Foundation Requirements for Adding a Second Story

If you're planning a home addition but the only viable direction to build is up, meeting the foundation requirements for adding a second story can be a significant part of the project. However, that's not to say you have to change your plans. Knowing what's necessary to complete the project before starting can eliminate many major surprises. 

Second-Story Addition Considerations

Adding a second story to a single-story home is a large remodeling project with a number of inconveniences, costs, and potential surprises to consider before jumping in. However, the project can also be valuable. That said, adding a second story isn't a good DIY project, and you'll want to hire a qualified home addition company near you for most, if not all, of the journey. 

Before committing to the project, consider the following factors and options:

• Adding a second story isn't automatically less expensive than enlarging the footprint of your home for an addition. Much of the determination will come down to the condition of the existing foundation.

• The new space will need additional mechanicals such as HVAC and electrical, which may mean upgrading or replacing the existing systems. 

• Adding rooms above with plumbing needs, like a bathroom or laundry, will cost more than adding waterless room additions.

• Reinforcement of the first story, if necessary, can be significant and intrusive.

• You'll likely want to find an alternate place to live during much of the demolition and construction phases.

• You may need to spend significant money to reinforce or otherwise alter your home's foundation.

Foundation Requirements for a Second-Story Addition

While precise foundation requirements for a single-story home versus a two-plus-story home vary widely depending on the geographic location, soil types, and home style, the basic rule is that the structure beneath the home must be robust enough to carry the house's weight and protect it from shifting. 

Foundation Planning

As part of your home renovation contract with your remodeler, the builder must determine the soil conditions and the condition of your existing foundation to receive a building permit for the project. Making these determinations and developing a plan to reinforce the soil and foundation, if necessary, is typically the work of a local structural engineer. Most often, your contractor will have one they work with for these kinds of projects. 

In some cases, your home's foundation and surrounding soil may work just as it is to support the additional weight of a second story. This is sometimes true in newer homes but seldom in older ones. Generally, if the existing footings and foundation are deep and bulky enough and don't show signs of frost heave, such as cracking or shifting, it's likely a good candidate for a second-story addition without concern. 

Reinforcement

If the determination is that your home's foundation or surrounding soil needs additional strength, there are several options depending on the current situation. Your project may require one or more of the following procedures: 

• Inject concrete grout into the soil surrounding the foundation to strengthen the ground that supports the structure.

• Repair the foundation if the existing structure suffers from cracks, frost heave, or deterioration.

• Dig below the existing foundation to add concrete mass, footings, pilings, or structural beams. Your contractor will refer to these methods as underpinning.

Second-Story Addition Foundation Costs

Without needing foundation work, the cost to add a second story to your home averages $100 to $300 per square foot of additional space. If your home's foundation shows signs of shifting, cracking, or sinking, expect foundation repair costs of between $2,160 and $7,780 before work can begin on the addition. 

If you discover that your foundation needs underpinning or other substantial work to support your new second story, expect to add at least $5,000 and up to $20,000 in severe cases to the project's cost.