Here is my concern: My plan is to add drywall to the underside of the rafters and collar ties. The intention is to have an open room with a high ceiling. However, I am concerned about the placement / integrity of the collar ties. They are placed a little over halfway up the rise of the roof. The rise is about 10', and the ties are centered at about 4.5' below the ridge, about 5.5' above the wall plate. This seems a bit high considering the pitch, etc. I have read that collar ties must be at or below the midpoint of the rise in order to give adequate support, generally speaking.
It is apparent that the ties in my roof were once attached at a lower point on the rafters, but had been raised about 18" from their original location. However, they are nailed and screwed to the rafters very well, and everything seems very solid.
I wish to collect general opinions on whether or not my current roof system is adequate enough to receive a layer of drywall, etc., which may add up to about 3 psf (lbs per square foot) of dead weight to the roof. I'd prefer to go with the heaviest drywall possible (5/8") for increased sound isolation, but realize I may need to comprimise and go with 1/2" or 3/8". This has yet to be determined, depending on the true integrity of the roof, etc.
Of course, I could add new collar ties at a lower point on the rafters and either leave or remove the existing ties, but I wish to keep the ceiling height as high as possible. I am happy with the ceiling height now, but just concerned about structural integrity.
An architect suggested adding runs of cable across the span at a lower point on the rise for added support, but I'd then need to lower the ceiling height considerably to hide the cables, or leave the cables exposed which I do not wish to do. As well, I do not wish to have collar ties running through the inside room.... the goal is to have a flat ceiling with no obstructions in the room.
I'd greatly appreciate any and all ideas, thoughts, and opinions on this subject. I can email a small detailed diagram if anyone is interested.
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