Casey Skirt Sew-Along | Full Derriere Adjustment (FDA) Tutorial


Hello again my dears! While my Pattern Testers were testing the Casey Skirt, a few of the more “hippy” testers suggested an adjustment that could be made to the pattern, to keep the back pleats flat, for those women who need a bit more room in the seat of their skirt. Thanks to their suggestions, I am going to share how to adjust your Casey Skirt Pattern if you need the bottoms equivalent of an FBA, or what I call, a Full Derriere Adjustment.


First, let’s talk about why you might need this adjustment. The Casey Skirt is designed on a slim-hipped base pattern. This works great for some, but others need more room in the back hip area of the skirt. This is different than needing more room in the entire hip area, which requires a completely different adjustment (grading from one waist size to a different hip size) than the one I am showing you today. This adjustment specifically helps those who have the front width of one size, but need the back width of a few sizes up. With that said, let’s begin!


First off, you will want to trace off your Back Pattern piece. You don’t have to include all of the seam allowance lines, etc. But you do want to trace off the Center Back line (the outermost pleat line), and the hip line, as they are crucial for this tutorial.


Take your tracing, and grab the lower side seam/hem corner.


Fold the tracing over on itself so most of the side seam extends past the Center Back line about 1-1/2″. This divides your skirt back into 1/3rd and 2/3rds approximately, to get nice dart placement. This isn’t an exact science, so you may need less than 1-1/2″, or more, depending on your size.


Crease the fold-line you just made.


Unfold your pattern piece and mark your crease line with pencil or marker. You can skip this step, but I always find it helpful to draw in my crease-lines so they are easier to see and cut.


Speaking of cutting, cut apart your pattern along the crease-line you just marked. Slip some paper underneath your pattern.


Making sure to keep the top, hip-line, and hemline parallel, spread the pattern pieces apart, 1/2 the amount of extra room you need in the derriere area. In this example, I was using the waist size of a size 4, but needed the hip measurement of the size 8, a full 2″ bigger. So I spread my pattern apart 1″. Tape your pattern pieces in place on your scrap paper.


Match up your hip-lines with a new line. On this line mark a dot, exactly halfway between the two pattern pieces. From this dot, square up (draw a perpendicular line) 1/2″.


Now we will draw in your dart. Join the upper left hand corner of the gap, with the top of the 1/2″ line you made in the last step. Draw a mirror line to this, joining the 1/2″ line to the upper right hand corner of the gap. Make sure these lines have the same measurement.


And, there you have your dart! Now let’s take a quick look at your hemline and see if it needs to be redrawn.


Re-join the curves of the hemline. If necessary, draw in a new curve, similar to the original so you don’t have any wonky edges. Pro tip! You can use the hemline of the Casey Skirt in a larger size to get the correct hem curve.


And there you have it! Your Casey Skirt’s back pleats will now lie straight, and you have a pattern that fits your body the way it should.

If you are following along with the Casey Skirt Sew-Along, be sure and tag your progress on social media with #caseyskirtsa and tag me @brijeepatterns on Facebook or Instagram.

Any questions?

Was this tutorial helpful?


Brigid E.

Author & Graphic Design: Brigid Everson | Photography: Charlotte Boyer

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