Sewing fly with zipper #Z01

1. This is required:

Pattern pieces made from shell fabric:

• Front pieces (VH) – 1 pair
• Fly facing (ZB) – 1 x
• Fly underlap (ZU) – 1 x

Pattern pieces from interlining:

• Fly facing (EZB) – 1 x
• Fly underlap (EZU) – 1 x

Paper pattern pieces:

• Front (VH)
• Template for the fly stitching (P-SZ)

Tools and materials:

• 1 zipper (see instrucion or at front pattern piece for required length)
• Pins and/or clips
• Hand shears
• Tailor’s chalk or marking pen
• Ruler

2. Iron on interlining

I start by ironing the interlining onto the wrong side of the slit pieces.

3. Produce fly underlap

I then fold the bottom of the slit in half lengthwise, right sides together, and sew the bottom edge (this is the side where the side notch are located) with a 10 mm seam width. Then I turn the piece over and press it in half from the outside.

4. Sew on the left fly facing

Now I overlock the front edge of the left front piece with the fly facing. First, I trim the front edge at the center front by 7 mm. This cutting line is marked in the pattern so that you can use it as a guide.

I now place the left fly facing from the top flush right to right on this edge, pin it in place and mark the end of the slot at the notch mark. Until then, I topstitch the pieces together with a straight stitch at a seam width of 10 mm. The slit end is secured with a forward and backward stitch.

At the level of the notch at the slit end, I cut the seam allowances right up to the seam. Before turning the edge, you can iron over the seam allowance or topstitch it down with a 2 mm gap on the facing side.

I then turn the fly facing inwards at the seam and iron it in place. I lay the lower cut edge of the facing to the cut edge of the front trousers. Depending on the design, the slit can also be topstitched through and through at the front edge, in which case you can skip the topstitching beforehand.

5. Overlocking the cut edges

I now finish the back raw edge of the fly facing, the crotch seams of both front pieces, the front edge of the left front piece and the back edge of the pressed slit underlap. I use my overlock machine for this.

6. Sew on zipper on the right side

The measurement of the required zipper length is noted on the pattern of the front pattern piece or/ and in the instruction. However, it can also be determined by measuring and corresponds to the length at the center front from the notch to the top edge minus 15 mm. I place the zipper right sides together (i.e. with the slider on the right side of the fabric) on the right front piece. Then I mark 8 mm from the front cutting edge and 15 mm from the top edge. I place the zipper tape at this marking and topstitch it on close to the edge.

The zipper is now folded over so that the right side is visible. Then I topstitch the seam narrow-edged on the front piece.

7. Connect the front pieces

Now I join the two front pieces together. To do this, I lay them right sides together. I sew the crotch seam exactly to the slit end with a seam width of 10 mm.

I then stretch the seam allowance in the curve by pressing. Caution – the seam itself should not be stretched so much.

8. Stitch the zipper to the left facing

I now draw the center front 7 mm parallel to the zipper on the right front piece.

I place the left front edge (where the fly facing was attached) on this line and pin it in place. Both front pieces are placed with the right side of the fabric facing up.

Then I turn the front pieces to the wrong side and pin the zipper to the facing. It is helpful to place a hand measure or ruler under the slit facing to prevent the front piece from getting stuck.

9. Fly top stiching

I place the fly template on the left front piece and draw the course of the slit.

I then pin the fly facing and front piece together.

There are many options for designing the fly and the short inseam. I have compiled a few examples here. You can single or double topstitch the slit, as well as the short crotch seam below the slit, which can also be left unstitched. You can work with a cross or lengthwise bartack at the end of the slit. However, this is only done after the underlap has been attached.

10. Connect fly underlap

From the inside, I place the slit underlap over the slit facing. I pin the serged long edge to the seam allowance of the right front piece and then sew it in place.

On the opposite side of the break, I join the fly bottom and fly facing with a short seam or bartack.

11. Bartack at fly

As described above, you can secure the end of the slit with a bartack. In this example, I have worked with a narrow zig-zag stitch with a stitch width of 1.5 mm and a stitch length of 0.4 mm. I first tried out the stitch on a test piece before applying it to the trousers.

12. Finished fly

And this is what the finished fly looks like.

Below you will find the link to the next step:

• Sew seat seam and leg seams #BE01

If you’re not quite ready yet and perhaps want to start at the beginning, you’ll find some links here:

• Preparing the pattern for cutting
• Cutting fabrics and materials

• Sew waist darts of pants #AB01