"ripping" deck joists 2

[skier1578]

In specifying deck joists where the client desires a flat ceiling I would typically specify ripping the joists so that they will slope to drain. For the first time I have a plan check comment telling me that this is not permitted by the code. Naturally, the plan checker did not site the code. Does anyone know anything about this?

 

[JAE]

I don't know what code your are under - in the IBC and NDS there are references to not allowing notching in the middle 1/3 of the span - this really isn't a notch, but maybe the checker is interpreting it that way.

If you rip the joist - then you effectively have a less deep member - and any calculations should be based on this reduced depth across the entire span.

 

[jheidt2543]

One solution might be to use the full depth member and ADD a tappered strip to the top of the joist.

 

[JAE]

Good idea.

 

[LPPE]

I agree with jheidt2543, and have used that detail successfully in the past. I also have never heard that ripping a joist down to a tapered section is "illegal".

 

[SacreBleu]

The tapered strip is good idea. We have used plywood "cleats" to fasten it to the joist.

 

[boo1]

I don't see any thing in the IBC or the FBC prohibiting trimming the joist. Typically Engineering analysis is acceptable as variation on the code.

The fastening method would have to resist the uplift forces.

 

[skier1578]

Thank you all for your responses. I spoke with the plan checker and he says that the "wood industry" officials, which he could not specify, have concluded that ripping the joists compromises the lumber grade and that his building department won't accept any calculation based upon a reduced member depth (which we had previously done).

 

[whyun]

I would suggest you speak with the plan reviewer's supervisor and CONFIRM that it is indeed their regulation. Hopefully the reviewer you are dealing with is not the head of the department.

Ripping a standard sawn lumber joists will not "compromise the lumber grade". Ripping the top flange of a engineered wood I-joists probably is not a good idea, and likely "illegal".

 

[SacreBleu]

IMHO - Makes more sense to add the tapered strip than to debate the issue of compromised lumber grade. After all, with the latter, you end up using the reduced depth of the ripped joist anyway.

 

[skier1578]

SacreBleu - I agree with you and have already moved on with the tapered strip instead of debating the issue with this particularly stubborn and unreasonable building department.

 

[RARWOOD]

I don't have a copy of the IBC handy or the 1997 UBC, however I believe that the plan checker acted appropriatly when he indicated that the practice of ripping a joist down to provide slope for drainage was not permitted by the building code.

I don't believe you could demonstrate that the joists comply with the code unless you had the joists regraded and then submitted an engineering analysis showing that stresses in the joists didn't exceed the allowable.

When you rip down a wood member you are voiding the grade, so unless you have it regraded you don't know what grade of material it is. Without knowing the grade you can't establish that it complyies with the code.

I have to go to a meeting so I will try to write a clearer explanation later.

 

[SacreBleu]

Does it void the grading because of the possibility that a knot or split may end up originating on the edge (top or bottom), rather than being within the "interior" area of the joist?

 

[RARWOOD]

The 1997 UBC in section 2304.1 requires that all lumber used in applications govern by chapter 23, conform to specific standards and grade rules specified in the code. This section also requires that the lumber grade be identified by a grade mark or certificate of inspection.

Lumber at the mill is produced in certain standard sizes, such as 2x 10 & 2 x12, to be used for specific applications such as floor joists. Grade rules have been written to establish design values for lumber of certain sizes and specific end applications.

Generally floor joist material is produced as 2x8, 2x10 & 2x12 either in #2 grade or #1 & Better.When lumber is remanufacture or ripped the size is changed and as a result it may no longer make the same grade as it did before.

If we look at a 16' long 2x12 and saw in a taper of 1/8" per foot our section would go from 11 1/4" down to 9 1/4". Basically it is reduced from a 2x12 down to a 2x10. If the 2x12 was of #2 grade material it would be allowed to have a 4 3/4" knot on the wide face centerline. Now if there was a knot of that size near the 9 1/4" end of the joist it would no longer be on the section centerline and also would exceed the maximum knot size allowed for a 2x10.

Summarizing the above, the reason you can't rip lumber down is that you are changing the location of the strength reducing characteristics, such as knots, in relation to the centerline of the section. Also the larger section allows for larger knots than are allowed in the smaller section.

 

[browntrout]

skier1578

RARSWC is correct.

Check out this document:

"American Softwoods Standard" DOC PS 20-99
Section 7.3.7:
"Remanufacture (ripped, resawn, or surfaced) of graded or grade marked lumber negates the grade or grade mark and the design values of the original product"

browntrout

 

[RARWOOD]

Sacre Bleu

You are correct.