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Rafter ties
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vegas paul
Silver Member
Re: Rafter ties
Commentary says (yeah, I know it's not code...) that anytime rafter ties/ceiling joists are raised above the top plate, engineering is required to determine if it is equivalent to the prescriptive requirements.
Commentary says (yeah, I know it's not code...) that anytime rafter ties/ceiling joists are raised above the top plate, engineering is required to determine if it is equivalent to the prescriptive requirements.
fatboy
Administrator
Re: Rafter ties
I agree with the gents above.
I agree with the gents above.
Re: Rafter ties
Ditto.
See also 2308.10.4.1:
...Where ceiling joists or rafter ties are not provided at the top of the rafter support walls, the ridge formed by these rafters shall also be supported by a girder conforming to Section 2308.4...
2308.4 Design of elements.
Combining of engineered elements or systems and conventionally specified elements or systems is permitted subject to the following limits:
2308.4.1 Elements exceeding limitations of conventional construction.
When a building of otherwise conventional construction contains structural elements exceeding the limits of Section 2308.2, these elements and the supporting load path shall be designed in accordance with accepted engineering practice and the provisions of this code.
2308.4.2 Structural elements or systems not described herein.
When a building of otherwise conventional construction contains structural elements or systems not described in Section 2308, these elements or systems shall be designed in accordance with accepted engineering practice and the provisions of this code. The extent of such design need only demonstrate compliance of the nonconventional elements with other applicable provisions of this code and shall be compatible with the performance of the conventionally framed system.
Ditto.
See also 2308.10.4.1:
...Where ceiling joists or rafter ties are not provided at the top of the rafter support walls, the ridge formed by these rafters shall also be supported by a girder conforming to Section 2308.4...
2308.4 Design of elements.
Combining of engineered elements or systems and conventionally specified elements or systems is permitted subject to the following limits:
2308.4.1 Elements exceeding limitations of conventional construction.
When a building of otherwise conventional construction contains structural elements exceeding the limits of Section 2308.2, these elements and the supporting load path shall be designed in accordance with accepted engineering practice and the provisions of this code.
2308.4.2 Structural elements or systems not described herein.
When a building of otherwise conventional construction contains structural elements or systems not described in Section 2308, these elements or systems shall be designed in accordance with accepted engineering practice and the provisions of this code. The extent of such design need only demonstrate compliance of the nonconventional elements with other applicable provisions of this code and shall be compatible with the performance of the conventionally framed system.
cboboggs
Moderator
Re: Rafter ties
I concur. Engineering required.
I concur. Engineering required.
Plans Approver
Silver Member
Re: Rafter ties
I agree also. But why is this in Residential Framing? Is it because it is the same, but different?
I agree also. But why is this in Residential Framing? Is it because it is the same, but different?
Plans Approver
Silver Member
Re: Rafter ties
OK, we have state-wide adoption, I'm not used to that type of situation. sorry.TJacobs said:
JBI
SILVER MEMBER
Re: Rafter ties
Although 'Bay Area' could mean any one of a number of places, I've heard it most in reference to the San Francisco Bay area of California... You know, the State that did not adopt a Res Code... That might explain the Residential framing question using IBC sections.
FWIW, I agree with the others... Engineer required.
Although 'Bay Area' could mean any one of a number of places, I've heard it most in reference to the San Francisco Bay area of California... You know, the State that did not adopt a Res Code... That might explain the Residential framing question using IBC sections.
FWIW, I agree with the others... Engineer required.
jar546
CBO
Re: Rafter ties
How about a ridge beam instead?
After reading the Note: at the bottom of Table 3.9 and 3.9A, I would only be comfortable with an engineer's stamp too. Or maybe you can increase the overhang to reduce thrust.brudgers said:
How about a ridge beam instead?
Re: Rafter ties
How about a ridge beam instead?
L/32 deflection? I don't think so.
If you have lateral deflection of the rafter after sheathing has been installed, it's not due to the location of the collar tie.
I doubt that the $50/sheet engineer is going to look at the issue either.
After reading the Note: at the bottom of Table 3.9 and 3.9A, I would only be comfortable with an engineer's stamp too. Or maybe you can increase the overhang to reduce thrust.jar546 said:
How about a ridge beam instead?
L/32 deflection? I don't think so.
If you have lateral deflection of the rafter after sheathing has been installed, it's not due to the location of the collar tie.
I doubt that the $50/sheet engineer is going to look at the issue either.
