hip drop and valley drop

[PDXFramer]

do you have to do a drop in a valley like you do a hip just curious thanks..


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[Cole]

What do you mean by drop-in?

Welcome to the forum.

[PDXFramer]

sorry I just meant hip drop ... this I understand really well just curious if I use the same formula on the valley rafters...

[Joe Bartok]

This is something I was going to get around to asking as well, and it seems like as good time a time as any. Hopefully the attached sketches of hips and valleys in section (not to scale) will explain what my question is.
Bevels are required on large timber hips or valleys (to the left in the attached drawing). The hip is dropped in 2” by 4” framing, since the work is hidden and appearance isn’t a concern. But what about the valley? Is a valley not dropped? Doesn’t look like it has to be.

[R Birch]

All,

Cutting Hips and Valleys is one thing that is much easier done than said. This might get lengthy.

I do not know how long the term “Dropping the hip” or “Hip Drop” has been around. I have been a framer for 32 years and I had not heard the term until I started participating in online forum discussions about two years ago. There are a lot of guys on these forums who say it’s a very old and accepted practice in the roof cutter’s world. I have always used a method that marks and cuts the Hip/Val rafter to fit perfect without need to make any corrective adjustments during the marking process. The basis for this method can be found in the Swanson’s “Blue Book”. The Blue Book is not a very well written book, in my opinion, and tends to confuse most readers. I had to read it several times myself.

The Blue Book calls there method “The One Number Method”. The BB does not ever mention a heel stand height drop adjustment. The term “Hip Drop” is not in the BB. They do show the outside wall corner cut to allow the square cut hip to fit as they show it being cut. (Poorly explained) The BB method only shows a single cheek cut at the top of the Hip. It does not say anything about Valleys at all. Their method shows the length of the Hip calculated from the same effective run that is used to calculate the commons. (Typically; Span, minus the Ridge, divided by two) This dimension result is applied to the top and side of the board, the hip/val plumb lines are marked at these points, the top is cut at 45 degrees (single cheek cut), the heel is marked with the same HAP (Heel Stand Height) as the commons.

Now this is where the BB blows it. They make a single bevel cut at the top, but make a square cut at the heel. ????????? I found that the cut at the heel should be made on the same bevel as the top cut, and then there is no need to notch the corner of the walls. What I found that works even better is to simply square cut the heel cut with enough relief to clear the corner. (3/4” extra relief will fit tight to the square corner the same as the “Hip Drop”, 1-3/4” will allow the sheathing to clear under the hip’s bird’s mouth comfortably.) The original plumb mark at the heel will line up on the wall just like the commons do. Because the hip is actually sitting at the intersection of two walls it is my practice to mark the heel stand on both sides of the Hip to aid with installing it. Both lines will line up on their respective walls at the corner. I modified their method to accommodate my preferred ridge layout that typically will have three commons converging at the end of the ridge. The BB method does not have king commons opposing each other at the ridges end, only one common at the hip end.

The double cheek cut at the top of the hip is known as a diamond cut and is probably the most common generally practiced method. I like it because with regular pitched roofs all the jacks for the hip will be cut the same length and will also “Shake Hands” when installed. This method calculates, marks, cuts and places the hip perfectly w/o need for the additional corrective measure involved in using the “Hip Drop” Method. (On a side note; It is necessary to do a hip drop if you make the Diamond cut first or before applying the calculated hip length. If you measure your hip from the precut diamond, then you are measuring/marking the hip at its center instead of its side and it will plane at its center instead of its side. The Hip Drop will compensate for this ……..error?? and correctly plane the hip. (as shown in the “Dropped Hip” view of Joe B’s diagram)

Another way to view cheek cuts on rafters is to view the common rafters as being cut with parallel 90-degree cheek cuts. The hip is just an angled common. The cheek cuts on it should also be parallel. But because the hip/val rafters are placed at intersecting walls, there are two perpendicular wall-planes, and two perpendicular ridge-planes to cut parallel cheek-plane cuts for.

