You can extend out to the rear of your property 3m on a semi detached or 4m on a detached without the need of permission. You will still require building requlations. All the info is on the planning portal website.
Most single story extensions take between 8-12wks and 2 story extensions take between 12-16wks.
Depending on the finished spec you require. Cost do vary as there are many things to consider when we price up any project. Typically most extension cost between £900- £1200/m2.
No, it is very rare you will need us out whilst we are extending your property. The only time we may disturb you is when removing walls from the old into the new. We always try our best to keep some sort of working kitchen/bathroom throughout the project.