skylight framing

[SHCanada2]

any idea why it frames like this.

 

nothing is holding up the rafters

 

 

even if i make it 22.5x48, it still does it

 

and if i move the skylight down, it does this

[rgardner]

28 minutes ago, SHCanada2 said:

any idea why it frames like this.

 

nothing is holding up the rafters

 

 

even if i make it 22.5x48, it still does it

 

and if i move the skylight down, it does this

Haven’t seen this.  Maybe post the plan.

[SHCanada2]

attached

172 Carringham Way NE2.plan

[Doug_N]

The program had a stroke when trying to calculate trusses for a 2" pitch roof with no depth and no flat ceiling over the room. 

 

.   If you change to conventional framing (rafters,) then the framing will generate.  If you make the truss have energy heels and include a flat ceiling in the room then framing will generate properly.  The image below is with trusses    CA did not generate an unable to generate trusses message, but if you look at a section, it becomes obvious that CA is struggling with a space that is too small in section for trusses to work.

 

[SHCanada2]

thanks,

 

I didnt think it was trusses because when i clicked on the member in cross section, it said it was a rafter:

 

but the roof dbx shows it as trusses

 

any idea why it would show rafters? you can even see the rafter tail generated in the section

[Doug_N]

1 minute ago, SHCanada2 said:

thanks,

 

thanks I didnt think it was trusses because when i clicked on the member in cross section, it said it was a rafter:

 

but the roof dbx shows it as trusses

 

any idea why it would show rafters? you can even see the rafter tail generated in the section

That is what you asked it to do.  So it attempted to follow your directions but failed.  Most time CA will post a warning, but my guess is that they didn't program an adequate error trapping routine for this case.  I suggest you send the file to CA support so that they can diagnose it.  More than likely nothing will be done about patching the current version because this is not a critical error, and a user can work around this fairly easily.  At least in my opinion.

[SHCanada2]

7 minutes ago, Doug_N said:

That is what you asked it to do.

i'm confused now. Where did i tell it to do rafters? the roof dbx shows trusses

 

[Doug_N]

1 minute ago, SHCanada2 said:

i'm confused now. Where did i tell it to do rafters? the roof dbx shows trusses

 

No, you told it to do trusses, and it tried to do that.  When CA can't do trusses it fills in spaces with rafters, and that is when the system broke down because it didn't do that completely either. 

[mLongChief]

13 minutes ago, SHCanada2 said:

i'm confused now. Where did i tell it to do rafters? the roof dbx shows trusses

 

Just now, Doug_N said:

No, you told it to do trusses, and it tried to do that.  When CA can't do trusses it fills in spaces with rafters, and that is when the system broke down because it didn't do that completely either. 

 

Just to expand on this, the automatic truss placement will only be able to place trusses in areas that have both a roof plane and ceiling plane present, as trusses need both in order to generate properly. In this case, the room is set to have no flat ceiling within itself and no custom ceiling is present, so the only structural space we have to work with is roof structure layer, which is only enough to fit rafters. If you want to force trusses in that space, you can manually place some, but that might not be ideal as they'll be exposed due to the lack of a proper ceiling plane.

 

Ideally, if the automatic trusses fail to build, we should fall back on rafter framing. Changing the roof plane to build with rafters like Doug suggested, it'll build the roof rafters properly, but we should automatically fall back to this better. I'd send the plan in so we can log and address cases like this better.

[SHCanada2]

58 minutes ago, mLongChief said:

Ideally, if the automatic trusses fail to build, we should fall back on rafter framing. Changing the roof plane to build with rafters like Doug suggested, it'll build the roof rafters properly, but we should automatically fall back to this better

 

got it, so in this case, when it fell back to doing rafters, it did not do it properly.

 

I will send in a ticket.

 

And for context in case someone is asking why not change the defaults to rafters, the use case is the main house has trusses, but this sunroom addition would have rafters. So the plan defaults would likely be trusses

 

 

[DRAWZILLA]

you can adjust each roof plane individually to have trusses or rafters. Combo is easy that way.