Drift load between doghouses on roof

[Thoughtclaw]

I'm designing a pair of doghouses in an existing building to accommodate machines that are taller than the existing roof. They're close enough together that the snow drift loads (as they would be if not for the other doghouse) intersect. I've attached a rough sketch showing the drift loads only. I'm thinking the load shouldn't be that high between them, since they will block some of the snow from going into that area, but I'm not sure how to handle that. Would you agree that adding the intersecting loads together would be overly conservative?

 

[dik]

Does ASCE have roof loading conditions for small obstructions? and can the dog houses be removed far enough from each other to be considered as two? Can the roof be easily reinforced?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[CURVEB]

I don't think it would be overly conservative to superimpose the drift loads. The way snow will build up on a roof is not easy to predict, it depends on the timing of the storms, temperature, wind, and other factors that are out of our control.

 

[CURVEB]

But there might be an exception that gets you out of the drift requirements: see ASCE7-16 7.8.

 

[dik]

That's why I was thinking of obstructions... drifting can impose a huge load... that may not occur.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Thoughtclaw]

Thanks, Dik and Curveb. I have 7-10, not 7-16, but I'm guessing you're referring to the provision that you can neglect drift if it's less than 15 feet? Both sides are longer than that. And unfortunately, they have to be where they are.

I'll go ahead and add the loads together. I appreciate the help!

 

[CURVEB]

Here is the 7-16 provision. There appears to be a new exception that might help:

 

[dik]

The loads may not be cumulative... do you have a partial roof plan that shows the units?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Thoughtclaw]

Thanks again, guys. The exception still doesn't apply because the projection is going to be flashed directly into the existing roof.

The only roof plan I have is the sketch I attached with my initial post. The units are denoted by X's.

 

[dik]

Thanks... should have looked at your sketch first off... those are physically the size of a 'real' RTU... and not a roof projection. Sketch above will be similar with a slight valley between the units...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik