Cantilevered trusses

[BnCKelley]

We use mostly cantilevered trusses and I'm curious how can I get my bottom of overhang even with the top of my walls, and sit my desired heel height at the face of the wall? Thanks

[Michael_Gia]

Ha!

 

Guess what? You can't do that easily in Chief.

Don't let anyone tell you it can be done.

There are lots of posts on this topic, but you'll be wasting your time.

 

Just build your roof, then take a cross section to figure out exactly how high you need to raise all of your roof planes using the Transform/Replicate tool and entering the corresponding amount in the "move", "Z Delta" box.  That's it.

 

When you first build your roofs you do have access to the "Raise/Lower From:________" in the Roof Height section of the Build Roof Dbx but there is no calculation to figure out what the "raise/lower amount should be.  Many have tried but I don't think there's a formula.

Of course, trial and error could work but unfortunately that Raise/Lower item is only available for one instance.  Then it's gone!

     After you've built your roofs you don't have access to that value when opening a roof plane DBX.  Which is another insane aspect of this wonderful software.  I never understood that one.  

 

You could over time develop a table of values corresponding to each roof pitch, I suppose...?

 

Anyway it's maddening.  

If I'm wrong I'd love to hear from someone. 

 

The problem is that Chief was designed for your typical site-built rafter by carpenters in the field, kind of the way you'd build a doghouse or shed for your livestock. (kidding).

Up here in the NorthEast we use mostly prefabricated cantilever roof trusses in order to get the proper heel height for insulation and ventilation.  This requires an eave that sits level at top of the top plate and extends out to create a vented soffit.

 

...and this isn't because we're so sophisticated, but because it gets so damn cold up here.

 

 

[Kiwideziner]

why not just adjust the baseline height, you know top of plate you should know the vertical depth of framing (tells you in the db)

Add whatever extra heel height reqd. Then when you draw a truss it will extend the bottom chord to form the soffit on top of the plate.

Or am I imagining something else. we only use trusses here. no pitching of roofs except when using rafters.

[Alaskan_Son]

On 10/28/2020 at 5:10 PM, Michael_Gia said:

Guess what? You can't do that easily in Chief.

Don't let anyone tell you it can be done.

There are lots of posts on this topic, but you'll be wasting your time. 

 

That's the spirit!!  ...and then you follow it up with a method that only takes a few seconds too.  Seriously though, your advice is super negative, discouraging to new users, and not very helpful, plus it's not even accurate.

 

A couple quick examples:

On 10/28/2020 at 5:10 PM, Michael_Gia said:

When you first build your roofs you do have access to the "Raise/Lower From:________" in the Roof Height section of the Build Roof Dbx but there is no calculation to figure out what the "raise/lower amount should be.  Many have tried but I don't think there's a formula.

 

Here's one of the easiest ways...

 

Open your Framing Defaults and change your Roof Structure thickness to match your Roof Truss' Top Chord.  Now open the Build Roof Dialog, uncheck Automatic Birdsmouth Cut and enter the desired heel height minus the displayed Vertical Structure Depth.  In fact you can even just copy and paste the value from right there into a formula in the dialog box that looks something like this...

...hit tab to make sure the calculation carries out and that should be all there is to it.

 

 

 

On 10/28/2020 at 5:10 PM, Michael_Gia said:

After you've built your roofs you don't have access to that value when opening a roof plane DBX.

Plenty of other easy ways to do this after the fact.  Here's one... 

 

Open the roof plane(s), Lock Pitch, and copy/paste the Top Of Plate Value and add your desired heel height to it in the Baseline Height Field.  Easy peasy...

 

 

Bottom line?  @BnCKelley, this can totally be done and it's really not very difficult to achieve.  Hope that helps.

 

NOTE:  The methods above were specifically meant to describe how to set the "... desired heel height at the face of the wall".  This may or may not be what any specific person was referring to.  It was not intended to address the suitability of this heel height for any given cantilever distance. 

 

[joey_martin]

8 hours ago, Michael_Gia said:

If I'm wrong I'd love to hear from someone. 

Select a roof plane, use TRANSFORM/REPLICATE tool, and raise the roof plane.

[Michael_Gia]

1 hour ago, joey_martin said:

Select a roof plane, use TRANSFORM/REPLICATE tool, and raise the roof plane.

That was my point as well. Transform/Replicate is the only way. 

No big deal, I guess, but it still stands that the Build Roof dbx has no easy or obvious mechanism to achieve what OP would like.
 

After you raise your roof to the proper level then you can calculate your “Fascia Top Height” and use that value to set all your other roof planes. 
...But amazingly that value, which would be easy to calculate isn't even available in the initial Build Roof dbx!

 

[GeneDavis]

If every job one trussed had same-pitched roofs, same length overhangs, and same-spec fascia and subfascia, then one could build roofs right for trussing with bottom chords framing soffits just right every time.  Just control it in the build roof dialog as stated above.

