Roof Projections And Parapets Snow

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

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. 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. About terms of use faq subscribe contact us accessibility. 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. Roof snow load snow drift load step fig. Section column axial compression web crippling stiffener steel column baseplate. See section 7 4 5 asce 7.

Check for ice dams and icicle loads. Fig i 7 fig i 8 fig i 23. See section 7 9 asce 7. Done calculate drift surcharge load.

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. 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. 20 ft of the roof multiply the drift load by the factor. Superpose the drift load on the base snow load.

Check for loads due to snow sliding from an upper roof. Parapets on modern roofs. 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.

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.