A quick elastic waistband is a great way to finish many shorts/pants/and skirts and serves you well as not only a beginner friendly waistline finish, but also a comfortable wearing garment. This tutorial features an elastic channel that is simply made by folding down the shorts pattern piece (there are other options to create a separate pattern piece for an elastic channel that attaches to the pant). Some prefer one process over the other which is absolutely ok! Just know there is usually more than one way to approach the same result when it comes to garment construction.
This tutorial uses 1.25'' wide elastic knit elastic. You can also use a non-roll elastic.
ELASTIC WAISTBAND CHANNEL
Mark fold line 1.75'' from top of short evenly along front and back of short. Press fold along this line first.
Fold another fold 1/4'' from top of short. Take your time making these measurments accurate to prevent your channel from ending up too narrow.
Pin your channel closed (center front and center back seams should match up, whereas side seams will not match up due to the side seam angles). I like to place a pin about 3 inches from center back as a "reminder pin" to stop stitching (blue pin pinned parallel along stitch line instead of perpendicular to stitch line).
Start stitching at center back, stitch 1/8 (or 1/6'') from edge of elastic encasing.
As you approach the side seam, note that the side seam on the elastic channel will NOT match up to the side seam.
As you approach "reminder pin", plan to stop stitching and back tack at pin.
Cut enough elastic to wrap around waist, (as I find elastics have different elasticity I usually skip using any type of formula and just go off feel after a fitting so I just make sure to cut enough). Pin a large/strong safety pin at one end of elastic.
Feed elastic through the channel. Take your time and prevent the elastic from twisting along it's journey. There should be 1/8'' of clearance (extra width in comparison to the elastic width) so that it slides through fairly effortlessly.
Pin ends together. At this point I try it on and make adjustments.
After you find the right elastic length, trim off excess leaving 1/4'' seam allowance.
Overlap elastic ends 1/2''.
Zig-zag stitch securing elastic together. Trim off excess.
CLOSE ELASTIC CHANNEL AND SECURE ELASTIC IN PLACE
Finish enclosing elastic channel. Stick your needle in at the end of the stitch line, and pull elastic/fabric straight. Pin if needed, just make sure you do not stitch though elastic when you close channel.
Trim thread and pull on shorts elastic channel to help distribute fabric more evenly.
SECURING ELASTIC IN PLACE
It is common to top stitch along your elastic to secure in place as well as add an aesthetic to your shorts. On mine I did this step on the back only to show a couple options. Stick your needle in at the side seam into your shorts (starting your stitch line in the back). Pull your elastic until you removed any puckering in your shorts, and stitch about 1/2'' from top of short along back of short.
When you release the shorts the elastic will recoil and create this ruching aesthetic that holds the elastic in place. Typically in RTW clothing this step will be done with a chain stitch (a stitch that is capable of stretching), but it also seems to work just fine with a regular home sewing machine as it is a very popular process).
Do this a second time about 1'' from top of short.
This stitch will divide the elastic into three equal sections.
The other option for securing your elastic to your shorts is to "stitch in the ditch". I did this on my center front seam on my shorts. Pull your seam apart and stitch right in the seam on top of your elastic encasing. I do this with the outside facing up.
Trim down your threads, once your elastic relaxes again the stitch line will practically disappear.
There you have it, an elastic waistband!