 

The OP stated that the spec was to have the bottom elevation of subfascia match precisely the plate elevation of wall, and to do that involves either a trig or graphical solution.
 

Wasn't said this way, but as "bottom of overhang even with walls."  I think I understood that correctly.

 

Easily done with Chief in a 2D section view, to arrive at the right z position for the roof plane.

 

But change anything, pitch, roof sheathing thickness, added shadowboard, subfascia size, overhang, and you're back to needing a new solution, BEFORE you generate a truss.

[PMMully]

Watching this thread it is interesting how you can control the birdsmouth cut, etc. But how many of you actually do this type of work these days, or is it simply to produce the design?

 

Curious how you are delivering engineered truss layouts on your construction drawings. In FL, just about every truss company uses Alpine Engineering, and then the firms are superimposing the truss drawings/cad on the foundation plan for the stamp set of drawings. What is the process that is most popular?

[BnCKelley]

Most trusses around here are Mitek and there are no drawings required on plans. The truss manufacturer provides individual pages in a notebook for every truss. Most overhangs are cantilevers, very few dropped tail. I'm very use to the Mitek software which is great for custom roofs. I don't understand the roof planes yet in CA but in Mitek u pick and choose where each plane (surface) will "cut" or mate with. You set pitch, heel and overhang and it's a breeze. 

[BnCKelley]

8 hours ago, joey_martin said:

Select a roof plane, use TRANSFORM/REPLICATE tool, and raise the roof plane.

That's another thing, I understand the way I used roof planes in Mitek software but I don't know anything about them in CA yet.

[Alaskan_Son]

11 hours ago, Michael_Gia said:

That was my point as well. Transform/Replicate is the only way. 

...aside from all the other ways.

[Michael_Gia]

44 minutes ago, Alaskan_Son said:

...aside from all the other ways.

This is the user forum not the fan club. 
 

The roof build dbx does not provide what OP is looking to do. 
Your suggestion is not a solution. It’s a Mensa level work around. 

[Kbird1]

On 10/28/2020 at 9:57 AM, BnCKelley said:

We use mostly cantilevered trusses

 

The Trial and Error Chief Method..... don't think much has changed since X8 in this regard

 

Framing a Cantilevered Truss Roof System (chiefarchitect.com)

[GeneDavis]

If one sincerely needs Chief to generate roofs that meet this truss arrangement soffit-formed-by-truss-chord detail, there will be a check box in the structural page of the BUILD ROOF dialog that would say, "locate roof with subfascia bottom elevation at wall height elevation," and then there, voila, you have your feature.  Automatic.  Wow.

 

So go ahead and write the suggestion and put it on the Suggestion subforum.  

 

Until then, you'll have to slug it out with existing tools, first generate a roof, frame it so as to place the subfacia, take a section view, draw a rectangular polyline to gage the height you need to move the roof so that subfascia bottom equals plate height, cut the temp dimension of the box height to the clipboard, go to the roof in a view so so as to select and move it, paste in the move distance, and THERE, you have your roof ready to build your perfect cantilevered truss.

 

I should have timed it.  Really quickly done.

 

In the three views here, I show how the heel height can change for an overhang that has the same pitch and overhang distance, but what has been varied is the roof sheathing thickness, the fascia thickness, and the addition of a shadowboard.  I set the fraction to 64ths for emphasis.  When you copy that move distance, you are at five decimal places in inches.

 

For a trussed job, my roof edge section will dimension heel height, overhang, and roof pitch, and it will call out the thicknesses of roof sheathing, fascia, shadowboard if there, and will call out size of subfascia.  They all play a role in the geometry.

[BnCKelley]

Correct, I have designed thousands of roof trusses, the heel heights can vary with the same distance overhangs, it really depends on the desired height at the end. We always used a particular, calculated distance at the very end, which we referred to as the heel when talking cantilevered, not to be mistaken as heel at the wall, that once a 2x6 was flushed on bottom and nailed in place, the sheathing would plane down the top chord and hit the 2x6 in the center of the thickness. Of course the pitches as well calculated in and this number is what I'd like to set my heel at wall to, but, it's not that critical to my drawings. What's mostly important is just getting the elevation look for the cantilevered trusses. I'm still not sure what everyone has mentioned, what's easier and less confusing, but the video from Kbird1 sure made it look quick and easy. Is this any way close to what you're talking about? If there is a different way though please let me know. Thank you Gene.

[Alaskan_Son]

On 10/28/2020 at 8:57 AM, BnCKelley said:

...sit my desired heel height at the face of the wall?

 

52 minutes ago, BnCKelley said:

it really depends on the desired height at the end. We always used a particular, calculated distance at the very end, which we referred to as the heel when talking cantilevered, not to be mistaken as heel at the wall...

 

You seem to be providing conflicting information as to what you're after.  Are you trying to set the desired heel height at the wall or the desired heel height at the very end of the truss?  The methods I mentioned above were in response to the first example and described ways of setting the desired heel height at the wall, but the second example requires totally different methods.  

