End Blocking for Floor Joists

[jar546]

Question:
In Seismic Design Categories A, B, and C, is solid blocking required where the ends of floor joists are lapped at an intermediate bearing support?

Answer:
No. In Seismic Design Categories A, B, and C, solid blocking is not required between joists at an intermediate support where the joists are lapped or spliced as required in Section R502.6.1. The lap or splice at the intermediate support provides continuity of the joist and therefore provides sufficient lateral support, as required in Section R502.7, to prevent rotation. Solid blocking, in addition to the lapped or spliced joists, is not required.

 

[wwhitney]

The lap or splice at the intermediate support provides continuity of the joist and therefore provides sufficient lateral support, as required in Section R502.7, to prevent rotation.

In Table R602.3(1) "Fastening Schedule" for prescriptive wood construction, I'm not seeing a specification for the fastening of two lapped joists over an intermediate support. So I don't see how you can say that the lap will necessarily provide "lateral support to prevent rotation" as required by R502.7. If I use 1 nail in the lapped region, is that sufficient? If not, how many nails is sufficient?

Cheers, Wayne

 

[Mr. Inspector]

I don't see it in the 2018 IRC. When did it start.

 

[jar546]

I don't see it in the 2018 IRC. When did it start.

That was an ICC committee interpretation from 2003 that still stands and has not been modified.

 

[wwhitney]

I don't see it in the 2018 IRC. When did it start.

2018 IRC R502.7 "Lateral Restraint at Supports":

"Joists shall be supported laterally at the ends by full-depth solid blocking not less than 2 inches (51 mm) nominal in thickness; or by attachment to a full-depth header, band or rim joist, or to an adjoining stud or shall be otherwise provided with lateral support to prevent rotation."

So when you have lapped floor joists at an intermediate support, the question is whether nailing the lap together provides "lateral support to prevent rotation" at those ends.

Cheers, Wayne

 

[wwhitney]

That was an ICC committee interpretation from 2003 that still stands and has not been modified.

Yet it sounds wrong on the merits. How can an unspecified lap splice be known to provide "lateral support to prevent rotation"?

If you calculate the torsional capacity of the floor joist, and calculated the length of the lap and nailing pattern required to transfer that torsional capacity, then yes you could say the lap splice condition is equivalent to a continuous joist. But where is that specification in the IRC? Without it, I don't see how the ICC's answer passes engineering muster.

Are such ICC interpretations binding upon jurisdictions that adopt the IRC?

Cheers, Wayne

 

[steveray]

I say yes..

 

[jar546]

Are such ICC interpretations binding upon jurisdictions that adopt the IRC?

The question should be: Should the ICC rescind interpretations that are no longer valid due to subsequent code changes?

 

[wwhitney]

The question should be: Should the ICC rescind interpretations that are no longer valid due to subsequent code changes?

What subsequent code change is that? The main text of R502.7 is identical between the 2000 IRC and the 2021 IRC.

Cheers, Wayne

 

[jar546]

What subsequent code change is that? The main text of R502.7 is identical between the 2000 IRC and the 2021 IRC.

Cheers, Wayne

Are there any changes at all, including references?

 

[steveray]

The question should be: Should the ICC rescind interpretations that are no longer valid due to subsequent code changes?

If they categorize them to a specific code edition, I have no issue with it…

 

[Yankee Chronicler]

Are such ICC interpretations binding upon jurisdictions that adopt the IRC?

My state doesn't adopt the straight ICC codes, we adopt them with state amendments. We have a state statute that says only the State Building Inspector is authorized to interpret the code. So, in this state, ICC interpretations are guidance only, not binding, even if the code section was not revised by an amendment when we adopted it.

 

[mtlogcabin]

Are such ICC interpretations binding upon jurisdictions that adopt the IRC?

NO read Number 3.
The final authority for code interpretations is the Code Official

Committee Interpretations approved by the ICC Interpretation Committee represent the official position of the International Code Council; however, the final authority of code interpretations is the responsibility of the code official.

Committee Interpretations - ICC

Committee Interpretations Committee Interpretations Committee Interpretations provide technical support and clarification of code text for adopting jurisdictions, design professionals, and members of the construction industry. Committee Interpretations are processed in...

www.iccsafe.org

 

[ICE]

however, the final authority of code interpretations is the responsibility of the code official.

That’s a CYA to protect the ICC.

 

[jar546]

If they categorize them to a specific code edition, I have no issue with it…

That would make sense.

 

[steveray]

That would make sense.

We have our own Connecticut list, which obviously are kind of sort of binding in Connecticut and they are all by year and/or code they were issued to

 

[Paul Sweet]

I still specify solid blocking between joists at bearing points.

