How Much Would It Cost to Add a Basement to My House?
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How Much Would It Cost to Add a Basement to My House?

This article was written as a response to the question: About How Much to Add a Basement
What are the details involving adding a basement to your house? What might it cost? Answers here.

So, you want to add a basement? There’s a couple of different ways we can go with this:

  1. One is to assume you’re adding it on paper (That you haven’t built the house yet),
  2. and the other is to assume you’re adding it to an existing structure.

First, the cheapest way to add a basement is to do it on paper, as in, before there’s a house attached to the dirt. You probably saw that coming. Also, depending on the cost of materials, it may be cheaper to “build down” than to “build up”. That is, concrete, which is used for foundations and basements, may be cheaper than lumber, used for framing above ground—and therefore, a basement might be cheaper than a second story. However, there are so many variables that it is impossible to say with much accuracy which might be true for you. Size of the house’s footprint, how high you want the ceilings (a 10’ ceiling is more expensive than an 8’ ceiling), the complexity of the architectural design, and on and on—these elements all make a big difference in the price tag of your project.

What options might you have to reduce cost? Well, when adding square footage to your house, you can save money by leaving the interior space unfinished. For instance, whether adding a basement or a second story or an attic with dormers, you can leave out the paint, trim, floor coverings, and, depending on building code in your area and whether or not we’re talking about a basement, maybe even the sheetrock. Depending on how much square footage we’re talking about, the savings could be $10,000 or more.

Here’s an important point about basements, however: egress windows must be installed that allow firefighting personnel to fit through them with all their gear. Consult your contractor for specifics on this, but suffice it to say, if you’re adding a basement, those little 1’ by 2’ windows of yesteryear are illegal. Each window will need its own excavation and retaining wall beyond the external footprint of the house. The positive benefits to this include added safety, as well as natural light in a normally dungeon-like space.

So, what if we’re talking about adding a basement to an existing structure? How about this: I know of a guy who took about ten years to excavate his basement, from under his existing house, using a couple of 5 gallon buckets and a shovel. What, you don’t want to go there? It would be a cheap solution to the problem! Okay, option one isn’t an option for most people.

Option two? It’s pretty much the only option available if you’re trying to preserve the existing house. After all, if you’re going to demolish the house, you’re starting from scratch and we’ve already covered those things. If you want to add a basement under an existing structure, you’ll need two things: a house-moving specialist and a second mortgage. Or a third, as the case may be. Or if you’re really blessed, just convert all those gold coins to cash!

Here’s the drill: what you basically need to do is disconnect the house from all the utilities, such as gas, water, sewer, and electrical. Then, a house-moving specialist will show up with lots of jacks, steel I beams, and cribbing (usually they look like railroad ties). Your house will be unbolted from its foundation, steel I beams will be run through under the floor, and it will be jacked up high enough to allow at least a small machine, like a Bobcat, under it. That little machine will then excavate enough earth to allow room for a basement. Once there’s enough room, your contractor will unleash the foundation crew, and they’ll set the forms necessary to pour the walls and the floor. Once everything is cured, the house mover will come back and set ‘er down, and all the utilities can be reconnected. Sounds simple, right?

Well it ain’t cheap. I would estimate, and this is a wild guess, that you should budget about $40,000 at the very least for a project like this. Why? Because there’s a lot involved, and it’s good to overbudget anyway. Besides, I don’t know if your house is a simple 1,000 square foot rectangle like mine, or a complex radiused edge Frank Lloyd Wright museum piece that’s 10,000+ square feet. I’m guessing it falls somewhere in between all this.

It just comes down to the fact that you’ll have to call your friendly local neighborhood contractor and go over the numbers with him. There really are an infinite number of variables on such a project. Whatever the case, it’s generally true that adding on to an existing house, however you do it, is cheaper than buying a different one. I hope this helps, and good luck with those buckets.

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Comments (1)
Due to water damage from the bathroom I have a floor under an interior load bearing wall that is in need of additional support. That section of my house in on a crawl space. If you can even call it a crawl space. there is a trough down the middle where the plumbing is. Because the 'entry' to the crawl space is too small to enter through we will have to go through the floor to install footings and bracing for the sinking floor. I thought heck instead why don't we just put in a basement. The area is 480 sq ft. Because that portion of the house was built back in the 50's by the then owner the existing foundation is no where near as deep as today's standards. We thought about moving and after reading your article it might be the way to go. But we are looking at at least $100K for another home. Surely a 480 sq ft basement won't cost $100K?