External concrete floor too close to DPC

I have a 1950s 3 bed terrace and in the back garden a concrete floor has been poured up against the rear of the house, but on the survey the mentioned it was too high, as it is only an inch or so below an air brick and 3-4 inches below the DPC. Not quite sure how thick the concrete is, but if it is similar to the front garden I think it will be about 6 inches

Rather than remove the whole concrete floor I was thinking of cutting a 6inch to 1 foot channel in the concrete and then digging out and filing with gravel for drainage. Not too sure the best way to cut the concrete floor although saw this floor saw on HSS and looks like it would do the job:

http://www.hss.com/g/43234/Floor-Track-Saw-Petrol-350mm.html

I guess I would try and cut the floor with a number of channels and then break up with a sledge hammer.

Wanted to check the above is the correct approach and also if there is anything i should look out for; a bit concerned I may cut pipes or cables commng out of the rear of the property!

Don't worry about hitting anything as a power saw will only cut to about 5 inches deep. The only possible thing you may hit would be a ntl/ cabletel line which are often frighteningly near the surface. Your channel along the wall solution sounds fine. Alternatively you could consider putting in some channel gulleys instead. Although they will require somewhere to drain to.

Good idea to cut a gulley and fill it with shingle, before you do though get some "Black Jack" or sinter proof and coat the wall below the floor level, just in case the water doesnt soak away quickly enough.
With regard to pipes and cabels never assume they will be deep enough not to hit. From the hire shop get a detector and scan the area you want to cut. I will work out cheaper than having to have a main repair that some lazy groundworker hasnt bothered to dig in deep enough.
Tell the hire shop what you want to do in detail they will give you the right tools for the job.

Tony

Thanks for the help and advice, really useful.

Adam

if you didn't mind the look of it, you could chase in a lead flashing to deal with the splash issue.