Crack in corner of wall

[The Money Pit]

Hello,
We have a crack in the corner of our lounge, the crack appeared about 3 years ago after we had new oak flooring installed. To install the floor we removed all the old floor boards and the placed insulation between the joists and reinstalled new solid oak tongue and groove boards.
The crack appeared about 4 months after the work was complete and didn't seem to get any worse until I noticed yesterday is seemed bigger.
I had taken photos back in Aug '18 and looked back at them and it had become larger.
I have attached the pictures from 2018 and last night so you can see the difference.
Can anyone please advise what this could be, the floor below seems solid but there is also a crack that runs horizontally along the wall.
I hope someone can advise. Thank you

 

[mrrusty]

I wonder - was the floor installed with an appropriate expansion gap all round?

 

[The Money Pit]

I don't know, could this cause the crack? I can ask our installer?

 

[mrrusty]

Timber expanding due to changes in humidity has considerable power - so much so that an old method of rock splitting is using dry wooden wedges that are then soaked in water so they expand http://www.dartmoorcam.co.uk/CAM/SplittingGranite.htm

so it's possible this could cause your crack - i've never seen it, but can imagine it is possible.

 

[The Money Pit]

Thank you, this does make sense as there are no cracks on the outside wall.
We will remove the skirting and check to see if there is an expansion gap and add one if there isn't.
Thank you again