 

[Sifu]

I have bumped into this before in a couple different ways. 507.2 does include "or shall be be otherwise provided with lateral support to prevent rotation". I tend to think of this section as having three parts: the first is a prescriptive option which is the blocking, header or rim. The second is more a performance option, which is the "otherwise", the third is for bridging to provide lateral support when the depth of the joist exceeds a 2x12, but that is no longer an option so we can skip it for this question. So take a typical dropped girder with an 8' lapped joist span on either side, with subfloor fastened with 8d nails at 6"/12", and likely adhesive, nailed into the joists across the top and toenailed to the girder at the bottom with 3-3" ,031 nails. Each joist has connections at the top and bottom. Is blocking required? Is the subfloor and the toenailed connection an "otherwise"? Now take that same floor on an exterior deck, but with only a cantilevered 2' portion past the dropped girder, with a band joist with 3-16d nails at each joist. The joist isn't lapped, it is not the end of the joist. Is blocking required there, or is the lateral support by the band meeting the requirement? There are illustrations for exterior wood decks that show blocking or "other lateral restrain" required over a beam (60% depth per 507.6.2). If the rim is within the allowable cantilever length, is the rim with 3-10d nails at the end of the joist, the toenailed joist to beam connection, and 5/4 decking secured at the top by 2-8d threaded nails the "other"?

All the connections I list are prescriptive.

Installing the blocking is easy, and few protest, but can increase the squeaks in floors. Some have protested the deck blocking as described. But since the code provides what I believe to be performance options, is blocking always required? Blocking does tend to stiffen a floor, but I don't think that is the intent of these code sections.

 

[SCBO1]

IBC 2021, Figure R502.2 does not indicate any blocking requirement between FJ's at the center where the two FJ's are spliced, however if there is one joist not attached to an opposite FJ, I would say it needs blocking.

I-Joist, what ever the manufactures requires. On a two story home the lower I-joist are typically blocked and Mr. HVAC guy knocks them out with his 32-oz hammer.

One thing that's disappeared is cross bracing (Bridging) use to see it all the time with 1x or steel, hardly anyone installing bridging.

Also I can't find where 2x8's or smaller do not require end blocking, has that been removed from code?

 

[mtlogcabin]

R502.7 Lateral restraint at supports.
Joists shall be supported laterally at the ends by full-depth solid blocking not less than 2 inches (51 mm) nominal in thickness; or by attachment to a full-depth header, band or rim joist, or to an adjoining stud or shall be otherwise provided with lateral support to prevent rotation.

I have a 32 foot wide single story house with two pony walls supporting the floor joist system. Each 2x nominal floor joist is 12 ft long so each end of the floor joist member bears on an exterior wall or a pony wall. They over lap and are spliced in accordance with R502.6.1. Is that one 32 ft long floor joist with 2 ends or 3 floor joist with and end at each bearing point that need to be laterally supported?

R502.6.1 Floor systems.
Joists framing from opposite sides over a bearing support shall lap not less than 3 inches (76 mm) and shall be nailed together with a minimum three 10d face nails. A wood or metal splice with strength equal to or greater than that provided by the nailed lap is permitted.

The lap or splice at the intermediate support provides continuity of the joist and therefore provides sufficient lateral support, as required in Section R502.7, to prevent rotation.

So if the 2x nominal floor joist where butt joined with a 2x wood splice would that also provide sufficient lateral support as noted above for the 32 ft joist length.
Just playing devil's advocate here.

 

[jfmann77]

All beam-elements (joists, girders) require adequate lateral bracing so that beam can provide support in bending about "strong axis" as intended, without failing prematurely......which could be catastrophic......... due to lateral buckling. Key factor for design capacity is length of beam segment without lateral bracing......often termed "unbraced-length" of beam.
For any beam, lateral bracing must be provided for edge of beam that is in compression when beam is bending due to load. This is because ......similar to column..........compression can cause lateral buckling.
For "simple" beam with supports only at each end......and for downward-acting force (load).......top edge of beam is in compression along entire length of beam........and bottom edge is in tension along entire length of beam. For I-joists, top "flange" is in compression and bottom flange is in tension.
For continuous beam with three supports, and for downward loading, flexural (bending) tension occurs along top edge (or flange) of beam at and near interior support........while compression occurs along bottom edge or flange. For remainder of beam, top edge is in compression and bottom edge is in tension.

For downward-acting force (load), lateral bracing for top edge of beam is typically provided by floor sheathing with adequate connections to beam.
Floor sheathing is often considered to provide "continuous" bracing..........though actual unbraced-length of beam is equal to spacing between connectors (nails)..........which may be 12 inches or more.

Lateral bracing is also required at each support to prevent rotation or twisting of beam, which can happen due to large "reaction force" being applied by beam to support (and by support to beam)..........and which could be major problem for beam stability without lateral bracing.
For lateral bracing at supports.....key issue is ratio of beam depth to beam thickness.........which should be relatively low as can be visualized. When beams (joists) are lapped and effectively connected, effective thickness of beam at that location is essentially doubled.
For engineering design..........lateral bracing at supports is often "judgment call"..........very often based on past-performance of typical details. However, conservative approach for this key design issue should always be taken since this is type of "overlooked" design issue that often leads to major failures.