Definition
A lapped zip is a zip insertion in which one side of the seam folds over the teeth to hide them, leaving one visible line of stitching beside the opening.
A lapped zip uses an ordinary zip, not an invisible one. One seam allowance forms a narrow lip that sits against the teeth; the other forms a wider flap, about 1 to 1.5 cm (3/8 to 5/8 in), that covers them, held by a line of topstitching parallel to the opening and squared off at the bottom.
It was the standard skirt and dress closure for decades and is still common in vintage patterns, at the side seams of skirts and trousers, and on fabrics where an invisible zip struggles, such as thick wool or tweed.
How it is done, in brief:
- Sew the seam below the opening and baste the opening closed.
- Press the seam allowances open. On the underlap side, fold the allowance so it extends about 3 mm (1/8 in) beyond the seam line.
- Stitch the zip tape close to that fold with a zipper foot.
- From the right side, topstitch through the overlap and the other tape, then remove the basting.
Allow at least 2 cm (3/4 in) of seam allowance along the opening; if your pattern uses narrower allowances, widen them there when cutting.
Compare with the invisible zip, which hides even the stitching, and the fly front, a lapped zip with an extra facing and shield.