upgrading snow load design

[Mr. Inspector]

Maybe an engineer or architect can answer this. About 50% of all the plans we get have a 30 psf snow load design which I always fail at a plan review because our area is 40 psf. Then the engineer or architect always will send me letter with their seal standing the plans are designed to 40 psf without any changes to the plan.

Why doesn't the engineer or architect say the true maximum snow load in the first place? This would save everyone a lot of time.

 

[mtlogcabin]

When he sends the stamped letter back simply ask him/her for their calculations. Either the drawing will change or the calculations will be provided.

 

[Mark K]

The snow load capacity should be supported by the calculations. What loads did the calculations show.

If the code requires a 40psf snow load and the drawings state that the capacity is 30psf the drawings should be modified either to change member sizes or to change the note saying 30 psf.

 

[Sifu]

I have several different snow loads depending on location, and they get them wrong often. Very seldom does the design change. If they want to continue getting comments and making resubmittals I am powerless to stop it. It costs them more than it does me. Some learn, some don't. It is usually a 5 or 10 lb difference, and the members are usually sufficient for the higher load after calcs are run.

 

[khsmith55]

What does your adopting Ordinance/amendments call for? Table R301.2 typically references Ground Snow Load NOT Flat Roof Snow Load per ASCE-7. Using the base formula in ASCE-7 a Ground Snow Load of 40psf equals a Flat Roof Snow Load of 30psf with out any further reductions. UBC use to use "roof snow load" then IBC/IRC went to Ground Snow Load. This may be where the confusion is coming from.

Ken

 

[Sifu]

We use ground only, specifically prohibiting a reduction for roof.

 

[Mr. Inspector]

What does your adopting Ordinance/amendments call for? Table R301.2 typically references Ground Snow Load NOT Flat Roof Snow Load per ASCE-7. Using the base formula in ASCE-7 a Ground Snow Load of 40psf equals a Flat Roof Snow Load of 30psf with out any further reductions. UBC use to use "roof snow load" then IBC/IRC went to Ground Snow Load. This may be where the confusion is coming from.

Ken

The 7 pages of sealed engineers cals and drawings i'm looking at now for solar panels on a slopped roof only says "Snow Load= 30 psf"

 

[khsmith55]

Sifu; I think you may be mistaken. The IRC and IBC SPECFICALLY references ASCE-7 and it is further referenced in the Reference Standards Chapter of the Codes. Unless the code sections and the Reference Standards have been amended by Ordinance then ASCE-7 CAN be used for design.
Ken

 

[mtlogcabin]

(20) Subsection 1608.2 is deleted and replaced with the following: "Snow loads shall be determined by the building official. In areas of the state outside of certified city, county, and town jurisdictions, the design snow load shall be based on the ground snow loads developed in "Snow Loads for Structural Design in Montana", Civil Engineering Department, Montana State University, 2004 Revised Edition.

We currently have a minimum for roof snow loads that exceed the ground snow when deductions are used. We had roof failures during the winter of 96/97 that where designed to the equivalent of todays ground snow with deductions for our area. That is the reason we have a minimum roof snow load in addition to the ground snow load.

 

[Sifu]

Sifu; I think you may be mistaken. The IRC and IBC SPECFICALLY references ASCE-7 and it is further referenced in the Reference Standards Chapter of the Codes. Unless the code sections and the Reference Standards have been amended by Ordinance then ASCE-7 CAN be used for design.
Ken

I would agree but here is the copied and pasted footnote under t30.2(1) from the ordinance.

*ground snow load = roof snow load, reductions for snow loads are not allowed

In my other work I have not found an AHJ that has the same prohibition, and most (if not all) take the reduction. But here at my main job it is not allowed.

 

[Jay]

I always design above the minimum required standards yet still leave the minimum required loads on my chart. For better or worse.

 

[mtlogcabin]

Open decks also have to meet the roof snow loads.

 

[Mark K]

(20) Subsection 1608.2 is deleted and replaced with the following: "Snow loads shall be determined by the building official. In areas of the state outside of certified city, county, and town jurisdictions, the design snow load shall be based on the ground snow loads developed in "Snow Loads for Structural Design in Montana", Civil Engineering Department, Montana State University, 2004 Revised Edition.

We currently have a minimum for roof snow loads that exceed the ground snow when deductions are used. We had roof failures during the winter of 96/97 that where designed to the equivalent of todays ground snow with deductions for our area. That is the reason we have a minimum roof snow load in addition to the ground snow load.

In California the building official is not empowered to change the required loads unless the jurisdiction, not the building official , has adopted and properly filed the local modification. Legislative bodies not individuals adopt laws.

 

[jar546]

Maybe an engineer or architect can answer this. About 50% of all the plans we get have a 30 psf snow load design which I always fail at a plan review because our area is 40 psf. Then the engineer or architect always will send me letter with their seal standing the plans are designed to 40 psf without any changes to the plan.

Why doesn't the engineer or architect say the true maximum snow load in the first place? This would save everyone a lot of time.

Very easy fix. Ask for a copy of the calculations.