Roof Truss Questions

[myrtsbnye]

I have a reno project where I have to draw the exiting roof system of the home. The client is adding an addition to the side of the home so we need to figure out the new roof lines.

 

Anyway, the home is basically U shaped with the garage forming one end of the U and bedrooms the other. The inset of the "U" is the entrance. 

The roof is constructed of trusses with a raised heel and bottom chord overhang (the overhang is level with the top plate of the wall). The roof has a gable over the garage and bedroom "wings" but is hipped everywhere else. The roof slope over the "Wings" is 10/12 and over the main house is 6/12.

 

When I set the roof properties to roof truss and then the height over the top plate to 14" for a raised heel then get Chief architect to build a roof it then ignores these properties all together. 

 

Is there a way to draw this roof without too much trouble? It's causing me (a newbie) fits.

 

Thanks for any help.

 

[DavidJPotter]

Welcome to the forum. Until you have successfully done everything, it is expected to give one fits. You can manually locate roof planes using the "Transform-Replicate" tool. For autogenerated roofs you would preset the "Raise off Plate" setting in the "Build Roof dialog" before building roofs. (The truss tool then fills the void you created that then exists between the underside of roof planes and the top of flat ceilings). So once that is set up correctly the truss tool then just fills what you created.

 

DJP

[CJSpud]

Myrt....

 

Are all the fascia heights for all roofs suppose to be at the same elevation?  What are your eave and gable overhang dimensions?

 

When you have trusses that have the bottom chord extending out to create the framing for your eave soffits, that type of truss is called a "canted" or "cantilever" truss.

[CJSpud]

Hi:

 

The attached plan has a roof that should more or less meet your spec's as you noted in your first post.  Note that there are 3 different roof overhangs:  18" CA default for the gables, 2' for the 6:12 eaves and 14-3/8" for the 10:12 eaves.  All the heel heights are set at 14".  The transform replicate tool was used to fine tune the heel heights to 14" once I built the roof.  There is a truss built for each section of the house for you to look at.

 

If you want identical roof overhangs all around the house, then you'll need to change heel heights somewhere or make all the roof pitches the same value.

 

RoofTrusses&14inHeel.zip

 

 

[Kbird1]

Hi Curt , was hoping you would see this post , you seem to have trusses figured out    , did you edit the truss in elevation to get the Cantilever shape or are those "Auto" trusses , and I am missing a setting or two somewhere.

 

Thx. M.

[Bill_Emery]

Mick,

The cantilever and vertical strut at the wall top plate will generate if the heel height is adjusted so that the bottom most tip of the top chord, and bottom of the bottom chord are at approximately the same height.

 

I think Curt may have hinted at this when he said that all of the heel heights are set to 14"

 

The truss can be edited to get a similar result when the chord heights don't align, but its not as clean.

[CJSpud]

No auto trusses.  I just pulled a dimension or two in elevation view after I built the roof to find out how much I needed to raise the roof to get a 14" heel.  If Chief allowed us to put a check mark in a box specifying canted trusses and also plugging in a heel height, it would really be easy, but the dialogs aren't set up that way.

[Kbird1]

Thx Curt, it is the Canted part I have issues with , energy heel etc works as expected, but checking the manual about this it mentioned editing the trusses manually if needed, so that was what I thought you had done , but there is no setting in the Raise/Lower box in your Plan so I wasn't sure.

 

I assume you used Transform Replicate to raise all roof planes the req'd distance then ? I  think it's a bit strange Canted isn't an option since "Canted" truss's are pretty Common.

 

@Bill , thx....but I will need to play with a cross section so I can "compute"  your information too 

 

" The cantilever and vertical strut at the wall top plate will generate if the heel height is adjusted so that the bottom most tip of the top chord, and bottom of the bottom chord are at approximately the same height."

 

Thx Guys,

M.

[CJSpud]

Bill:

 

I actually had not "discovered" the relationship of the bottoms of the top and bottom chords and whether or not a canted truss with a vertical member over the wall would be generated.  In my example, it luckily worked out that the trusses built that way when I moved them up (so the bottom chord would cant).

 

A project I am currently working on, for whatever reason gives me mixed results.  The carport area is 30' wide; 6:12 roof pitch and 2' overhangs and the trusses have the canted bottom chords and the vertical member at the wall (see below):

 

 

The house area is 40' wide with the roof pitch and overhangs the same as the carport, yet Chief will not put the vertical member over the wall as shown below:

 

 

It doesn't look anywhere close to being what you'd expect a truss to look like without that vertical member at the walls, BUT, as has been stated by Chief, the trusses it generates are not structural ... just a representation that the roof is supported by trusses.

