A lapped zipper is a useful middle course between an exposed zipper and an invisible one. The zipper teeth remain accessible and the installation is reasonably forgiving, yet a narrow flap of garment fabric covers most of the closure. It suits skirts, dresses, trousers, and lightly structured jackets, especially where a traditional finish feels more at home than a nearly invisible zip.
The calmness of a lapped zipper comes from its order of work. The seam is first assembled and basted closed. The zipper is then placed behind that seam, one side at a time, before the upper fabric layer is folded across and topstitched. Trying to judge the overlap without these marks usually leads to an uneven lap or a line that wanders.
This method describes a centred back or side opening with a conventional zipper. Check the pattern before beginning: some designs include a waistband, facing, placket, or seam allowance arrangement that should be completed in a particular order.
What you will need
- A conventional zipper in a suitable length for the opening
- Garment fabric, cut and seam allowances marked
- Lightweight fusible interfacing, if the opening edge is soft, loosely woven, or prone to stretching
- Matching thread
- Tailor’s chalk or a removable marking tool
- Pins or fabric clips
- A hand-sewing needle and thread for basting
- A zipper foot for the sewing machine
- Seam ripper, iron, and pressing cloth where needed
Choose a zipper that is a little longer than the opening if that is what is readily available; the excess can often sit above the garment’s upper seam line or below the finished opening, depending on the construction. The important point is that the slider has enough room to move and that the zipper stop lies below the point where the opening must end.
A regular nylon-coil or polyester zipper is often easy to sew and comfortable in lightweight garments. A metal zipper can give a firmer, more period character, but avoid stitching across its teeth and take extra care at the lower stop.
Prepare the opening before the zipper goes near it
Stability matters more than speed. If the opening edges are on a bias, curved, or cut from a fabric that frays and stretches readily, fuse a narrow strip of lightweight interfacing to the wrong side of each seam allowance. Keep it inside the seam allowance where possible so it does not alter the hand of the visible fabric.
Finish the raw seam allowances if the garment fabric requires it. For a lined garment, the lining may be handled separately later, but the outer garment opening should still be stable and cleanly pressed.
With right sides together, mark the zipper opening on the seam line. Mark the top seam line too, particularly if a waistband or facing will later cover the upper end. A small horizontal mark at the base of the zipper opening is valuable: it is the point where temporary basting ends and the permanent seam begins.
Sew the seam below this mark with the normal seam allowance and a secure backstitch at the top of that permanent seam. Above it, baste the opening closed with a long machine stitch or hand basting. Press the full seam open from the wrong side.
Photo by J Williams on Unsplash.
The closed, pressed seam now acts as a guide. It keeps both sides of the opening aligned while the zipper is applied, and it gives you a clear line to remove only after the zipper has been secured.
How to sew a lapped zipper
The side that forms the overlap is traditionally often placed on the left when the garment is worn, but pattern instructions and garment conventions may differ. What matters is deciding which side will lie on top before sewing.
1. Position the zipper behind the basted seam
Lay the garment wrong side up with the pressed seam allowances open. Close the zipper and place it face down beneath the basted seam, so the zipper teeth sit directly under the seam line.
Set the top zipper stop below the garment’s top seam allowance or at the position specified by the pattern. The lower zipper stop should sit just above the point where the permanent seam begins. Pin or hand-baste the zipper tape in place through one seam allowance only at first.
There is no need to pull the zipper tape tight. Let it lie flat against the fabric. A zipper that is stretched while being sewn can later draw the garment into ripples.
2. Stitch the underlap side close to the teeth
Choose the seam allowance that will remain underneath the finished overlap. From the wrong side, stitch that seam allowance to the zipper tape, keeping the stitching fairly close to the teeth without catching them.
A zipper foot lets the needle travel near the raised teeth. Stop with the needle down, raise the presser foot, and move the slider out of the way when necessary. It is usually easier to begin with the zipper partly open, then close it as you approach the lower stop.
Keep this first line of stitching within the seam allowance. It should not show on the right side of the garment.
3. Form and press the overlap
Turn the garment right side up. The other seam allowance will become the visible lap. Fold its pressed edge over the zipper so it covers the teeth and overlaps the first stitched side evenly.
A lap of about 1 to 1.5 cm is common, though the exact width should suit the garment and pattern. On a small scale, an overly broad lap can look heavy; on a sturdy skirt or trouser opening, a slightly wider lap may lie well.
Measure the fold from the seam line at several points rather than trusting the eye alone. Pin it flat, keeping pins away from the path of the zipper teeth. Press the fold gently, using a pressing cloth for delicate or heat-sensitive fibres.
