Types of Roof Moisture Surveys
Option 1 – Under-Roof Infrared Moisture Surveys
An under-roof moisture survey is accomplished when the thermographer determines differences in mass between and wet and dry substrate by looking up at the roof from the inside of the building. This only works when there is a direct line of sight to the underside of the roof, which obviously has limitations.
If working in an open gym, or a like building, a direct line of sight is usually possible. However, if a structure has acoustic tiles or something else that blocks the camera from the roof, the obstacle must be removed. This is often far too laborious to be considered viable.
This is the only technique suitable for vinyl-backed fiberglass insulated roofs because the air gap between the insulation and metal deck prohibits infrared viewing from above. Compact roofs are not suitable for the under-roof method, because the looking-down method is far easier.
Option 2 – On-Roof Infrared Moisture Surveys
This is the most used method of roof thermography. Two person crews comprised of an infrared thermographer and an assistant conduct the survey with help from the building owner or their representative. The crew must have access to all areas of the roof in order to collect data, so conditions need to be relatively good.
While a number of factors will influence the speed at which an inspection may be carried out, a professional thermography crew can survey up to 100,000 square feet of roof in a single night. Areas on the roof containing subsurface moisture are marked directly and along the perimeter of the wet areas. Visual photos of the affected areas are also photographed and matched up to pertinent sections in the report.
Option 3 – Elevated Vantage Point Roof Moisture Surveys
A better vantage point for infrared imaging is further away from the subject, as long as the spatial resolution is high enough to create an image of adequate quality. Data generated from these surveys is more useful, because high quality spatial resolution is combined with the high usability of the infrared image.
In actuality, the only reason a crew would ever get close to a wet area on a roof is to mark it. This is a common mistake made by novice thermographers when they try to get close up images of wet spots on the roof by filling the photo’s frame with the anomaly.
Option 4 – Aerial Infrared Roof Moisture Surveys
Aerial surveys are the most efficient way to detect roof moisture. Roof surveys must be conducted on a night when the roof is dry, there are low winds, and no precipitation. However, there is a longer window with aerial infrared because slight differences in radiated heat from wet and dry areas on the roof are recognizable for a longer period of time. To produce usable imagery from the survey, high resolution systems must be used from a high viewing angle. This means that infrared cameras used for on-roof surveys are incompatible with the requirements of aerial surveys conducted thousands of feet above the roof.
Aerial infrared roof moisture surveys are best conducted under the following conditions:
- Large roofs
- Roofs that are inaccessible
- Roofs that pose a danger
- Roofs where access is impossible
- When wide areas must be inspected
- Difficult roofs
A quality scaled CAD drawing of the entrained moisture areas on the roof has significant benefits for the owner of the building. Areas of concern on the roof are accurately marked, making for a clear and concise report. One of the biggest advantages of aerial infrared surveys is that the thermographer can wait for optimal conditions. If image quality is suffering at one point in the night, the imager can return at a later time when ambient light conditions are better.