Floor Framing and Rim Board Construction Details

EWP Training Series: Module C

This module introduces trainees to best practices in the design of engineered floor systems. It includes recommendations for I-joist and rim board layout, and the proper use of joist hangers, squash blocks and web stiffeners for transferring vertical loads. It also includes a review of framing details and recommended notching and drilling practices to maintain structural integrity.

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Training objectives: Upon completing this course, students will be able to identify and describe:

  • Best practices in designing engineered wood floor systems
  • Recommendations for Rim Board in I-joist floor systems
  • Proper techniques for notching and drilling I-joists and Rim Board
  • Correct use of web stiffeners, squash blocks and blocking for I-joist floors
Approximate length: 50 minutes.

Participant Questions and Answers

How would I determine what size beam or joist to use if more than one works based on my span and load?

There are many factors in making a decision for the best size or depth of a beam or I-joist. The first thing to verify is availability of the product. Availability of joist series and depths varies based upon your location. Next determine if you have height or on-center spacing restrictions. It’s always best to compare the overall floor system cost as compared to the lineal foot cost of a joist. When comparing systems you’ll find that if you can increase the depth of the floor it will allow you to increase your on-center spacing. By doing this you can design the floor with less joists thus reducing the overall cost of the floor system. Thirdly, determine if you have a critical area in the floor that needs special attention such as a marble floor. In this area your deflection criteria would be particularly important. Every floor system is different and often there are multiple factors that need to be considered.

Where is the best place to cut a hole or notch an I-joist?

I-joists stresses are lowest near mid-span and highest near the ends. This is evident when you look at hole charts for I-joists, where larger holes are permitted in the web area only, further from the bearings. Notches in I-joist flanges are prohibited and if any are observed the joist should be replaced or be evaluated for a repair.

Are web stiffeners required in I-joists when installing hangers?

Some hangers don’t require web stiffeners but this applies when the joist top flange is laterally supported by the sides of the hanger. Although, a designer may need to add web stiffeners when required to increase allowable reaction values. Check with manufacturer’s recommendation when in doubt.

Can Rim Boards also be used as headers such as over traditional 32” wide basement windows?

It depends on the applied load even though in most residential construction, the answer is affirmative. However, this applies only when the design load does not exceed the rim board capacity. Check with APA W345.

When do I need blocking over interior bearing supports?

I-joist or rim board blocking is required under all interior loaded bearing walls or where I-joists are NOT continuous over support.

Can a longer nail be used beyond 8d of 10d?

I would need more specifics where this would apply but to answer the question it is NOT recommended if you’re toe nailing rim board to the end of an I-joist. In other situations it may not cause a problem. Always check with the product manufacturer to verify.

Nailing through the rim board into the end of the I-joist flange is not usually called “toe nailing.” The primary concern of this nailing is mostly on the nail diameter, but it is true that the nail length may increase the likelihood of flange split.

If 3-1/2" SCL solid blocking is shown on plans, can you use I-Joist compatible Glulam beams or SCL?

Yes that would be acceptable. Any type of SCL that is the matching depth of the I-joist would be fine.