Change Birdmouth Of Rafter After Roof Plane Is Built

[dshall]

Can I not change the birds mouth cut on the fly?  Roof built,  I want to change the birds mouth cut......  I can't do it,  is this so?

[raltd9245]

What happens when you lower the roof

[dshall]

What happens when you lower the roof

great question Ron,  the plates go down. I want top plates to stay at same  location. 

 

I have 4x6 rafters on a 2X12 WALL,   2X12 WALL,   I want to raise roof 2" but I want the top plates to stay at same elevation...   by changing the birds mouth or cut,  I should be able to do that.

 

I think what I am realizing is we must define the birds mouth cut prior to building roof,  not after....  I assume this makes sense.....

RAISE ROOF 4%22 KEEP TOP PLATES AT SAME ELEV 1.plan.zip

[johnny]

There is a user here named "Scott" who will often do a video and answer this question like this.....hopefully he sees this and makes a vid.

[dshall]

There is a user here named "Scott" who will often do a video and answer this question like this.....hopefully he sees this and makes a vid.

You would think so, but I think this problem is too hard for him.....  is that you JPC?  Dog gone you,  I still don't know why we did not get together when I was in Washington....  probably because you are too important to meet with me.

[ebdesign]

If you don't want to raise the roof & want the wall plate to stay the same hgt, isn't your only other option to adjust the rafter depth?

Or move the entire roof plane (inc the baseline) relative to the wall?  but that is- in effect- moving the roof plane up/down.

[Kbird1]

what am I missing ? not understanding ?  can't you just alter the birdsmouth cut in the Build Roof DBX by 2" to raise it ? ( turn off auto ABC 1st)

[dshall]

what am I missing ? not understanding ?  can't you just alter the birdsmouth cut in the Build Roof DBX by 2" to raise it ? ( turn off auto BMC 1st)

But what am I missing. The roof planes are already built. If they are already built, you can't adjust birds mouth for those roofs already built.

And yes Jim, other option is to adjust rafter depth, don't want to do that.

I will do vid in am so I better understand.

[Kbird1]

After you already built the framing ?  yes you can (well I can?), go back into the Build Roof DBX , turn off A.B.C  , make the birdsmouth cut -3 1/2 " instead of -5 1/2 "  and the roofline pops up 2 "

 

Or make roof height 2" instead of 0" for the same effect.

  

you do have auto rebuild roofs on right    ( or rebuilt after trying it?)

 

I will check out the vid tomorrow cos I guess I am obviously missing something in your question , seems to work here....

[dshall]

Here is a link to the BIRDS MOUTH VIDEOS.  Some interesting stuff here.....  but maybe more info than you want.....

 

https://chieftalk.chiefarchitect.com/index.php?/topic/2646-the-birds-mouth-videos-by-dsh/

[DRAWZILLA]

Thanks, Scott, another in depth study. Informative for sure

[Kbird1]

Ok , lost those 31 minutes j.j. ,   I'm no expert at Chief , but I have been Building for 30+yrs, so I may "see" things a bit different than you, but generally the BM Cut, seat cut is equal to the Wall framing thickness so the ceiling lines in right at intersection of the wall and Roof Framing, which is why Chief tries to automatically set that cut distance depending on the wall framing, note that the DBX is often slow to update ( no apply button) so you may need to close the DBX and reopen it immediately to check it. eg if you change the Auto. BM Cut in the Roof DBX to say 3 1/2"  the seat cut will still show 5 1/2" until you close the DBX and reopen it. 

 

You are right, in that you can not adjust the Birdsmouth for a individual roof plane ,  you can however do it for the entire roof in the Roof DBX if that works for your Plan.

 

If you want to Raise the BM Cut on a single Roof Plane , raise the Roof Plane's Baseline via the Wall DBX, with the pitch locked, it has the same effect . But if you have no ceiling (Joists) in the Room, you would need to lower the room height ,by an equal amount so the apex of the Ceiling/Wall joint is still at standard height.  ie 109 1/8"  (or accept the extra height-- pics below)

 

The Wall plates don't jump up and down on a normal wall ( for me) , but that wall with 3 different thickness you had, is a special condition and different wall plate heights etc would be expected depending on what you are trying to line in as you saw, it's not uncommon to see different Plate heights when trying to plane the rooflines in especially if the Roofline is Complicated and you want the seat cut as wide as possible for bearing.

 

these are some "snips" I took as I was playing with this , I used X6 Trial as I thought from your comments it was doing something different than X5 , and as I said no expert here in Chief ,so maybe I am still doing something wrong or not seeing something?

 

if you play with this more , make sure Auto Roofs is still on ( had this prob. myself tonight) as playing with any roof plane manually forces it off .

 

 

[dshall]

Appreciate your time.

