While making a pattern, it is always important to remember to allow space for the seam, as you can’t sew right on the edge of the cut fabric or else it will fray. This is what is known as the seam allowance, seam allowance is the area between the stitching and edge of the fabric.On patterns the seam allowance is most often marked by a small notch which indicates how far from the edge the stitching line is to be sewn. On patterns for home use the seam allowances are sometimes unfortunately not marked on the pattern, leaving the sewer to rely on the make instructions.
Seam joins more than one pieces of fabric. All layers of fabric sewed together must have the same seam allowance, the raw edges must line up evenly to create an equal seam allowances on all of the pieces being joined.The basic principle of seaming is; two pieces of fabric are laid on top of each other and a needle and thread goes back and forth along a line, joining the two together.
Seam allowances can vary from a small amount (6mm) up to a larger amount (1.5cm), sometimes more allowance may be left to make adjustments. In haute couture sewing it’s usual to make the seam allowances much larger to allow space for fittings, and to allow for alterations later on, the same is true for some areas of tailored suits. But for commercial garments the seam allowance will be at the minimum amount required in order to get the most out of the fabric.
General rules for seam allowances
- If a seam allowance is too large when used around a curved area then it will become too cumbersome to manage and may cause seems to be hard to ease together.
- Larger seam allowances can be trimmed or slightly cut into in order to better fit around curved seams.
- Seams which need to curve around areas of the body such as collars and armholes are normally smaller, about 6mm.
- Seams which require a special finish are normally larger (1.2 – 1.5cm). This would be for seams that require a French seam, a flat felled shirt seam, a bias binding etc.
- You will need to allow more seam allowance where you have a closure such as a button placket or a zip. You may need to leave about 2cm seam allowance for a zip.
Different ways to finish seam allowance
- Serged edges are commonly found on store bought t-shirts or jeans it’s the type of seam at the sleeve or legs, serged edge usually requires a serger, which is a standalone sewing machine that pretty much does nothing but serge edges.
- You can make serge sewing look using single needle sewing machine by sewing the two layers together then trim one of them to half then bend the another one over and over stitch all the seam allowance.
- The zig-zag stitch is a great alternative to a serge stitch. It’s fairly quick and easy to use and comes as an option on most (home) sewing machines.
- To finish your edges with a zig-zag stitch, carefully trim your allowance down to 1cm and then zig-zag the edge. You can adjust the stitch length to make it a wide zig-zag for fabrics that are not likely to fray or more close for fabrics that fraying more.
- Top stitching requires you to stitch from the outside along the seam line; for example, 0.5com from the seam line. You can see an example of this by looking at the seams on a pair of jeans. The pockets and legs are top stitched. It gives a decorative look and also stabilizes the fabric.
- French seams are an excellent way to finish silk and semi-transparent fabrics. A French seam is sewn in while the garment is being assembled. Rather than sewing the right sides together and then finishing off the raw edge, the wrong sides are sewn together using half seam allowance, then flip the fabric right sides together and sew on at less than half seam allowance.