What Is A Rim Joist?

Many people are unaware of what a rim joist is. Or how crucial it is to their home’s structure and efficiency.

The rim joist, which runs along the outer edge of your floor joists, is crucial for supporting your home's structure and maintaining energy efficiency. Ignoring issues with a damaged rim joist can lead to significant long-term costs, potentially costing you thousands of dollars. 

Understanding their function and dealing with any issues helps you avoid major repairs to keep your home comfortable and energy-efficient. Let's explore what a rim joist is and why it's crucial to maintain it in good condition.

What is a rim joist?

Put simply, a rim joist is a horizontal board that runs along the edge of your home's floor. It forms the outer boundary of the floor structure. 

The rim joist is located at the top of the foundation and connects the ends of the floor joists (those beams directly underneath the floor). Its main purpose is to distribute the weight of the walls and roof and provide support and stability to the home. It also helps insulate the space by sealing off the ends of the floor joists, preventing drafts and moisture from entering.

Why rim joists are so important

Your home's strength, foundation, and energy efficiency rely on the rim joist. Unfortunately, it's often installed without proper insulation, causing heat to escape. 

Because rim joists are in a prime location, they're prone to energy loss, air leaks, moisture damage, and pest intrusion. It's super important to keep them in perfect condition to prevent substantial energy loss and expensive repairs.

How to inspect your rim joists

Checking the quality of your rim joists is more complicated than it seems. It involves measuring moisture levels in the wood, finding small or hidden air leaks, evaluating insulation quality, and checking for any movement or shifting. Since this part of your home is so important, it's best to consult a professional. 

At Thrasher, we offer FREE inspections to either reassure you about your foundation or uncover any potential problems. Our team has the tools and expertise to thoroughly assess your rim joists, helping ensure your home’s structure and foundation are solid.

How we can help you

At Thrasher, we frequently encounter issues with rim joist insulation and energy efficiency. That's why we offer RimTight, our specialized rim joist insulation solution. Depending on your home's needs, we can use spray foam, flashing and batting, or rigid board insulation to provide the best results. 

• Spray foam is a type of air sealing and insulation that utilizes two-part polyurethane foam. The material is pressurized and sprayed from a gun onto the rim joist. Once applied, the spray foam expands one to several inches. The finished product is a 1 to 3-inch thick closed-cell spray foam insulation and vapor barrier.
• Flash and batting is a technique of insulating rim joists that involves both spray foam and traditional foam batting. This technique requires a thin layer of spray foam insulation to be applied against the rim joist, providing an air-sealed cavity. Once that is done traditional insulation batting is stuffed into the cavity to create the insulative barrier preventing heat loss.
• Rigid foam board is the final and best option for sealing rim joists. This method requires cutting rigid insulation boards down to size and adhering it to the rim joist cavity. Once placed in the cavity, the foam board is picture framed around with single-part expanding foam. The result is a clean-looking and effective insulative barrier, air sealant, and radiant heat reflector.

So what should you do?

Whether there are physical signs or damage or something you might not know about, the best thing to do is get a free inspection from us here at Thrasher.

We'll provide you with a comprehensive guide and information on improving your home's strength, energy efficiency, and pest protection. Contact us for your free inspection today.