Gaps around PVC-U windows

That is a minimum gap to allow for movement within the building and windows as they move due to temperature. Bigger than that depends on how the window fits an opening as they are rarely square

 

If you've got gaps of more than 10mm both sides, it's wrong.

 

For heavens sake!

 

Normally 50mm gap about right, window fits easier.

 

So many variables sometimes you have to fit a sub cill to raise a window up to comply with building regs or to allow for tilt and turn windows. Sometimes it is cheaper to get standard sizes and pack and cap with trim rather than pay the extra for custom made.

Although this was what I discovered a few months ago when I removed some trim around a window - this was excessive gaps! For some reason windows had been fitted that were 200mm narrower than the opening.

 

For heaven's sake.

And it looks like they just covered the gap with a bit of trim!

 

They had, not even cement or foam and in the bottom picture that's daylight coming through.