Jeans Sew-Along: The Seat Seam and Fly Extension

Today we are preparing for the addition of the zippered fly.  To do this we will add the fly extension and sew the seat seam.  Before we begin, ensure that both jean legs have the zipper and fly notches thoroughly marked.

Now we need to prepare the extension.  You have cut two extensions (mirrored) but we only need one.  Select the extension that matches the left leg (it looks like the photo above).  Apply interfacing if you haven't already and finish the curved edge using your choice of a serger, zig zag stitch or pinking shears.

Lay the extension on the left leg with right sides together.  The top of the fly extension lines up with the top of the jeans.  Pin.

Stitch the extension in place using a 5/8" seam allowance.

Finish the seat seam allowances using a serger, zig zag stitch or pinking shears.  Make sure to finish both the jeans front and extension seam allowances during this step.

Press the seam allowance towards the fly extension (or, in other words, press the fly extension away from the jeans front).

Now the extension has been added, it is time to stitch the seat seam!  We will be stitching from the back up until the fly notch (the lower notch).  Prepare for this by placing the legs with right sides together.  I like to keep my pant legs right sides out and simply place them together as they will look when they are finished (see the photo below).  Alternatively, you could turn one leg inside out and place the other pant leg inside of it so that right sides are together and pin the seam that way...whichever method makes more sense to you!  I like to skip the step of turning a leg inside out.

Either way, make sure you line up the yoke seams and inseams!

Stitch the seam using a 5/8" seam allowance.  Backstitch thoroughly when you get to the fly notch.

Check that the inseams and yoke are indeed lined up.  If they are slightly off you can just stitch rip the area around the intersection and ease the two pieces together so they match perfectly.  If they are quite a bit off, you may need to re-do the seam!

Once you're happy with the results, stitch the seat seam again to make it extra strong.

In order to allow the seam allowances to be stitched to the left front (this topstitching is completed in a later step), it is necessary to clip into the right front seam allowance at the fly notch as pictured below:

Fold the fly extension to the wrong side of the jeans and press.  To keep the extension crisply in place, edgestitch along the extension seam until the zipper placement notch (the upper notch).

Finish the fly preparations by pressing the right fly seam allowance under only 1/2" (not the full 5/8".  This allows you to slightly offset the zipper so it does not peek out from the fly opening.

Our preparations are now complete and we are ready to create the fly during the next sew-along post!  Don't worry, we'll take it step by step and by the time it is complete you will be very proud of your creation!