia.com/definition/4216/slabs-on-grade
  3. Patil, R. Pier and Beam Foundation Constructionor https://constructionor.com/pier-and-beam-foundation/
  4. What is Pile Foundation? Types of pile foundation Civil Engineering https://civiltoday.com/geotechnical-engineering/foundation-engineering/deep-foundation/176-pile-foundation-definition-types
  5. Three types of concrete foundations Concrete Network https://www.concretenetwork.com/concrete/foundations.htm