Attaching separate interior facings

Hello everyone :slight_smile:

I am finishing my first steeked sweater, but am having trouble with the armhole facings. When I knit the sleeves, I knit them directly into the sweater so I didn’t make the extra flap to cover the steeked edge. I’ve knit two strips that I’d like to use for the facings out of a much lighter weight yarn to reduce bulk around the armholes. However, I’m having trouble figuring out the best way to attach them?

I need to attach them to the back of the knitting but in a way that won’t create pulling or puckering. I’ve seen video tutorials on attaching plackets, but I’m having trouble finding something on how they tack down the facing edge. I’m assuming this is how you would do both sides in my case?

After trying various google searches, I’m still coming up empty. Any help would be appreciated : )

The short facing is a very neat finishing for the cuff up sleeves on Norwegian sweaters.
Techknitter has a very nice illustration for this at the end of this post:

You would just use this technique on both edges of the facing. A thinner yarn works best but I have used sewing thread on a thinner weight knit baby sweater. It’s just not as stretchy as the thin yarn which is ideal.