Does anybody no the answer, damp/timber joist problem

[toppin]

A question which hopefully somebody will no?? Why in some old terrrace houses is the ground floor solid to the rear but floorboards and joist to the front?

I have a seriouse problem to the front of the house where damp has caused all the boards and joist to rot, so bad that the floor has collapsed.

The house is and end terrace with a public sewer running parrallel to the gable end so im wondering if the drain is leeking, causing the damp. im wondering if i should put in new joist and boards or backfill the lounge, install a damp course and have a concreate finish. Would this help prevent damp?? Any ideas of prices between the to? Many thanks, Dave.

[welsh brickie]

I would fill in and concrete level with the existing floor and have company lay ashphalt over the entire ground floor.This will stop any damp penitrating whatsoever.Replacing the floor with new timbers and leaving a void for airflow is ok but if the sewer is leaking it will seep into that area.