Texture distorted on UV unwrapped face I am not sure what I did here. I have unwrapped this face and in the UV editor you can see that it is covering the entire thatch part of the quad but there appears to be an invisible diagonal line distorting the texture:



What's going on here? There are no additional vertices on the face that I can see.
The diagonal line is caused by unproperly scaled UV coordinates for the face. Original face resembles trapeze where the bottom parallel line is longer and the top one - shorter. In order to avoid any distortions of the texture the UV map for that rectangle should also have those forms - one side shorter than the parallel one. 

If scaling unchanged UV map you'll notice how it distorts:



The easiest solution would be to unwrap again in order to restore original proportions. However you can scale those edges on the map to roughly respect original ratio as well.