Roof Dead Load Calculation
Roof Dead Load Calculation
(OP)
When figuring total vertical loads for gravity or seismic loads, does anyone adjust the roof dead loads for the slope of the roof? ![[ponder] ponder](https://www.tipmaster.com/images/ponder.gif)
I just looked at a 12:12 pitched roof, and if you compensate for the pitch, the flat projected dead load is increased by about 25%. I've never done this before, but I will now as it seems reasonable to me. Obviously, for lower pitched roofs, the results will not be as dramatic, and at some point, neglected. However, I feel that the results here are worth considering. The effect is to increase the normal 12 to 15 psf dead load to more in the range of 15 to 19 psf.![[pc2] pc2](https://www.tipmaster.com/images/pc2.gif)
This seems so basic, but I have never heard of it before.
I know. I'm dangerous.
![[ponder] ponder](https://www.tipmaster.com/images/ponder.gif)
I just looked at a 12:12 pitched roof, and if you compensate for the pitch, the flat projected dead load is increased by about 25%. I've never done this before, but I will now as it seems reasonable to me. Obviously, for lower pitched roofs, the results will not be as dramatic, and at some point, neglected. However, I feel that the results here are worth considering. The effect is to increase the normal 12 to 15 psf dead load to more in the range of 15 to 19 psf.
![[pc2] pc2](https://www.tipmaster.com/images/pc2.gif)
This seems so basic, but I have never heard of it before.
I know. I'm dangerous.Mike McCann
MMC Engineering






RE: Roof Dead Load Calculation
But like you I am lazy and ignore it on "low" slope roofs such as 4:12 and less.
But I typically round every dead load up, which compensates for this somewhat. For example, I assume a GWB ceiling, which really weighs 2.5 psf, to weigh 3 psf.
DaveAtkins
RE: Roof Dead Load Calculation
I hadn't thought about it much either. In special cases like your high slope, yeah it makes a little difference.
In most of my analyses, dead load is a non-conservative consideration (high uplift) so less is more for me.
Ron
RE: Roof Dead Load Calculation
Thanks for verifying that I am not crazy.
Mike McCann
MMC Engineering
RE: Roof Dead Load Calculation
RE: Roof Dead Load Calculation
Interesting to read the different processes.
RE: Roof Dead Load Calculation