Notes on adding seam allowance

One of the first tutorials I created for this site was about how to add seam allowance to a pattern. If you are going to draft your own patterns, this is really something you are going to need to know how to do (and it's also a greta place to start if you want to learn some basic pattern making principles). In today's tutorial, I'd like to expand on the basics a little. I'd suggest checking out the previous tutorial first if you are unsure how to add seam allowance, and then come back to this tutorial. 

I did work experience with a local fashion designer while I was at university. One day a week I would go to her studio and help out with whatever tasks she needed help with. I learned a lot about things like how to cut fabric, how to trace patterns etc. (which have all really come in handy), but I'd say the best lesson I learned was about marking seam allowances. I remember being asked to add seam allowance to a particularly strange shaped pattern and realising I didn't know what to do when the pattern came to a point at one side. The designer I was working for told me to think about how the piece needs to sit once the seam is sewn and pressed and that should help me work it out. This now seems very obvious, but at the time it was a real 'wow' moment. From that moment on I never struggled, and it is a way of doing seam allowances that I have brought into my patterns. Over time, I have learned this is not always the way it is done and users of my pattern always get really excited about it and see it as a nice little detail in the process, that helps you achieve a really beautiful and professional finish in your hand-made wares. So I thought I'd share it with you today!

An example

Here is an example of what I am talking about from the Rushcutter sewing pattern (as the old saying goes, a picture really is worth a thousand words). This is the pattern piece for the raglan sleeve, and you will notice that at the seam where the sleeve joins to the centre front panel the seam allowance comes to a strange looking point. 

The reason for this is that, after this seam is stitched and then pressed open, with the seam allowance cut like this, it will be able to sit flush with the edge of the sleeve. This will help you get a lovely clean finish when you attach the sleeve to the armhole of the dress. 

How to do it

Take the pattern you are adding seam allowance to. For the sake of the example, I have just used the front pattern piece from a sleeveless top pattern. (which I showed you how to make last week).

Start by adding seam allowance to the straight seams. I'd suggest between 1.2cm (1/2in) and 1.5cm (5/8in).

Add seam allowance to the curves. Curved seams require a slightly smaller than standard seam allowance (as this helps when you are sewing them) so I'd suggest 6mm - 1cm (1/8in - 3/8in). If you're not sure how to add seam allowance to curves, there is information about it in my previous tutorial on adding seam allowances. 

What I didn't go into in the last tutorial was what to do at intersection points. It's not a problem if your pattern piece is made up of straight seams on all sides, but if, like in the example, your pattern has a mixture of straight and curved seams, you will have to add one extra step to the process.

Focus on one particular area to start. I will start with the shoulder seam. Fold along the shoulder line. This is the original shoulder line, not the seam allowance line. By folding along the shoulder line you are able to see what will happen when the seam is stitched and pressed open (which is normally the case with shoulder seams).

Take a tracing wheel (or awl) and trace over the lines that indicate the seam allowance on either side of the shoulder seam (the armhole and the neckline) for approximately 2-3cm (1in).

Unfold the pattern and you will see that you have transferred the shaping to the shoulder seam. 

Use a ruler and pencil to join the dots created by the tracing wheel. 

You will see that when you fold back the seam allowance on the shoulder seam, it now sits flush with the armhole and neckline.

Next, we'll move onto the side seam.

Again, fold along the stitch line. 

Use a tracing wheel to trace along the armhole and hem line (the seam allowance line, not the stitch line) for approximately 2-3cm (1in). 

Unfold to see the lines that have been transferred to the side seam and mark with a ruler and pencil.

Repeat process form all pattern pieces, and that's it, you're done! 

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Throwback Thursday: How to add seam allowance to a sewing pattern

Last week, I showed you how to draft a skirt block from your own measurements, and then how to add shaping to the darts at the waistline, as part of The Skirt Series.

Before going ahead and making a toile to see how it fits, you will need to add seam allowance and pattern markings (which will be in tomorrow's post). 

What is seam allowance?

Seam allowance is the extra space you add around the edge of a pattern piece so that it can be sewn together.

