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How to End a French Seam Above a Vent

Make a smooth transition to a vent
Threads, Issue #210, Aug./Sept. 2020
Completed vent.

When you’re working with lightweight fabrics, a French seam is often the finish of choice. But if there’s a side-seam vent, you need a way to neatly end the seam and create a sturdy, good-looking treatment at the top of the vent. I’ll show you a clever method. Try it with shirt-weight linen, cotton, and sheer fabrics—the very textiles that call for a light, clean finish. Avoid applying it to loose or open weaves, however: You’ll end up with a hole at the point of transition. The process shown is for a pattern with 5/8-inch-wide seam allowances, but you can adapt it as desired for wider allowances in the vent area.

1. Thread-trace and sew the seam. Place the layers with wrong sides together. On the top layer, thread-trace the point where the seam ends and the vent begins, with crossed horizontal and vertical lines. Place the vertical line on the seamline, 5⁄8 inch from the cut edge. Machine-sew the seamline down to within 3⁄4 inch of the horizontal basting, using a 3⁄8-inch-wide seam allowance. Reduce the stitch length to 1.0 mm, and curve the stitching line to the left, to end at the basted intersection. Leave long thread tails.


2. Trim and clip the seam allowances. Along the seam portion, trim the allowances to half their width (3⁄16 inch); stop trimming where the seamline curves away from the edge. With small, sharp scissors, clip into the seam allowances from this point to the basted intersection. Don’t trim the thread tails.


3. Press the seam. Press it as sewn, then press the seam allowances open. Then fold the work with right sides together and press; make sure the seamline is at the exact edge of the seam allowances.


Press under the vent edges and edgestitch.

4. Sew the seam. Stitch at 1⁄4 inch, enclosing the seam allowances as you do. Sew to within 1⁄2 inch of the intersection, reduce the stitch length to 1.0 mm and continue to the basted horizontal line. Stop and remove the work from the machine without backstitching; leave thread tails of at least 3 inches. Press the seam as sewn, then press the allowances to one side. In the vent section, press the allowances to the wrong side along the 5⁄8-inch seamline.


5. Complete the vent. Press the top points under on a diagonal, then press the vertical edges under by 1⁄4 inch. Edgestitch to secure: Sew up one side, along the top point, and down the other side.


Completed seam and vent, (RS).


Completed seam and vent, (WS).

6. Hide the thread tails. Thread them, one by one, into a needle and pull them through between the seam allowances to hide them. This is neater and more secure than trimming.


Ruth Cabble sews and teaches from Long Island, New York, and at LongIslandSewing.blogspot.com.

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  1. sewing1942 | | #1

    It would have been easier to see if this was done on a plain fabric.

  2. sew4th | | #2

    Just the technique I wanted to learn, but the illustrations were challenging. The fabric printed in tiny stitch-like lines seemed specially chosen to hide the stitches. (To be fair, Threads is usually very good at teaching complicated techniques with clear illustrations and photos.)
    After squinting at the magazine, I came to online in hopes of better illustrations and at least these same images were bigger on my monitor.
    Still, I love Threads and this method is just what I needed for my projects today.

  3. neaton333 | | #3

    Thanks for re-doing the photographs! The technique is much easier to understand now.

  4. user-267364 | | #4

    My old eyes Thank You!!! Challenging for sure and I really wanted to get this -- now I do

  5. User avater
    Stashnow | | #5

    This is an interesting method for having a slit and a french seam. Another method can be seen on a free sewing pattern by Lauren Boyle from Perth, Australia - Wide Strap Maxi Dress from Peppermint Magazine Sewing School issue #44 https://peppermintmag.com/sewing-school/

    Lauren has drafted the top of the slit such that it fits into the French Seam and works beautifully.

    Peppermint Magazine offer a new free pattern each issue all from different designers and are very useful.

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