Roof Live Load Reduction

[twells12]

When should the roof live load be non reducible? It is reducible per IBC 2003 and 2006 for structural elements with tributary area over 200 sf. I see no reference to when a structures roof live load should not be reducible if the tributary area is over 200 SF.

Thanks for any help.

 

[shin25]

I think there is a limit of live load above which you are not allowed to reduce live load effect. It is probably 80 psf?

 

[msquared48]

You cannot reduce live loads of 100 psf or greater.

Technically a live load, although the code might term and deal with it separately, snow loads should not be able to be reduced either since since the load is uniform when it falls - it falls on the whole roof, not just part of it, and probably drifts too. Hence no supported area reduction for structural framing members.

Mike McCann
McCann Engineering

 

[Lion06]

mike-
I would always consider snow as a roof load regardless of whether it is a deck or whatever else it may be. Roof loads are not reducible per code, correct?

 

[msquared48]

In general, yes. However, a waterproof deck is technically a "roof" over the unit below. Technically, at 40 psf LL, that is area reduceable, although the structural members probably will never have enough contributory area for the reduction to be utilized.

Mike McCann
McCann Engineering

 

[archeng59]

the building codes allow for a roof live load reduction for tributary area and roof slope. The equation in the IBC is Lr=LoR1R2. R1 is for tributary area above 200 sq. ft. R2 is a reduction factor for roof slope above 4:12. Snow load is different than roof live load. I live in a municipality that does not allow any roof live load reduction. 20 psf no matter the tributary area or roof slope.

 

[fasboater]

I agree with archeng59 per IBC snow load is reducible and live load is not.

 

[CJJS]

fasboater,
I think archeng59 is saying that roof live load can be reduced.

 

[fasboater]

My mistake, I was thinking general live load not roof live load. Roof live load Lr is reducible.

 

[msquared48]

Professionally, I would never reduce a roof snow load for my above reasons stated, even if it is allowable.

Mike McCann
McCann Engineering

 

[civilperson]

Steel deck roofs are non-reducible.

 

[haynewp]

Where does it say that steel deck roofs are non-reducible?

 

[VTPE]

If you read the code carefully, it states that only the loads stated in the Live Load Table are reducible. neither minimum roof live load, paritition loads, nor snow loads are listed in that table, so by the letter of the code, they are not reducible. Please note that yes, i did say partition loads are live loads. check the code.

 

[archeng59]

Roof live loads are reducible as long as you meet all of the appropriate criteria in section 1607.11.2 of the IBC.

 

[WillisV]

VIPE,

I agree with you that by a strict reading of the code only live loads in the table are reducible. It is not, however, the intent of the code to dissallow the reduction of the partition live load. I got a code clarification opinion from ICC which stated that partition live loads were indeed reducible.

 

[TVL76]

archeng59.....section 1607.11.2 of the IBC

Is that from the 2006 IBC? Can you attach a copy of that, Please?
Thanks

 

[sandman21]

IBC 1607.11.2: Reduction in roof live loads.
The minimum uniformly distributed roof live loads, Lo, in Table 1607.1 are permitted to be reduced according to the following provisions.


1607.5 Partition loads. In office buildings and in other buildings where partition locations are subject to change, provisions for partition weight shall be made, whether or not partitions are shown on the construction documents, unless the specified live load exceeds 80 psf. The partition load shall not be less than a uniformly distributed live load of 15 psf.

 

[connect2]

Willis V you commented on my previous thread.

All above, I started a thread on this very subject re partition loads, considered Live in ASCE-7. My question was the interpretation of ...'In office buildings and in other buildings where partitions are subject to change ...'. My question was would you consider residential apartment buildings and hotels to be buildings where the partitions are subject to change? and therefore require a minimum partition allowance of 15psf? For seismic the effective weight must include 10psf where a partition allowance is used. Have a hot one going on with a local building official on this one so any comments, experience or opinions would be appreciated. My opinion in these types of buildings (residential apartments and hotels) the probability of moving partitions or unknown partitions, as compared to an office building is zero, fire separations between suites, especially when the occupancy live load is 40 psf residential vs 50 psf of an office which will dictate an future use of the building at the end of the day. Looking for some input here. Has a huge seismic and foundation implications.
Don't know how to reference this previous thread so I'll bring it back up as it stopped after WillisV's reply

 

[archeng59]

TVL76, I cannot post a copy of the code without violating the copyright laws.