ASCE 7-98 Drifting

[jike]

Drifting is computed using the length of the roof upwind of the drift, lu per figure 7-8, ASCE 7-98.

If you have a parapet perpendicular to the wind direction which blows the snow off of the upper roof, can the distance to the parapet be used for lu?

 

[samdamon]

Jike- Is the parapet on the high or low roof?

 

[JAE]

I don't think you can take advantage of a parapet on a higher roof to "block" the snow from continuing to migrate off the higher roof.

Also, note that you need to also include windward drift (see Figure 7-7)

 

[Ron]

Parapet only affects leeward consideration and becomes part of hd. Essentially no help from parapet.

 

[jike]

SamDamon, the parapet is on the high roof.

JAE, I am aware of the windward drift requirement.

I would think that the parapet would block some of the drifting potential, but the code does not mention whether this is allowed.

 

[samdamon]

Jike- I agree with the other posters that there is no reduction in the drift load on the lower roof if the high roof has a parapet. It might actually hurt because having the parapet means the snow can pile higher on the lower roof. The "hc" dimension in Fig 7-8 would need to be measured to the top of the parapet el. rather than just to top of high roof el. Regards.