Author Topic: Truss Calculators  (Read 369593 times)

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Offline Medeek

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Re: Truss Calculators
« Reply #175 on: November 22, 2015, 11:06:42 AM »
The plugin allows the lookouts to be either flat or vertical and structural or non-structural.  According to the code if you are overhanging 12" or more then what I have shown is not going to work.  I'm going to leave it up to the user to specify the configuration.  If I restrict it too much then a number of designers/architects who are already using this plugin are going to gripe about it, even though I completely agree with you.  Locally here along the beach I never specify anything other than structural lookouts especially with our wind loads. 

Measuring from the bottom makes sense.  Every roof I've ever helped sheet has always been started at the bottom now that I think about it.  So depending on the fascia type (dropped, beveled, flush) the location of the bottom edge of the sheathing will be determined and hence the starting point for the lookouts.  I can make that work.

Where the lookouts are structural the gable end truss has a dropped top chord to match.  If you notch the gable end truss does this cause any problems with the inspector or building dept.?  I realized the gable end truss is not structural but the docs from the truss manufacturer's always warn against notching etc... so I'm wondering if that becomes a problem.

What would be your treatment at the peak with the lookouts.  Notice I've run a lookout on each side of the ridge. 
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #176 on: November 22, 2015, 12:00:29 PM »
Outlookers get a little complicated depending on whether they are structural or not.  Typically around here (Ocean Shores, WA) we see them at 24" on center and they are usually structural.  The top chord of the truss is dropped either 1.5" or 3.5" depending on if they are oriented horizontally or vertically.  With structural lookouts the first lookout from the eave is usually non-structural since the dropped top chord truss will have a special slider attached to top chord to achieve the overhang. See image below:



Usually the sheeting goes on starting at the bottom so based on that the lookouts would be measured from the bottom edge of the sheeting so that they line up with the seams every 48".

I've seen a single vertical placed the ridge when the outlookers are vertical however what is common practice when the outlookers are horizontal?

Notice the different configuration of the top chord when the drop is only 1.5" (oriented flat).



If the overhang is zero then this slider or splice goes away.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #177 on: November 22, 2015, 12:40:22 PM »
A dropped top chord with flat orientation might look something like this:



Without an overhang the gable end truss becomes:



Note that the outlookers would probably be spaced from the bottom at 24" on center.

Another interesting point to note is that if the overhang or top chord of the truss is a 2x4 and one wants to use structural 2x6 vertical outlookers at the gable end.  How would that work, I don't think it would at least not easily.  If the outlookers are structural and vertical I will constrain them to be the same depth as the top chord in order to simplify things.
« Last Edit: November 22, 2015, 12:53:45 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #178 on: November 22, 2015, 02:00:32 PM »
Usually I'll have an outlooker near the ridge, if I don't have one close enough to suit me I'll put one there. Then my ridge string will find the peak of the first barge rafter and I'll nail it to the outlookers on that side. The second fly should just bump in up top and nail to lookouts on your way down.

Notching is forbidden, not ordering the trusses, and the gables, correctly is how I usually end up notching the gable truss. I've never been called on it but it is incorrect, a dropped gable end is the correct way to build it.

Offline Medeek

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Re: Truss Calculators
« Reply #179 on: November 22, 2015, 02:16:46 PM »
Usually I'll have an outlooker near the ridge, if I don't have one close enough to suit me I'll put one there. Then my ridge string will find the peak of the first barge rafter and I'll nail it to the outlookers on that side. The second fly should just bump in up top and nail to lookouts on your way down.

Can you expound more on this paragraph?  I'm not sure what the second fly is, (the other rake board).  Even though I might be an engineer doesn't mean I understand all the finer points of framing.  Usually I never worry about these sorts of details, the framers and contractors take care of it.

I'm going to assume then that you measure the outlookers from the bottom and they are spaced at 24" o/c, if the last set of outlookers are close enough to the peak then an outlooker at the peak is not inserted, if not then you put one there. 
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer


Offline Don_P

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Re: Truss Calculators
« Reply #180 on: November 22, 2015, 05:54:10 PM »
I was trying my hand at creative writing (not too successfully) and using what I consider to be interchangeable terms for the same members... lookout and outlooker and barge, verge, or fly rafter. So, I'll find the peak with my first barge rafter and then when I bring up its' mate from the other side they will simply meet at the top against each other. I'll usually screw a gusset on the backside that will be covered by the soffit later.

