Hi there,
I’m looking for some info on laying out a timber valley. I already have the ridge and purlins in place – purlins are both level to each other and the ridge is centered between them exactly. A diagram would be helpful to illustrate the plumb, seat and cheek cuts. Any ideas?
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Get yourself "The Very Efficient Carpenter" by Larry Haun published by our sponsors Taunton...more than enough ideas for all your Qs.
Edited 9/6/2006 2:08 am by piko
Check out the Timber Framers Guild website.....
http://www.tfguild.org/
In the upper right corner, select "Hawkindale Angles" and hit "go".
Jon
cjtk07
I've been timberframing my place for a while now and The one bit I've found is how tough it is to do exactly the sort of thing you are doing..
I'm a try it kinda guy. That is I get something up in place and keep trying 'til I get a solution..
For example I had a friend do a carefull drawing of the angle length and bevel of each timber I needed to put a round tower up on my roof.. Each one wound up being a differant length, angle, and bevel. His drawing while accurite wound up beingwrong!
In the end I dropped a plumb bob measured it and used a angle finder to work out the bevel plus trail and error to work out the angle.. When I finished the circle was within a 1/4 inch of perfect so I pinched it together and called it finished..
Crude and time consuming but it really, really, works and I'm willing to bet many buildings thoughout time were built just that way..
"I'm looking for some info on laying out a timber valley. I already have the ridge and purlins in place - purlins are both level to each other and the ridge is centered between them exactly."
I don't understand what you’re looking for. Are you looking for the plumbcut measurements at the top and bottom of the hip?
What is the pitch of the roof asd how big are the timbers?
What saw are you using to cut the timbers? Are you using a handsaw?
This is where the sidecut numbers on the framing square come into play if you’re not using a big power saw.
I got everything up, but I'm still wondering if there is a way to calculate the back cut angles of the plumb cut and seat cut on the valley jack rafters without doing multiple trial and error tests? The pitch I'm working with is 4 1/2 / 12 and the valleys are at 45 degrees to the main ridge and new ridge. The valley timbers are 8 1/2 " x 12" and are dropped so that they are fully exposed. Thus I'm setting the valley jacks on top. Any ideas?
Todd.
Listen to Jon & go to the Timber Framers Guild site. It may take a bit for the light bulb to go on but you can absolutely figure all the lengths & angles using the Hawkindales. Or you can hire somebody who knows his stuff to figure it out for you & even draw pictures for you
Trial and error is great if time and money mean little to you. It's really the best way to accurately account for variations in timber dimensions and straightness.
However, if you're like the rest of us, you don't have forever to cut a single valley, or an extended reach forklift parked on your property to trial fit each iteration.
The Hawkindales work great. Measure and verify the dimensions of your frame, download the spreadsheet, and enter your own data. It'll give you every angle you need. Make sure you check your valley timber for square, straight, and twist. If it's really bad, you're going to have to apply some Square Rule techniques.
Visualizing the complex roof angles is a noodle-twister, but it's manageable. The very first valley rafter I cut required only some quick tuning with a block plane to fit like a glove.
Good Luck!
"Listen, strange women lying in ponds distributing swords is no basis for a system of government."Jon
There's no such thing as trial and error when framing a Hip-Valley roof. All the angles (and hence dimensions) follow from the Major or Main pitch, Minor or Adjacent pitch, and Plan angle between the Hip roof eaves (or Valley roof ridge lines).
The Timber Framer's Guild site and forum are a great source of information. Click here if you wish to understand the theory behind Complex Timber Roof Framing and Joinery Mathematics. It's pretty heavy on the theory: I've touched bases the geometry, trigonometry and linear algebraic methods of solving the angles required to frame a Hip-Valley roof. There are also links to photos, 3D models, calculators, etc.
Online Math Notes and Sketches: A little bit of everything here but the math is generally slanted toward framing a Hip-Valley roof.
Below are links to a couple of web based calculators you may find helpful. Whenever possible I have used the Hawkindale angles as defined at the TF Guild site:
Framing and Joinery Angle Calculator #1
Framing and Joinery Angle Calculator #2
Moving on to your jack rafter, here is one possible geometric solution:
Compound Angle: Jack Rafter intersects Valley. The Jack Rafter Side Cut Angle (P2) and the complement of the Common Rafter Pitch Angle (90° – SS) are laid out on the stick and the cut is made with a chain saw.
Normally the end of the rafter is fully housed and tenoned in the Valley rafter. To achieve this the acute angles are Chamfered or Square Cut. That slideshow only shows one of the cuts; there is another similar cut along the plumb line. The attached pdf document explains the reasons behind chamfer cutting members where they intersect one another.
EDIT: The subject of Jack Rafter bevels was recently discussed in this TF Guild Forum thread.
