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Joists & Band Boards

The rim joists are an integral part of any subfloor framework and contribute to a home’s structural integrity.

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Few homeowners pay attention to their subfloor during home construction. They leave everything to the builder. As a result, they have little to no understanding of the subfloor and its components, one of which is the rim joist. 

A hands-off approach to home construction can have costly repercussions. Poor installation can lead to floors failing before their time. But that’s not the only problem. Unsealed joists can also drive up humidity levels in the crawl space, leading to energy inefficiencies and damp floors. 

Let’s take a look at rim joists and how they’re installed so you can better appreciate the role they serve in your home and take good care of them. 

What Are Rim Joists? 

The rim joist, or band board, is a part of your subfloor that carries the weight of your walls. It works in tandem with outer joists that form a band on your floor’s framework. In a home with two or more stories, the rim joist does more than bear the weight of the wall. It also supports the upper floor and the walls above as well as the roof. 

Wood is the choice material for creating rim joists. Not just any wood will do; solid timber that doesn’t have knots will have to be used. More and more builders are also turning to laminate wood and engineered wood products. All the materials are usually of the same size to ensure the joists and rims flush. 

What Do Rim Joists Do? 

In a home or building, the rim joists provide lateral support to other floor joists. They stop the floor joists from caving in under your building’s weight. Additionally, they cap off the end of your other joists. In turn, this prevents the formation of cavities that might open your home to the elements. 

Rim Joist Installation 

When framing your flooring, your contractor ensures that the rim joists run perpendicular to other joists and parallel to the length of your home. Standard joists span from the front to the back in many rectangular homes. Such an arrangement ensures the joist gets enough lateral support and caps off cavities. 

Joists are usually set on the upper part of the basement or foundation wall and then nailed to the subfloor framing using nails. The nails are then fastened with metal strapping. This prevents the joists from splitting due to high winds or tremors. 

Options for Insulating the Rim Joist 

Like any curious homeowner, perhaps you’re wondering what options you have for rim joist insulation. Here are a couple of good options. 

1) Spray foam insulation: Closed-cell spray foam insulation is a fantastic choice for insulating your exposed rim joists. It’s suitable for hard-to-reach areas as well. Applying an inch or more of spray foam creates an effective barrier that prevents air leaks and drafts. 

2) Foam board insulation: Here we have rigid panels made from polystyrene or polyurethane. Standard sheets measure four by eight feet, and their thickness can be anywhere from a quarter of an inch to two inches. 

Repairing Damaged Rim Joists 

If water or moisture gets into the crawl space, it’s only a matter of time before the rim joists start rotting. This tends to happen a lot if the sill plate is installed next to the floor or wasn’t treated properly before installation. There’s no recourse for water-damaged joists but to replace them. A team of repair experts will raise the floor and then remove the rotted joists and install new ones. 

Protect Your Rim Joists 

In your effort to keep moisture out of the crawl space area, you’ll discover that your rim joists/band boards are one of the weakest links. They can let in moist air, which can make your walls and floors damp, cause wooden support to rot, and encourage mold growth. 

Don’t let moist outside air ruin your crawl space area and damage vital subfloor fixtures like your rim joists. The waterproofing experts at Foundation Recovery Systems can help properly insulate the crawl space and seal it up with a 20-mil plastic vapor barrier

Be sure to request a free crawl space inspection and repair quote from us today. 

FRS Service Area Map with Des Moines

Our Service Areas

Des Moines Location

2401 SE Creekview Dr.
Ankeny, IA 50021

Kansas City Location

211 SE State Route 150
Lee's Summit, MO 64082
(816) 774-1539

Moberly Location

1401 US-24
Moberly, MO 65270
(660) 202-8662

Springfield Location
1820 N Barnes Ave
Springfield, MO 65803
(417) 612-8286
St. Louis Location

1625 Larkin Williams rd.
Fenton, MO 63026
(314) 207-9995