Dropping Hip Rafters
Dropping hip rafters is required in order for the jacks to plane properly with the rest of the roof.
Since a hip rafter travels at a 45 degree angle to the commons the stand of the rafter must be reduced in order for the jack rafters to plane properly.
The lowering of the stand of the hip rafters is the best way to accomplish this. Reducing the stand is much easier than beveling the top edge of the hips.
The only time I ever bevel the hips is if there is a finished cieling with open rafters.
The amount to lower or bevel the hip is different for every pitch, the steeper the roof pitch the more the hip needs to be dropped.
The thicker the hip rafter the more drop that is required, sometimes the hip is doubled up with dimensional lumber making it three inches wide. other times glue or micro-lam beams are used.
How Much to Drop Hip
The easiest way I know of to find the drop is to draw a 45 degree line across the top of whatever lumber you are using for your hips. Then measure the length of this line and divide it in half.
On regular framing lumber, one and a half inch, this works out to 2 and 1/16 inches. Divided in half is 1 and 1/32 inch, we will not worry about the 1/32 and just use the 1 inch number.
To find the amount of drop we take the pitch of the roof with a run of 1 inch and the rise is the amount we need to drop the hip.
Below is the Construction Master paperless tape numbers for a 6 inch pitch.
1. INCH RUN
6. INCH PTCH
0 1/2 INCH RISE
So if the stand of your common rafters is 6 inches then your hips need to be 5 1/2 inches.
Dropping Hip Rafters Chart
The following chart is for standard 1 and 1/2 inch lumber.
- 12=1 inch
Not Dropping Hip Rafters
Below is a picture of what your roof will look like if you choose not to lower the hips.
As you can see this will create quite a bump that even fifty year shingles will not cover.
Links to Related Carpentry Pro Framer Pages