Floor Joist to basement center beam joint

[jbos333]

Hi all! Merry Christmas!

Dumb question for you,

Can I hang floor joists from the center basement beam with joist hangers (to code)?

Looking to put the beam up on top of basement wall instead of in a pocket to save some headroom on a standard 8' poured wall.

I'm sure it's been covered here somewhere but my search didn't turn up what I was looking for.

Thanks!

[rick91351]

How wide are you spanning? 

With I joists you might not have to center beam at all.     

[PEG688]

 Should be fine.   Posting stays the same under the beam. 

Glue the joist into the hanger bottom, as hangers tend to squeak , top flange style hangers tend to squeak more , the "I"  joist/ TJI / BCI engineered joist  top flange being the worst / most likely to squeak ,  hangers.  Construction adhesive does reduce the chance squeaks.

 

[jbos333]

Thank you for the replies. My span is around 24' (basement walls 24' outside dimension). So 12' + 12' with center beam. If there are reasonably priced I-joists that will free span 24' I would be open to that also.

[PEG688]

You'll do better hanging them , you'd lose height wider/ taller  joist.    24' a long span for a "I " joist and you'd be looking at a 14" ish one , I'd guess about the same for  GLB used as a a joist. And the deflection / bounce of the floor would be a bad thing. 

You could ask the lumber yard to price out the options.   

[jbos333]

Thanks, PEG688.

I think I'll just stick with 2x8's @ 12" O.C. That should be a stiff enough floor, no?

Actually, I just looked up pricing, 2x10's would only add about $100.00 to the cost of the joists.

[MountainDon]

2x10 on 16" centers can span the 12 foot easily in most popular species and make a nice solid floor

AWC Calculator

[Don_P]

There are a couple of pro's and con's of a flush girder, what you are proposing, and a dropped girder.
The flush girder saves headroom below but blocks the ability to cross the building up in the joist bays with things like plumbing and HVAC, it might matter, it might not. A dropped girder doesn't require the hangers, creates a stronger support for the joists and better loading of the girder. The bays are unobstructed over the girder, it costs headroom.

The "properties of sections" that model how the shapes perform in the engineering formulas that are used to create the span tables might show why one chioce might perform better than another.
http://theownerbuiltcabin.com/calculators/TT/MomentCalculator.htm

A 2x8 has a section modulus, the number used in bending strength calculations, of 13.14"³. It has a moment of inertia, the number used in stiffness, deflection, calculations, of 47.63"⁴

A 2x10 has a section modulus of 21.39"³ and a moment of inertia of 98.93"⁴

What the numbers show is that going a size deeper builds strength faster than decreasing spacing and using more 2x8's. Then, when you look at how much deepening the section just 2" affects stiffness and it's a no brainer if you can handle the depth. For the volume of wood used, going a size deeper improves things faster than anything else. The old saying is "Deeper is cheaper".

[jbos333]

Thanks Don_P, the lack of full access across the span in the joist bay is something that didn't even cross my mind. And I don't suppose there are any ways to put hole in the girder. At least not safely/or to code.

[Don_P]

I don't tell subs this. You are allowed to use the same notching provisions as joists and rafters, start reading at about R502.8.

Now think about what happens when a subcontractor bores a max sized hole right beside a maximum edge knot along the bottom edge. If one joist surrounded by many other joists, not a big deal. With a girder, each ply is part of a single member carrying the floor, I'm not going to voluntarily let Bubba carve on a beam.

The LVL suppliers also publish allowable hole charts. A hole in an LVL girder gives me less heartburn. With all the glued up layers, a defect like the knot above is never crossing the full thickness anywhere. Defects are dispersed.

If you can, pick one or two places to drop under and box off somehow.