“All-this” means that when you mark/measure the Hip, the points marked will represent the long to short of the pitch cuts and also the long to short of the cheek cuts. When marking Valleys the points marked represent the long to short of the pitch cuts (same as hip) but the bevels for the cheek cuts are reversed for Valleys and the top mark is the short point of the bevel cheek cut and the heel’s mark is the long point of the check cuts for the valley’s heel. The HAP is marked prior to cutting the valley heel. Once all the cuts are made at the heel there will be an apparent difference in the heel stand height of the valley as compared to the hip. Cutting them this way will plane the valley jacks to the top of the valley. (as shown in Joe B’s valley illustrations) For single (1-1/2”) regular pitch valleys on pitches greater than 5/12 it is my preference to drop the valley some to prevent bulging the decking at the valley. I still prefer to have the jacks plane to the valley short of center as to insure good solid contact of the sheathing and also it is more forgiving to non-perfect sheathing cuts. As Joe B. shows the heavy timber valley, it should be “V” beveled to keep valley jack placement simple.


Some things that are important to emphasize is that the cheek cut bevels have to be perpendicularly located across the rafters to work. All rafters have to have a constant HAP at the heel. When making long point cheek cut there will be an apparent shortening of the rafter but it will measure at its center what it was marked at its sides.


But by far the biggest benefit to using this method is that it works for Irregular Pitched roofs too. It how ever does not equally center hips and valley over the corners. It will place them proportionately by the ratio of the irregular pitches. The line of intersecting planes does remain centered over the corner. HAPs for both pitches must be equal.

I hope I have not board anybody with this. =)

Richard Birch

[PDXFramer]

good points I started cutting the roof today and got allot done. I have done lots of roofs in the past just wanted some other opinions to see if it would be faster but I just did it my way and it is working out fine I will post some pics twords the end of the week when more is put togehter...

-Ty

[Joe Bartok]

This might get lengthy. I'm sure no one would accuse me of doing the same thing. :twisted:

Actually, thanks for the response, I'm definitely not bored (or board :D , as the case may be). I am a little out of context, not being familiar with the Blue Book, and my experience as far as framing with "two by" lumber is limited. "Dropping the Hip" I have heard of, and it seems more economical than a lot of extra calculating and cutting since the framing won't be seen in any event.

Some more related questions, for anyone interested:
Sizing: Hip, valley and ridge board sizes are governed by the formulas in the drawing Depth_Formulas. The equations return an equal depth between the members in question, but this isn't good enough. Our hips, valleys and ridges have to exceed the common rafter depth. Again, with framing of this nature there’s obviously not much sense in a doing lot of extra work and cutting the lumber to size in nit-picking detail. Is there a rule-of-thumb or standard procedure that governs the depth selected in these pieces? Do we use the next largest size returned by the calculation? Or have it engineered?

[Joe Bartok]

"Math-Lite" question:
I've been playing around with the numbers, and here's my thinking. The HAP for the Hip rafter has to remain the same as on the Main Common rafter in order maintain the continuity of the plane of the roof. But even for rafters of the same depth, the Hip plumb cut and Common plumb cut values are different. So: Is the Hip Drop simply the difference between the Common rafter plumb cut and the Hip Rafter plumb cut? In other words, the "correction factor" for the plumb cut on the bird's-mouth?

[PDXFramer]

yes that is it ...

[R Birch]

If the single thick hip (typically 1-1/2”) is marked/measured from the pre-cut diamond, or center, of the board as is popularly done by most of the forum participants (Here and other similar forums) then the “Hip-Drop” corrective step is necessary to make the hip plane correctly.

If the single thick hip board is measured and marked on its side prior to cutting the diamond cut, the “Hip Drop” shortening adjustment is automatically achieved while performing the diamond cut. The apparent shortening of the hip occurs at the top and makes the “Hip Drop” adjustment unnecessary. Using this technique will require that one of two things be done at the heel of the hip though (assuming that the hip has a typical tail, nothing extra would be necessary for a bobtailed hip.) You will have to cut some extra material out from the back of the marked heel cut to clear the corner, or cut a reverse, or inverted, diamond at the heel to make it fit tightly. I opt for the extra clearance normally. It’s a quicker and easier square cut.

I noticed in PDXFramer’s pic of his hip at the corner that he has used the “Hip Drop” technique by stepping-off the heel ˝ thickness of the doubled hip beam and applied his HAP at the upper plumb mark. This planes his Doubled hip beam perfectly. The tail’s length was measured from the original line and cut as the long point. He could have (may have) measured from the adjusted mark and cut the short-point of the diamond at the tail.

