How to Sew A Fly Zipper

Aug 07 2021 1 Comment Tags: Sewing tips

Before you start -  make sure that you've read the instructions of the pattern that you're using first & completed all the relevant steps preceding installing the fly zip. I'm using the Megan Nielson Ash jeans here but this method can be used for any garment that requires a fly zip that doesn't have a grown on fly which is integrated on to the pattern piece, such as the Tilly & the Buttons Ness Skirt. Also ensure that all your notches are clearly marked from the pattern.  Read on to the end for some more tips & pattern ideas.

You will need both Front pattern pieces of your garment, the Fly & the Fly Extension (sometimes referred to as the shield), along with the correct sized zip (8" in this case) & a zipper foot.

I've made the fly extension in a bright fabric to make it easier to see which pattern piece I'm referring to.

  1. Start by sewing the fly extension - Right sides together, sew the bottom curved seam only, then turn through & press. (Check your instructions for the seam allowance, mine was 1/4")
  2. Finish the raw edges of the front crotch, the raw edge of your Fly Extension & the outer curved edge of the Fly (the yellow dots denote the notches, so that you can see them clearly).
  3. Take your zip & place it on top of the fly extension, the left side of the zip should line up with the left side of the extension (the part the you have just overlocked). Line up the notch of your extension with the bottom of the zipper stop & sew at 1/4" using your zipper foot.
  4. With the Right Front facing up place the Fly Extension on top with the zip sandwiched in between, aligning the straight edges & notches & sew to the bottom of the Fly Extension at 1/4"  seam allowance using a zipper foot.  
  5. Clip into the seam allowance just below the Fly extension
  6. Flip out the Fly extension, so that the Right Front piece, the zip & the Fly Extension are all facing up, press & top stitch, (using a top stitch thread).
  7. Take the Fly piece & place on top of the Left front leg Right sides together, straight edges & notches aligned & sew at normal seam allowance (5/8" for this pattern)
  8. Grade the Fly seam by half & press the Fly to the wrong side & top stitch, around 1/16" away from the pressed edge, using top stitch thread.
  9. Take your 2 Front pieces & baste them Right sides together at the crotch seam finishing at the bottom of the fly. Again using whatever seam allowance your pattern states, mine is 5/8" (you're going to be unpicking this later but it helps to keep everything in place for the next stage, so use a nice long stitch)
  10. Flip over to the front & you should find that left front sits nicely over the Right front, covering the zip & the topstitching on the Right front. Put a pin in the top to secure the position. (If you have notches for centre seams the folded left front should align with the notch for the right centre seam)
  11. Flip back over to the wrong side & pin the Fly extension onto the Right front out of the way to reveal the zip, if you've done everything right the zip should be upside down, as you look at it & right sides together with the fly.
  12. Pin the zip to the FLY only, make sure you're not pinning to the Front of the jeans & sew. Using a zipper foot, sew 1 row of stitching close to the edge of the zip tape & then another row close to the teeth.
  13. Unpick the basting stitches around the crotch area & pin the Fly extension & Right crotch out of the way using pins.
  14. You're going to topstitch the FLY to the Front of the Left side of your jeans. You can baste the Fly down to give you a guide or pin from the wrong side & draw with chalk using your pattern piece as a guide, as I've done. Topstitch 2 even rows up to the centre around 1/4" apart
  15. Sew the centre crotch seams back together at 5/8" using your normal stitch length.
  16. Flip the SHIELD into position behind the zip & add a bar tack to secure the Zip Fly on the inner curve of the topstitching. (Your machine may have a setting for a bar tack or you can set it to a zig-zag stitch & make the stitch length & width shorter, mine was set around 1.5 length & 0.2 width - just play around & test before stitching your jeans). 


A few extra Tips & Tricks

  • If your foot is struggling to pass the zipper pull, stop sewing with your needle in the down position. Lift your presser foot & pull the zip either up or down away from where you're sewing.(Don't forget to put the zipper foot back in the down position before restarting to sew!)
  • When using Top Stitch Thread, rather than sewing backwards & forwards to secure your stitches, consider pulling the thread through to the back & tying off.
  • Don't use top stitch thread in the bobbin, it can cause the stitches to bunch up underneath (nest).
  • Make sure you use the correct size jeans zip to prevent having to trim through the metal teeth. Jeans zips have a locking mechanism to prevent them randomly sliding down too!
  • Don't be tempted to miss out the bar tacks as these keep the fly shield in place & stop it flapping around, which in turn helps to prevent your bits getting stuck in the zip - you've been warned!

Here's some patterns to try out your new skills:

Cashmerette Ames jeans

Cashmerette Ellis Skirt

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  • Very clear instructions, feel that
    I could give it a try. Thank youX

    Jean on

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