What you need to know when designing with Engineered wood, 1: safety

In this series of three blogs, we’ll talk about three fundamental factors to consider when designing with engineered wood flooring components. These are, in order of importance, safety, comfort and performance, and logistics.

In this first of three posts on the subject, it’s safety first, as usual.

Building codes

Design professionals naturally abide by the building code requirements of their area. This can include a combination of model building codes and local building codes.

Model building codes standardize building construction practices across the country. Consequently, a municipality or local government that adopts a model building code is saving itself the trouble of developing its own code. It just needs to concentrate on enforcing it. That said, some municipalities add on additional building codes as well. The point, of course, is to maximize safety for building occupants.

Now, let’s look at the important aspects of the model building code, for engineered wood floors.

Load conditions

There are three load condition categories. Live loads, Dead loads, and Special loads. The Live loads are always specified in the model building code.

Live loads are temporary loads (people, furniture, and movable items) uniformly applied to the floor system. For example:

Residential living spaces:             40 pounds/sq ft.

Office use:                                           50 PSF

Retail use:                                          80 PSF

Assembly areas:                             100 PSF

Dead Loads are permanent, non-moveable elements (floor framing, decking, ceiling finish, insulation, mechanical systems, etc.). Design dead load is determined by the sum of the ACTUAL weights of all these items per square foot.

Special Loads are permanent and represent concentrated loads on specific areas of a floor system (lines, points or areas). They may result from roof framing, interior bearing walls, large mechanical units, large fixtures, etc. Snow loads are part of this category. They’re not permanent, but they can linger for several weeks.

Deflection performance

Deflection is the up and down movement of a floor. The building code dictates a maximum deflection for a floor under full loading, to avoid cracking of ceiling material and flooring materials. It is measured as “L” over the deflection criteria number. “L” is the length of the floor joist, expressed in inches.

Three factors affect deflection performance. The length of joist span, load conditions, and framing member stiffness.

To reduce deflection, you can do things like reduce the on-center joist spacing or increase the joist depth. Engineered wood joists usually give the best deflection performance.

Fire endurance performance

Building codes set out the amount of time a flooring system must withstand fire, in order to give occupants sufficient time to get out, but also for the firefighters and safety personnel to extinguish the fire with minimal bodily risk. Depending on the area, the codes can dictate this time to be 1 hour, 2 hours or more.

Multi-family and institutional residences, as well as single family housing with a built in garage, generally require living unit separations by fire resistant floor/ceiling assemblies.

Because of the importance of fire safety, municipalities or local governments will sometimes add further regulation, such as for sprinkler installation or baffling within the floors or ceilings, to increase fire resistance.

Seismic performance

For areas where seismic activity is present, building codes have requirements for lateral force resistance. Resistance to back and forth movement is drag load. It is not measured with individual components, like joists. Rather, measurement encompasses the entire systems called ‘’Shear walls’’ of which the joists can be a part of. Furthermore, the designer does have to be aware of the forces the joists must be able to carry in such a system (drag strut capability). The designer can get this from the manufacturer.

Safety is of utmost importance to us

Finally, let us know if you have any questions on the above subject matter. We also have training material that goes into deeper detail on how to design floor systems with engineered wood joists. If you’d like more information, contact us.

In part two of this series, I’ll talk about comfort/performance considerations.

2 Responses

  1. Steve Nason

    Stongbacks- The strong backs aid in the deflection of the joists.

    • Sylvain Blais

      Hi Steve, thanks for your comment.
      You are absolutely right, strongbacks reduce deflection and also increase transversal rigidity, and I should have included it. They are a really inexpensive way to increase floor performance. Don’t know if your read it but here is a blog post on strongbacks that Eric Pendland put out about a month ago.

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