If you want to add sleeves to the Harrison Shirtdress, that’s totally do-able!
Your first thought might be: easy, I’ll just sew the sleeves on from the Harrison Shirt. However, the Harrison Shirtdress is drafted with a sleeveless armscye which means it isn’t quite as simple as that. Sleeveless armscyes are drafted differently to sleeved armscyes, coming up higher under the arm, and narrower in the shoulder. However, if you have a copy of the Harrison Shirt and the Harrison Shirtdress, then you can make this one adjustment and then add sleeves without a problem.
How to adjust the Harrison Shirtdress armscye
Alter the front
We’ll be altering pieces 1, 2, and 3. You can see from the image below they’re very similar, but the armscye shape is a bit different (as well as the length).
Start with piece 1 (front side). Lay the Shirtdress pattern piece (in black below) on top of the Shirt pattern piece (in red below), lining up the princess seam notches.
Place a piece of tracing paper over the two pieces. Now trace off the armscye of the Shirt piece (in green below), but for the rest, trace the Shirtdress piece. So your final piece is shaped like the long shirtdress piece with the Shirt armscye.
Repeat this process with the middle piece
And then the center front piece
Now you have your new, altered pieces (remember to transfer the notches, too!):
Alter the back
Now, we need to go through the same process for the back pieces. First, create the new side back piece:
Then for the yoke, it’s easy: just use the Shirt yoke rather than the Shirtdress yoke! No adjustments needed.
And here are your revised back pieces:
And that’s it! You can now sew up your Shirtdress using the Harrison Shirt sleeve pieces and instructions from the Shirt pattern.