What sparked the question was a project with auto birds mouth on. I was using 4x6 rafters on 2x12 walls. With auto birds mouth on, you can imagine very little rafter left at end (huge c cut, not good). I had no ceiling to hold plates down, hence the need to alter birds mouth since roof already built and I did not want plates to rise.

Question: hip roof, 4" wall meeting 12" wall in corner, auto birdsmouth on, auto build roofs on, 24" eave defined......will CA build with 2 different birdsmouth seat depths resulting in two different eave overhang, or will CA build constant overhang and ignore auto birdsmouth?

I think what I got out of this exercise was the need to be more aware of the autu vs defined birds mouth seat.

Thanks again for your input.

[dshall]

......

Question: hip roof, 4" wall meeting 12" wall in corner, auto birdsmouth on, auto build roofs on, 24" eave defined......will CA build with 2 different birdsmouth seat depths resulting in two different eave overhang, or will CA build constant overhang and ignore auto birds mouth?......

and the answer is.......

 

Square house, hip roof, (4) different wall thicknesses,  a 4", 8",  12"  and 16" wide wall.

 

WITH AUTO ROOFS ON AUTO BIRDMOUTH ON...... constant eave and  constant birds mouth seat,  birds mouth seat takes it's cue from the smallest wall,  the seat does not get it's width from the wall it sits on.....  makes sense to me.

 

WITH AUTO ROOFS OFF AUTO BIRDSMOUTH ON  (manually built roof)...... varying eaves, varying birds mouth seat,  .....  makes sense to me.

 

So this leads me to believe that if I build my roofs manually (and I do),  I should probably define the birds mouth seat  (no auto birds mouth) for mosts applications......  there is always the exception.

[dshall]

One final  note,  same house,  no ceiling:

 

 if I raise the a roof plane 2"  over the 4" or 8" wall,  the wall raises 2"

 if I raise the a roof plane 2"  over the 12" or 16" wall,  the wall DOES NOT RAISE

 

inconsistent behavior to be aware of.

 

If I raise all roofs at the same time in 2" increments,  ALL 4 walls will not ALL raise with each successive raise, to get the thicker walls to raise,  a greater change in the roof raise is required....  again inconsistent behavior to be aware of.

[dshall]

I know I know,  TMI.....  I was pretty happy not knowing all this crap.

[lbuttery]

Scott:

 

I was taught that once the roof is built it is independent of the walls

 

this was before auto-build features were added

 

but I'm guessing that with auto-build off walls and roofs are still "independent"

 

Lew

[DRAWZILLA]

I always start out using the Auto build roofs, then turn it off and go from there.

[Kbird1]

Thanks Scott , I was trying to understand this myself ,as I had done it before ,though not with your particular settings , I'll have a bit more of a look at it so I understand what is happening.

I build roofs like Perry , auto then fix the "screw-ups" or weird conditions manually ,reading Lew's Post above, I don't know if that changes things if you do yours all manually ?

Mick.

[Kbird1]

One final  note,  same house,  no ceiling:

 

 if I raise the a roof plane 2"  over the 4" or 8" wall,  the wall raises 2"

 if I raise the a roof plane 2"  over the 12" or 16" wall,  the wall DOES NOT RAISE

 

inconsistent behavior to be aware of.

 

If I raise all roofs at the same time in 2" increments,  ALL 4 walls will not ALL raise with each successive raise, to get the thicker walls to raise,  a greater change in the roof raise is required....  again inconsistent behavior to be aware of.

It's a bit strange Scott , I played with this tonite again and if I AutoBuild the roof over the square house with .6.8.10.12" walls

I don't get these inconsistences , wall plates stay where they should,(109")whether I raise the roof planes individually or, all 4 roof planes together via group select ,so might be a good case for building Auto 1st then Fix if needed, ie the "Perry Method".

I did however have different fascia heights etc when building the roof manually over the same different width walls but did not test if the "Same height Eave " button would fix this inconsistency. Something for a Manual Roofer to check out probably.

M.

[dshall]

That is wierd Mick. I did auto build, you are getting different results than I. So if you raise all 4 roofs 8" via transform replicate, your wall plates do not raise?

[Kbird1]

I use group select > changed the Birdsmouth by 2" per your original experiment.....

 

I just tried it again ,group selected and transform/rep. move 8" on z axis and the original plates stayed as did the ceiling and chief built a short wall above with new plates , so weird yes , if I do the same at 2" it doesn't build the small wall it alters the Birds mouth.

 

Not sure if this is possibly cos of the weird wall arrangement being 6/8/10/12" around the building.

 

M.

 

 

 

[dshall]

I'm so stupid, why didn't I ever post a pic, I was doing it without a ceiling, so sorry.

[Kbird1]

Ahhh okay I wondered about that

Yep it appears that Chief goes back to using the narrowest wall for the height set (109+8") and then gives the other walls a full width Birdsmouth Seat cut ,which varies the plate height and screws up the ceiling lines though the fascia heights appear correct.

M.