How to Sew a Semi Flat Felled Seam

The semi flat felled seam is the most popular seam for professional-looking canvas projects. The semi flat felled seam is commonly seen in projects including bimini and dodger tops, covers, upholstery seating and more. Our video tutorial will teach you how to sew this essential seam technique for canvasworkers and other sewers.

With the semi flat felled seam, there is one row of stitching exposed to the outside, or top side, of your project and two rows of stitching hidden on the underside. However, if you are sewing a dodger, bimini, awning or other overhead structure, those underside rows of stitching will be visible. Only one row of stitching on the top side of the fabric means less UV damage to the thread, which is an excellent benefit of using this seam.

We strongly suggest that you use basting tape to help keep your fabric layers together. It makes sewing this seam much easier when your fabric is not at risk of shifting or sliding. Basting tape also helps reduce fabric puckering and even helps to make seams more water resistant — an added bonus if you are sewing for your boat or patio.

If you do use basting tape during seam construction, make sure you choose a basting tape with a width smaller than your seam allowance. That way, when you splay your fabric open after sewing the first row of stitches, the basting tape is not exposed to the right side where it can attract dirt. In our example piece, we chose a 1/2-inch seam allowance, so we used Seamstick 3/8" Basting Tape for Canvas (#122064).

To complete the first row of stitching, baste the fabric panels with the right sides facing each other. You can use a sewing guide to help you sew a straight line and keep your seam straight. Sew the first row of stitching 1/2 inch away from the fabric edge. Next, splay open your fabric pieces and make sure the 1/2-inch fabric tail on the underside of the fabric is pushed to one side of the assembly. Sew another row of stitches 1/8 inch away from the first row of stitching, making sure the fabric tail is pushed to the same side so you are sewing down the tail. The semi flat felled seam is now complete.

Here's a quick breakdown of the pros and cons of the semi flat felled seam.

Semi Flat Felled Seam Qualities

Pros:

• Strong seam (95% fabric strength).
• Only one row of stitching exposed to UV rays.
• More water resistant than overlapping seam.

Cons:

• Uses twice the seam width (1/2-inch seam uses 1 inch of fabric).
• Not as water resistant as full flat felled seam.

Watch our short video to learn how to sew a semi flat felled seam. If you're interested in learning the full flat felled seam, check out our blog on that seam construction technique (#300442XHT).