Closeup on the corner of a poured concrete foundation for a modular home

Modular homes were once pretty uncommon, but their popularity has come a long way. They’re less expensive, faster to construct, durable, and very high quality when properly built.

While setting up your modular home, it’s not unusual to be confused about whether it should be attached to the foundation.

Keep reading to learn more about modular home foundations, the different ways to attach the homes to their foundations, and the advantages of each method. 

How Do You Attach a Modular Home to a Foundation?

You can attach a modular home to the foundation using engineer-approved nailing strips, nailing plates, screws, and bolts to fasten it to the sill plate. The foundation is usually made of cement, wood, and stone. It may include a basement or crawl space to allow various connections. 

Now, let’s look at this process each step of the way. 

Attaching a Modular Home to the Foundation: Step-by-Step

A large truck called a toter will deliver your modular home to the site attached to a carrier inside. Here are the steps to take as soon as it arrives: 

  • Prepare the foundation – the foundation has steel frames constructed with beams to support the home. The steel beams are then cross-linked, and outriggers are welded to the structure to give additional stability to the support system.
  • Prepare the site – the modules are usually quite large, so they must be placed near the crane. Aside from nearness, they also have to be in a position where the crane can easily pick up the sections to put them on the foundation.
  • Detach the module from the carrier – if the home is still on the carrier, you will need to remove it so the crane can lift it easily. To do this, carefully detach all the bolts and carrier clips and attach the floor system of the modules to the carrier.
  • Unpack and inspect the modules – remove the shipping plastic and other packaging materials. Inspect the modules to ensure that no nails are sticking out. Check the energy seal outside the marriage wall to ensure it’s in good shape.
  • Lift the modules – insert cables into the rail holes of the crane and use a spreader bar to avoid scratching the sides of the modules. Use a rope on opposite sides of the home to slowly guide the movement.
A crane lifting a modular home panel.
  • Sit the house – the modules should be lifted from the carrier in a tilted form. This way, they can be placed on the foundation with the lower side going first. Again, check the alignment of the units and adjust them as needed.
  • Anchor the modules – screws, nailing strips, nailing plates, or lag bolts can be used to attach the perimeter rail of each module to the sill plate.
    This process anchors the entire floor joist system firmly to the foundation sill plates before other attachments such as wedges and welds are used. You can also use carriage bolts to strap the higher walls to the sill plates. 

Types of Modular Home Foundations

Three types of foundations can be used for anchoring modular homes:

  • Basement foundation
  • Crawl space foundation
  • Helical screw pile foundation

Of these types, the basement and crawlspace foundations are the more popular foundations for modular homes. 

These foundation types are efficient, safe, and stable for modular homes. You can choose the style you prefer based on your needs and the recommendations and input from your professional builder.

Basement Foundation 

A basement foundation is built about eight feet (2.44 meters) below the ground. It has added room in the foundation, and concrete pillars and walls will be poured in to support the space before your modular home is attached.

A partially-built basement foundation for a modular home

This foundation is usually more expensive, but it is super resistant to earthquakes, aside from offering extra space in your home. 

Building codes usually have more specific requirements for basement foundations than others, so if you’re opting for this foundation type, be especially careful to follow the legal specifications.

The dimensions must also be exact because the modules to be anchored at the site are built to tight specifications. There is no room for adjustment during the attachment, so the foundation must be made to precisely align with the structure anchored to it.

If you plan to resell your home, a basement foundation can also help increase your property’s value, giving you a significant return on your investment. Remember that the increased return isn’t free though—a basement foundation needs particular framing, so it costs more and requires more time and precision to build. 

Crawl Space Foundation

This foundation type utilizes a crawl space—36 to 48 inches (0.91 to 1.22 meters) of conditioned area at the bottom of your modular home. 

The space is much smaller than a basement because it’s designed only to elevate your home and give access space for setting up connections like plumbing pipes and electrical wires for utilities. 

An illuminated crawl space under a modular home

A wider crawl space can be covered with a brick facing to serve as an improvised mini-basement for storing outdoor items.

The crawl space foundation type gives your home solid resistance against invasion by harsh elements like frost or wind. However, there is less space within the foundation, so it may not hold up so well under high pressure such as floods. 

If the space doesn’t give your home enough lift, it could also make your home prone to termite infestations or the effects of high humidity. Crawl spaces that are not cared for or cleaned could also be vulnerable to mold and other pests.

Choosing to install a crawl space foundation may mean you’ll miss out on having a lot of extra room in your modular home, but you’ll get to save money because it costs less to install them than basement foundations.

For additional space, a more economical option could be to build a detached garage or storehouse, usually for a lesser cost than a basement foundation.

Helical Screw Pile Foundation

Helical screw piles are quite similar to giant screws. The difference is that they’re pretty huge, with a diameter of 9-17 inches (22.86 to 43.18 cm) and a flat head.

The pile toes of the screws are driven into the required ground depth at regular intervals to create a stable, durable foundation for the building. The modular home can then be attached straight away to the screw pile foundation.

Screw piles are not as popular as basement or crawlspace foundations, but they’re much cheaper and can be installed in as little as a day! In addition, screw piles have minimal disturbance to the earth and are removable and reusable.

Factors To Consider While Choosing a Modular Home Foundation

Before putting up a modular home foundation, be aware of the following:

  • Local building codes – your foundation has to comply with the state and local building codes in the jurisdiction of your home site. 
  • Weather protection – the home and foundation must be frost-protected or built below the frost line. You should also confirm your level of flood hazard, wind load, and snow load with your local building office.
  • Soil type – basement foundations are not advisable in regions with unstable grounds such as clay soil, wetlands, or flood-prone areas.
  • Basement purpose – if the basement will be used as a living space, you have to install egress windows and doors in the foundations.

Conclusion

A modular home is an excellent choice for getting your dream house on a budget, but the home is only as strong as its foundation. Attaching the foundation properly is hard work, but a dwelling that can stand the test of weather and time will be worth it! 

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