Auxiliary Reference Information | Drafting | Seam Allowances and Hems

Updated: Jul 10, 2019

Seam Allowances on Flexible Patterns

After your Flexible Pattern has been tested and all alterations made you can now add on your Seam Allowances. Of course for all small pattern pieces that are not affected by alterations you would simply go ahead and draw your Seam Allowances.


The amount of Seam Allowance to add is dependent on;

  • Type of fabric (if it frays you may wish to add on extra Seam Allowance while you work with the pieces)

  • Personal preference.

  • Position of the seam on the garment for example if there is no wear and tear or space is tight you would have a smaller Seam Allowance.

  • If you are sewing a couture garment which typically allow for larger seams for various reasons (to assist with weight for draping, to assist with fitting, to allow extra to let out if required at a later stage, to not skimp because the emphasis is on quality, and also to accommodate fraying fabric).

Seam allowances typically range from ¼” to 2” and pattern manufacturers all have their own idea about what is the right size but it really is your choice what you would like to use.


Generally I will use;

  • ¼” around necklines or tight curves waistband, for bindings and belts, lapels or collars or seams on pockets, anywhere you need to reduce your bulk (you could start with ½ on all seams then grade them down after sewing which does help with accuracy as it is easier to sew a bigger seam allowance than a smaller one, this does waste a little fabric but in the grand scheme of things we are only talking of very small amounts).

  • ½ for most other seams including seams on darts.

  • ¾” for seams which require zipper installation although that is personal preference you can simply use ½”.

  • On a couture garment I would usually not have a defined seam allowance but will allow anything between 1” – 2” of extra in the seam allowance space.

  • Don’t forget that on a hem you may also need some extra seam allowance for a turn under, perhaps ½”.

You can log what Seam Allowance you are going to use on each Seam on your Pattern Record Card and use this to refer to when drafting Seam Allowances as a double check.


Drafting a Seam allowance

So for Flexible Patterns only we will look at how you can now add on Seam Allowances to your Pattern pieces.


I will use pen to make it easier to see but you would use your pencil as usual.


Before you start consider that you may wish to keep a Master copy of your Flexible Pattern without Seam Allowances just in case you feel you would like to go further with another test fitting or try out other options prior to adding Seam Allowances.


All of your Pattern Pieces will need to be cut into their smallest parts into a Cutting Copy i.e. if you need to cut up a Princess Line or trace off a Facing then you will need to do this. You need to have a full set of your separate Pattern pieces for your Flexible Pattern. It would be this full set with Seam Allowances drafted onto (that you will manage on you Pattern Record Card) that you could preserve if you would like to use it over and over again. At this point each pattern piece may have already been cut out and so have no spare paper for Seam Allowance so you could either tape the piece onto paper or just trace it off again for a cleaner finish.


Now the painful part is over with let’s get working on adding Seam Allowances.


Remember to refer to your Pattern Record Card to determine what the Seam Allowances are for each seam for each pattern piece, or if you do this the other way around ensure that you record the Seam Allowances on the Pattern Record Card, the card can come in useful when you come to sew up a Seam.


It is useful to use a see through ruler to measure Seam Allowances from the Sewing Line as you can lay the ruler on top of the sewing line at the required measurement and then draw down the side of the ruler, having both a long and short ruler handy will help with long seams and curves.


Here is an example of a small pattern piece, a pocket bag.












It requires ¼” Seam Allowance on the top and the bottom and ¾” on either side.











It is easy to draw this on as the lines on the pattern piece are straight.


On a preserved copy of this pattern piece you don’t need to draw in the whole of the Seam Allowance. I mark the start and the finish lines on the Seam Allowances and also note the sizes too as a reminder.

One thing you can do also is to Notch your Seam Allowances and later create a Tailor Tack to show where the seam should be sewn. I prefer not to do this because I always refer to my Pattern Record Card to check and confirm every Seam Allowance but this is just my preference. If you were passing this on for someone else to sew or construct then it might make sense to Notch all of the Seam Allowances.


Here is an example of how to draw a Seam Allowance on a curved pattern piece.


