Snow Loads Question

Rob Keeble

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12,633
Location
GTA Ontario Canada
Had another dump of the white stuff last night here.

So i have a question that has crossed my boy scout mind.

Having observed the extensive damage the ice storm caused to enormous trees here, just before Xmas , and although we had a little melt occur the last few days, it was not sufficient to do much melting.

So we have a layer building on the roof which looks likes its set for the duration of winter.

The layer is about 2 inches of snow followed by at min 1 inch of solid ice followed by what was before last night another 2 inches of snow.

Now i guess that top layer of snow is at least another 2 inches thicker so its up to 4 inches. Now the most recent is not as compact as the prior stuff so I guess its not as heavy.

But my question really is has anyone got an idea of what or how one determines when its necessary to do something to get rid of the load. Like what amount of snow is typically catered for in snow load calculations.

I can see snow load calculations being different for different areas given historical and anticipated snow loads so I suppose its a bit like how long is a piece of string. But anyone have any kind of frame of reference.
 
Rob, frankly there are too many unknown variables involved to directly answer your question: roof pitch; uniform vs. concentrated loading; depth & consistency of snow/ice; wind direction & speed, and maintenance. The construction on homes is controlled initially by the state & local building codes, and by the local building inspector, providing he/she is competent & inspects the construction at the specified construction milestones. I think you can get a good idea from the link Larry noted above, but I think the best person to answer your question would be your local building inspector, again providing he/she is competent.
 
Thanks Larry for the doc link, i can see how this question is how long is a piece of string.
@Carol, yeah its Landlords issue but i dont wish to be under the roof when it goes or have to have my life put on hold while we recover our belongings. :)
This is a very old place. Here is a picture of ice/snow on the garage which is really not in as good a shape as the house. My tools and machines are in there otherwise i would not care. What makes me concerned is simply the very basic issues i have had with the side door opening and closing so i get to see the movement.
In addition the way the rafters meet the wallplate has them looking rather bent. But thats not new been like that since we moved in.
uploadfromtaptalk1389978807520.jpg

Note this was before last nights dumping.

sent from s4
 
If the side door is telling you that there is some settling going on, and you are apparently concerned, then you, or your landlord, could throw up a few temporary posts & beams under the rafters that'll get you through the winter, until a more permanent fix is done.
 
show picture of the inside roof area, sounds like you dont have any collar ties.. as for the load you show, it appears to be around 8" total and mostly snow.. i wouldnt worry about that little bit but you can contact your land lord and give him the option and then you have done your part.
 
If the side door is telling you that there is some settling going on, and you are apparently concerned, then you, or your landlord, could throw up a few temporary posts & beams under the rafters that'll get you through the winter, until a more permanent fix is done.


As Al said, some temporary supports should get you through the winter. Also look at the snow fall history for your area. If the roof has had major accumulations on it in the past, then it should hold up to lesser loads. If your roof structure is trussed, deflection may be a good indicator of when to put your temporary supports up. Rig a weighted no-stretch type line to a key rafter and measure deflection between the weight and the floor. That should tell if the trusses are deflecting and how much. If you can get to the ridge, you could try the same there.
 
show picture of the inside roof area, sounds like you dont have any collar ties.. as for the load you show, it appears to be around 8" total and mostly snow.. i wouldnt worry about that little bit but you can contact your land lord and give him the option and then you have done your part.

Will try get one tomorrow Larry. But i had another look today when clearing snow and i think you right aint that bad.
News says we in for another couple blasts so i was thinking ahead. :)
Will check with the Insurance illuminati (swmbo) make sure we covered. :)


sent from s4
 
I go with let the sun melt it. Mother nature put it there she can remove it.:thumb::thumb::rofl::rofl::rofl::rofl:
Oh and that roof should be good for a few feet of snow not inches. Somewhere between 2 and 4 but a lot of things have to be factored in. You can take a pic of 3 feet of snow and send it to 3 engineers for a engineered weight and you will come up with 3 answers as to how much it weights a SQF. It will be a very long 2 to 3 page answer but at the end of the day they all three are just guessing and blowing smoke that they know. :thumb::rofl::rofl::rofl:
 
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All cool ideas. Didnt manage to get a pic yesterday i was too busy cutting ply in the cold. Then discovered pocket holes (my new favorite hack joint) dont like less than half inch ply. :(

But on the removal idea, i can see those tools working well both the "invented one" and the hillbilly one, however as my picture should show there is a one inch or more solid ice layer covering at least 2 inchs of base snow under it . So best that can happen here is to have the snow above the ice sheet come down.

I wont mention how i got a cut on the eye knocking ice off the awnings this house has :rolleyes: I am just going to leave it and heck what happens happens.
 
I go with let the sun melt it. Mother nature put it there she can remove it.:thumb::thumb::rofl::rofl::rofl::rofl:
...You can take a pic of 3 feet of snow and send it to 3 engineers for a engineered weight and you will come up with 3 answers as to how much it weights a SQF. It will be a very long 2 to 3 page answer but at the end of the day they all three are just guessing and blowing smoke that they know. :thumb::rofl::rofl::rofl:

So many variables - wet snow (heavier); dry snow (nearly weightless). Local meteorologists are using the rule of thumb that 10 inches (25cm) of snow is about equal to 1 inch (2.54cm) of rain. A cubic foot of water is 62.4 pounds (28.3Kg), and an inch thick layer of water (or ice) should weigh about 5.2 pounds (2.36Kg) per square foot (25.4Kg/M²).

So (in theory only) 25cm of snow should load your roof at somewhere around 25.4Kg per square metre. If it's dry, powdery snow, then the load would be a lot less. Very wet snow might be more. Like I said - So many variables.
 
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