 

By the way, neither the 30' trusses nor the 40' trusses were designated as being energy heel trusses.  That just comes with the turf when canted trusses with enough overhang are used ... you'll get some sort of energy heel out of the deal.  If I designate the 40' trusses as having an energy heel and force the trusses to rebuild, then Chief will give me a vertical member at the wall, BUT, Chief takes away the canted bottom chord in the process (see next image):

 

 

If I select the truss and edit its shape at the overhang, it reverts back to a canted truss with no vertical member at the wall.  Like I said in my 1st post, it would be nice to have a bit more control for canted trusses ... a check box we can put the check in to get the bottom chord to extend out to the subfascia would work for me.  They (the CA dudes) could leave the rest like it is, if checking for an energy heel would give us the vertical member at the wall without messing anything else up.

 

My 2 cents worth at this moment.  Maybe there's a way to use some trickery to get it to work right .... if so, I haven't discovered it yet.  I don't have a clue why my 40' truss built differently than the 30' truss ... I am assuming it has something to do with the truss width and the way the code is written to insert the angled truss members at a certain spacing.

 

 

 

 

[Kbird1]

So if you play with the Top and Bottom Chord spacing you still don't get the vertical over the wall on the 40" trusses?,

 

M

[Bill_Emery]

Curt,

Here I've drawn a 30 foot and a 40 foot building with a 6/12 pitch, and 24" overhang.  I've raised the roof 10 7/8" as I described in my earlier post.  This method gives me the cant, and the vertical strut in both buildings.

 

The cantilever and vertical strut at the wall top plate will generate if the heel height is adjusted so that the bottom most tip of the top chord, and bottom of the bottom chord are at approximately the same height.

[CJSpud]

I guess I should try and drop the roof a couple of inches and see what happens at the walls.  Thanks.

[Kbird1]

Thanks Bill , Got it now   just needed to visualize what you were saying while looking at an elevation.

 

other tips for further Readers...

 

Make sure Trusses is checked in the Build Roof DBX and

 

Until you build all your trusses you will have a small wall showing in elevation due to the 10" raise ( 6/12+ 24" overhang) and CA assuming Rafters till you MultiCopy the rest of your trusses , (see pic below) it then disappears after a rebuilt.

 

 

Another question ....What is the correct placement of the reduced height gable Truss on a gable wall to Auto eliminate the Gable wall framing? I would assume behind the sheathing but I can't seem to find the sweet spot even with a framing rebuilt.

 

 

thx.

[CJSpud]

Mick:

 

If you've checked for your roof to have trusses, I don't believe your gable walls will actually have wall framing built with the rest of your framed walls.  Did you check for trusses in the build roof dbx?  Maybe I am missing something.

[Kbird1]

I did check that Curt and it is ON , but perhaps I need to try a new plan , as my Practice plan maybe as confused as me , with all this checking  and rebuilding framing etc.

 

*** no same in new plan , so I think I am missing something , not you    I either get the full gable wall or with the stop at ceiling setting on the wall,  one the same height as the "raise above plate" measurement same as before .

 

I thought perhaps like the Roof rafters the Gable Framing would be auto eliminated if a truss was placed there.

[CJSpud]

Mick:

 

That's weird ... mine was a simple test plan ... trusses designated ....didn't do anything cute with energy heels or canted trusses .... siding 6 wall type ... Chief built the attic gable walls as siding 6 the same as the main level.

 

When I built the wall framing (I was on Floor 1), I immediately checked my 3D framing overview to see if any attic gable wall framing was clashing with the gable trusses .... nothing.

 

Next, I went up to the attic level and then opened the framing dbx and clicked to build wall framing ... again, no framing was built.  Based up my results, I conclude that when you put a check mark in for roof trusses, that Chief will not frame the attic level gable walls, which makes since to me.  If it would have, I would call that a bug.

 

Not sure what to say about the results you are seeing.  We obviously must be doing two different things since our results are different.

