Or going through both with a power saw maybe. This 25mm thing sounds like something that started out as a sensible guideline that then got set in stone in the regs. Personally I've never worried much about it, except from the point of view of an inspection picking it up.
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.
Are you a trade or supplier? You can create your listing free at DIYnot Local
