It’s always a nice touch to have a simple vent at the back or side of a slim fitting dress or skirt. The vent not only makes the garment aesthetically attractive it serves the practical purpose of providing just enough give so the wearer can sit or bend without splitting any seams. The tighter the fit or the less give in the garment fabric the more reason to add vents.
Adding a vent to any garment that’s not designed to have one can be easily done by simply not sewing the back (or side) seam to the hemline. Press and tack down the 5/8” seam allowance and you are done. But, adding vents that look professionally done and will lie nice and flat requires a bit of pre-planning before the bottom pattern pieces are cut.
The difference between a properly sewn vent and one added at the last moment is the vent seam allowance. A proper vent has a seam allowance that is roughly 1 1/4" to 1 ½" in width — the same as a regular hem allowance. By making the hem and vent allowances the same the corners will miter equally making for a beautiful finish on the inside (or underside) of the garment. Furthermore, with an extended seam allowance interfacing can be added (when the fabric dictates such) which makes the vent lie flat and remain crisp.
The process of adding a simple vent, in this case to an unlined skirt or dress bottom, begins before the bottom pattern pieces are cut. For the best placed vents the actual hemline and the point at which the vent will begin must be determined. Once that’s done the rest is easy.
Here is the proper way to add a vent to a skirt or dress.
Add the vent seam allowance to the skirt/dress bottom pattern piece. First and foremost determine whether the vent is being added just for aesthetic reasons, or is it there to allow movement in a slim fitting bottom.
From there determine where you want the vent to begin. Then determine approximately where you want the hem to land. For the vent to be effective, in other words provide movement, it needs to be no less than 3"- 4" long. In my example, I have added a 6” vent to the back of a pencil style skirt.
Cut a piece of fusible interfacing that mirrors the shape of the added vent seam allowance. Fuse the interfacing to the vent seam allowance.
Finish the seam edge and hem edge as desired. In my example both were finished with an overcast stitch done by a serger. Other options may include using hem tape for the hem edge, turning and stitching the seam edge (for lightweight fabrics only) or either zigzag or use pinking shears to trim the edges.
Stitch the back seam to the point where the vent opens and press open. Fold the vent allowance (1 ½”) towards the underside of the garment on each side and press in place. Now turn up the hem - in this case 1 ½” – and press in place. The creases formed by the pressing are important here and will help guide mitering the corners.
The corners are now ready to be mitered. Begin by opening up the vent and hem allowances and with a fabric marking pen mark the pressed creases so they intersect. Now fold the corner so the seam allowance edges meet and draw in a line that is 45 degrees.
Stitch along this line to complete the mitered corner. Trim away the excess fold. Turn the vent and hem back in place. Now hem the bottom as usual. If the vent is long, hand stitch the vent allowance to the garment to keep it in place.