Ask the Sewaholic: What is the reason for a centre back seam?

I mentioned how I love getting questions through the contact form the other day, and it’s true! I get a lot of awesome questions and always try to answer them as completely as possible.

Just before I left on vacation, I received a really interesting question from a reader, and thought you might be interested. I asked her if I could use our Q&A convo for a future post, and she said yes!

After reading my post on matching prints along seamlines, Samantha wrote:

Great post on matching prints along seams!  I realized that I usually ‘cheat’ on back seams where there is no zipper, and simply remove the seam by cutting the pattern on the fold (minus the seam allowance).  You seem to be a very knowledgeable sewer who could tell me what I messing up by doing that … what IS the reason for a back centre seam when the seam is straight anyway?

Here’s my reply – I added the photos above to help illustrate points 1, 2 and 3 for added clarity!

Hi Samantha!
Thanks for visiting and I’m glad you enjoyed my post on matching prints!
Regarding your ‘cheating’ technique, you haven’t really done anything wrong, as long as the seam is completely straight not curved, the original piece asked you to cut along the straight grain, and you remembered to remove the seam allowance (not mocking you, I’ve done it myself!)
Why is there a centre back seam? Well, a few reasons.
One, and usually the most common one, is because there’s a zipper at centre back, so the seam needs to be there to insert the zipper.
Two, if the seam is not completely straight, then the seam is there for extra shaping and fit. (If you were able to put it along a fold evenly, then this wasn’t the case on yours…)
And three, sometimes the centre seam is there so that the pieces can be put on the bias. So if you remove the fold, then your pieces might not hang correctly, or worse, they might have used the bias of the fabric to stretch (like in a bias slip) and therefore you might not be able to get the skirt on if you cut it straight!
Also, in older patterns, there’s a fourth reason. Fabric in the 30’s, 40’s and 50’s seemed to be made in 35″ or 45″ widths, so if you wanted a nice full circle skirt, it would be impossible to cut in one piece. The centre seam was there so you could get a full circle out of your fabric, the only way would be to add a seam. (Does this make sense?)
Thanks for asking! Would I be able to use your question in a future post? I bet a lot of people are wondering the same thing and this answer might be relevant and interesting.
Have a fantastic day!
All the best,
Tasia

The same theory applies anywhere you have a centre seam: backs of jackets, front seams of skirts, front bodice seams. You COULD place it on the fold, just make sure it won’t compromise the fit and drape of the finished garment.

Hope this was helpful! If you have a sewing question, feel free to use the contact form and send it over. I’ll do my best to answer – and if I can’t, it’s a great excuse to learn something new!

If I get enough questions, I could start a series of regular posts on ‘Ask the Sewaholic’ – what do you think?

Be back soon!! Hopefully I’m out visiting exciting new fabric stores and soaking up the sunshine!

, , ,

16 Responses to Ask the Sewaholic: What is the reason for a centre back seam?

  1. Angela August 16, 2010 at 9:29 am #

    Those are good things to keep in mind. Thanks!

  2. Darci August 16, 2010 at 9:31 am #

    Great question and fantastic answers! I’ve often wondered about that, myself. Thanks, Tasia!

  3. Jessica August 16, 2010 at 12:03 pm #

    I think the point about vintage patterns is helpful – I often wonder why they have seams in incongruous places, and now it makes sense! I’m a making a dress right now that I’ve removed the center back seam on, since I’m leaving out the zipper, and hope it turns out!

  4. Amy August 16, 2010 at 12:31 pm #

    Oooh I was wondering this the other day and now you’ve answered it! That makes sense about the drape of the garment now, thanks :D

  5. Katherine August 16, 2010 at 7:59 pm #

    Just a little bit to add…

    If you want to put your fabric on the fold, and the seam is curved (eg CB seam of a blouse) you can sometimes overcome this by putting in a dart to get the fit right. The dart can either be on the CB fold or you can move it. Sometimes I do this when making up a woven pattern in a knit, when I don’t need the zipper.

  6. Tasia August 25, 2010 at 5:50 pm #

    @Katherine: Thanks for adding the suggestion about the dart! I’ve done this on straight skirts, where I’m trying to squeeze it out of a very small piece of fabric. The less seams the better!

  7. lakaribane August 27, 2010 at 7:48 pm #

    I would like to add another reason for CB seam and back zipper: if you have an halter or strapless dress/top, both the seam and the zipper help keep the back close to your body to hold up the dress or top since there are no straps to hang the garment from the shoulders.

    I’m obviously talking about garments without elastic casings at the back neckline.

  8. Betty May 31, 2012 at 10:01 pm #

    Thank you so much. I am just making a skirt and wondered why I couldn’t leave out the back seam as I prefer a side zip.

  9. LA July 26, 2012 at 5:20 am #

    Thank you!! this has saved many hours puzzling over a vintage pattern I’m cutting!

  10. Jane July 1, 2013 at 3:48 am #

    I am wondering about whether to have a centre back seam on a kimono. Probably it is there on traditional kimonos because the fabric is generally narrow – but I am wondering if having a back seam also adds to the ‘solidity’ of a cape – you know, makes the whole thing feel better, more professional, more substantial?

    • Tasia July 1, 2013 at 11:46 am #

      I think you’re right, it’s because of the narrow fabric. You may also be right that having the seam keeps the back in line, I’ve never worn a kimono so I can’t say for sure!

  11. julia November 10, 2013 at 8:46 am #

    Hey :),
    I’m trying to recreate a knit convertible dress. In the garment I’m looking at for assistance there’s a CB seam which elastic has been sewn into to create that gathered/ruffled look. The version I’m making I want to be a lot cleaner and remove that back seam BUT it allows for a better fit. The block that I’m using is for a body suit. Do you think I could remove some more of this excess at the SS’s and perhaps add an eastic at the back waist to remove the remainder (created from removing the CB seam)?
    Maybe I just have to try it out.

  12. LLBB November 30, 2013 at 10:34 am #

    thanks – i’m revisiting this and it’s super helpful! I’m debating taking the center back seam out of a dress i’m making. I think i’m going to go for it. I fall in to situation three above so I think the worse that will happen is that it will hang weird. hopefully if i let it fall before i hem i’ll be okay…:)

  13. Tosin Oketunji August 22, 2014 at 12:50 am #

    Hello Tasia!

    Thanks so much for the good work you are doing with Sewaholic.
    I have a client that has a small bum and she needs me to make her a dress that will accentuate what little she has.
    I made a toile in which i introduced a dart along the center-back seam.
    That helped a little by fitting the dress more snugly to “the small of her back” and accentuating a little bit, the beginning of her bum.

    During her fitting however, she said she wanted the dress to hug more tightly in the space between her bum and the hem of the dress.

    Can i introduce some shaping from directly under her bum to the hem-line?
    Also, how will this affect the slit?

    Thanks a million!

  14. Flo Renfroe December 13, 2014 at 1:12 pm #

    I’m making a sheer coat to go over a dress for my daughter to get married in and the pattern has a back seam. I don’t think it will look nice with a back seam in this sheer white fabric. Do you think it will be ok to cut it on the fold instead?

    Thanks,

    Flo

    • Tasia December 15, 2014 at 8:58 am #

      It depends on the pattern piece, but I agree, I’d want to eliminate as many seams as possible in sheer fabric. Take a look at the reasons in this post – is the seam shaped? What will happen to the grainline? and then make your decision!

Leave a Reply