Step 1: Build Pony Walls

Build a 24" high pony wall (tall) 18" away from the windows. Anchor it to the floor with tapcons.

Build a 4" pony wall (short) on top of the existing window ledge, both being at the same height.

Step 2: Install Joists

Install 2x4 horizontal joists from the outside pony wall (tall) to the inside pony wall (short). Put 3/4" plywood on the top side as the seat and 3/4" plywood on the vertical face of the tall pony wall to form the bottom bench part of the seat.

Step 3: Make the Vertical Studs

Cut 1x6 pine to lengths of 18" and taper them from 5-1/2" to1/2". These will be the vertical studs of the back rest (Images 1 and 2).

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    Image 1

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    Image 2

Step 4: Attach the Plates to the Studs

Cut the top and bottom plates made of 1x6 (bottom) and 1x4 (top), and lay them out at 16" on center (Image 1).

Nail the plates to the studs to form the back rest and then install 3/4" plywood on the face (the part your back rests on) (Image 2).

Before installing it on top of the bottom part of the bench, install 1/4" plywood on the face that looks at the street (Image 3).

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    Image 1

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    Image 2

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    Image 3

Step 5: Finish the Bench

Now that the bench is nailed together it is almost complete. Attach it back to the base and nail 1/4" plywood to the face of the back rest (Image 1).

Add 3/4" wood trim cut to fit outside using a nail gun.

Sand the bench down and paint it (Image 2).

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    Image 1

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    Image 2