I use that alot in my work I would cut the strips wider than you need so you can trim down to 1/2" after you sew onto the first edge. Otherwise you will have a less than accurate sashing size. You will need to really watch your seams so they are straight or your sashing will have spots that are smaller and larger than 1/4" when you are done.
I would use a 1" strip. 1/4" will go on the first edge and then you will need 1/2" from that seam. So you will be cutting off 1/4" but it is worth it to get a more accurate look. It will save some frustration later.