Btw PDX, nice work! One way I can always gage a roof cutter’s competence level is by his ability to make the Hip’s tails cuts as you have shown. It seems that not all know how to do this. Very Cool!

I have done a step-by step photo display of a model hip being cut without using the “Hip Drop” corrective adjustment. Notice the inverted diamond at the heel. It shows that the marks made on the hip really represent parallel cheek cuts. But it is much simpler to just cut a little extra out for clearance at the heel. The original HAP lines line up on the walls too, just like the commons.

Pardon the weathered wood; it was all I had laying around the house at the time.

[R Birch]

I see that when I attached my photos they are in reverse sequence. These next three are in the correct order.

[Rich]

Nice graphic representation R Birch.. I might make this into an article if that's ok with you. Much better explanation than I could hazard :)

[Cole]

Great Post!!!

[Dragon]

I'd glad I didnt have to explain it.

Nice post.

[R Birch]

Yea Boy, I appreciate the positive feed back. 8)

Rich,
I don’t have any problems with your putting this under your Member's Articles page if you would like. I should have put this together, “like this” (w/photos), a long time ago. The photos should help make my earlier post more understandable too.

Just more proof that…..
“A picture is worth a thousand words”
And six pictures are even better.

Cole, Thanks. :D

Dragon,
Right on man! :wink: It’s one of the toughest things I have ever tried to explain in type. I mean, “Just mark it and cut it”….didn’t seem to do it.

Showing the guys at work always had them “Clicking” right in though.

Joe Bartok, :)
For guys that use the “Hip Drop” method, then the answer to your question is as PDX answered, “Yes”. The problem I have with the terminology, “Hip Drop”, is that it can needlessly confuse and complicate things. But it’s not likely to go away because someone comes along and shows everyone how to “Drop” the “Hip Drop”. I have a feeling that maybe it was easier to explain the “H D” method over the “Drop-less” method I outlined. It certainly is more popular on the forums, and in most books too.

And while I have no proof, I speculate that if you were cutting these rafters 100+ years ago with a hand saw it would be much easier to put a single cheek cut at the tops of your hips as the Swanson’s “Blue Book” shows. This method would be complimentary to handsaw era technology. If you laid out your walls and roofs from the out side corners, then the layouts would easily stack and quite often there would not be commons located at the end of the ridge to require the double compound-bevel diamond cut of roofs laid out from the effective run of the Commons. This “from the corner” method of layout can be found in Marshall Gross’s “Roof Framing”, but so can the “Hip Drop”.

One thing’s for sure, we don’t all think alike. :lol:

[Joe Bartok]

“A picture is worth a thousand words”
And six pictures are even better.

Richard:
Well said! An excellent photo essay; I get the picture.
BTW, the reason for these recent questions is that I'm trying to come up with something I attempted and abandoned years ago: a framing calculator that not only generates angles but returns dimensions as well.
The participants of this forum can look at your sequence of pictures and understand the geometry (or whatever abstract concept is presented), a computer or calculator needs a formula.
Much like the last effort, the framing calculator is a bust again. There are soooo ..... many possible arrangements of rafters, valleys, purlins, etc ... the only thing that will cover all the bases would be to create the equivalent of Auto-Cad, or some equivalent program with a graphic interface where the user can sketch what they want on-screen.
Thanks one and all for the responses.

[Rich]

Joe - IMO you're better off creating a calculator for specific situations instead of trying to make it for all situations. Like you said - there are way too many variables and different configurations. For a teaching tool I think a couple situations would be ok to get the basics .. as a production tool - it's too late to use a calculator when you're in the field cutting :) Unless you're mobile I guess.

[R Birch]

Joe B.

