Damp Roof Comment

 

Detect underlying damp or moisture using Infraredthermal imaging, conductivity, radio frequency, video endoscope equipment and drain down pipe cameras.
Moisture is an efficient conductor of heat energy and wet insulation is in fact worse than no insulation. Underlying moisture in flat roofs, for example, can often be detected and visualised with high resolution infrared thermal imaging equipment operating in the appropriate wavelength.

Flat roofs with parapet walls often leak with the manifestation of damp walls and ceilings in the lower floors. Parapet walls are a weakness with respect to water ingress, especially on tall buildings. High winds around internal and external wall angles can create eddies which double back on themselves and in turn create miniature whirlwinds. When carrying rain or dense water vapour, the high increase in velocity can penetrate the smallest of gaps.

Rampart Image

Typical Rampart Construction

The above sketch shows a typical method of parapet cavity wall construction. The red areas are D.P.C membranes. The green are weep holes and a tie showing central drip off.

There can be numerous ways that water can ingress into a parapet wall and track down the inner skin. For example:-

1. Coping slabs dis-bonded owing to old and porous mortar. Dis-bonding can happen because of thermal and wet/dry movement, especially with long lengths of slab. This is made worse by solid fillers or mortar between the slab end joints.

2. Joints between non-porous materials will absorb moisture more readily especially under wind pressure.

3. DPC not extending fully and turned down on the outer leaf. Water can track under the DPC and saturate the inner leaf below the DPC.

4. Sagging or torn DPC, water can collect and travel off ends and distorted joins.

5. Lack or absence of weep holes. Water collection cannot escape above the DPC.

6. No DPC directly beneath the coping slabs or one that extends over both leaves.

7. Parapet internal corners. These areas are especially prone to leakage because of the wind effects and the more complex and more fragile DPC detail both in the parapet wall and the skirting.

Bricks

Brick Deterioration

The thermal image above shows saturated brickwork above the DPC (blue) and a lower characteristic funnelling shape where the DPC has been bypassed. The moisture in this case can be seen not to have entered under the asphalt roof covering but had travelled to the walls and ceiling of the floor below.

Although in this case the moisture was not visible to the naked eye, care must be taken with infrared equipment to ensure the images are interpreted properly. External moisture is constantly evaporating and therefore appears cold. Sub-surface moisture can have the opposite thermal appearance since it may be heated from the building and is slow to change with respect to ambient changes. A thermal imager is therefore used as a tool to very quickly detect and provide a visualistion of moisture patterns, extent and travel direction. Density layers (density slicing) can often be visualised as temperatures and this may be interpreted to determine the core of the moisture. The data then must be confirmed by more conventional conductivity and other testing methods.

Roof 1

The photograph above shows the skirting dropping and pulling out of chase. This was due to movement differences. The consequence of this was moisture ingress finding its way beneath the roof felting and damp walls in the rooms below. The thermal image below clearly shows the underlying moisture. The light yellow temperatures highlight the moisture extent and spread.

Roof 2

Water that has found its way under an asphalt covering will readily soak into the porous screed laid over the concrete. This moisture can take a long time to dry even after remedial work has been completed. It is important therefore to repair known leaks as soon as possible. Sub-surface moisture is usually easy to detect and display on a thermal imager if the building is heated. As previously discussed, moisture is an efficient conductor of heat energy and damp areas will display a differential surface temperatures) to the surrounding dry areas. Flat roofs on unheated buildings can also be very effectively surveyed with IR under certain weather conditions and therefore nearly all year round. The techniques and image interpretation are however different.

Roof 3

This is a photograph of a blister in the asphalt on a flat roof. Asphalt being black absorbs solar gain and undergoes extreme changes in temperature and some movement throughout the year. Blistering however is normally caused by underlying trapped moisture which vaporises under heat. The vaporisation creates pressure and the hot and therefore soft asphalt blisters. Traffic over the roof surface will easily break the blisters especially during cold weather when the asphalt is less flexible. The thermal image below shows blisters as a result of entrapped moisture.

The round yellow areas on the roof are blisters. The entrapped moisture is conducting the heat from the building to the surface. This roof has particularly severe moisture ingress.

Roof 4

 

The image below shows another typical thermal image of a flat roof with moisture ingress:

Roof 5

In this example the light yellow/white area is moisture beneath the felting. This was a particularly easy diagnosis since the felting had corrugated and become brittle. Many of the peaks and troughs had split allowing water to enter and spread. This is simply a good example of how under surface moisture can appear on a thermal imaging monitor.

This particular roof had no over covering, such as chippings, and the sun’s UV had over time damaged the felting.

The thermal image below is of a pitched roof and the manifestation of moisture under the surface is clearly evident. There was no visible evidence of this moisture.

Roof 6

Unpainted galvanised metal clad roofs are particularly difficult to survey with thermal imaging equipment because of high reflections of sky temperatures, nearby buildings and structures etc. We have developed techniques to minimise unwanted data and successfully discriminate damp areas along joint overlaps and wet or missing insulation.

Thermal imaging can pinpoint rising and penetrating damp in buildings immediately by providing a complete picture of the moisture. In most cases, the characteristic shapes and trails will identify direction of travel and the source of the ingress. Supported by video recorded endoscope, (boroscope) and conductivity measurements, a very detailed survey can be conducted.

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