Staggered Pitch Roof

I chose a gable roof at a 6 12 pitch with 2x10 rafters spanning 16 feet from exterior walls to a 2x12 ridge board to carry design loads of 30 pounds per square foot psf live load and 15 psf dead load.

Staggered pitch roof.

Most manufacturers specify at least a 4 12 roof pitch for installing them meaning for every foot the rafters extend out from the ridge beam they drop down 4 inches. The 45 degree roofs seen on a frame houses are 12 in 12 but roofs can be even steeper consider the mansard roofs introduced by french second empire architects in the middle of the 1800s. In this scenario the unbraced rafter spans are relatively long the design loads relatively high and the roof pitch relatively shallow. The staggered approach to installing insulation reduces thermal bridging in the roof assembly.

Pitched roofs begin with with slopes greater than 3 in 12. The picture below shows the pitch of a 7 12 roof slope meaning that for 12 of horizontal measurement roof run the vertical measurement roof rise is 7. Must the rafters on either side of the ridge line up or can they be staggered along the ridge board. If i m using asphalt shingles i always protect the sheathing with ice and water shield first pulling it onto the fascia and rake boards and cover it with trim.

A fact sheet on roof insulation published by johns manville rs 7386 notes that as much as 8 percent of the thermal efficiency of insulation can be lost through the joints and exposed fasteners of installations that use only a single layer of insulation. For example random width and preferably multi colored slates that are 16 inch 18 inch and 20 inch long can be nailed so that the top edges of all of the slates line up with the chalk lines. Another method of installing a staggered butt slate roof is to use slates of different lengths. Sloped faceted staggered and layered installation methods to create inspiring designs stay code compliant.

I am framing a gable roof with common rafters attached to a 2x12 non structural ridge board. Roof pitch is a measurement of a roof s slope expressed as a ratio. Christopher deblois a structural engineer with palmer engineering co. Suitable materials for pitched roofs.

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