Joe Bartok
Edited 9/15/2006 10:54 am ET by JoeBartok
Edited 9/15/2006 11:20 am ET by JoeBartok
Joe,When Timber framing the valley like he's doing by dropping it and sitting the valley jacks on top of the valley, how much would you take out of the structural integrity of the top of the valley if he beveled it and mad a V and sat the valley jacks in there?Joe Carola
I don't really understand what is being "dropped" but if it's an 8 1/2" × 12" Valley I wouldn't think it's hurting as much as cutting housings and tenons. That's a pretty good chunk of wood. The longest Valley we've made that I can recall off the top of my head was 10" × 12" and about 26' long; it had three sets of housings 4' apart along its length.
A rough rule of thumb is the strength of a beam varies in direct proportion with the width but varies as the cube of the depth.
EDIT: I get it. Duh! Where the jacks meet on top of the Valley is where the Valley trough would normally be (that's the "drop") ... so ... a bigger seat cut in the Valley. This wouldn't have much of an effect the way we do Valleys. They die into a housing on the wall anyway, or as in one case the Valley sat on a large beam so we just notched the beam.
Joe Bartok
Edited 9/16/2006 10:42 am ET by JoeBartok
Edited 9/16/2006 11:35 am ET by JoeBartok
Edited 9/16/2006 11:37 am ET by JoeBartok
Joe,I'm thinking he's dropping the whole valley down and the valley jacks are sitting right on top. So he can bevel the top of the valley to form a V and just make plumbcut marks on the ends of both valley jacks and butt them into each other.Or he does nothing to the top of the valley but he would have to put a compound angle on the seatcut. It's not a level seat cut. It would be the opposite angle of the bevel angle.Joe Carola
I see what you mean now Joe. Bevelling the Valley will have some effect. Usually as a rough guesstimate we would consider the depth at the center after backing as the working depth. The pitches for this roof are pretty shallow and the trough depth is only a hair over an inch.
A lot of other questions here (Valley length? loads?) that are best answered by an engineer. Off the cuff, the Valley is stronger without bevelling but I would say not to worry about the amount taken out if it is bevelled. The 10" × 12" Valleys in my example were 10/12 pitches intersecting at 90° in plan. The trough depth worked out to about 2 9/16", there were pockets cut out for the purlins, and it was still good enough to satisfy the engineers.
That cut you show on the jack rafters would be the same as the square cut or chamfer in the animation I posted.
Joe Bartok
Edited 9/16/2006 12:25 pm ET by JoeBartok
Edited 9/16/2006 12:27 pm ET by JoeBartok
Joe (Framer): I got thinking some more about your proposed cut on the jack rafters and it might be a good way to go. The material removed by bevelling and hence the strength of the Valley rafter is conserved and it might be just as easy to square cut the jacks than bevel the Valley.
cjtk07: The attached a sketch (not to scale) shows the chamfer anatomy and layouts. The easiest is to mark a line 1.08931 in. (the value of the Valley trough depth if it were backed) parallel to the bottom edge of the jack rafter, on the face which meets the adjoining jack rafter. Then cut with the saw blade square (zero blade bevel).
The other layout is the dimensions of the triangle created as the square cut passes through the plumb (side) face of the jack rafter. This would be the preferred method where the dimensions of the material are too large to permit cutting with a saw. The wood is removed with a chain saw and finished with a planer.
If the jack rafter intersects a log Valley the chamfer cut and housing depth will vary due to the irregularity of the material. The best move here is to give the dimensions of the triangle with respect to a unit housing depth: .26516, 1.43886, 1.51038. The layout on the jack rafter is the unit depth values multiplied by the actual field measurement with respect to the trough line as viewed in section.
Joe Bartok
Edited 9/18/2006 9:41 am ET by JoeBartok
Edited 9/18/2006 11:37 am ET by JoeBartok
The second moments of area posted above were incorrect have been deleted. The depth of the Valley is 12 inches and for some reason I thought it was 10 inches. A corrected version will be posted in the near future.
Joe Bartok
Edited 9/18/2006 11:37 am ET by JoeBartok
Summary of values for the second moments of area:
8½ × 12 Rectangle = (8.5 × 12³)/12 = 1224 in^4
Valley with 1.08931 deep backing = 1069.59773 in^4, about 87.4% of the full rectangle value. The neutral axis shifts from the center of the beam to 5.73199 in. from the bottom edge.
Guesstimating by subtracting one inch from the Valley depth returns:
(8.5 × 11³)/12 = 942.79167 in^4.
In case anyone wishes to double check these figures the attached diagram has a brief summary of the values used in the calculations.Joe Bartok
Since the valley jacks are sitting on top of the valley, your seatcut would have to be the bevel angle as if you were to bevel the bottom or top of the valley.Since your not using a saw big enough to set at 45� you need to know the sidecut angle.For your 4.5/12 pitch, the sidecut you can set with your framing square at 11.23595" or 11-1/4" on the body of the square and 12" on the tongue and mark the 11-1/4" side. Do that at the top and bottom of the valley jack.The bevel angle for the valley would be 14.37�.If you want to learn how to figure this stuff out. There are many ways to give you the exact answer. Are you comfortable with trig or a Construction Master Calculator? This is the angle your looking for at the top, I assume.Joe Carola
I just figured that your valley jacks are 8.5" also.Joe Carola