I am not a professional but will give you some advice based on my experiences.

I made a pinch pleated drape for my large sliding glass door several years ago. We have a wood overhang outside which blocks some of the afternoon sun. I did not line the drape but I did use buckram in the header. The fabric was medium weight home decor cotton...not super thick. After sewing the header, there was a lot of stiffness & thickness in the header for the pleats. If I was to have also included blackout lining in that header, it would have been too heavy & thick for me to work with. It may be a good idea to make a separate blackout lining in your case. I would make the lining about an inch less (than the finished drape) in width as well as length.

I have sewn a small window panel that included blackout lining sewn in to it. I did not do pinch pleats for this panel. I used rings & clips instead. The blackout lining was inserted into the header before sewing. I used a double fold of the fabric at the header but did not fold the blackout. The blackout goes all the way up into the top of the header. Same idea for the side hems...the fabric is double folded but the blackout is not. The blackout did not need to be sewn at the bottom...it's not sewn in to the hem.

Hope this helps a little.

Back side of small drape with blackout (rings & clips)

Bottom hem and sides

Thanks so much. I'm concerned if the blackout is separate when the drapes are opened they will not fold into nice pleats. What do you think?

kaayluvr - You bring up a good point. I don't know the answer to how the separate blackout lining will fold/pleat. Hopefully, someone who has experience with this situation will respond with some ideas.

If you don't get any responses, soon, you should post this on the Home Decorating Forum. There are a lot of sewing people over there and that forum seems to get more traffic.

One thought may be to skip the buckram all together. Having the blackout lining inside of the double folded header may give enough stability for the header.

Just wanted to thank everyone who responded and to let everyone know how the drapes turned out. I ended up making the lining separate and hung the lining from the clips that were on the curtain rings. I used drapery hooks on the panels to hook to the rings. So all you see are the rings on the rod. The pleats came out great using buckram they are crisp and the right fullness. When open and stacked to the sides they look fine although there is a bit more fullness at the bottom than top. When closed they look like normal pinch pleated drapes. I would do it again this way. Sorry no pic I don't know how to post one.

Thanks for the follow-up. I really like hearing how projects turn out!
I'm so glad it worked well for you to make the lining separate.
I'm trying to picture in my mind how it works....you have rings with
clips for the blackout. Then, on the same rings, you hooked your pins (from the pinched pleated drapery fabric). Is that correct?

Sounds good. I wish I could see pics!

What fullness did you use for the blackout lining?...1, 1 -1/2, 2, 2-1/2, or 3 times the window width?