I've always had this hairline crack in my ceiling but just today I noticed it has gotten much worse. Why is this happening and what should I do about this issue?
My house is around 15 years old and it is made of drywall.

 

As to why it happened, there could be a few reasons. One is the house could be settling. Are there any cracks in the foundation? You could tape it & use joint compound. However, it could happen again.

 

The way that cracked it almost looks like no tape was used there.

 

What is above this area of the house? Has the gap on the crown moulding also gotten worse?

 

Is there any give if you push up on the drywall on either side of the crack?

 

Woops, I'm really sorry for not replying sooner. I thought I had set up email notifications for replies but I hadn't.

@ShortyLong What do you mean by the foundation? The base that the house is built on? If so, I don't have any visual on it. I'm not very knowledgeable in this area. I'm just a teenager trying to save the family home from imminent collapse haha. I even had to google what crown moulding was. Btw I realised I should've mentioned that this is an Australian double story house and this crack only appears on the second floor.

@XSleeper I'm not sure what is on top of it. The area above it is the roof space and I've never been in there. But we don't store things up in the roof space if that's what you mean. As for the gap in the crown moulding. I don't remember it being cracked before but it doesn't seem to have gotten worse since I took the photo. I'll attach another photo of a more close up shot though.

@marksr There is a very small amount of give when I push either side. I'd say about 1 millimeter or so.

 

Since this is just on the 2nd floor and assuming all the doors still fit [open/close] properly we can probably rule out any foundation issues. I wonder if attic ventilation or insulation has anything to do with it. Has it been extra hot or cold lately?

 

Actually my toilet doors have trouble closing properly but I thought it was the wood expanding from the wet weather. We ended up shaving down the door to get it to fit again. And yes, the weather has been very cold, always around 12 degrees Celsius with outside having lows of 3 degrees Celsius.

 

Changes in temperature and more importantly changes in humidity can cause the wood framing to expand/contract slightly. Sometimes that is enough to cause cracks in the drywall or caulking on the wood trim. If that is the case, there is a good chance the crack won't be as wide when the weather warms and dries up. More insulation in the attic could help along with making sure the attic is well ventilated.

 

Oh, So it's not a big deal and it'll just keep coming and going with the weather? I was afraid my whole ceiling was going to collapse or something.

 

It is something you need to keep an eye on but at this time I doubt there is any danger of the ceiling falling.

 

Phew that's good, thanks for all the advice! I'll update the thread if it gets any worse.