Thanks for the compliment. I’m glad you understood it. I have been trying to nail down the correct verbal description for this “abstract concept” that you observed my attempt to explain. It is really based on one of the simplest geometric concepts of sets of parallel lines that intersect, and for parallel planes that intersect, and the mirrors that are created when such things happen. 8)

I created a roof calculator using Excel much like the one Rich has suggested with separate pages that solve for different tasks. Incorporating the “Concept” shown in my pictorial reduces the Hip/Val scenarios to a simple “One Number” application. In a sense, it basically renders the thickness of hips and valleys irrelevant. This concept works for all square-house roof scenarios, Regulars and Irregulars. It eliminates the “Hip Drop” necessity too. Broken hips are a snap and can be used as a good example of the underlying concept because they are just like cutting a bobtailed hip w/o a heel cut. 8)

This concept helps prevent “Information Overload” on my spreadsheet. (“IO”, Where’d I get that?) :)

I do not think that for most stick framed roofs that a purling calculator is useful as most guys will just OTJ it, where support is needed, anyway. JMHO on that one.

Study the stuff I sent you. I think you’ll find it useful when creating your calculator. If I can be of assistance, feel free to ask. I know I’ll be picking your brain on a frequent schedule for some other ideas I have.

I wish you the Best of Luck and I’ll be talking to you.

Btw, what kind of telescope do you have? :wink:

Regards, Richard Birch

[Joe Bartok]

Rich, you are so right! I wasn't kidding in another post about the Excel worksheet that took 600 hours to create and was never finished. The current online dimensioning calculator I'm leaving as is. It solves the dimensions for the theoretical working points and centerlines and a few basic dimensions such as plumb cuts. From my point of view, even this is redundant.
The variables get worse when custom work, irregular surfaces and joinery enter the equation. Here's how I deal with field work, not too much reliance on the computer, just a few printouts:
A list of the Main (or Major) Span angles, and one for the Adjacent (or Minor) Span angles. Most of these angles won't be found in rafter span tables. As required the angles can be converted to over-12 values, or over-"whatever" values for larger layouts. Rafter differences in length and spacing on the valley are done on-the-fly from the list.
The other printout(s) is for the purpose of joinery involving mortises and tenons. At best, we may be dealing with dressed timber where the widths may vary by 1/2 an inch. Logs don't even have this virtue, every housing must be measured, and I have no idea what a dimension is until that measurement is taken. There are seven different "standard" joints I use, each involving several angles and dimensions. The attachment an example one such joint, "Rafter meets Valley".
The best way to deal with the unforseen is to set the variable for the housing depth (there's a calculator specifically created for this purpose) at one and make a printout of a list of the dimensions with respect to the unit value. This gives us a list of factors that can be applied to the actual measured value taken in the field.
If time permits, since every angle on every face of a proposed joint is known, another good idea is to make scale 3D models of the joints. For a valley, I actually make two models. One is rectangular in section with the compound angles cuts at the peak and feet. The other model has all the bells and whistles; backing angles, chamfers and tenons, angles between the various planes labelled, etc. It's a real bonus in the field to have a model of what your shooting for in hand, it sure beats working from a drawing.
Last but not least, there's good old-fashioned geometry and projection.
Hope that didn't bore everyone, but since the subject (somewhat off-topic) of working in the field came up, I thought I'd elaborate on my little corner of the world.

EDIT: Richard B., I see you've posted in the time it took me to type this up. As far as calculators go, what I've found is that they all use the same underlying math, but as far as application goes, it seems everyone has to come up with whatever works for them.
I know I’ll be picking your brain on a frequent schedule for some other ideas I have.
Pick away! It's getting lonely down there in the Math Forum. :(
And there's always my dreaded (and not well organised) geocities blog.

[PDXFramer]

here is a link to the last roof I just got done with cutting this one has lots of work in it check it out and let me know what you think ...

-Ty

http://www.pbase.com/framerpdx/brandons_house&page=all

[Joe Bartok]

PDX, it might have been lots of work but it was worth it in the end. That roof looks good! I'm getting this feeling of deja vu; I've know I've seen that roof somewhere before ... :wink:

[PDXFramer]

Oh yeah I forgot to mention I have done that same roof a few years ago lol ... I promise this will be the last time I do that roof...

[PDXFramer]

Hey Joe,

are you from Ontario, Ca ?

just curious I was down there this weekend for a funeral ...

-Ty

[Joe Bartok]

I'm in Ontario, Canada.

[Puffah]

great looking roof pdx. One thing that I find hard to figure out is, how do you plot for where jacks intersect the valley and hip. Is there a way of calculating this or do you cut to mathmatical length and let sit where they fall?