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Re: Finishing a curved ceiling - need some advice

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Dennis ---

You might consider pre-loading the roof beams during the re-installation
work.  When released, that will give the new finish some residual
compression.  Just a thought.....  

Russ Nester
On Wed, 13 Oct 1999 15:26:59 EDT Seaintonln(--nospam--at) writes:
>I was the EOR of a custom home here in the desert. The roof was 
>designed as a 
>double radius GLB structure that looks something like the letter S on 
>The great room is adjacent to a split-level. The downward curve of the 
>occurs in the Great Room while the Upward radius reaches it's peak 
>above the 
>split level.
>Structurally, the roof is performing as expected, however, the 
>aspects of the roof have caused a few problems in cracking of the 
>ceiling attached to the bottom of the GLB framing.
>The roof is lightly loaded, but is still very flexible. The top of the 
>is built up using expanded polyurathane to create slope and drainage - 
>is a very lightweight material.
>The GLB's are deflecting under dead load (no assumed live load is 
>and I would expect the deflection to occur until a point of 
>equalibrium due 
>to the dead load weight has been reached. 
>I believe that the contractor installed the ceiling finish incorrectly 
>for a 
>radius roof. He used one layer of 1/2" Gypsum to form the ceiling. The 
>is (from my memory) around 45 to 55 feet - so the curvature is not 
>There is continued cracking both at the seams of the drywall and in 
>the field 
>of the drywall. 
>The owner has asked me to help him resolve the problem. Here are some 
>of the 
>suggestions I had to offer:
>1. Remove and replace the ceiling to allow the radius to be formed 
>from two 
>layers of 1/4" gypsum board which is intended to allow the layers some 
>for movement. I believe that the USG book covers special conditions 
>curved surfaces are covered.
>2. Remove and replace using metal "Hat" channels between the joists 
>and beams 
>and the Gypsum to allow for flexibility in the ceiling without 
>of cracks in the gypsum.
>3. I also suggested that the owner might consider finishing the 
>ceiling in an 
>elastomeric finish which would stretch with the movement in the roof.
>4. I have heard that the ceiling should have been finished in lath and 
>plaster which would have been more forgiving for movement and creep as 
>lath would allow some play in between the materials.
>Do any of you have some specific suggestions as to how this problem 
>can be 
>corrected. I don't feel that this is a structural issue since the roof 
>properly designed and is within the allowable code limits. However, 
>this does 
>not help the client whose frustration level is high and can't seem to 
>the problem.
>Please feel free to address me privately at SEConsltnt(--nospam--at) if you 
>do not 
>feel that this is appropriate for the list.
>Thank you,
>Dennis S. Wish PE

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