7 Ways to Fix a Bouncy Floor

Are your floors putting a little too much spring in your step? The only good bouncy floor is the inflatable building at a kid’s birthday party! If you notice a springy bounce when you cross the floor, it’s time to learn about fixing a bouncy floor.

I contacted carpenters and contractors and asked for their help explaining what causes a bouncy floor when you need to worry about it, and the most common ways to address the issue. Most of the solutions are DIY-friendly, but there is a catch: for all but one solution, you need access to the floor joists from below. That means having a basement or accessible crawlspace. If your bounce is occurring on the second floor or over a slab or finished basement, then you’ll have significantly more work involved.

What Causes Bouncy Floors?

“‘Bouncy’ floors usually result from structural issues within the floor,” explains Joshua Parrish, general contractor and co-owner of Hammer and Handsaw. Parrish says those issues can include undersized or improperly-spaced joists, inadequate support, and poorly fastened plywood.

Brandon Walker of ASAP Restoration agrees. “There are many things that can cause a floor to trampoline,” he says. “One of the most common is poor construction, coupled with aging or sub-par materials.”

Improper Installation

If floor joists are spaced too far apart or aren’t sufficiently sized, they won’t provide enough structural stability, and the entire flooring assembly will shake as weight is added. Another common installation issue is subfloor fasteners. If these aren’t installed properly, the floor will develop a gap between the subfloor and the joists, resulting in a bounce.

Improper Modifications

It’s not unusual to see homes where past homeowners have hacked out a floor joist section in order to make room for tall exercise or playroom equipment. Another common issue is when a large pass-through for electric or plumbing lines are carved out in the middle of the joist span.

Water Damage

Water exposure can damage sub-flooring, joists, or sill plates. If any of these begin to rot away, they can give a bouncy floor feeling.

What Is Floor Deflection?

A floor’s “deflection” is the distance it moves when weight is placed on it. All floors have some level of movement, but it’s usually imperceptibly small. If your bouncy floor is noticeable and it bothers you, then it’s an issue. If you don’t notice it, you probably don’t need to worry about it.

However, don’t confuse “can’t notice” with “stopped noticing after a while.” This is something I personally struggle with. For example, I moved into a beautiful old house with a noticeable bounce on one side of the living room. I made a mental note to fix it, but only after I finished fixing the wiring, the roof damage… you see where this is going. Fast-forward a couple of years, and I’d totally forgotten about the bounce until a visiting carpenter pointed out that the floor hadn’t, in fact, fixed itself.

How much deflection is acceptable for a floor?

Building code provides a few different deflections depending on the size and material of the flooring and the usage of the space. But for a typical living room, bedroom, or other living space, here’s the rule of thumb: Take the floor length and divide it by 360. The result is the acceptable deflection.

Both Parrish and Walker suggest using the “L/360 rule” as a guideline, while also noting that all floor bounce must be taken on a case-by-case basis.

Sometimes, the deflection is below the L/360 threshold, but it still feels bouncy. In those cases, you can typically tighten it up by using one of the methods described below. If the deflection is over that L/360 number, you may need to act more aggressively and call in a pro.

How to Measure Floor Deflection

The easiest way to measure floor deflection is to use a laser level, but a long straight edge or level can also work. Use the laser or other level to establish a baseline and take a measurement. Then, apply a load to the floor (enough weight to trigger the ‘bounce’ you’ve noticed). Take another measurement while that load is on the floor; the difference between those measurements is the floor’s deflection.

Sagging vs. Deflection

Deflection only lasts as long as the additional weight is on the floor. If your floors “sag” — meaning they have a noticeable downward bowing even when no additional weight is added — you may have a more serious issue. If that’s the case, consult a contractor or structural engineer.

Solutions for Bouncy Floors

Fixing a bouncy floor almost always involves bolstering the structure, either by adding stiffness or distributing the weight load across a wider area. The experts I spoke with provided a number of possibilities, but the best solution for your floor will depend on the source of the bounce, the severity of the issue, how much access you have to the floor joists, and what, if any, mechanical lines run through the bouncy section of the floor.

Be sure to match the fix with the actual cause of the problem. For example, if you shore up a water-damaged joist without stopping the water infiltration, all you’re really doing is hiding the bigger issue.

Add Bridging

Bridging, sometimes called “X-bracing,” are distinctive, angled strips of wood or metal installed between joists, allowing multiple joists to share a weight load. This solution is relatively easy and inexpensive, making it a good solution to try first. Even if your joists already have a row of bridging at the center of the span, adding a row on each side of the existing bridging will stiffen the floor.

Add Blocking

Blocking is the same concept as bridging, but using solid lumber that’s typically the same size as the joists themselves.

Add Plywood

As a joist bends downward, the lower edge bends slightly to one side or the other. A layer of 3/4-in. plywood firmly fastened to the undersides of joists helps prevent this side-to-side bending and stiffens the floor. A rock-solid bond is crucial; use lots of screws and construction adhesive.

Add a Post

An adjustable steel post can be an easy fix for bouncy flooring if the bounce is limited to a specific joist or two. The post supports the joist and helps hold it steady.

Add a Beam

A beam runs perpendicularly below the floor joists, distributing the forces from above and letting the entire floor (and walls) share the load. Beams leave the basement space open, while a wall is a good choice if you are already planning to divide the basement.

Sistering Floor Joists

“Sistering” means setting a new joist along the length of an existing one, effectively doubling the joist’s width. This results in added strength and stability that can dramatically reduce floor bounce. The downside is that sistering multiple joists can be a big job, especially if you need to re-run mechanicals such as plumbing or electrical.

Upgrade Subflooring

Brandon Walker suggested a solution that may also work for those who don’t have access to floor’s underside: a subflooring upgrade. “Not all subflooring is equal,” he points out. If the installed subfloor is too thin, then it might be the cause of the bouncing floor. “One of the best ways to fix this situation is to increase the thickness of the subflooring.” Of course, you’ll also have to tear off and relay the finish flooring, so this solution does take a fair amount of work.

When to Call a Pro to Fix Floor Deflection

Call in a pro if your floor deflection is past the L/360 guideline, if the floor is sagging rather than bouncing, or if the source of the bounce has impacted multiple parts of the structure. If you don’t trace the source of the bounce back to the core problem and resolve the cause, fixing a bouncy floor is only hiding a larger issue.

Parrish recalls one such property that required far more than a simple fix. “I found evidence of water damage in the kitchen, which compromised the floor and wall framing,” he says. “So after demolition, we had to replace the joists, sister additional joists, repair the damaged ledger and reframe the wall. If we didn’t replace all of these, the integrity of the floor would not be fully addressed and could lead to further structural problems.”

About the Experts

• Joshua Parrish, a licensed general contractor and construction business owner with nearly a decade of experience in home renovations, property flips and new construction. He is also co-owner of the Hammer and Handsaw blog, which features home improvement tips, property flip stories, DIY projects and more.
• Brandon Walker has been in the painting and construction industry for more than 20 years. After running his own company, he decided to advance his skills as a Superintendent with ASAP Restoration.

Sources

• American Wood Council: Tutorial for Understanding Loads and Using Span Tables
• International Residential Code (IRC); Chapter 5: Flooring