ceiling hole (weird Icicles)

[Lighthouse]

I'm trying to design a roof that is flat on top and sloped on bottom, so that it tapers towards the fascia.  Then I want to put skylights in it.  Since there is no way to create a tapered roof that I'm aware of,  I did it with a  PS drawn in elevation to create the taper.  However, when I put the holes for the skylights in plan (holes in the PS), it doesn't work because the PS was drawn in elevation (to get the taper), and not drawn in plan.  So then I tried creating a flat roof on top with an angled ceiling plane below, with skylights on top and holes in the ceiling plane that align with the skylights.  This worked, but the ceiling holes have weird icicles hanging down at the corners which I can't get rid of.   To simplify it, I created a new test plan that just has an angled ceiling plane with a hole in it.  I get the same icicles in the corners.  Does anyone know what causes this?  Here's a pic, test plan is attached.  thanks 

 

hole in ceiling.plan

[Kenoeightspot]

Create a flat roof plane the add a sloped ceiling then place your skylight.

[Lighthouse]

William, you're a genius!  I was making it more complicated by trying to manually create the ceiling hole separately from the skylight.  I didn't realize that a manually created ceiling would understand that it had a roof above with a skylight in it and create the hole automatically.  Thanks much!

[Lighthouse]

1 hour ago, Kenoeightspot said:

Create a flat roof plane the add a sloped ceiling then place your skylight.

 

[Lighthouse]

On second look, I think you have the same problem in the sample you attached.  If you look carefully at the corners of the ceiling plane at the skylight cutout, you will see the "icicles" I referred to

[Kenoeightspot]

Here is the plan, I added a roof with ceiling next to your roof

flat roof sloping ceiling.plan

[Lighthouse]

I took your plan and attempting to modify it to my specs and ran into similar problems.   I'm actually trying to create a 4' deep roof that tapers from 9" to 5" over 4'.  I want openings in the roof (but not actual skylights, they would be flush with the roof frame).  When I changed your skylight to just an opening, the skylight shaft stuck out above the roof surface.  I have tried numerous experiments with varying the thickness of the roof structure and ceiling structure, but they either result in the skylight shaft penetrating the upper roof surface, or the icicles coming off the corners of the ceiling surface below.  I'm getting obsessed!  I've attached your plan with the skylight changed to an opening, but you can just do the same on your plan to see the result.

test 1.plan

[Lighthouse]

It appears that the issue is not related to the roof, just the ceiling plane.  If I take a blank plan, drawing a ceiling plane, and place a hole it it, the ceiling plane hole has a shaft around it equal to the thickness of the ceiling structure (which makes sense).  However, if you attempt to change the thickness of the ceiling structure (in order to reduce the shaft), it's starts to get weird.  It seems like once I reset the ceiling structure to anything below 9" the problems begin. Maybe it is just a software glitch.