If you do not plan to make up a toile of your pattern (in the case of pattern blocks), then there is no need to add seam allowance. When you are using a block to create a pattern it is much easier to use it without seam allowance and then add seam allowance once the pattern is complete. 

How do I add seam allowance?

I find that the easiest way to add seam allowance is with a long transparent ruler. Not to worry if you don’t have one though, you can just use and ordinary ruler and mark the seam allowance width at intervals along the seam and then draw the line through all the points.

I have two different rulers, which I find super helpful. One only shows centimetres, but also has lines to indicate the millimetres in between. This one is very handy for when I'm adding 6mm seam allowance to a neckline or 12mm to a seam.

The other, which I have used for this tutorial, only show has a line for every 5mm. If I am using a 1cm / 1.5cm / 2cm seam allowance, then this is definitely the one I reach for, as there are a lot fewer lines to get confused by!

Before getting started

Before getting started, have a think about the seam allowances you plan to use. I know some commercial patterns use the same seam allowance on every seam, but I think you are much better off changing the allowance depending on the seam. This will help you get a much cleaner and more professional finish.

The seam allowance required will have a lot to do with the fabric you are using, and how you will be finishing the seams too. For example, if you are making a silk chiffon top, it is best to use a narrow seam allowance, so you are not left with bulky seams that show through. A silk chiffon top is a delicate piece of clothing, that is not worn everyday and is normally hand washed, so it can afford to have smaller seam allowances. But, if you are making a pair of trousers or a coat, you need seams that a stronger (particularly in places where tension is put on the seams - e.g. the crotch of trousers) and therefore need a seam allowance that is wider than what you would use for your chiffon top. 

Standard seam allowances

I have put together a table to help guide you with how much seam allowance to add, but as I said, it is up to you! If you click on it, you can download a printable version of the table. It may be handy to put up on the wall in your sewing room!

Adding seam allowance to your skirt block

This tutorial will show you the method I use for adding seam allowance to a pattern, using a skirt block as an example. This method can be used to add seam allowance to any pattern.

Decide on how much seam allowance you will be adding (using the table above if needed) and find where the line is that indicates that width on your ruler. 

Lay that particular line (the width of your seam allowance) along the side seam of your pattern.

With a sharp pencil, or pacer, draw in your seam allowance, being careful to keep your ruler in place. Be sure to extend the line past the original line by a couple of centimetres (this helps when we add seam allowance to the other seams).

After marking the side seam, it's now time to move on to the hip curve.

If the seam you are adding seam allowance to is curved (which it is in this case) you will need to mark the seam allowance with a broken line. Line up your seam with the ruler and draw a small line (in this case, two lines).

Then pivot your ruler to you next point (I tend to do this every 1 – 1.5cm) and continue marking the seam allowance with a broken line.

For tight curves (such as the bodice neckline) mark your seam allowance guidelines closer together to ensure a smooth and accurate curve.

Continue pivoting until you have gone around the whole curve.

Next, on to the waistline. Before starting to add seam allowance, extend both dart arms, as well as the centre line, by a few centimetres. This will help when you are adding seam allowance to the top of the dart.

Mark the seam allowance on the waistband, and then follow the angle of the dart, when you get to the first dart arm. Repeat for the other side.

Continue along the waistline, towards the centre front, pivoting the ruler when necessary. 

The centre front does not need seam allowance, as you will be cutting this piece on the fold. Just extend the centre front line a little beyond each edge, so that it can intersect with the seams on the other sides. 

Mark the hem allowance by measuring down the centre front and side seam from the stitching line. 

Join the points to create the hemline. 

By this stage, you should have worked your way around the whole pattern.

Now to do something about those broken lines. 

Draw in your curve by joining the broken lines to form a smooth curve. You can do this by carefully pivoting your ruler, using a French curve or something else round (like a large mug or plate depending on the shape of the curve). A good way to check if your curve is smooth is, with the pattern flat on a table, to crouch down and look at the curve at eye level. You will quickly see if there are any sharp points!

Repeat for the back pattern piece. And you are done, your pattern now has seam allowance!

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I would love to know if I have convinced any of you to try doing some pattern making yet?

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