This is what has been on my sewing table last week…it has caused me a great headache and I actually ended up making two Burda skirts 116 2010/9.
Apologies for the long technical post, but I hope it will be of help.

So, after having tried to gather information online, rummaging through sewing books and emailing lovely ladies who worked on this project before me, I thought it would be good if I tried to document my process in a picture tutorial. In fact, I wasn’t able to find these steps anywhere.

In the end with some trial and error and reading through this Burda book  K 695  Sewing Mannual or Sewing is easy  ISBN 9 770944 569000 (I don´t think it’s sold in the US)
I managed to crack the code

This project was a puzzle for me because:
1. The lining has a regular seam allowance in the vent area

2. And the exterior as a asymmetrical lining, e.g. on side is wider than the other.
As you can see in the picture that is one side of the vent.
The other side that you see folded back on top, is half of the other vent.

If you are getting an headache by now…well, that’s how I felt. I realized I had never learned this in my sewing classes nor online. And the instructions without any drawing were very impossible for me to understand.
So, here is what you are supposed to do if you ever encounter a pattern like this. Don’t panic.
(sorry for some blurry pictures, I was eager to finish my skirt)

The vent has two sides:
The top vent is the shorter part that lies on top of your finished skirt. You will recognize it because you will have marked the diagonal sewing line on it.
The bottom vent is the wider side that lies at the bottom

1. Mark all lines diligently on your fabric with basting thread so you will now where to fold. It takes slightly longer but it pays back

2. Serge or zig-zag along all edges so they are nicely finished. From now on we are working on the wrong side of the fabric.

Exterior

3. Fold up the hem all around the skirt

4. Fold back the top vent along the basting line

Once folded the vent will end up where the pin is.
Don’t fold under the seam allowance (this is what I did before, but it’s wrong!)

5. Finish the corner intersection with a slip stitch or mitered corners
I chose the second option (I am so proud of the result…it was my first time!)
On Threads you can find a very nice tutorial on mitered corners (just bear in mind that we are not folding under by 1/4 inch as we don’t need to)

6. Press and congratulate yourself for finishing the first side

7. Now fold the bottom vent along the basted line.
I took the picture before hemming the skirt. Normally your hem will be already up.
So, what you’re supposed to do is fold back (towards the inside, wrong side, of the skirt) only one part.
The second parallel basted line is simply for reference for later.

8. This is the view from the inside after completing the previous step

9. At this point you will notice that you vent is not laying down flat.
This is because you need to clip the corner of your seam allowance right above the vent

10. Finish the corner intersection with a slip stitch or mitered corners
Just like you did for the other side

12. Ensure your vent is well aligned. The vent is pressed to one side, your vent will be pressed to the left side. Here I am showing you the right side, since I actually made two vents.

Turn the skirt to the right side so we can finish off the vent

13. Your exterior is now done

Lining

To finish the vent area of your lining I assume you will have already attached it along the waistline and zipper.
If, like me, you don’t know how to do it, this is a great video (no hand sewing involved)

Also your hem will have already been folde up and stitched

1. Press open your vent seam allowances on your lining
(I took the picture before hemming my lining!)

2. Pin the lining to the beginning of the vent on the skirt exterior.
This will ensure your fabric won’t shift.
Make sure you only pick one layer of your exterior (you could work on your ironing board to avoid issues or put a cardboard between the two layers)

Pin the lining to the bottom vent.

3.Cut horizontally the other side of the vent on the lining. The cut in the corner on a 45 degrees angle.
Here is a drawing from the Burda book of this step and the following.

4. Pin the fabric across the top and side by folding back the fabric by your seam allowance
(see above drawing)

5. Slip stitch the lining to the exterior. This is what your vent will look like now
(This is actually a picture of the other vent so it’s the mirror image of the above…sorry!)
Looking back at this picture I realize I should have probably closed the lining opening a bit more (further down…compare to the drawing where you don’t see the stitching across)…it will be for next time

Slip stitch along the vertical line so that the lining will be attached to the back vent
(the hem will stay loose as usual)

6. Give the skirt a final press and you’re done!!!!

I realize I should have probably put together a video to make things easier, but I hope those pictures will help you out if you ever venture in the vent lining area.
It is possible to avoid some hand-stitching when attaching the lining (I actually did machine stitch the sides) but it requires some fiddling, so might prove more difficult in the end.

A word of advice to avoid frustrations on the real garment (like my first skirt)…try out this procedure on some scrap fabric. You just need to reproduce the rectangles for the vent area. I did it after the first failure…and that’s when I discovered I wasn’t supposed to fold under the seam allowances.

Additional information:
Back vent tutorial on a Fashionable stitch
Vent tutorial on Fashion incubator
Easy guide to sewing linings
Reviews on Burda 116 2010/09 (those ladies were very nice to reply to my email)

Ok, I’d better go and take some pictures of the finished skirt.But before I go, one question: What is the project that gave you the worst headache?