I like the aesthetic of buttons as a closure, and find myself drawn to them in many designs.
Buttons and buttonholes can be placed on a placket, or you can just add an extension to the centre front or centre back to support them.
For a shirt, I would choose to make a placket, but to simplify a design (in the case of this dress), I sometimes prefer the simpler method.
To start, decide whether your buttons will be on the centre front or centre back of the pattern. Take the appropriate pattern.
To save the acrobatics required to do up buttons in the back of the dress when my wardrobe assistant isn't around to help, I decided to put the buttons in the front (I also do really like the aesthetic of buttons up the front).
The buttons will lie on the centre front or centre back, so you will need to add a small extension to the pattern to allow for this (light blue section in image above).
To work out the width of your extension, you will first need to consider your buttonholes.
Will they be horizontal or vertical? (If the buttonholes are vertical, the extension will not have to be as wide as if they were horizontal).
Normally I would make the buttonholes vertical, as generally that is the way it's done in modern ready to wear garments. But as I was working from a garment in my wardrobe, I decided to do it the same way as the dress, which, as you can see in the photo, is horizontal.
If you were making a placket to support the buttonholes, they would need to be vertical, due to the limited width of the placket. But in the case of a button extension it is somewhat up to you.
And how wide should they be?
To do this you will have already needed to have selected your buttons. I normally don't buy my buttons until the garment is made, so I know I have chosen exactly the right button, so if you are the same, just estimate the button size you will be using - it won't make a big difference at this stage.
According to this blog, the width of a button hole is the diametre of your button plus the width of the button, plus 3-4mm "wiggle room." Once I found the width of my button hole (in my example they were 25mm), I added 1cm to determine the length of my extension (total 35mm). This is probably a little extreme, I'm sure a 25mm extension would have been sufficient, but as I said, I was using a dress as a guide, so just went with the flow.
Mark the width of your extension at the neckline and the waistline (or hemline of the pattern if the pattern extends beyond the waist).
Join the end points of these lines, and voila, you have completed the button extension.
You will now need to create a facing pattern for the centre front (or back) to finish the seam and provide extra support for the buttons and button holes.
Determine the width of your facing by doubling the width of your button extension.
Mark this distance at the waistline and hemline of the pattern, measuring from the end of the extension.
Join the endpoints of these lines together to create the facing.
You can have a facing that is a separate piece (simply trace the facing piece onto a separate piece of paper - as shown above - and add seam allowance to both patterns), but I prefer to attach facings to the main garment, when possible.
To do this, lay your pattern on a separate piece of paper and trace around it. Leave some space on one side of the pattern (close to the centre front or centre back) so that you can transfer the facing pattern in the next step.
When you have traced the pattern, lift it and flip it over so that you can transfer the facing onto the pattern. Match the actual pattern with the traced pattern at the centre line. Once aligned, use a weight to hold the patterns in position.
Use a tracing wheel to transfer the facing pattern onto the paper underneath.
Remove the original pattern, to reveal your new pattern underneath.
The line between the body of the pattern and the facing will become a 'fold line.'
After you add seam allowance to the pattern, be sure to add notches at either end of the fold line, so you know where to fold once the fabric is cut.
For most fabrics, you will need to add fusing to the section where the buttons are placed - draft a separate pattern for this section so that it can be cut from the appropriate weight interfacing.
The pattern for this piece will simply be double the facing.
To make this pattern just trace around the facing pattern and cut out on fold.