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Step Lap Rafter Seat on Timber Frame Plate

Step Lap Rafter Seat

This is a view of a step lap rafter seat on an 8×8 plate. The joint gets its name as the rafter laps over the plate to create an overhang for shedding rain water off the roof away from the side of the building. And as the notch looks like a stair step.

The amount that the rafter tail laps over the plate in this drawing is 2″. The step is usually set back the same amount.

I have shown what the step lap rafter seat looks like at the end of the plate and two feet in the center from the end.

In this drawing, the rafter is a 4×6. And it is at a 12/12 roof pitch. The rafter tail will be shown in another detail.

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4 thoughts on “Step Lap Rafter Seat on Timber Frame Plate”

  1. Hi Jim,

    Is there a minimum pitch angle below which the step lap rafter seat won’t work? I am attempting a basic frame with mono pitch roof with a 4:12 pitch, 7×6 plates and 5×4 rafters and am struggling with the rafter seat joinery, trying to avoid the birds mouth!
    Kind regards

    Steve Rogers

  2. I’m not sure. But you can over hang the plate with a crow’s foot joint in stead of a bird’s mouth. Just make sure that the fasteners are strong enough.

  3. Nikki Collins

    does the rafter become attached to plate with fastening or does it float
    what stops it from detaching?

  4. Katrina Williams

    We generally recommend attaching the rafters to the plate with structural screws

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