Roof Projections And Parapets Snow

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

Roof projections and parapets snow.

Section strength bolted connection lag screw withdrawal. See section 7 9 asce 7. Section column axial compression web crippling stiffener steel column baseplate. Generally the wind will create snow buildup against higher surfaces e g.

20 s 20 where s is the spacing in feet. Check for loads due to snow sliding from an upper roof. Roof snow load snow drift load step fig. 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.

Superpose the drift load on the base snow load. Parapets often go unnoticed on modern houses as they can appear as the line of a flat roof. Parapets on modern roofs. 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.

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. For simplicity asce 7 16 requires a windward drift on each side of the unit based on the larger of the two fetch distances. See section 7 4 5 asce 7. 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.

The drift on the upwind side of rooftop units rtus is a windward drift as it is for parapet walls. G 5 snow drift load obstruction fig. Parapets can be both a safety feature designed to stop falls from the edge of the roof and also a constructional and stylistic feature a large percentage of flat roofs also feature a parapet of some height. Fig i 7 fig i 8 fig i 23.

Done calculate drift surcharge load.