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Bouncy Floors

Kendall Holmes

"The kitchen floor in my turn-of-the-century house has quite a bounce to it. Without rebuilding our entire kitchen (it's not in the budget this year) how can we solve the problem?"

Bouncy floors are pretty common in older houses, but if it makes you feel any better, even new houses can have springy floors. At a house warming party to celebrate the completion of a friend's new home, I once watched a wine glass "walk" across the kitchen table until it teetered on the table's edge--simply because of the bouncy floor!

How can this be? Because while a floor needs to be strong to hold the weight of things that are placed upon it (refrigerators, kitchen tables, people standing on it during a party) it needs even more strength to feel stiff. To solve the problem you (or, better yet, an experienced carpenter) need to add more stiffness.

The question is where to add that stiffness. To find the answer, let's take an imaginary walk into your home's basement.

As you look up, you'll notice a series of floor joists spaced every 16 to 24 inches. A foundation wall supports one end of each floor joist. A carrying beam probably supports the other end of each joist--and a series of posts supports this beam. You'll also notice that a subfloor rests on your floor joists, while the finished floor rests on the subfloor.

So why is your floor springy? Here are the main possibilities:

  • Like my friend's new home, your floor may have been bouncy from the day your house was built. Perhaps the subfloor is too thin; perhaps the floor joists aren't sturdy enough; or perhaps because the floor joists are plenty sturdy, but they're spaced too far apart.
  • Rot, termites and other pests may have weakened the joists, the subfloor, the posts or the carrying beams.
  • Sloppy contractors (another old-house pest!) may have weakened the floor joists by cutting into them to add a plumbing pipe or a heating vent.
  • Or maybe your floors are bouncy because they suffer from all these problems, or at least several of them.

If your inspection reveals rot or termites, you'll have to tackle these problems before doing anything else--by improving ventilation (for rot) or calling in the exterminators (for termites). Then you'll need to add more support.

The most common way to stiffen old floors is to add a new floor joist immediately next to each existing joist, or halfway in between. Adding a properly sized joist next to each existing one (a technique known as sistering) will make the joists stiffer--but your floor will still be bouncy if the subfloor is too skimpy. Adding a properly sized joist halfway between each existing joist will stiffen a subfloor--but is more difficult than simply sistering on new joists to existing ones.

How big do those new joists have to be? How do you install them? What if the carrying beam rather than the floor joists seems to be the problem? Unless you're an experienced do-it-yourselfer, you should let a contractor or carpenter answer these questions and then carry out the repairs.

But now you know what your carpenter will be looking for--and why.


Ken Holmes is an award-winning print and web journalist and editor, as well as a former contractor.

About the Author
By Kendall Holmes, The Old House Web

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