The answer really depends on many factors. Overall, architects can be useful where there is some architectural input - i.e. some design - but you are planning a square box extension and you definitely don't need an architect for that. It also depends if you are employing a builder. If so I would strongly advise against just getting a builder to wing it under a building notice. All the reports I've ever done for courts when jobs have gone sh1tfaced have been where people get builders to build stuff in that way. In your case you are self-building and this depends on the experience of the self-builder. I have produced drawings for several very good builders, on their own personal projects, who would be more than capable doing it themselves, but they prefer to have drawings to work to. And apart from anything else, having good drawings to work to helps thinking ahead and working out materials and logistics to the point that you probably save what they cost in the first place. Much of my work comes through builders who are called to look at jobs - sometimes quite simple jobs - but the clients have no design. They won't touch it. As one builder told me a while back, the days of working on the fly are long gone.
Grand designs; get an architect. For square boxes; find a good chartered surveyor or a technician. PS. the prices you were quoted are about right.
Grand designs; get an architect. For square boxes; find a good chartered surveyor or a technician. PS. the prices you were quoted are about right.