Shorter front and longer back
ackets, especially suit jackets can have a front piece that in a seating position is too long. This results in ugly folds of superfluous fabric in your lap. You can escape this by making the front piece shorter. The back piece often causes the opposite problem when the fabric is not enough to cover the space between the jacket hem and the waistband of the pants/skirt. Is it easy to fix by making a longer back piece.
ADAPTING THE PATTERN
The simplest way of doing this is of course to shorten or lengthen the pattern pieces and just cut them in a straight line by the hem. Measure how long you want the front piece by measuring your “front” in sitting position. Measure from the shoulders seem (where the front and back pieces are sewn together) and down to your thighs. Then measure the front piece of the pattern and take away the piece below your line.
Measure your backside, from the shoulder seam down to the top of the seating cushion. Measure the back piece of the pattern and extend the length of it as far as necessary. When sewn together the jacket will look like this.
If you want a softer line from the back to the front piece, avoiding a sharp step at the side seam you can round off the edges of the pieces. Trace down the hemline of the front piece at the edges and trace the hemline of the back pieces up to meet these at the side seams. A warning: it is harder to make a good-looking hemline if you choose this solution.
ADAPTING READY MADE JACKETS
If you want to change a jacket, which is long enough in the back but too long in front, you start by unpicking part of the side seams. Then you shorten the front pieces in the same way you would have done if you had sewn it after an altered pattern. If you want a softer line at the sides trace down the front pieces to meet the back.
If the jacket is not long enough at the back you can use the fabric piece cut away from the front of the jacket to lengthen the back. This will of course look better on a single coloured fabric.
Longer front and shorter back
A lot of wheelchair users sit with a slightly bended back to get a better balance. This is what causes the gap between jackets and pants/skirts. If, you instead sit with a straight back you will have the opposite problem. The excess material in the back of the jacket creates lumpy folds. This is uncomfortable, ugly and can create pressure sores.
To avoid this problem you can shorten the jacket in the back in the same manner as when shortening a front piece.
Either, you take a piece of the back part of the jacket at leave the front piece whole, or you can shorten the back piece by facing the hemline down to the length of the front piece at the side seams.
Try on ready made waist length jackets
Another alternative is to sew or buy waist length jackets. Suit jackets of Bolero type are often very classy with nice details at the front and cuff lines.
If you can get hold of an old fashion waitress jacket you could try to cut this to pieces and make a pattern of it.
Waitress jackets of the old type
are often a little more complex to sew. The front and back pieces are often split in several parts so you will have to sew more seams than usual. The advantage is that this type of jacket has a very good looking fit for somebody with a straight back at the same time it is made to function with a lot of upper body movements.