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Transmitting loads to the Stuctural elements

Uncle Bob

Uncle Bob

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"2003 IRC, R602.3.2 Top plate. Wood stud walls shall be capped with a double top plate installed to provide overlapping at corners and intersections with bearing partitions. End joints in top plates shall be offset at least 24 inches. Plates shall be not less than 2-inches nominal thickness and have a width at least equal to the width of the studs."

Code change in 2006;

"2006/2009 IRC, R602.3.2 Top Plate. Wood stud walls shall be capped with a double top plate installed to provide overlapping at corners and intersections with bearing partitions. End joints in top plates shall be offset at least 24 inches. Joints in plates need not occur over studs. Plates shall be not less than 2-inches nominal thickness and have a width at least equal to the width of the studs."

I can understand the second (uppermost) top plate end joints, not being required to occur over studs (example: a rafter and ceiling joist or floor joist, secured over the end joint); where pressures from dead loads and live load movement (reroofing, joist traffic, etc) shouldn't cause the two plates to seperate.

But, the inference is that the first (lower) top plate end joint also, does not need to occur over a stud; and in this case, (example: a rafter and ceiling or floor joist, occuring over the end joint); where movement caused by live loads could cause the two top plates to seperate at that point.

Am I nit-picking; or could this be a problem over time? I don't believe the nailing together (one (1) 10d nail, 24" o.c.) of the two top plates is designed to carry dead and live loads to the structural elements; without the lower top plate end joints being supported by a stud.

"2003/2006/2009 IRC, R601.2 Requirements. Wall construction shall be capable of accommodating all loads imposed according to Section R301 and of transmitting the resulting loads to the supporting structural elements."

I seek everyones view; but, would like some Engineer's input here also.

Thinking out loud,

Uncle Bob
 
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At best the end of a lower top plate would have 3/4" of bearing surface if the splice occurred directly over the nominal 2X stud. Is that enough to properly transfer the loads? Like you I will wait for the Engineers input.
 
My sense is that while splicing over a stud is preferable, that it is not likely to cause a problem in typical residential framing. Given the 24" minimum lap at least one plate will be continuous over the each stud spacing.

I probably could calcuate situations where this wasn't enough but I would not be surprised to find that they still performed adequately. This could be because the predicted loads never occured or because some other factor caused the plates to perform better.

Sure there is more risk but the proscriptive provisions of the IRC in many cases accept more risk. If you are uncomfortable with the risk permit the building using the provisions of the IBC and have the residence fully engineered. Of corse the design fees would cost more and it could be more expensive to build but that is part of the trade off, uncertainty versus expense.

Some possible mitigating conditions would include.

--If joists were located over the studs (prefered practice) there would be no problem.

--Joist not located midway between the studs would reduce the bending stresses.

--Plywood sheathing would carry some of the load.

--Continuous rim joists redistribute loads from the floor above and reduce the loads on the plate.

Bottom line is that I see no smoking gun that says it is unsafe. The code allows this thus I do not see how the building official can say otherwise.
 
Any good framer knows the difference it makes. That is why there are so few good framers around. I don't think the code should be telling you what you don't have to do.
 
If you read the code carefully, you will note that at least one of the plates will be continuous over each stud. That is sufficient for proper vertical load transfer.

The 24" overlap and the required nailing is sufficient for proper horizontal load transfer.

I don't see a problem with the code.
 
There isn't a problem with the code... this particular language came in because alot of inspectors were referencing an illustration out of the old CABO code which showed the joints over the stud (to the point that some inspectors were requiring the addition of an additional stud under each joint... (I had this argument with a former co-worker who required it... ICC said it was NEVER the intention in the international codes).. I think this was maybe even an editorial change.
 
Thanks for the replies,

If the intent of the double top plate, is to require a minimum support, of a double top plate for support of point loads; such as rafters, trusses and joists; especially between studs on 24" centers; then, to an old carpenter, it just doesn't make any sense, because there is no way the support is equal to the double top plate requirement; and, I respectfully disagree with you folks who know a lot more about this than I ever will.

But, I shall defer to your judgement; in practice, :D

ps. Can anyone direct me to a section of the 2009 Building Code that has the same allowance "Joints in plates need not occur over studs"; for a one or two story apartment building?

Uncle Bob
 
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It's not there, UB.. most of the load is going to be on the upper top plate.

In the IRC even with a single top plate with studs 24" o.c., the code describes how the top plate needs to be spliced in the cavity between studs.
 
Peach,

"In the IRC even with a single top plate with studs 24" o.c., the code describes how the top plate needs to be spliced in the cavity between studs."

"most of the load is going to be on the upper top plate."

No, most of the load is going to be on the studs.

If you are refering to the Exception in R602.3.2 for a single top plate; it also states " provided the rafters or joists are centered over the studs"; and that would not put the load we are discussing between the studs. It puts the load directly on the studs.

Uncle Bob
 
UB: Some of the concepts that we learned as young bucks like 16" oc and stick on stick have been tossed out. Think of 19.2" spacing concept. joists end up in the bay. The engineers feel that 2 plates carry the load. Think again on 12" oc . Same issue. The days of true balloon framing and the switch to plat form framing have changed the rules of thumb. I agree the over lap is needed. always has been needed. The way we build today is different. Just face it.

Pre constructed panel wall made off site and placed on the floor framing have drive this issue. Toss in I joists and eliminate a few studs and we say money. I often laugh when I read about "The Silent Floor System"! I can't help to wounder if they are referring to no squeaks or to the fact that you don't hear them when they fail.
 
Francis,



Thank you very much. I really enjoyed seeing Engineers discussing this subject among themselves. They are true professionals.



Wow, thanks,



Uncle Bob
 
Good link, Francis.

I agree that it's best to keep the splices at or over framing studs, but residential loads are light enough that the plates can handle a load off the stud. The sheathing will also help stiffen the top plate(s), as long as it is rated for shear and properly nailed.
 
Good link.. thanks.. but they are talking engineer speak primarily about the moments of a really (really) long span.

Engineers bore me, frankly.
 
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