Hip and Valley Factor • Hip & Valley Rafter Slope Chart
By Roof Online Staff • Updated September 27, 2023
Table of Contents
- What is a Hip and Valley Factor?
- Hip and Valley Factor Formula
- Hip and Valley Rafter Pitch is Different from the Roof Pitch
- Roof Pitch Measurement Tools
- Table: Hip and Valley Factors
- Related Pages
Note: The values discussed on this page and given in the hip and valley factor table apply to regular hips and valleys, where the roof sections have the same slope and meet to form a 90-degree angle and the hip or valley forms a 45-degree angle with the eave. The information on this page will not apply to the hip rafters on an octagonal roof, for example.
What is a Hip and Valley Factor?
The hip and valley factor is a number that is multiplied by the run, or horizontal distance covered, of a common rafter to determine the length of a hip or valley rafter. Repeat, the horizontal distance covered, not the length, of a common rafter.
For precision, the thickness of the ridge board and any eave overhang should be taken into account when determining the run.
The hip and valley factor varies according to the slope of the roof, as shown in the table below.
Hip and Valley Factor Formula
For a roof slope expressed as “X-in-12” (rise-in-run), the hip and valley factor is determined by finding the square root of ((rise/run)² + 2) for the slope of the adjacent roof sections.
Divide the rise by the run (the run is 12). Square the result. Add 2. Find the square root of the result.
Hip and Valley Rafter Pitch is Different from the Roof Pitch
On a related note, the pitch (properly the “slope”) of a hip or valley rafter will not be the same as the pitch of the adjacent roof sections. The slope of the hip or valley rafter will be lower than the slope of the adjacent roof sections.
This is because the hip or valley rafter has to rise the exact same total amount, from the height of the eaves to the height of the ridge, but it has to do it over a longer distance.
Where common rafters (the regular rafters) rise a certain distance over 12 inches, the hip or valley rafter will rise the same distance over 16.97 inches.
While the slopes of the common rafters are expressed as “X-in-12″, the slope of the hip and valley rafter on the same roof will be “X-in-16.97“.
So where two roof sections intersect to form a 90° angle (a regular hip or valley), and each roof section has, for example, a 6-in-12 slope, the hip or valley rafter at that intersection will have a slope of 6-in-16.97.
Expressing the same thing using degrees: the roof sections in the above example have a 26.57° slope, while the hip or valley rafter will have a 19.47° slope.
Remember that the heel cut, seat cut, and head cut for a hip and valley rafter will have angles that reflect this difference in slope. Do not cut them according to a template you have been using for the common rafters.
Roof Pitch Measurement Tools
If you want to verify the slope of your rafters to an amazing degree of accuracy and you like cool new tools, you should check out this digital level.
It’s probably be way too expensive for what you need. This is what professionals use. It will tell you the rafter’s slope in degrees, rise/run, or percentage, and automatically convert from one to the other.
As a (much) cheaper alternative, we recommend this slope finder. It’s very inexpensive and very accurate.
One more thing: if you’re using this table, you should consider getting yourself a construction calculator. This one is very good.
Table: Hip and Valley Factors
|Hip and Valley Factor Table|
|Hip or Valley
|Hip or Valley
|Hip and Valley Factor|