They function as diaphragms transmitting lateral wind and seismic loading through the walls to the foundation.
Roof trusses on cmu wall.
In older houses with masonry walls it is common to find a 2x8 lumber plate that is bolted or strapped flat like a plate to the top of the masonry wall.
Floor and roof systems for use with loadbearing structural concrete masonry walls serve three primary functions.
70 mm deep notch is cut into the tops of the concrete masonry webs to allow placement of reinforcement that is continuous with the bond beam reinforcement in the side walls.
The ledger is needed to properly attach the perpendicular roof trusses to the top of the structure.
Connecting a roof system to a concrete masonry wall is similar to connecting a floor system to a concrete masonry foundation wall in that most roof systems bear directly on the walls below.
We always spec and typically see from all truss suppliers a metal plate shop applied on the heel of the truss to provide a moisture barrier between the concrete cmu wall and the wood truss.
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Simpson also makes some plates that can be applied in the field prior to erecting the truss.
A ledger is a horizontal board that is attached to the top of the the wall.
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The girder which by definition supports the inboard end of other framing members can be anywhere from 3 to 11 feet back from the corner.
The trusses or rafters are then connected to this plate.
And they act to support the walls from out of plane loads.
For hip roofs the code specifies that hip and girder rafters or trusses be connected to exterior wall plates.
Walls that are constructed of concrete block that need to be covered with a roof will require the use of a ledger.
Cmu wall to engineered roof truss.
Roof trusses attach to a ledger that is on top of a block wall.
In older homes the connection may be made using 2 or 6 16d nails in a toe nail configuration.
This is standard here in florida.
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They transmit the vertical dead load and live load to the bearing walls.