I have a single skinned garage I would like to add a side door too, it's dense blockwork AFAIK (at east it's a beast to drill), I'm aware that strictly speaking Building Control Approval will be needed, I guess a simple concrete lintel with a 100mm bearing each end will suffice. It will be at least 665mm from the corner so as not to breach that particular regulation. Not sure if I will DIY or get someone in yet, I aim to buy a second hand or ex-display or similar door and have the opening built to suit. Any issues with my thoughts?