This is the top part of a Back Draft traced off and ½” Seam Allowances are being added to every Seam (the Neck and Armhole can be trimmed down after stitching rather than fiddling around with a smaller Seam Allowance).




The Centre Back Seam Allowance has been drawn in using a longer ruler lining up the ½” mark on the Sewing Line and then drawing down the outside of the ruler.







The curved seam has to be marked out in stages all the way around the line. I find a smaller ruler more easy to manoeuvre on curved seams, although please forgive the neon ruler I can’t seem to get a short ruler that is see through with inches marked lengthways!



These lines are then firmed up freehand or with a curved ruler.

And the same is done on every Sewing Line until all Seam Allowances have been added.




Once completed all Seam Allowances will need to be trued, usually you will be tweaking were a Seam Allowance fits into a curved Seam. To assess this fold back a seam that you would sew for example the Shoulder Line. Then using your Tracing Wheel trace over the edge of the Seam Allowance on the adjacent seams in this case the Neckline Seam Allowance edge and the Armhole Seam Allowance edge.


Once opened up you will see the new position of the Seam Allowance for these two edges to help blend in the Shoulder Seam Allowance into the Sewing Line.


You would now draw this new position and cross out the old line.





Just to confirm this again here is the trued up seam for the Base Armhole.







This is the new position drawn in.

Trueing Seam Allowances is an especially important thing to do on Seam Allowance for Hems covered below.


Ensure that all Notches are then transferred out to the Seam Allowance as this is where you will place any marks or tacks on the Fabric in the Seam Allowance out of sight especially if you prefer to use pen or scissors to make a snip although I prefer Tailor Tacks.


Hems

There are a multitude of ways to create Hems. We will look at a very simple way to complete a Hem that is sufficient for most uses at the Base of Tops, Dresses, Skirts, Sleeve’s etc.


A Hem is usually an extra length of fabric at the bottom of the pattern piece that folds to the posterior of the garment and fold up wards and sewn into position.


Some Hems will be positioned on pattern pieces that get narrower as they go down like a Sleeve and some will be positioned on pattern pieces that get wider as they go down like an A Line Skirt. The important thing for Hems is that they fit the pattern piece like a mirror image of the pattern as they sit behind it. They will also have a Seam Allowance that with be turned inwards to give a clean finish to any raw edge on the inside which will also need to sit tucked in mirror imaging the shape of the pattern piece. You can get the shape right by trueing up both sides of the Hem and Seam Allowances. If you don’t do this then you could be creating a sewing issue for yourself later and it will affect how the piece hangs so truing is a very important step in the process.


Using the Mini Template for a Skirt Back I have drawn a line 2” below the Base of the Skirt for the Hem. I prefer a good sized hem as it give weight to a Skirt and a more luxurious feel, it is worth the extra fabric. I have also drawn another line ½” below that to allow for a Seam Allowance on the Hem.









The next thing to do is to True up the Sides. So fold on the Hem Line folding to the back.





Fold again on the Seam Allowance Line, folding back again.






Then fold as you would sew with the Hem folded back and he Seam Allowance folded under.






Take your Tracing Wheel and Trace the Side Line, on this example the Centre Back is a Straight Line so this line would continue through the Hem and Seam Allowance so you would not need to trace this Side.





Open out the folds and draw in the shape for the Hem and Seam Allowance at the Side Line.







Now this example shows an almost straight line so let’s have a look and see if we can exaggerate this a little. If the Side Line of the Skirt had an extension and a Flare the Shape would be different. I have redrawn the Sideline and redrawn the shape of the Side Line for the Hem and Seam Allowance in blue to show how a Side Line can change shape drastically over a Hem and Seam Allowance.



All Hems are Notched on the Hem Line at the Side Line (inside the Side Seam Allowance), in fact you could even label the Hem Line or mark Fold Line to remind you. I also Notch the Seam Allowance on a Hem anything to help me when sewing it up.


Here is an example of what this would look like if you were to add a Hem onto a Sleeve shaped pattern piece.


Again a Hem Line has been drawn in, you could use 1” to 1 1/2“ for a Hem on a Sleeve, and also you can see a Seam Allowance added too.










After folding and tracing here is the shape of the Sides for the Hem and Seam Allowances.






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