Offline Medeek

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Re: Truss Calculators
« Reply #181 on: November 22, 2015, 09:37:25 PM »
Agreed there are too many terms for the same thing.  I'm still trying to figure out the difference between rake board, barge board, barge rafter and fly rafter.  The gusset makes sense otherwise how do the two barge rafters stay together, unless a toenail will hold them, but probably not very well.

Same roof with vertical structural outlookers:



« Last Edit: November 22, 2015, 10:23:34 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #182 on: November 23, 2015, 04:57:41 AM »
There it is,
pushing towards good-better-best, then run 22.5" blocking between outlookers over the gable truss...blocking over the bearing. Then if wind controls begin hurricane ties from lower outlookers to gable truss, the bottom corner is the highest wind load, then work your way up tieing them to the frame as needed. I would consider that here on some of our ridgetops that are in the special wind region. (You're probably in a SWR if you have to stake the little blue shack out back down.) I think there is a detail in the WFCM, I'll check tonite.

Offline Medeek

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Re: Truss Calculators
« Reply #183 on: November 23, 2015, 09:43:40 PM »
Outlookers enabled under advanced roof options for Monopitch and Attic truss types.



Also fixed all truss types so that the outlookers are measured from the bottom.  I also added the option to include outlookers at the peak.
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #184 on: November 24, 2015, 03:28:49 AM »
Found the "Rake overhang outlooker uplift connection requirements" in the '12 WFCM, pg 174&175. They kick in at 110 mph, 2' max overhang, 20" outlooker limit, greater than half inboard with a metal tie inside the wall from outlooker to studs, blocking required between lookouts.

as an aside for another problem we seem to bump into often, this is in the prescriptive section, they have heeljoint tables to raise rafter ties to halfway up, more generous than the codebook but this manual is also directly referenced in the code.

Offline Medeek

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Re: Truss Calculators
« Reply #185 on: November 24, 2015, 11:27:21 AM »
I like to call out a Simpson H4 for my Outlookers, locally. 
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #186 on: November 25, 2015, 02:20:23 AM »
Version 1.1.4 - 11.25.2015
Structural outlookers (vert. & horz.) enabled under advanced roof options for Common (Fink) truss type.
Structural outlookers (vert. & horz.) enabled under advanced roof options for Common (Fink) truss type with raised heel (vertical w/ strut).

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #187 on: November 25, 2015, 04:27:16 PM »
Version 1.1.5 - 11.25.2015
- Added Double Fink common truss type.
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Common (Double Fink) truss type.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #188 on: November 26, 2015, 03:08:43 PM »
Version 1.1.6 - 11.26.2015
- Added Fan and Mod Queen common truss types.
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Common (Fan & Mod Queen) truss types.



Four more common truss types still need to be added:

- Double Howe
- Mod Fan
- Triple Fink
- Triple Howe

For very large buildings one could also consider:

- Quad Fan (10/5)
- Quad Fink (10/9)
- Quad Howe (10/10)
- Quin Fan (12/6) ...
« Last Edit: November 26, 2015, 03:26:33 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #189 on: November 28, 2015, 05:02:47 AM »
Valley Sets are here:



Proceed with caution though I just put it together so it is still a bit rough around the edges.  Further testing and refinement is necessary but it seems to be working fairly decently.

Currently the main roof plane and two points need to be selected rather carefully I'm not sure I can do much about that, if not I will need to document in some detail how to use this function.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #190 on: November 29, 2015, 01:57:01 AM »
I've addressed a few bugs with the valley set algorithm and tested it in as many configurations and orientations as possible.  It it more solid now.  I suggest downloading the latest version of 1.1.7 that I just uploaded to the server.

Note that the plane of the main roof that is selected needs to be a rectangular shape at the moment to properly register (1st point selected).  I usually just select the top face of one of the top chords of the trusses.  The second point should be at the centerline of the last truss of the secondary roof line and at the ridge (peak) of this truss, the third point is also at the ridge (peak) but at a point towards the main roof.  I really need to put the manual together to document this feature and how to use it, or at least a video. 

I also updated the geometry algorithm slightly so that it adds additional verts a 48" o/c when the valley trusses get too large.  This is keeping in line with standard practice on these types of valley sets.  I can also make this an input if someone requests that it be such.

This update was not that complicated (valley sets) other than trying to figure out how to place the set based only on a plane and two points. Obtaining this information and then figuring out the math and code to compute the vertical distance between the bottom of the first valley truss where it rests on the main roof plane and the peak of the secondary roof line was the slightly painful part. The actual geometry of the valley set was surprisingly easy to code.

