Boarding the Dormer - ceiling to slope

[crispy_wafer]

Boarding out the dormer, I've boarded the ceiling, gearing up to board the slope.

 

Should I cut the boards to go on the slope at an angle at the top to create a flush joint where it meets the ceiling, or can I leave the square edge?  Is there a type of beading available to create a sharp angle?

[Russell griffiths]

No need to angle them,I looked for a trim to go from my vaulted ceilings to the flat area, I did find some, but after asking 3 plasterers to use them they all looked at me like I was insane and said just round the corner off. 
I didn’t like that answer and went on a plasterers forum, they all said the same, round it off. 
 

so we put a tight coat of bonding along that line, then added a fine plaster reinforcement mesh 200mm wide, then another tight smear of bonding over the mesh, all flattened out using a wet brush to feather the edges, the plasterer then skimmed the lot. 
I haven’t even got a hint of a crack anywhere and I’m glad I didn’t go for the straight line as I think I would always look at it to check it’s straight. 

[crispy_wafer]

Ok, assumed having a nice tight straight angle was the go to.  But I think you are onto something actually, I'm bad enough with my straight edge as it is, checking and double checking, and as it's my bedroom I'll be waking up and looking at it every day!

[Nick Laslett]

@crispy_wafer, I think I would do as @Russell griffiths suggests and discuss with your plasterer. 
 

Ours was happy to use corner beads, but every dormer is different. We have a table top roof, so they used mesh and rounded that joint. 
 

 

 

 

We only used plasterboard for the upstairs ceiling, we used Fermacell everywhere else.

Edited March 17 by Nick Laslett