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�, + Framing a cathedral ceiling - Fine Homebuilding Question & Answer Page 1 of 3
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<br /> Framing a cathedral ceiling CODE REQUIREMENT� �
<br /> Q:The plans for a house I am building call for a great room with a cathedral ceiling.The room measures 26 ft.along the eaves walls an in.
<br /> I remove the ceiling joists withoul the ridge sagging or the walls bowing out?
<br /> S.A.Macioce,Pittsburgh,PA
<br /> A: Contributing editor Scott McBnde replies:To avoid a sagging ridge or bowed walls in a cathedral-ceiling structure.first you've got to understand how a lypical roof frame works.
<br /> A plain Flat-ceiling gable is aclually a procession of light trusses,usually spaced 16 in.o.c.Each truss is composed of two opposing rafters and a ceiling joist.The rafters are in
<br /> compression,pushing outward on the eaves walls,and the ceiling joists are in tension,pulling inward on lhe eaves walls.
<br /> As a first option in enlarging the ceiling space,you can move the ceiling joists up the rafters,making them collar ties,as shown in the drawing below.The portion of each rafter that
<br /> extends below the collar tie is actually a cantilever;its stiffness transmits the tension action of the collar tie down to the plate,preventing the walls from bowing.The farther up the
<br /> collar tie is moved,the longer the cantilever of the rafter becomes.Depending on the stiffness of the rafter stock,a point will be reached where the rafter staRs lo bend outward
<br /> below the collar tie.This pushes the walls out and allows the ridge to sag.As a general rule of thumb,when ceiling joists are moved up to become collar ties,they sliould be moved
<br /> up no more than one-third the length of the rafter.
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<br /> The next option you can consider in opening up the ceiling frame is to remove some of the ceiling joists or collar ties while leaving the full complement of raflers in place.Typically,
<br /> this is done by leaving every third col�ar lie and removing the two in between,as shown in the drawing.You still have rafters 16 in.o.c.,so you can easily cover the underside of thE
<br /> roof with drywal�and its outside with plywood.But the spacing of the ties is reduced to 48 in.o.c.,and the flat ceiling is eliminated.The collar ties can be wrapped with drywall,or a
<br /> higher grade of lumber can be used and left exposed.In a frame like this,the remaining collar ties are often doubled up,putting one 2x on each side of the rafter.This balances the
<br /> construction and makes it look beefier.(The channel between the 2xs is a good place for concealed track lighting;light can be bounced off the sloped ceiling down into the room.)
<br /> Bolts are the best fasteners for the rafter/collar-tie connection.If you nail the collar tie to the rafter,use plenty of 16d commons and angle them toward the center of the building;thi
<br /> will cause them to dig in as the rafter pushes out.
<br /> REVtEiN�p for C DE CpfV�pL�q��
<br /> PLAN CHECKED BY C��ATE �-z3- ��-/
<br /> http://www.finehomebuilding.com/how-to/qa/framing-cathedral-ceiling.aspx 7/9/2014
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