Someone on BurdaStyle asked for online, printable instructions for inserting a fly front zip, so I have written some. You can use these instructions even if your pattern isn’t designed to have a fly front zip. If it has a waistband, however, you will have to draft a new one or use some other method for finishing the waistline.
First , get your front pattern piece and add a strip the length you want your fly front to be (up to 8ins (20.5cm) and no less than 5ins 12.5cm)) and 1 3/8 inches (3.5cm) wide. Attach it to the centre front of your pattern. (I made mine too narrow, as I later found out! Mine was also too short for comfort, but I only had a 4 inch zip handy — thrifted from my brother’s old jeans.)
Cut your fabric and sew the front crotch seam (if it is in trousers; sew the centre front seam if it is in a skirt) up to the end of the fly extensions. Backstitch to secure, and baste the rest of the way. Press to set the stitches, then press the seam open. You will find the crotch seam a lot easier to press open if you have a tailor’s ham, but if like me you don’t have one yet, fold up some excess fabric into a similar shape and have a go with that.
Place the zip face down lined up the basted seam. Pin it along the left tape to the extension only. Then using a zipper foot, stitch the zip to the extension, very close to the teeth.
Pick up the unstitched side of the zip and let everything else drop to the zip’s right (see photo –>). Stitch close to the zip teeth through the three thicknesses (i.e. the folded extension + the zip tape).
Now flip the zip onto the other extension and stitch the outer zip tape to the extension only.
Baste the shape of the topstitching on the RS of the garment. It doesn’t matter if you don’t catch the zip in the stitching, just as long as it goes beyond the zip, because the zip is already secured to the extension. Stitch on the RS, being careful to keep everything where it should be underneath, and not getting stitched into wrong places.
Now to make the zip guard, which is considered by some (but not me) to be optional. Cut a rectangle of fabric as long as the fly + 1/2 inch (1.5cm) and twice as wide + 1 1/4inches (3cm). Fold it in half lengthwise, press, then overlock the raw edges. I don’t have an overlocker (serger) so I used one of the stitches on my sewing machine.
Pin it to the garment through to the RS if you must, though ideally to just the extension. Baste. Stitch. If you are sewing to the garment fabric, do so from the RS, holding back the fly front, and sewing near the zip teeth so that the stitching won’t show when you wear the garment.
If your machine doesn’t have a bar tack or you simply don’t like them, here is a way to finish your zip guard invisibly from the inside and stop it from flapping about (I just invented this bit on Sunday). Stitch across the lower corner of the guard, zip and extension, being careful not to get the metal part of the zip or you will break your needle.
Now you can attach your waistband or facing and you’re done.
Thanks to Sandra Betzina whose free online video of making a fly front, and brilliant book (Power Sewing, Taunton Press) taught me this method. You can also find a similar method in SewStylish magazine (the jacket issue from 2010).