Photo by Roman Spiridonov on Unsplash.
4. Mark the topstitching line
The visible stitching normally begins at the top of the opening, travels down the overlap close to its folded edge, then curves or angles across near the lower zipper stop to secure the lap. This lower turn is what holds the flap in place and prevents it from pulling open during wear.
Use tailor’s chalk to mark the line before sewing. Keep it parallel to the folded edge. At the bottom, make a gentle curve or a short diagonal toward the seam, stopping above the zipper’s lower metal or plastic stop. A sharply squared corner can work on tailored garments, but a gentle curve is often easier to sew smoothly.
Before stitching, check the zipper from the inside. The underlap side should be lying flat, clear of the teeth, and free from pins in the zipper path.
5. Topstitch the lap from the right side
Using a medium stitch length, stitch along the marked line from the top downward. Sew steadily rather than quickly, keeping the folded edge at a consistent distance from the zipper foot.
At the lower turn, shorten your speed, not necessarily the stitch length. Pivot gradually around a curve, or take one or two small adjustment stitches through an angled turn. Finish with a secure backstitch where the line reaches the seam area.
Avoid stitching across the zipper teeth or the lower stop. If the stop is close to your intended turning point, end the line a little higher rather than forcing the needle through a hard obstruction.
6. Open the basted seam
Turn the garment wrong side up and carefully unpick the basting along the opening. Begin near the top and work downward, removing only the long temporary stitches. Leave the permanent seam below the zipper intact.
Open and close the zipper several times. The slider should move freely, the lap should cover the teeth without pulling, and the lower end should remain neatly anchored.
Photo by Tomas Sobek on Unsplash.
Finish the upper edge neatly
The top of a lapped zipper is usually enclosed by the next stage of construction: a waistband, facing, collar stand, or lining edge. Complete that layer only after checking that the zipper closes easily and that the two upper edges meet at the proper level.
Where a facing meets the zipper, keep the zipper tape clear of unnecessary bulk. Trim only where the pattern permits, grade thick seam allowances if needed, and hand-stitch a small section of facing to the zipper tape when a machine line would be awkward or visible. A few discreet hand stitches can hold an inner edge in place without flattening the outer lap.
Press the finished opening from the wrong side first, then lightly from the right side over a pressing cloth. Do not press directly over plastic teeth with a hot iron.
Common difficulties and their remedies
The lap is wider at one end
This usually begins before topstitching. The fold was not measured consistently, or the zipper shifted while the first side was sewn. Unpick the visible topstitching, re-press the fold, and mark its distance from the seam at top, middle, and bottom before trying again. Basting the fold by hand can be more reliable than using many pins.
Ripples appear beside the zipper
Rippling often comes from tension between the zipper tape and the garment fabric. Check that the tape was not stretched during sewing and that the fabric was not pushed or pulled beneath the presser foot. On light or soft fabric, stabilize the opening with lightweight interfacing. A test on scraps can help you settle machine tension and stitch length before working on the garment.
The zipper teeth catch in the flap
The overlap may be too deep, the underlap may have shifted toward the teeth, or loose thread ends may be in the way. Open the zipper and inspect from the wrong side. If fabric is caught, release the nearest stitches, smooth the layer away from the teeth, and resew only the affected section. Do not force the slider; it can damage delicate fabric or bend the zipper.
The lower end of the lap pulls open
The topstitching turn at the bottom is too high, too short, or not anchored into the seam area. Add a short line of stitching that reaches toward the seam below the zipper stop, keeping well clear of the teeth. The lap needs this small anchor to remain closed in use.
The top edges do not meet evenly
This is usually a placement issue rather than a zipper issue. Check the original top seam line, the location of the zipper stop, and whether one side was pulled upward during sewing. It may be necessary to release and reposition the upper few centimetres of zipper tape before the waistband or facing is attached.
A few habits that make the method easier
Press after each structural step: after sewing the seam, after opening the seam allowances, after folding the lap, and after final stitching. Pressing establishes the shape before stitching has to hold it.
Baste when the fabric is slippery, bulky, checked, striped, or especially precious. Hand basting takes a little longer at the table, but it is easier to remove than a misplaced machine seam and gives the layers time to settle accurately.
Finally, let the zipper remain a working mechanism rather than something to be hidden at all costs. A lapped zipper is not meant to disappear completely. Its virtue is that the closure is protected by fabric, straightforward to use, and neatly integrated into the garment’s seam.