Low Slope Roof Rain Load

Low slope roofs i e roofs with slopes less than 1 2 inch of vertical rise for every 12 inches of horizontal run 1 2 12 are common in commercial and multi family projects including wood frame.

Low slope roof rain load.

More commonly roll on membranes such that use heat to bond seams together is used as a roofing material. A low pitched roof is anything that is any roof with a pitch of 3 12 or less. Technically you should use the actual rafter length when adding up the weight of roofing materials. Uses the least amount of roofing material.

Roof design and practice published by pearson inc drainage design published by the rci foundation and. The 1 4 in 12 design slope is reduced more from live load and long term dead load creep to exacerbate water retention. Low slope roofs are often more susceptible to leaks. For dead loads you are correct.

Wind pressures on low slope roofs published by the. Many studies on roofed structures have been performed in the past. The present study demonstrates the pressure variations due to wind load on the pyramidal roof of a square plan low rise building with 15 wall openings through cfd computational fluid dynamics simulation. Per ft while the nrca calls for no ponding water on the roof 48 hours after a rain during conditions conducive to drying roofing manufacturers have their own requirements.

Many roofing shingles do not allow applications onto roofs at this pitch. We construct our residential style roofs at a minimum slope of several inches to the foot pitched to external gutters that have been sized to meet building codes. This is because water tends to be stagnant on a flatter surface of a low pitched roof as compared to high pitched ones that lets the water flow freely downward. Patterson has coauthored.

It s a good idea to become familiar with all three perspectives and build to the most restrictive. For these projects rain and ponding loads should be a design criteria and when appropriate factored into the roof design loads. I ignore the slope. Rain totaled 8 inches at new york s jfk airport 5 inches in philadelphia and 11 inches in seabrook farms nj.

That shouldn t mean much to the roofing industry. Of two roofing manufacturers general manager of a roofing contracting company and for the past 34 years has been a consulting engineer roof consultant. A structural member designed and installed to a 1 4 in 12 design slope deflects under the initial short term dead load to create a roof surface slope less than 1 4 in 12. To do this i use conservative too heavy dead loads and full snow loads regardless of pitch.

Rain also can add to snow loads on low slope roofs. Codes prescribe a minimum slope of 1 4 in. Easy to access and.