Valley Angles

[nas]

How does one calculate the angles of a valley between two different pitch roofs?

Nick

[Jim_Rogers]

Nick:

I personally have not had a lot of experiences with valleys.

But I will try to help you as much as I can.

What are the two roof pitches?

Jim Rogers

PS what is the size of the valley timber?

[timberwrestler]

The Hawkindales are one method:
http://www.tfguild.org/tools/tool2.html

Will Beemer's articles in Timber Framing Mag., When Roofs Collide, is another method that's related to the Hawkindales. 

And you could draw it with either developed drawing techniques or in 3D, but you'd need to know what to draw.

It's not for the faint of heart, as there are LOTS of angles.

[Jim_Rogers]

TW:
Thanks for that link.

Jim Rogers

[Aikenback]

all that hawkinstuf is just more math class for me, the easiest way is cut the cheek or side cut on the plumb cut of the valley rafter for each side. you can get the proper side cut by drawing the travel of the hip/valley on a piece of plywood. meaning if you have a 8/12 one side and a twelve twelve on the other, the distance an 8/12 travels to get to the same height as a 12/12 is 1/3 farther. so the angle the valley
travels can be laid out on paper or plywood. 16" one direction (12+one third more(4)=16). there you have your side cut on the plumb-cut. then just mark your ends of the valley with the corresponding common rafter angle. use a test piece and follow the line. and for god's sake don't tell anyone how you did it. tell them you are a genius at math instead. ;D P.S. i have alot of experience with roof theory etc.

[Aikenback]

six kids!! your pretty good a multiplication, anyway. :D

[MrPete]

That is the same way I do it Aikenbac.  12/12 pitch is a 45* angle so it's not to tough to figure your angles from there.  I think a 10/12 is 37* if I remember right.

[Aikenback]

I didn't fully explain the valley/ hip part. basically, you need to find the values in two right angled triangles. one laying flat showing the common rafter run, the ridge distance from the point of the heel of the valley to the point the valley meets the ridge. figure out those values of those three sides of that triangle, it doesn't matter which side of the roof you use, just pick one. if you don't understand this just draw a picture of the roof from above (plan view). pick one of the triangles that appear and figure out those lengths (Pythagorean). the diagonal is the "run" of your valley.

step two, the other triangle.

the "run" is now one side of the vertical triangle. the other right angle side is the rise of your roof. if it is 8/12 and the building is 24 feet wide, that would mean the ridge is sitting at 12 feet from the edge of the building (middle). so 8x12=96. so the rise, (second side of vertical triangle) is determined. A sq+ B sq = C sq. do the sq root and that is your valley length. the angle of the plumb cut is found by holding the framing square on the run of the valley and the rise of the valley. you just have to take those numbers and make them smaller by dividing them both by the same number until they fit on the square. now you have the length, plumb and level cuts, and your side cuts all done on site with math figured out centuries ago. you need a calc that does square root and a framing square......oh, and a saw and a pencil. bear in mind there is "shortening" adjustments that need to be figured. this is only for a "theoretical line". the thickness of each member affects the "actual" length. After you get to this point, go back to your "plan view" drawing and draw the thickness lines of the members so the actual material size is drawn. these are your "shortenings" and they are always measured on the horizontal plane, not down the rafter, but perpendicular to the plumb-cut (horizontal). oh, and the valley will be offset to the lower slope side from the center of the valley line. you can find out how much when you cut your side cuts on your valley plumb cut on your test piece. then there is the birds mouth too, but I'm tired.

Simplified Roofing is a little black book that is all anyone will ever need. its the best book I've seen. hopefully its still available for any one interested. I gave my copy away.

I hope this helped.

[Aikenback]

mr pete, you must be a math genius

[nas]

I believe you math geniuses just made one out of me ;D  I think I can figure this one out.  Will keep you posted

Nick

[giant splinter]

Nick
Are the intersecting roofs both "mains" or is the unequal pitched roof that intersects the main a dormer or porch of some kind , or a wing of the building such as a garage? and is the roof span different than the main roof span?

[giant splinter]

Nick
The reason for the questions is to see if the intersection you are working on would work with a method known as a "California Overlay" or "overlay Valley intersection" in some roof framing and possibly not in snow loads in excess of 50#/ square foot.
This intersection rests on the common rafters and is reinforced by adding some extra common rafters , collar ties and a flat valley 2X8 with the valley jacks resting on the flat valley plate and connected to its own ridge. This is not used in intersecting main roof framing and is typical of dormer and porch intersecting roofs.It also might not apply to your project, or be approved by your building department. I did a search but have not found the proper link for you and I will continue to try to find the proper link so you can get a better idea of how this works. It wont work on open beam roof framing but is a short cut for intersecting roofs that meet with unequal pitch or angles other than 90 degrees and can be faster on additions or new frame construction.
I sure hope this is of some help and I will try to dig up a link for you.

[nas]

It is for my front porch, so it is open, exposed framing.

[giant splinter]

You could still use the overlay method if the main roof is not open beam in the house,it would require a clip wall over the top plate of your existing exterior wall similar to a gable end wall only set up over the plate line. Then everything forward of the building line that is porch could be tied in and up to you on the type of construction.
Great place for a timber frame porch or heavy open beam look with custom hardware bold posts and nice braces.
sounds like a fun project Nick ..... should look great.

[timberwrestler]

I did assume the valleys would be with timbers (I guess cause this is the timber/log forum).  Cutting a regular (45 deg in plan) hip or valley with 2x material is pretty straightforward.  Set you saw to 45, mark your plumb cuts, cut away, and nail the jacks on.  You can do that with timbers, but you've got to be more accurate (because the cuts are all longer), and you'll want to use structural screws to attach the jacks.

If you want to house or mortise/tenon the jacks, then you need to get a whole bunch of other angles from the Hawkindales (like the clip angles).  And if you want to do purlins square to the roof, then it gets even a little more crazy.  You can also get all of those angles by drawing more triangles, like Aikenbach was referring to.

9/12 is 37 degrees.  I like 9/12, cause it's a 3/4/5 triangle.