A swayback adjustment removes the horizontal folds of fabric that pool just above the back waist on a bodice, dress, skirt or trousers. The cause is a back that is shorter at the center than the pattern allows for, usually because the lower back curves in strongly, and the fix is to take a horizontal wedge out of the back piece at the waist: 1 to 2.5 cm (3/8 to 1 in) deep at the center back, tapering to nothing at the side seam, then redraw the center back line straight. The front is not touched.
How do you recognize a swayback problem?
Stand sideways to a mirror in a toile or a close-fitting dress and look at the lower back:
- Horizontal folds across the back, just above the waist, that stay when you stand straight. The fabric has nowhere to go and collapses into one or two pleats.
- A waist seam that dips at the center back when it should be level, or a skirt waistband that sits lower at the back than at the sides.
- The back hem of a skirt or dress rises at the center, and the side seams swing toward the back below the waist.
- The center back seam of trousers folds under the waistband and the back pockets droop.
The folds are horizontal, which is the key. Diagonal lines pointing at the seat or the hips mean something else, usually a full seat or hip, and the post on how to read drag lines separates the two. A swayback pool also often comes with a prominent seat or a forward tilt of the pelvis, and the two fixes are done together: the seat needs length and width below the waist, and the swayback removes length above it.
Is it really swayback, or is the bodice too long?
A bodice that is too long everywhere folds all the way round the waist, front and back, and the fix is to shorten the bodice evenly across the whole piece. Swayback folds are at the back only, and the front waist sits where it should. A quick check: lift the back of the bodice at the waist seam until the folds vanish, then look at the front. If the front has not moved and the side seams are still vertical, it is swayback. If you had to lift the front as well, shorten the whole bodice first and reassess.
How much do you remove?
On a toile, pin a horizontal tuck across the back at the fold line, right above the waist, until the folds disappear and the waist seam is level. Measure the tuck at the center back, where it is deepest, and at the side seam, where it should taper to nothing. Double the depth of the pinned tuck, because a tuck removes twice its width. A common result is 1.5 to 2 cm (5/8 to 3/4 in) at the center back.
Without a toile, compare measurements. Measure your back waist length from the prominent bone at the base of the neck down the spine to the natural waist, and compare it with the pattern's center back length on the stitching line, from the neck to the waist seam. The difference is the amount to remove, provided the shoulder and the back armhole fit; if the pattern is longer than you everywhere, that is an overall shortening instead.
Anything over 3 cm (1 1/4 in) is unusual and worth a second look at the posture and the seat; the glossary entry on the swayback adjustment summarizes the amounts.
How do you do a swayback adjustment on a bodice with a waist seam?
Work on a traced copy of the back bodice with the stitching lines drawn.
- Draw a horizontal line across the back, 2 to 3 cm (3/4 to 1 1/4 in) above the waist seam, from the center back to the side seam, at right angles to the center back.
- Mark the wedge. Below the line at the center back, measure down by your amount, say 2 cm (3/4 in), and mark. At the side seam the wedge is zero.
- Draw the lower line of the wedge from the center back mark to the point where the horizontal line meets the side seam. The wedge is a long thin triangle.
- Fold the wedge out by bringing the lower line up to the upper line and taping it, or cut the two lines and overlap. The center back is now 2 cm shorter; the side seam is unchanged.
- Straighten the center back. The fold has put a kink in the center back line. Redraw it straight from the neck to the waist. On a piece cut on the fold, the center back must be straight anyway; on a piece with a center back seam, the kink would be sewn as a curve, which is fine if you prefer a seam that follows the back.
- True the waist dart. The dart legs now meet at a slight angle. Redraw them straight to the same width at the waist, and shorten the dart if its point now sits lower than before.
- Check the waist seam. The back waist is unchanged in length, since the wedge was taken out of the height only. The skirt or trousers attach as before.
The guide to sewing darts covers truing a dart after an alteration, since a dart that has been folded through changes shape slightly.
How do you do a swayback adjustment on a dress without a waist seam?
A shift dress or a princess-seamed dress has no waist seam to hide the wedge in, so the wedge is folded across the full back piece and the center back is restraightened below it. Draw the horizontal line at the waist level, take the wedge out as above, then redraw the center back from the neck to the hem as a straight line. The lower back will have swung inward slightly where the wedge closed; blend the side seam and the hem so they match the front. For a cut-on-fold back, the redraw is essential, because a kinked fold line cannot be cut.
On a dress with a center back zip, you can sew the wedge in as a curve in the seam instead: shape the center back seam inward by the amount at the waist, tapering over 15 cm (6 in) above and below. The shift dress pattern page shows a back with a center back seam, which makes this the easiest dress to fit a swayback on.
How do you do a swayback adjustment on a skirt or trousers?
The same wedge, taken out at the top of the back piece rather than the bottom. Lower the center back waist by your amount, 1 to 2 cm (3/8 to 3/4 in) typically, and redraw the waist seam as a smooth curve from the new center back point to the unchanged side seam. The back waist is shorter in height at the center, and the waistband sits level. On trousers, lowering the back waist also shortens the back rise, which is what a swayback body with a shallow seat needs; if the seat is prominent, add the length back below the waist by scooping the crotch curve.
Does made-to-measure drafting fix a swayback?
Partly, and more than most adjustments. The pool of fabric comes from a back waist length that is shorter than the front relative to a standard body. A pattern drafted from your own back waist length and front waist length, taken separately, gets the center back and center front to the right heights, which removes most of the excess. Sewly measures both and draws the back and the front from them, so a made-to-measure bodice from it carries much of the swayback adjustment built in. What it cannot know is how sharply the back curves in between the shoulder blades and the waist, which is a shape rather than a length: check the first toile from the side, and if a shallow fold remains, take a small wedge out as above and keep the amount for next time. The guide to making a toile shows what to look for.
Common mistakes with the swayback adjustment
- Taking the wedge straight across at the same depth from center back to side seam. That is an overall shortening of the back; the side seams become shorter than the front and swing.
- Removing it from the waist seam allowance when sewing, without altering the back piece, which shrinks the waist height but leaves the center back kinked and the dart askew.
- Fixing a prominent seat with a swayback adjustment, or the reverse. The folds look alike from the back; check from the side.
- Forgetting to restraighten a cut-on-fold center back. The pattern will not lie on the fold.