Self adhesive flashing membrane under the shingles prevents leakage on low slope roofs.
Low slope roof live load.
1 cover the entire surface with a self adhesive flashing membrane such as grace ice water shield there are many equivalent products.
Resilient synthetic rubber membrane widely used on low slope roofing projects for over 50 years in the united states and worldwide.
However in my practice i typically use the horizontal run of the roof for both types of load.
Technically you should use the actual rafter length when adding up the weight of roofing materials.
For a low slope residential roof there are two main options.
On a roof with a slope greater than 4 to 12 the live load limit is typically adjusted downward from 20 psf to 15 psf to allow for the relatively greater dead load on the steeper roof.
To do this i use conservative too heavy dead loads and full snow loads regardless of pitch.
Residential low slope roofing can generally be divided up into two broad categories.
Steep slope roofs have the greatest pressures in the perimeter and corners as well as the roof peak and eaves.
For low slope roofs wind pressures typically have the greatest magnitude at the roof perimeter and corners.
Installation is important when it comes to putting a single ply roofing system on a building.
And ice reduces a roof s snow load and dries more quickly than a light colored roof.
Finding the right products for your low slope roof.
Boca also allows you to reduce the snow load for roofs with slopes greater than 30 degrees presumably because snow will slide or blow off steeply pitched roofs.
The 1 4 in 12 design slope is reduced more from live load and long term dead load creep to exacerbate water retention.
For dead loads you are correct.
Larger flat roofed applications low slope such as residential condominium complexes row homes and town houses and smaller applications such as residential porch and garage transitions from the main home where the slope of the roof changes dramatically.
Other geometric discontinuities may have increased pressures as well especially those at greater height on the structure.
For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are.
The membrane will outlast the shingles and seal around all nail penetrations.
Therefore a roof designed and installed to a 1 4 in 12 slope deflects downward and needs to be analyzed as a susceptible bay according to asce 7 10.
Minimum slope for low slope roof systems with any roofing material a slope of at least 1 4 inch per foot is recommended to promote drainage and minimize ponding.
