You usually don?t need planning permission for a loft conversion BUT you do need to comply with the building regulations and be issued with a completion certificate by the local authority.
I would be concerned if your loft conversion was done without going through the proper channels and you could have big problems when it comes to selling the property. The other concern of course is that if your loft conversion wasn?t carried out in compliance with the building regulations there may be real safety worries.
You need to consider your options whether that be contacting your builder again, consulting a structural engineer or seeking the advice of the local building control officer.
