Over Spanning Of Roof

Since pitch is the rise over a 12 inch run divide the run by 12 to get the multiplier in this case 120 12 10.

Over spanning of roof.

The cheapest option would be to leave the old roof in place and place the new rafters over the existing roof. The tables below give maximum spans for rafters and beams. The best case scenario for an overlay is sound decking. And a roof with no sidewalls where flashing is needed to tie in the roofing material to the exterior walls of the home.

Dead load weight of structure and fixed loads 15 lbs ft 2. Snow and rain which usually pile up on a flat roof run off the slanted roof thus prolonging the lifespan of the roof. 2 are indicated below. The pitch fraction represents a certain amount of vertical rise over the entire span.

A sloped roof has numerous advantages over a flat roof the most important of them being that it allows for quick and effective water runoff. In snowy areas your roof should be at least 10 12 40 to allow snow to shed while the safest roof pitch in very windy areas is between 4 12 6 12 18 5 26 5. Make sure to document the number of chimneys skylights or other obstructions and include dormers in your measurements. Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.

Live load is weight of furniture wind snow and more. Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot. If the rise is 4 feet over a 24 foot span then the roof pitch was said to be 1 to 6 the pitch can be expressed numerically as a fraction. A roof that rises 8 feet over a 24 foot span was said to have a 1 to 3 pitch.

1 ft 0 3048 m. 1 psf lb f ft 2 47 88 n m 2. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. Use premade roof trusses premade roofing trusses will be easier and take less time than installing a stick built roof.

First measure the length and width of each surface on the roof then multiply these values to get the square footage of that surface. Douglas fir maximum horizontal roof rafter span for lumber grade selected structural and no. For a gothic style the rafters must equal the span 60 while an elizabethan style requires the rafters to be longer than the span.