Someone has clad the underside of the rafters with OSB (John - if you are thinking about sarking boards, they are generally often plywood, but are fitted on top of the rafters and carry the membrane, so you'd stilll see the rafters). No way to know what is above that OSB without either taking id down or drilling a hole in it with a hole saw. The extra strutting in the ceiling joists, together with their dimensions points to it having probably been built with provision for conversion - and then the sparky got in there, the cabbage!
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local