Where extensions are built without professional help, it is not unusual to find that they are not constructed in accordance with best building practice. If the owner extending his or her home is not getting a loan from a lender, the question of getting an architect or engineer to certify that the extension or conversion does not require planning permission (or has been built in accordance with approved plans) does not usually arise until the house is being sold. Even if the owner is getting such a loan, the question of certification often does not arise until too late i.e. when the work is nearly finished.
Problems with planning, building regulations and certification require careful consideration by a competent architect/engineer/surveyor experienced in such matters, in consultation with a solicitor experienced in conveyancing. Whilst all professionals’ certificates are qualified to some degree, the original designers’ affirmations and opinions are by far the most authoritative; anything later is a much more subjective opinion based on far more restricted information and may be found wanting if tested.