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Floor Joists

Floor joists are a critical part of any building’s overall structural design. They help to keep your floors straight and sturdy.

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While most homeowners today choose to build their homes directly on a concrete slab, those built over open spaces such as a basement or crawl space almost always use floor joists. Floor joists provide weight-bearing support to the floor above. As a homeowner, you need to ensure they are up to standard at all times. 

What Is a Floor Joist? 

A floor joist is a horizontal floor-framing member that bridges an open space. These members span from wall to wall, wall to beam, or beam to beam to provide support to the floor above the basement or crawl space. Joists are spaced at regular intervals and covered with subflooring panels, OSB (Oriented Strand Board), or plywood. 

This helps to complete the floor’s structural assembly and create a solid, continuous platform on which to install your flooring. When integrated into the framing of a building, joists help keep the floor level and steady. 

Types of Floor Joists 

While floor joists come in many different materials, the most common floor joist materials for residential construction include solid or engineered wood. 

Solid Lumber 

Solid lumber is often the most economical choice of joists. However, its cost is relative to the type of wood used, the wood’s grade, and board size. All these factors also affect its lifespan. Solid lumber holds up well against fires. 

Engineered Wood 

There are two common types of engineered wood joists: 

  • Joists: Also known as TJI’s, I-joists provide an eco-friendly floor joist option. These joists offer a long span distance – at least 20 feet long. They also have a low moisture content after production, giving them minimal flex and a higher load-bearing capacity than solid lumber. I-joists do not hold up well to fires or water because of their thinner inner material. 
  • Open-web floor trusses: This type provides a flexible range of depth and web options, allowing for longer spans and greater loads. Just like I-joists, wood trusses have a low moisture content after production, meaning they shrink less. They also utilize less wood than solid lumber, making them environmentally friendly. 

Telltale Signs of Failing Floor Joists 

A sagging floor is the biggest telltale sign of damaged joists. Other signs to look out for include: 

  • Moist, rotting wood 
  • Sticking or jamming doors 
  • Bowing beams or ceiling 
  • Cracks in the interior drywall 
  • Bowing crawl space supports 

Once you notice any of these signs, you need to have the joists repaired immediately. 

Common Floor Joist Issues 

Understanding typical floor joist issues is crucial to coming up with the perfect solution. Some common floor joist problems include: 

Wood Rot 

The support holding up your home comprises wooden joists. Without proper sealing and waterproofing, your crawl space becomes prone to moisture and humidity. These conditions create the perfect breeding ground for mold and wood rot. Over time, these fungi can destroy the integral strength of your joists, posts, and girders. Hence, your joists may sag and cause the floor above your crawl space to sink or slope. 

Poor Construction 

Sometimes, contractors build crawl spaces with joists that are too few, while other times, the spacing is the issue. When there aren’t enough joists to support the weight of your household, the beams may begin to weaken and sag down. This may cause uneven floors and create an unsafe environment for your home. 

Termite Damage 

Termites eat just about anything that contains cellulose, including floor joists. When termites attack your floor joist, they compromise its integrity, leading to loose or saggy floors. 

Fixing and Protecting Your Joists 

Any damage to your floor joists presents a safety problem and needs immediate repair. To protect your frames from rotting, start by addressing the moisture issues in all areas of your home especially the basement or crawl space. Ask your carpenter to check and fix broken or damaged floor joists. Where repairing is not sufficient, consider replacing the joists altogether.  If the floors above still feel wobbly after your joists are repaired, consider adding extra floor joists to provide additional support. 

We also encourage you to have the crawl space, which houses the joists, sealed. What this will do is it will lock out moisture and make it difficult for pests to get in that may threaten the integrity of your joists. This is something Foundation Recovery System can help you with. To get started, schedule a free inspection

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Ankeny, IA 50021

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Kansas City, MO 64153
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211 SE State Route 150
Lee's Summit, MO 64082
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Moberly, MO 65270
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Springfield, MO 65803
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Fenton, MO 63026
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