Roof Projections And Parapets Snow

Walls and parapets drifts on lower roof sections snow accumulation deposits in roof valleys and drifts on the leeward downwind side of objects obstructions and ridges known as aerodynamic shading figure 8.

Roof projections and parapets snow.

Done calculate drift surcharge load. For roof projections l u shall be taken equal to the greater of the length of the roof upwind or downwind of the projection 33 outline minimum roof snow load thermal factor unbalanced load drift load on adjacent roof parapet wall rtu drift sliding load on adjacent roof ponding faq s 34 sliding load on adjacent roof sliding load on lower roof in 7 05. The drift on the downwind side is a somewhat reduced leeward drift composed of snow originally on the roof upwind of the rtu plus a small contribution from snow originally on top of the rtu itself. Generally the wind will create snow buildup against higher surfaces e g.

See section 7 4 5 asce 7. 20 s 20 where s is the spacing in feet. Roof snow load snow drift load step fig. The drift on the upwind side of rooftop units rtus is a windward drift as it is for parapet walls.

Check for ice dams and icicle loads. Parapets on modern roofs. For simplicity asce 7 16 requires a windward drift on each side of the unit based on the larger of the two fetch distances. Drift snow is snow that has been transported by the wind and deposited at obstructions such as buildings parapets mechanical equipment and changes in roof geometry.

Section strength bolted connection lag screw withdrawal. Drifting snow generally causes large loads at relatively concentrated locations on buildings and other structures when compared to flat snow loads that blanket an entire roof area. See section 7 9 asce 7. Fig i 7 fig i 8 fig i 23.

About terms of use faq subscribe contact us accessibility. Section column axial compression web crippling stiffener steel column baseplate. G 5 snow drift load obstruction fig. Parapets often go unnoticed on modern houses as they can appear as the line of a flat roof.

20 ft of the roof multiply the drift load by the factor.