 

Here's some images of my results:

 

              

 

Here's the plan if you want to see the results I got:

 

GableWallFraming-TrussedRoofTest.zip

 

I did a bit of editing of the lookouts and the dropped gable truss on one end of the model.  The views for the images are saved in the project browser.  By the way, I do something very similar to what Bill does for attic gable walls.  I make a "skinny" wall type that might be something like this for layers (from outside to inside):  5/8" siding; house wrap/weather barrier; 7/16" OSB sheathing; 1-1/2" fir framing [to represent an actual gable truss with finishes complete].  If there's a framed wall below, then I align the outside of the fir framing layer with the same layer on the level below.  Since I do lots of ICF plans, the outside of the OSB gable wall sheathing will align with the outer foam layer of the ICF wall on the level below.  For aligning/placement of attic gable wall trusses, I pretty much do the same thing ... outside of framing to outside of framing [framed walls level below attic] or I set the gable trusses back 7/16" if there are ICF walls below.

[Bill_Emery]

Mick,

If you don't want the gable end framing to generate, you'll have to check "end truss" when you open the DBX for the truss at the gable

[CJSpud]

Mick:

 

My BAD ... I actually had my default ICF walls in my model when I first started working on the roof.  I "manually" changed all the ICF walls to siding 6 walls, including the attic gable walls after the walls were built.

 

So, I went back and redid the test and I think I found out why you are getting wall framing for your gable attic walls.  My bet is that you built the wall framing "before" you built (created) your truss(es).  If you build the wall framing before your gable trusses (or maybe any trusses ...??? didn't check that) are in place, then the gable walls will get their stud framing built just like you would do for a manually framed gable wall. 

 

However, if you create your roof trusses right after you build the roof, but before you build the wall framing, then you shouldn't get any wall framing showing up for your attic gable walls. 

 

Hope that helps.

[CJSpud]

Bill:

 

Did we say the same thing?

[Kbird1]

it's something simple you are doing I am not ..... let me look at your plan.... thanks ALOT on this appreciate it.

 

no wall framing yet , only 1/2 trusses in

 

Frame the wall and

[Kbird1]

I see now we have a Regional difference in how things are done    ....saw it as soon as I opened your plan , we don't use end trusses here the Reduced gable truss is just that , and has no vertical webs and we just sheet over the Webs.  As soon as you change the Reduced gable truss to be an END TRUSS the wall framing disappears... DOH !  and the lookouts connect properly..... apologies Curt....I assumed the Reduced gable would also be auto "End" since that is the only place to use one I am aware of ????  damn...sorry again for wasting your time. 

 

Mick.

[Kbird1]

Mick,

If you don't want the gable end framing to generate, you'll have to check "end truss" when you open the DBX for the truss at the gable

 

Now you tell me    where you been all afternoon   

 

why a reduced gable isn't also and end I don't know....

[Bill_Emery]

Mick,

you can use the "reduced truss", without checking "end truss"; but you'll have to change your gable wall definition to keep it from framing.

I change the main layer to "opening, no material" and give it a thickness of 1 1/2" so it aligns with the truss. this way no wall framing is generated in the gable end.

[Kbird1]

Thx Bill , I see you and Curt have the Same idea , I had not thought of making a special wall type and drawing my own Attic walls in , but thanks to you as well for today's lesson.... use the "END" SETTING on TRUSSES ON THE END so they work properly... Doh !  got to remember to stop thinking how I do it on the Job and What CA needs to do it right....

 

I was thinking I should suggest that Reduced gables should automatically get End truss "features" but without the vertical webs but that's just how I see it done here, and is likely cos they charge more for end trusses only ..... 

[CJSpud]

I was thinking about dropping the roof of my current project an inch or two so I could get those vertical members over my exterior walls but decided it might be easier to just change the top chord depth of the trusses from 2x4 to 2x6, which would put the bottoms of the top and bottom chords very close to each other at the fascia [bill's idea] .  The project is in an 80 lb. snow load area so the truss manufacturer may design the trusses with a deeper top chord anyway. 

 

I selected one of the trusses in a 3D framing overview, opened the truss dialog and changed the top chord depth to 5-1/2" > OK and BINGO, the truss rebuilt with a vertical member over the walls as desired and per Bill's advice.  This works as long as the trusses aren't intersecting a truss base for a perpendicular intersecting roof (such as a garage or carport roof in an 'L' configuration].  All of the trusses that tied in with the truss base for the carport roof of my project WOULD NOT build a vertical member over the exterior bearing walls [side of trusses opposite the truss base]. 

 

That is a little hiccup that I would like to see fixed in a future update or version.  Even though Chief's trusses are VISUAL ONLY (not structural), I think the roof trusses would be a lot more professional looking if they resembled the real thing.  Maybe we need a "insert member" tool for our trusses?!?