I am sure that it is something many people already know, but for me I am not routinely inserting zippers into coats, but when you need to do it, you figure it out and get on with it. This sample represents a coat with a centered zipper, an offset facing, and has a Peter Pan collar. It was also quilted, but that is neither her nor there really, just an added layer!
Step one. My pattern is Nett so all the lines are sewing lines. I have my centre front stitched through the quilting and the backing. Press the seam allowances of the CF back to give it a light crease.
Measure from the centre of the zipper teeth to the edge of the zipper tape. That is 1.5 cm by my ruler.
Mark a line on the CF body seam allowance 1.5 cm away from the CF.
This is a guideline for sewing the zipper in. lay the edge of the zipper tape against the drawn line. Stitch the zipper in approximately .5 mm in from the edge of the tape.
Fold the CF edge back on the crease you ironed in. Check to see that the teeth are in a good position. The stitch line is 1 cm away from the CF line.
Next the facing. The next stitching line needs to be marked 1 cm from the CF. Mark a line 1 cm inward from the CF on your facing. This line will be sewn to the previous line of stitching you just created.
You can work it out so you have a line to visually run the edge of the zipper tape against or you can just pin the facing in place and stitch line to line.
The facing seam and the previous stitch line for the zipper are right on top of each other.
Done? Now you will fold back the CF of the body again and see that on the inside, the facing is now set back 1 cm back from the CF edge.
Nice! If you have a stand collar where all the seam allowances will live up inside the collar you can go ahead and catch all the CF layers down by topstitching, or if you are careful, and things look fab, stitch either just beside the facing seam through to teh fronts, or edgestitch the facing edge from the inside.
If you have a collar such as I do- a peter pan style, one that requires the seam allowances of the neckline to be opened, then you must wait until the collar is installed before topstitching the CF.
This type of garment has a fabric facing around the whole neckline. The only place the facing and body are attached at this point is the CF zipper insertion.
Bag out/ prepare your collar as usual.
Open up the front body and facing at the CF so they are flat. Match the CF seam of the under-collar to the CF of the body at the neck. Pin or baste it all around the neck. Stitch*. (*it just may make it easier to have one section already stitched while you pin and prep the top collar/facing neckline side). Pin or baste the top collar all around the neck line of the facing, pushing the seam allowances of facing/zipper seam away from the CF. Stitch.
As I said you can do this all in one go it you wish.
Here you can see what happens at the CF area.
Trim, clip and press the seam allowances of the neckline open, on the body and the facing.
Press and whack it with a hammer if it needs encouragement!
Turn right sides out and check the placement of everything.
Go back inside the facing at the neck and hand stitch or machine the opened neckline seam allowances together face to face.
I think you are done.
Topstitch as desired.
One advantage to this is that all the seam allowances are not all concentrated at the CF which can get quite bulky.