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The Importance of Rim Joist Insulation

rim joist

It’s common for inexperienced homeowners to try to fix their crawl space problems with a 6-mil plastic liner. However, this solution can’t prevent the unconditioned air from coming through the walls, dirt floor, and rim joists. Even if you close your crawl space vents, the cold air will still come inside your home and cool it even more during winter. This is due to the nature of rim joists and possible cracks in your foundation walls. Here’s how to keep them in perfect condition.

What Are Rim Joists?

Rim joists are the primary structural elements of any home’s floor frame. They are the ribs that create a frame that the exterior or foundation walls support. The ends of floor joists rest perpendicularly on the rim joists.

Rim joists are visible during the construction of a new home. They look like very thick bands of wood and span the entirety of the floor. The design of rim joists is such that they can support a lot of weight, which is why they are often made of solid wood without any knots.

Regular joists and rim joists form a 90-degree angle, with the latter parallel to the longer side of the house. When construction crews are building a floor platform, they will install rim joints on top of foundation walls, nailing them into the framing. They will also reinforce them with metal. This will prevent them from separating from the floor in case of strong winds or even earthquakes.

The Purpose of Rim Joists

The main purpose of rim joists is to provide support for all other joists. The rim joist keeps them from bending due to the weight they need to withstand. Apart from that, rim joists are used to cover the ends of the other joists to prevent exposed cavities. This stops moisture from freely entering homes and damaging their foundations.

It’s also important to mention that you should keep an extra eye on them during construction because they have a major role in your home’s overall functionality. Construction crews must not cut any corners while installing rim joists.

What Is Rim Joist Insulation?

If you have moisture problems in your crawl space, you might consider insulating your rim joists. Insulation is important because water is one of the most dangerous enemies your lower-grade level can have. As such, every homeowner should waterproof their below-ground areas.

Moisture and cold air can easily come in through your crawl space cracks, gaps, rim joists, and vents. With time, your lower-grade area will become humid enough to start endangering your home’s structural integrity, safety, and comfort. Some of the problems moisture in crawl spaces can cause includes rot, energy loss, and mold infestations.

Your best choice is to try to keep your crawl space in top shape. This means insulating your rim joists. Such a solution will prevent moisture from entering your crawl space and can help create a healthier environment for you and your family. The same applies to both new and old homes.

Types of Rim Joist Insulation

Before you contact professionals to insulate your rim joists, here are three typical methods they might implement while working on your crawl space:

1. Spray Foam Insulation

This first insulation option is probably the most popular out there. The reason is that it will easily seal all the areas that are difficult to access. Spray foam prevents outside air from coming in and reduces drafts near the floorboard. Additionally, it is environmentally friendly and doesn’t attract pests. However, if you don’t install it properly, it can obstruct utilities, wiring, and piping. It’s best not to experiment with it and instead contact professional help.

2. Foam Board Insulation

If you have a moderate budget, you can still insulate your rim joists by using foam board insulation. It will still keep moisture out of your below-grade unit. This type of insulation comes from polyurethane or polystyrene and is available in sheets. What makes it so great is the fact that you can use it for other types of insulation too. Moreover, it’s pretty common for homeowners to use foam boards for almost all parts of their homes.

3. Fiberglass Insulation

Your third yet still affordable option is to use fiberglass insulation. This type comes from plastic with fine glass fiber reinforcements. Contractors use it to insulate not just rim joints, but basement walls, whole crawl spaces, and even attics. Still, fiberglass insulation is air permeable, so it might become prone to mold problems over time.

Need Rim Joist Insulation? Call Foundation Systems of Michigan?

In case you’re having problems with your crawl space, don’t try experimenting with it. Instead, schedule a free inspection and repair estimate with the experts at FSM. Our team provides service to residents in the Detroit area, Grand Rapids, Traverse City, and surrounding areas in Michigan. With our help, you’ll be on track to waterproofing and insulating your crawl space and ensuring the health and safety of your loved ones.

Rim Joist Insulation FAQs

Costs vary based on crawl space condition, size, and required repairs. Following a free inspection, our experts will provide a no-obligation estimate with detailed costs and financing options. 

Many insulation varieties last 15-20 years but can degrade due to moisture if the crawl space isn’t properly sealed and encapsulated. Foundation Systems of Michigan’s ExTremeBloc™ rigid foam board insulation is designed as a lasting solution. Reach out to us for more information and to arrange a free inspection

Because glass fiber is used for the strands that make up fiberglass insulation, when the insulation becomes wet, it briefly loses its capacity to withstand heat. Nonetheless, it will still keep its insulating qualities provided it has had time to dry out and hasn’t been compacted.  

However, wet insulation won’t often dry very quickly in an exposed crawl space. 

Leah Leitow

Leah Leitow

Content Writer

Leah is a Content Writer for Groundworks with nearly ten years of experience working in the foundation repair industry. Her experience ranges from working with homeowners to find the right solution to training inspectors and staff. In her background as a Michigan journalist, she gained invaluable insight into people's lives throughout our state. Leah lives in metro Detroit with her husband and two sons.

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