Deck with Snow and Live Loads (at the same time?) 1

[bigmig]

Here is an easy one that I'd like to get some opinions on. We live in the mountains (i.e. 8 or more ft of snow a year)where exterior decks are common. Most decks sit adjacent to their respective building, which drifts and/or slides even more snow onto the deck. According to the building codes (IBC) I need to run snow and live together (.75SL+.75L+D) to get my "max" effect. My boss argues that no one will ever be on the deck when there is a huge snowbank on it, so he says we should run live or snow on a non-concurrent basis (1.0SL + DL). What do you all think?

 

[Lion06]

If you were truly designing for 8' of snow, I don't think I would include a LL on top of that. Even if someone does go out to shovel, you'll never full LL.
Additionally, with that much snow, I would be really surprised if 0.75snow + 0.75LL was more critical than 1.0snow.

 

[PEinVA]

bigmig,

I personally agree with your boss. Maybe in order to satisfy both criteria, you can justify a lighter live load (30psf) instead of the a 100psf live load. It is completely unfeasible to have 100 psf LL and 50 psf SL occurring simultaneously. However, the formulas already partially address this by using a .75 factor.


What are the DL, LL and SL? Will it make that large a difference? I would imagine the drifting would control anyway if you're in the mountains.




RC
All that is necessary for the triumph of evil is that good men do nothing.
Edmund Burke

 

[bigmig]

The 8' of snow is the ANNUAL snow fall in a year. The amount of snow on the deck could range from about 5' at the drift, to 2 1/2' where there is no drift. The local building dept. calls for 75 psf flat roof snow load. Consider that there is a 8'x8' hot tub on the deck that the owners shovel a path to in the winter.....just to play devils advocate.

 

[JJMT]

I typically treat the live load on a deck as a roof live load (Lr), my reasoning is that a exterior deck is very similar to a promenade (you might have a couple guys out side during your snow event but you're not going to have a deck party). This gives you:
D+Lr or D+S
D+0.75Lr or D+0.75S
I think a more interesting question is, What snow load do you use for a deck that is covered by a roof?

 

[civilperson]

Follow the code. Some year the snow fall will reach 12 feet or fifteen feet, (and then a spring rain). Your calcs will save you when you follow the code and the collapse is investigated.

 

[emmgjld]

My take from 30+ years on the Western Slope, to include the Gunnison/Crested Butte area.

Snow load is not always snow. Worse case I've seen is an unmaintained condo, after the mid-winter thaw and more snow is falling on top of the frozen slush, now ice.. The old snow melted but did not drain away.

Now add to that the large pile of firewood, stockpiled on the deck for that romantic evening, which is still in the future.

Plan high. I have seen some sad cases in the land which gets 8 to 10 feet of snow, sometimes.

 

[ctcray]

With that much snow (75psf), and you mention an 8x8 hottub which is going to have a significant impact on the size of deck members by itself, is the extra 30 or 40 psf of Live Load gonna break the bank?

My biggest concern would be an adequate ledger connection, which I would avoid if at all possible on a deck like this. Otherwise, I don't think combining the Live and Snow load is going to make your design appear bulky or overkilled. The hot tub will do that all by itself. =)

 

[bigmig]

Thanks for all your responses. I agree with everyone who says that there is almost no chance that you will experience
40 lbs of live load on a deck when there is a huge snowbank on it. I also agree with the code which says people do strange things on their decks in the winter (i.e. wood pile, hot tub party etc.). "Speak into the microphone Mr. Engineer, about how you thought...." said court of law.

 

[haynewp]

In this case I wouldn't worry too much about it I don't think, but generally I don't feel the code load combinations are up for such discretion whether it makes sense or not.

 

[rday]

This does seem like a simple questiion to me. There is no reason to NOT follow the code prescribed load combinations.

Don't the plan notes reference the building code? Ours do and also specify that the more stringent shall prevail in cases of conflict.

Aren't you, by sealing the plans, stating compliance with the code referenced on the plans? I believe you are.

I would not want to make your bosses argument in court or before the State Board.