Roof Live Loads & Equipment 1

[jrbear]

I am analyzing existing structures for the addition of new roof-top equipment. The equipment is not permanent (ballasted frames) and therefore I have been conservatively considering not only dead, wind, but also roof live load in the area of the new equipment. Roof live load by definition accounts for the load produced during maintenance by workers, equipment, and materials. The new equipment would serve as an obstruction and would not allow any of this type of loading within the area of the obstruction. Therefore, I have always considered my analysis conservative and yet I can find no justification in the codes to do otherwise. The equipment would have to be removed in order to re-roof for example. I am looking for some justification to consider only the existing dead, new equipment load, and any snow, drifting, or wind loads associated with the equipment (in my region snow does not control over roof live, but obviously would need to be considered in combinations if roof live is not). A similar argument could be made for permanent equipment such as RTU's. Does anyone know of any commentary or obscure code reference that I can point to other than the intuitive. Perhaps this is worth an SEI code revision or footnote. A possibility- could the last sentence in the ASCE 7-05 definition of Roof Live Load be modified to include items other than 'planters or other small decorative appurtenances'? Thoughts? Sorry for the length.

Thanks,

 

[frv]

This would fall under "engineering judgment".

I don't know that you have to go to such pains to justify it; I think it is reasonable and have used this assumption myself