My employer would only complain if the side-project would reasonably make me less efficient within my contracted hours. So if I were doing 40h (5 full workdays here) every week and I'd be putting in 40h/w as well.
The other gotcha is that side-projects shouldn't be in any way competing directly with my employer. If you work in product-development that is pretty easy to isolate. Agencies on the other hand could basically make anything for a client. So that's a bit tricker.
No idea what of my contractual limitations are actually enforceable, though. And they've never complained about side-projects because my own projects aren't anywhere near something they would accept as a client.
The other gotcha is that side-projects shouldn't be in any way competing directly with my employer. If you work in product-development that is pretty easy to isolate. Agencies on the other hand could basically make anything for a client. So that's a bit tricker.
No idea what of my contractual limitations are actually enforceable, though. And they've never complained about side-projects because my own projects aren't anywhere near something they would accept as a client.