Saturday, April 9, 2016

Sloping Ridges

It's been a while since I've had a sloping ridge in a roof. So, I drew it out in SketchUp to find the angles needed for this equal pitched roof. The first thing that was obvious, I would never be able to draw it out full scale on the jobsite. A sloping ridge is actually hip rafter , so we need to draw out the intersecting eave lines to find the eave angle, or point of intersection. These intersecting eave lines can often be extremely long and require a lot of drawing room on the jobsite.  So, drawing it out in a CAD program is very helpful,  but not always practical either.

The roof has one corner of the building with the typical 90° eave angle. Using any calculator we can find the standard angles for the hip rafter slope angle at an 45° angle from the corner of the building. For the next corner of the roof the eave angle is 120°. Using my RafterTools+ for iPhone we can enter the roof pitch and an eave angle of 120° to find the hip rafter slope angle off the 120° eave angle.

For the sloping ridge we can subtract 90° from the 120° , which leaves us with an Eave angle of 30° that we can use with the RafterTools+ for iPhone to find the slope angle of the sloping ridge.

Here's a drawing of the typical roofs most of us cut and stack here in American homes. The building turns at an 45° angle. The sloping ridge can be calculated using an Eave angle of 45° with the RafterTools+ for iPhone. (135° - 90° = 45°).