Depends where you live in Scotlnad possible to apply for retrospective permission - unauthorised works, but have to provide Building Control with engineers certification on structure works - best checking with Local Authority who will advise best action.
get a full structural survey carried out and ask them to specifically look at the dormer if you are worried.
if you just want an engineer to sign off the dormer to say its structurally sound, i think you will have a limited choice as why would they take on the risk for very little money. they have no idea of the current strength of the material except from experience, and if it fails in the next 10 years (depends on warranty) you will make a claim against them, even though it may be nearly 36 years old!
planning permission wise - its an addition to the original so will need to comply to regs. if its on the back i dont think you need permisson - permitted develpment? otherwise may need it, i imagine it will be ok as already there and no one has conplained. speak to the duty planning officer who offers free and impartial advice. although they arent always able to help its a good place to start
either get the current owners to sort it out, or get the solicitor to withhold a retention - payable when the dormer is signed off.
worst case - this may involve having it removed completly and rebuilt to obtain a warrenty, or removed due to planning restrictions.
maybe planners would be worried about overlooking and insist on translucent glass instead.
i'm sure it will be fine as its been there for 26 years.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!