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Rim Joist

Rim joists are one of the primary structural elements of your home’s floor frame. Since they create air openings, make sure you insulate them.

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If you have dealt with crawl space issues in the past and tried to fix them with a 6-mil plastic liner, it is possible that your contractor has warned you that this method will not address the unconditioned air coming from the walls, dirt floor, and rim joists. They may also have talked about closing your crawl space vents and they informed you that cold air can enter your home through rim joists and cracks in the foundation in the winter. While most homeowners know what foundation and dirt floors are, many haven’t heard the term rim joist. So, what are rim joists, what is their purpose, and should you insulate them? Let’s take a closer look at band boards, also known as rim joists. 

What Are Rim Joists? 

In order to properly explain what rim joists are, we have to first talk about joists in general. These beams are the primary structural elements of your home’s floor frame. Basically, they are ribs that create a frame, which is then supported by the exterior walls or the foundation walls. When a layer of plywood subflooring is added to the top of the frame, you have a floor platform. Now, the end of these joists that rest on the exterior or foundation walls are attached to a perpendicular joist called the rim joist. If you were there when your house was under construction or you had an opportunity to see an unfinished house, you were able to see a band of solid boards running along the foot of each floor level. Those bands are made up of the exposed faces of the rim joists. These joists are designed to withstand a lot of weight, so they are made from solid wood that doesn’t have any knots. 

What Is the Purpose of The Rim Joists? 

The main task of a rim joist is to support all the other joists. It keeps them from bending due to the weight they need to withstand. Another purpose of a rim joist is to cover the ends of other joists, so there aren’t any exposed cavities. Otherwise, moisture would be able to easily enter your home and damage your foundation. Since rim joists have such an important role, builders must not cut any corners on them. 

How to Install Rim Joists 

As mentioned, rim joists and regular joists form a 90-degree angle. Rim joists are parallel to the longer side of the house. So, for example, in a rectangular house, rim joints are placed in a front-to-back direction. When builders are creating a floor platform, they place rim joists on the upper levels of the exterior walls or the foundation walls and nail them into the framing. This connection should be reinforced with pieces of metal strapping to prevent separation of the floor in case of strong winds or an earthquake. Rim joists are nailed to each joist with three nails that go through the outside face of the rim joist and stop at the end of the joist. 

Rim Joist Insulation 

If you have a moisture problem, your contractor might have suggested insulating your rim joists. Why is this important? Well, as you may know, if it is not properly waterproofed, a crawl space can easily become moist. Unfortunately, moisture and cold, winter air can easily enter the crawl space through cracks, gaps, rim joists, and vents. When this area of your home becomes humid, there is an array of problems that can occur, from rot and energy loss to mold infestations. Keeping your crawl space in top shape means maintaining your home’s health. By insulating rim joists, you can prevent moisture from entering the crawl space and create a healthier environment. Whether you live in an old home or a newly built one, you can benefit from rim joist insulation. However, before you call the contractors, let’s take a look at the three most common insulation methods. 

Spray Foam Insulation 

This insulation method is popular because it can easily seal all the areas that are difficult to access. The spray foam will prevent outside air from getting in and will reduce drafts near the floorboard. It is safe for the environment and won’t attract pests. However, if not installed properly, it can obstruct utilities, wiring, and piping, which is why it should be handled by a professional. 

Foam Board Insulation 

Foam board insulation is a more affordable solution if you wish to keep moisture out of your below-grade areas. Foam board is made from polyurethane or polystyrene and comes in panels or sheets. This product is not just good for joist rim insulation. In fact, you can insulate almost any part of your home with it. 

Fiberglass Insulation 

Another affordable solution is fiberglass. It is made from plastic reinforced with fine glass fibers and contractors use it to insulate not just rim joints, but basement walls, crawl spaces, and attics as well. However, fiberglass batts are air permeable so this type of insulation in the rim joist is prone to mold issues

If you believe that you could benefit from rim joist insulation or you have questions about the rim joists in your crawl space, do not opt for a DIY project. Instead, call professionals in North Carolina and be at ease knowing that the job has been properly done. Contact Tar Heel Basement Systems today to schedule a free inspection. One of our experts will visit your home, assess the situation, and recommend the best solutions for your home. 

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