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Dangers of Overextending Floor Joists


You might not realize it, but your sagging floor is not because you added a new heavy couch in the living room. Sagging floors are indicative of a shifting foundation, which, in turn, affects floor joists.

What Are Floor Joists?

Floor joists are part of a subfloor and provide added support to the flooring above them. Joists usually are made from strong wood, such as Douglas fir, Eastern white pine and Southern yellow pine, but some construction companies may choose to use synthetic material, such as plastic. Joists need to be placed evenly under the subfloor to grant access to wires and plumbing, and they need to be in the best locations to maximize support. Joists also need to be level and flush with the subfloor as well as the foundation on which they stand.

When floor joists are termed “overextended,” it means the joists were constructed to be too long for the structure on which they were installed. Supports may be spaced too far apart, and this can lead to a sagging floor.

In older homes or homes built without a concrete foundation, joists were just rammed into the dirt. If you were lucky, there was a little concrete poured around them. Wood also eventually rots when exposed to moisture in the air and dirt. These combine to weaken and shift the joists, which, in turn, shifts the support given to the subfloor. Even a concrete floor can shift, moving the joists.


In the Midwest, crawl spaces are common, and some do not have concrete foundations. This exposes wood to large amounts of moisture. To check if the wood is rotting, stick a sharp object such as a screwdriver into the wood near the ground. If the wood falls away or the instrument easily goes in, the wood is rotting and needs to be replaced.

For those with concrete foundations, water still can find ways in to damage your basement or crawl space. When it rains, soil absorbs the moisture and expands, pushing against concrete and moving soil around. Concrete is porous and even small foundation cracks let water in and widen. As soil shifts, it moves from being hard and flat —supporting your foundation — to becoming loose and creating air pockets into which your foundation shifts. This shifting can affect the floor joists.


In addition to foundation cracks and sagging floors, other damage can occur as a result of a shifting foundation and joists. An unstable foundation may cause cracks or bowing in basement walls, unhealthy mold may start growing, wood may warp and pools of water may sit on the foundation floor.

Above the basement or crawl space, homeowners might notice cracks in windows or have difficulty easily opening and closing doors or windows. Long cracks could show up, running along the ceiling and down a wall. Floors in any location could start to sag when you put weight on it or may already be sagging.

Fixing a Foundation

If your crawl space doesn’t have a concrete foundation and signs of damage are showing up, now might be the time to install one. If you have a concrete foundation, there are ways to lift and level it so non-rotted joists supporting the subfloor can do their jobs.

Slabjacking is a method by which a specialist makes small holes in the concrete foundation and injects a foam under the foundation. The foam expands, filling any soil gaps and stabilizing the concrete. Another method of added support is to attach helical piers and wall anchors. Experts place steel beams and a support system on the foundation’s outside to shore up the walls and base.

Acculevel Is Your Foundation Expert

At Acculevel, our focus is on foundation and basement repair and waterproofing. If you live in the Midwest and have noticed that your home’s floors have begun to sag or there are foundation cracks, our team would love to hear from you. We offer free in-home estimates, with no pressure to hire us — although we hope you will. Your home’s foundation is the most important part of the house, and we want to help you be safe. To make an appointment, contact our friendly staff at (866) 669-3349 or email us at [email protected].

Kelly Kater

Over her twenty year career, Kelly has worked in a wide variety of fields: secondary education, nursing, biology, elder care, the postal service, multicultural development, and academia. She has developed a skill for translating industry-specific jargon into everyday language. Her goal is to share the knowledge and experience of the Acculevel team with homeowners, in a way that is both engaging and informative.

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