It is always advised to have an expert look at the roofing structure and then suggest the ventilation system. Ideally the ventilation system is designed at the time the roof is constructed. However, with time, certain blockages and other external factors tend to dislodge the ventilation system. This requires for a re-check and re-calibration of the roof venting system. Care must be taken that the vents and hoses are not blocked and proper air circulation is possible and allowed within the roofing structure. It will ensure the longevity of the building and also ensure that there are no leaks and related problems in your roof for a long time.