The real challenge will begin when I try to add some hip sets, I may push that out for awhile.
« Last Edit: November 29, 2015, 02:11:10 AM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #191 on: November 29, 2015, 02:24:37 PM »
Here is an example of a large valley set with a Monopitch Primary Roof and a Common Secondary Roof.  Notice the pitch of the monopitch roof is 6:12 while the secondary roof is 12:12.



Rather than calculate the overhang for the secondary roof it is just as easy to to trim the truss tails back and adjust the fascia so that it lines up with the fascia of the main roof after the fact.

Even with all the automation of certain tasks there is still a good bit of manual editing required when complex roof lines are involved however I find that SketchUp has a very intuitive interface for trimming solids and once the basic geometry is there the rest is usually not too much trouble.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Don_P

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Re: Truss Calculators
« Reply #192 on: November 29, 2015, 04:32:54 PM »
Doing that you end up with unequal overhang widths. You really need to be able to specify finished overhang widths.

Offline Medeek

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Re: Truss Calculators
« Reply #193 on: November 29, 2015, 06:30:13 PM »
With the main roof sheathing:



Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #194 on: November 29, 2015, 06:32:26 PM »
Doing that you end up with unequal overhang widths. You really need to be able to specify finished overhang widths.

You can input the overhang widths however to match vertically to the main roof fascia would require some calculation.  It's almost just as easy to specify an overhang that is too long and then go back in and adjust the overhang manually so that the fascias match up.  I will give this some thought though, there may be a better way to approach this.
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #195 on: December 03, 2015, 04:57:23 PM »
I was doodling and tried it with a mix of stick, common and scissors with valley sets. I'm still getting the hang of things.
The common rafters controlled heel height, I matched the height above plate of the common trusses to the common rafters when I next inserted them. I clipped the truss tails back to 22-1/2" to match the common rafters and everyone was fine at the gutter line, all 4/12. Then I inserted scissors, my version didn't have height adjustment so I aligned the trusses at the gutter line and raised the wall. You can see where I draw in what I call the gutter line, or the drip edge, to help me keep things aligned as I work.


I'll need to play with pitch combinations, this all worked fine. My fear is that if you clip tails to adjust, the bearings will drift.

Offline Medeek

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Re: Truss Calculators
« Reply #196 on: December 03, 2015, 05:30:17 PM »
Wow, very cool.  I've been busy the last couple days working on some local stuff so I haven't had much chance to add new features or pay too much attention to the boards.

When you get the  model finished send me a copy of the SketchUp file so I can examine the gutter lines if you don't mind.   My next thing is to add in rafter roofs, but the issues with heel heights and fascia or gutter lines is very important.

Looks like you figure out how to use the valley set feature, I really need to document this in a manual otherwise I'm going to get a lot of confused people.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Truss Calculators
« Reply #197 on: December 07, 2015, 04:25:20 AM »
Version 1.1.8 - 12.07.2015
- Added Gable Rafter Roof.
- Advanced options enabled for gable rafter roofs (sub-fascia, outlookers, sheathing, and rakeboards).
- New submenu item and toolbar icon added for rafter roof type.
- Plugin divided into multiple files for ease of management.



Structural outlookers for this type of a roof are still somewhat of a question.  If they are horizontal it makes sense to notch the gable rafter but what if they are vertical?
Nathaniel P. Wilkerson, P.E.
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Offline Don_P

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Re: Truss Calculators
« Reply #198 on: December 07, 2015, 02:38:37 PM »
omit the gable rafter for structural lookouts, they rest on the top plate of the rake wall.

There is a code restriction on birdsmouth depth now... deleted what I really think of this. The notch can be no deeper than 1/4 of rafter depth. The old rule was that a minimum of 3.5" was left above the birdsmouth for tails up to 2' horizontal span.

Offline Medeek

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Re: Truss Calculators
« Reply #199 on: December 08, 2015, 07:16:05 PM »
I actually just noticed the 1/4 rafter depth rule a few days ago on a local project, I was not aware of the old rule, interesting.  I think in the plugin I will allow for deeper birdmouth cut since a lot of my clients are in Australia and Europe and I have no idea what their codes specify.  However, I will probably make it throw a warning when the notch is deeper than 1/4 the rafter depth.

Version 1.1.8 - 12.08.2015
- Structural Outlookers enabled for gable rafter roofs (vertical & horizontal).



Notice in this case I have left the gable rafter in place but notched clean through it so essentially it is blocking.  However, I have given the option for removing the gable rafter entirely.  You will also notice that the gable rafter is the same depth as the outlookers, when you choose "CUSTOM" for the gable end rafter it allows one to specify the depth of this rafter. 

 There are almost too many options, at some point I need to put together a manual explaining how to use this thing.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer