Whenver I try to preview the render, using the Ctrl+B render box I get these strange transparent strips I haven't tried rendering the whole model yet (as it isn't finished) but I hope they won't affect it? They popped up seemingly without any cause and occur no matter what I box select. Anyone know what to do?
When you did ctl + b and drew the box to render you only selected that part that you see rendered. There is more to the scene but you would need to redraw your box (ctrl + B) around the whole box outlined in red (the render view).
Just ctrl + b around the entire red square and you should be fine.
The ctrl + b is just for rendering a certain part of your scene so you do have to waste time rendering everything.