Re: Rafter ties
Someone has to stamp the plans regardless. That someone is going to be a licensed DP (architect or engineer). That is technically engineered at that point. Whether or not he/she specifically gives you calcs for the rafter above the truss plates isn't really an/the issue. Which is not to say it should be blown off. If the plans examiner does catch it specifically, he certainly can/should ask for it.
edit: :lol: That's funny I typed in arkitect (spelled correctly) and the BB rewrote it "man with pencil who draws".
Someone has to stamp the plans regardless. That someone is going to be a licensed DP (architect or engineer). That is technically engineered at that point. Whether or not he/she specifically gives you calcs for the rafter above the truss plates isn't really an/the issue. Which is not to say it should be blown off. If the plans examiner does catch it specifically, he certainly can/should ask for it.
edit: :lol: That's funny I typed in arkitect (spelled correctly) and the BB rewrote it "man with pencil who draws".
Re: Rafter ties
What's the goal, safe buildings or code administration?
Is the building any safer because an engineer ignored something that is outside of typical engineering practice, than if a non design professional ignored it?rktect 1 said:
What's the goal, safe buildings or code administration?
Re: Rafter ties
What's the goal, safe buildings or code administration?
We all have our strengths and weakneses. I said if the plans examiner catches it, great. Good for him. But we all do not know everything nor do we all know the correct path to correct it. Hopefully between all of us 98% of it gets caught. That may be a stretch though so whether it was an engineers miss or arkitects miss or plans examiners miss is irrelevant. The plans still reguire being signed/sealed.
Is the building any safer because an engineer ignored something that is outside of typical engineering practice, than if a non design professional ignored it?brudgers said:
What's the goal, safe buildings or code administration?
We all have our strengths and weakneses. I said if the plans examiner catches it, great. Good for him. But we all do not know everything nor do we all know the correct path to correct it. Hopefully between all of us 98% of it gets caught. That may be a stretch though so whether it was an engineers miss or arkitects miss or plans examiners miss is irrelevant. The plans still reguire being signed/sealed.
jar546
CBO
Re: Rafter ties
I have been tempted in the past to just accept an engineer's stamp but realize that I am not looking to cover my butt, I am here to ensure safety. If I know it is wrong at my level an engineer or architect certainly should too.
Safe buildings is the answer. Of course this has caused me some headaches in the past when I rejected an engineer's stamped repair spec because it was outside the design criteria of Ch 16 of the IBC. There was nothing he could have "engineered" that would have worked. Only a system that has been through a certified testing procedure could have been used. He filed a compliant with PA L&I because I would not accept his rubber stamp with no calculations.brudgers said:
I have been tempted in the past to just accept an engineer's stamp but realize that I am not looking to cover my butt, I am here to ensure safety. If I know it is wrong at my level an engineer or architect certainly should too.
RJJ
Co-Founder
Re: Rafter ties
I agree with Jeff & those that feel it must be designed.
I agree with Jeff & those that feel it must be designed.
Re: Rafter ties
Raising the the tie up half the rafter means you need six nails instead of three, because the load has doubled.
It's not rocket science.
"Design" doesn't necessarily require a pencil or a slide rule (hint, Jeff).RJJ said:
Raising the the tie up half the rafter means you need six nails instead of three, because the load has doubled.
It's not rocket science.
Re: Rafter ties
Not quite rocket science, but not trivial either.
Expect double the load.
As is the case with other simple dowel connections, double the nails means double the resistance unless the wood splits.
Tie would not require additional cross section as tension is reduced the further up the rafter it goes...that's why the additional forces pass to the the heel joint.
Perhaps only 5 nails. Perhaps the tie needs to have a larger cross section.GHRoberts said:
Not quite rocket science, but not trivial either.
Expect double the load.
As is the case with other simple dowel connections, double the nails means double the resistance unless the wood splits.
Tie would not require additional cross section as tension is reduced the further up the rafter it goes...that's why the additional forces pass to the the heel joint.
Re: Rafter ties
As is the case with other simple dowel connections, double the nails means double the resistance unless the wood splits.
Tie would not require additional cross section as tension is reduced the further up the rafter it goes...that's why the additional forces pass to the the heel joint.
I don't know if your analysis is correct or not. Iam not interested enough to care but
If one needs to double the nails, one generally needs to change the cross section. (The problem does change from no bending forces to having bending forces. But the details can be worked out by an engineer from a prescription.)
Expect double the load.brudgers said:
As is the case with other simple dowel connections, double the nails means double the resistance unless the wood splits.
Tie would not require additional cross section as tension is reduced the further up the rafter it goes...that's why the additional forces pass to the the heel joint.
I don't know if your analysis is correct or not. Iam not interested enough to care but
If one needs to double the nails, one generally needs to change the cross section. (The problem does change from no bending forces to having bending forces. But the details can be worked out by an engineer from a prescription.)