Snow Loads from Saw-Tooth Roof on Lower Roof

[WpgKarl]

Assume a saw-tooth high roof, with 2 peaks and a low roof on either side of the saw-tooth roof which is subject to drifting loads. The peaks of the saw tooth are 8.32 m high (27.3 ft). Using the National Building Code of Canada, what plan dimensions (w and l) would you take for the upper roof dimensions - one of the saw tooth roofs or both of the saw tooth roofs combined?

I assume that when wind blows from one side, it will scour the snow from the windward side and deposit it on the leeward side (in the valley), but it won't hop over the next saw-tooth and onto the low roof at the far end? In other words, the upper roof area available to deposit snow on one of the lower roofs is equal to the plan dimensions of one of the saw-tooth high roofs, not both of them?

 

[dik]

If Winnipeg, then the snow will fill in the valleys and you will essentially have a flat roof <G>.

In the NBCC Commentaries, there is provision for a sawtooth roof, but it's a little obscure. The effect on the lower roof, I would treat it as a 'flat roof', the height of the saw tooth. In a windstorm with snow, the change in velocity would roughly be the same as if it were a flat roof; the valleys would be relatively static.

I also have wind loading for this from an earlier NBCC publication. The data is the same that the current NBCC uses and from the same 'Swiss' source. The older publication has a lot more conditions and is background. I will send you a copy of this via eMail.

Dik

 

[WpgKarl]

Hi dik, I checked the numbers and the max snow load in the valley due to sliding, & drifting, is less than 1.0 m deep, while the valley is 8.32 m high, so I considered only one of the saw-tooth roofs for drifting loads on the low roof.

If the peaks of the saw-tooth were more shallow, then I guess if the drifts filled up the valleys completely, one should consider the entire plan dimensions of the upper roof, when calculating the low roof drift loads.

Thx