[Alaskan_Son]

5 hours ago, Michael_Gia said:

This is the user forum not the fan club. 
 

The roof build dbx does not provide what OP is looking to do. 
Your suggestion is not a solution. It’s a Mensa level work around. 

 

I may or may not have fully understood what exactly the OP was after in my attempt to help offer a solution, but it doesn't take a genius to understand the methods I spelled out if you actually put in a little effort to comprehend them.  I can't help but think you didn't even read them because they included little more than basic addition and subtraction using information supplied right there in the dialog box. 

[Chrisb222]

9 hours ago, GeneDavis said:

So go ahead and write the suggestion and put it on the Suggestion subforum.  

 

Until then, you'll have to slug it out with existing tools

 

You say that as if simply making the suggestion will quickly produce the feature.

 

I know that's not what you meant, just quippin!!

[Chrisb222]

9 hours ago, GeneDavis said:

take a section view, draw a rectangular polyline to gage the height you need to move the roof so that subfascia bottom equals plate height, cut the temp dimension of the box height to the clipboard, go to the roof in a view so so as to select and move it, paste in the move distance,

 

This is basically the method I use.

[Michael_Gia]

6 hours ago, Alaskan_Son said:

I may or may not have fully understood what exactly the OP was after

I think you got that part right. 

[GeneDavis]

So who's gonna write up the suggestion for the enhancement that automates the section-view-measure-then-cut-and-paste-to-move-roof-height tapdance?

 

I'm waiting.  

If you want a feature, you gotta write it up over there in Suggestions.

 

[GeneDavis]

And read carefully what the OP, fluent in MITEK truss design software but not yet up to speed in Chief is saying about the roof edge geometry.

 

It's really just a version of how soffit z-position is controlled by subfascia size, and how the heel height RESULTS FROM that spec.

 

And re-read it to understand how it differs from Chief's code, which adds into the assembly, sheathing thickness and fascia thickness.

[Alaskan_Son]

3 hours ago, Michael_Gia said:

I think you got that part right. 

 

If you think I was misunderstanding the question then you could just say that. 

[Alaskan_Son]

To anyone following along and/or struggling with this same issue being discussed here,

 

After reading through this thread and some other similar threads on the same subject, I've concluded a few things:

 

1. If you want to see any improvement in this area, you'll need to describe your issue a little more clearly.  The burden of describing the problem is on you because you're the one having the problem, and if you can't describe it accurately, no one can effectively help you with it.  Plus, Chief can't fix what they don't understand either.
2. This problem doesn't seem to have been brought up in the suggestion forum...at least not that I could find.  If it's not getting reported/suggested then its not gonna get changed.
3. The challenge is a bit more complicated than some are letting on.  For example it was my supposition based on the initial post that the OP wanted to set a specific pre-determined, user-definable heel height at the exterior wall.  This is a perfectly valid way of configuring a truss but would result in variable overhangs depending on the specified roof pitch. The methods I spelled out in my first post were specially geared at ways to set this user defined heel height.  After reading through the thread again though, I'm starting to believe that contrary to the way the question was posed, what was really wanted was a way to FIND that required heel height at the exterior wall.  This is another perfectly valid method of configuring a truss but unlike the first method, it would result in the opposite; a user definable overhang and variable heel height depending on the roof pitch.  There are also other valid methods that would result in a variable truss tail or sub-fascia height but I won't go over those because I doubt that anyone is talking about that.

Anyway, I don't disagree that Chief could give us a better way, but again, the problem needs to be spelled out at least a little more clearly, and needs to be presented that way as a suggestion, either in the forum or sent in directly to Chief.

 

Until Chief gives us something better, all we can do is find ways to get it done using the tools we have NOW.

 

There are several methods we have now of accomplishing both of the main truss configuration methods I mentioned above.  As others have already pointed out, it can be pretty easily done by taking a section view and finding the required numbers, but it can also be done using formulas so that you don't have to take any measurements.  I took the liberty of writing some custom text macros that carry out the calculations for you and have attached them below.  I'll leave them available free of charge for a limited time.  Simply download the macros, Import via Text Macro Management, select the desired macro, click Edit, change the appropriate values, and then copy value(s) from either the New Result or Expanded Macro Value fields.

 

There are 4 macros:

-One for calculating the required heel height or Raise Off Plate Value using a standard Pitch (12 in 12)

-One for calculating the required heel height or Raise Off Plate Value using a roof Angle (45.0)

-One for calculating the required overhang using a specific heel height and a standard Pitch

-One for calculating the required overhang using a specific heel height and a roof Angle

 

 

NOTE:  I recommend setting your Number Style to decimal inches or decimal millimeters before transferring values.  Your subfascia height in a metric plan for example might say 138 when in fact it is 137.5.  It’s important that the numbers being entered are accurate.  

[Ridge_Runner]

Thanks, Michael, for taking the time to do this and making it available.