Floor Joists

[97Harley]

Had a meeting with a contractor who was quoting a job for my client. He told me that in Florida you cannot use 2x6 SP#2 floor joists and the code calls for 2x8 joists minimum. I researched and could not find anything referring to standard lumber size restrictions. In fact, I have a chart printed from the FBC 2020 listing 2x6 SP#2 joists at the top of the chart. The house I am adding additions to was built in 1945 and it has 2x6 joists at 16" O.C. throughout. Am I wrong in calling for the same floor joists for the additions? The structure is set on piers off grade about 30".

 

[driftLimiter]

If you have a strong reason to push for 2x6 then ask the contractor to show you where it is required. I don't know your spans or loadings, but man 2x6 for floor joists we don't do that much around here. Around here we have concerns about shrinkage, warping, etc that may not be a strength concern, but a big source of liability for houses is just whether or not the floor squeaks or feels bouncy.

 

[JStructsteel]

I dont see any restriction. Just put on your drawing (2x6 or code min.) for this contractor, that way he can argue it with the home owner if they choose too.

Now, perhaps local jurisdictions have special requirements. Use this as a opportunity to educate yourself if he is right.

 

[97Harley]

Thanks for the input. I always specify glue and 8d ring nails at 6" O.C. for subfloors with blocking. The free span is 9' maximum for 40 and 10 loading with no cantilever for 2x6 SP#2. I want to keep the pier heights the same without having to adjust for the 1.750" difference, which the contractor said would do.

 

[phamENG]

I can't speak to the Florida Building code specifically, but I will say that I would not use 2x6's in that application. They technically meet code minimum deflection requirements, but code minimum and occupant comfort/satisfaction are NOT the same thing (as driftLimiter was alluding to).

For wood floors to perform well, you should shoot for a minimum of L/480 for joist live load deflection and L/600 for girder live load deflection. I get L/378 for this setup.