Answers to common questions about Open Joist™.
What is Open Joist?
An open-web floor truss assembled through a unique process of finger joinery and waterproof structural adhesive instead of metal plates.
Is Open Joist approved for use under U.S. building codes?
Yes. Open Joist has been approved for use by IBC and IRC code agencies. IAPMO has issued UES Report Number ER 501 for he product.
What sizes are available?
Open Joist is available in six standard depths:
- 9-1/4" deep, in lengths of 3' through 20' (in 1' increments)
- 11-7/8" deep, in lengths of 3' through 23' (in 1’ increments)
- 14" deep, in lengths of 3' through 25' (in 1' increments)
- 16" deep, in lengths of 3' through 30' (in 1' increments)
- 18" deep, in lengths of 3' through 31' (in 1' increments)
- 20" deep, in lengths of 3' through 32' (in 1' increments)
Why aren't longer lengths available?
Like dimension lumber, Open Joist is a bottom-chord-bearing product that is butted or overlapped at intermediate bearings such as beams or walls, making longer lengths unnecessary. Unlike dimension lumber, Open Joist's clear span capabilities are extensive and are equal to or greater than other engineered wood joists.
What are Open Joist's clear-span capabilities?
Clear spans depend on truss spacing and floor loading requirements, but the maximum clear spans achievable (distance between bearings) with Open Joist are:
- 9-1/4" depth = 19'-9" clear span
- 11-7/8" depth = 22'-9" clear span
- 14" depth = 24'-9" clear span
- 16" depth = 29'-9" clear span
- 18" depth = 30'-9" clear span
- 20" depth = 31'-9" clear span
Why is Open Joist so strong?
Open Joist is an engineered floor truss that takes advantage of the structural power of the triangle and the forces of compression and tension working together to create superior strength.
How does Open Joist's cost compare to other products?
Open Joist typically offers a cost savings of 20% to 30% when compared to metal-plated floor trusses. Comparing foot-for-foot cost, Open Joist is directly competitive with wooden I-Joists. When floor systems are designed to take advantage of Open Joist's strength, the cost of floor framing can be less than when dimension lumber is used. Open Joist has the highest strength-to-cost ratio of all engineered floor joists.
Is Open Joist primarily a residential construction product?
No. The superior strength and highly competitive cost make it a natural choice for many commercial construction projects. The product's strength/cost ratio makes it an attractive floor-framing system for almost any building project.
Does Open Joist issue floor system designs using a deflection criteria of L/480?
As an open-web floor truss, Open Joist normally issues floor-system designs using the standard floor truss deflection criteria of L/360, because open-web floor joists allow the use of "strongback" bracing. Strongback bracing ties a large portion of the floor system together to accomplish "load sharing" and to restrict deflection and bounce. Open Joist provides clear-span tables and uniform load charts based on L/480 deflection criteria. Open Joist floor systems are designed to this criteria when specified (some state building codes and fire assemblies require L/480 criteria).
How long will the glue in Open Joist last?
Open Joist uses a phenol resorcinol adhesive that is resistant to water, heat and fire. This structural adhesive is the standard of the engineered wood products industry (also used by I-Joist and Glu-Lam manufacturers) and has been in use since the late 1940's. It is safe to say that the wood fiber in an Open Joist floor truss would disintegrate from age before this glue would break down.
How can Open Joist help me have an eco-friendly building project?
Open Joist can help maximize your potential to earn Leadership in Energy and Environmental Design (LEED) points under the Materials and Resources (MR) category. By using efficient framing measures such as open web floor trusses, you can earn LEED points for your building project. Other points can be earned by increased waste diversion and low-emission adhesives and sealants. By using FSC-certified Open Joist, you can earn additional LEED points.
How do I get the exact length I need?
Open Joist is available in one -foot increments, and each truss can be trimmed up to 11" (5-1/2" maximum off each end). Using the stock lengths of Open Joist, you can achieve any desired length.
Do I have to trim both ends equally?
If the total amount to be from the truss is 5-1/2" or less, only one end need be trimmed. Even when both ends must be trimmed to reach the desired joist length, it is not necessary to trim equal amounts from both ends. The only governing factor in trimming Open Joist trusses is that at least 1-3/4" of the trim block at the end of the truss must remain to rest on bearing.
How can I be sure I've installed Open Joist correctly?
An engineered floor system layout is supplied with every shipment, along with general and information for framers. Generally, a builder only has to keep in mind a few things when framing with Open Joist. Leave at least 1-3/4" of the end block when the end, and do not cut or notch the web area of the Open Joist floor truss. For the most part, framing with Open Joist is no different than framing with dimension lumber.
What kind of special blocking and bracing is required?
A 2x4 or 2x6 "strongback" bracing run through the open webs is sufficient to tie the floor system together. In most cantilever and point-load situations, simple nail-on plywood gussets provide adequate strength for extra loads.
Do I need extra bearing to support Open Joist floor trusses?
No. You only need a bearing of 1-1/2" in all normal loading situations; therefore, trusses can be butted together over a 2x4 intermediate bearing wall.
Is there some way to avoid the glue marks on Open Joist trusses?
The assembly process for Open Joist floor trusses results in some unavoidable glue runs and spills. The glue can be scraped from Open Joist trusses or painted over if the trusses are to be left exposed.