Note: Instructions below for making this block were clarified and modified August 2021. I had left out several important steps! And I made a slight change to make this block easier to get to your exact size.
Another advanced basic unit is the Split Rectangle quilt block unit. Sometimes this unit is called the Half Rectangle Triangle or HRT. You can find examples of this unit in action in the following quilt block designs:
Now, don't be fooled into thinking these units will work just like half square triangle units. They won't. They are an entirely different animal. Also, they are an intermediate block and not for the faint of heart! They may take you a bit of practice!
For starters, a half square triangle will always have the same height and width. This is not the case with Split Rectangles. They can come in a variety of height to width ratios, as shown below.
One important thing to know when making these units is that the diagonal can either go left to right or right to left. Since the two different directions are mirror images of each other, care must be taken when cutting your fabrics to make sure you haven't reversed the unit.
The formula for making Split Recs is pretty differently from making HST's too. Recall that when making Half square triangles, you will add 7/8" to your finished size, then cut on the diagonal. To make Split Rectangles, first determine the finished size of your rectangle, then add ½” to the width and height. You can add a little more if you want to give yourself a little more wiggle room.
Here's an example: Suppose I want to make a finished Split Rectangle that measures 3"x 6". I would need to cut rectangles that are 3.5" x 6.5"
Once your can cut your pieces, draw a line along the diagonal on the back side of one piece.
Arrange your pieces, right sides together, but with the diagonal line piece skewed on top, as picture below.
Once your pieces are in position, sew a seam 1/4" from the drawn line on each side. Once the seams are sewn, cut along the diagonal and press open. Then trim your piece down to the desired size.
A tool that makes easy work of Split Rectangles is the Split Recs Tool by Studio 180 designs. I've found this tool to give me great results and it really speeds up the cutting process when making these units.
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