Changing flat roof to pitched, rainwater pipe connected to foul sewer

Slinky

Our house has an attached garage which is also attached to our neighbour's garage. Both garages have flat roofs, which extend to over the entrance hall and downstairs cloakrooms in both properties.  At some point in the past, our house has had guttering fixed across the front of the garage, across the hall & cloakroom, turning at 90 degrees to run along the cloakroom wall, finishing with a downpipe that exits into the same drain as from the kitchen. This is of course, connected to the foul sewer, which is in contravention of current building regs, although may not have been at the time it was done.  Our neighbour's property doesn't have this guttering.  All the water falling on both garage roofs runs to guttering at the back of the garages and into surface water drainage. 

We would like to put a pitched roof over the entrance hall/cloakroom as they are very cold.  Given we are already breaking current building regs with the guttering running into foul sewer, would we be able to put the guttering from the new roof into the existing downpipe?  We are talking about an area of roof about 2x3 meters. Logistically it would be very difficult to connect the guttering to the surface water drains which are at the back of the property. The only other option would appear to let the rain run onto the garage roof and drain that way.

FreeBear

The regulations require you to use a soakaway, a permeable area (rain garden), a water course, or as a last resort, a combined sewer. A foul water sewer must not be used... But this is where the regulations are an !!!!!!... A combined sewer is a mix of foul water and surface water drainage - Go figure.

If you have space at the front of the property, and soil conditions allow, you could install a soakaway (using a SUDS crate or two).

Slinky

I'm not sure we could get a suds crate 5 meters from the wall and 2.5 meters away from our boundary, particularly as we would have to go across or underneath the foul sewer which is just over a meter down.