1. Cracks

Structural or thermal movement leading to excessive differential movement between the substrate and the roof covering can cause this. As the roof covering gets older it is less able to cope with this type of movement and is often an indicator of the end of the serviceable life of the roof covering.

2. Asphalt Creep

The surface cracking in this asphalt is caused by the movement of the asphalt due to flow and/or creep. One theory is that mastic asphalt behaves in a viscous-elastic manner and creeps slowly to assume the profile of the supporting substrate under normal in-service temperatures.

If high temperatures are experienced then the flow properties will become more fluid, such that the asphalt could easily sag into undulations in the substrate.

3. Mechanical Damage

This is mechanical damage, caused by something being dropped onto the asphalt roof surface. Asphalt, although flexible when warm, is brittle when cold. If a roof is regularly trafficked, protective walkways should be provided.

4. Slumping

Problems often occur at details such as this abutment. Here, some slumping and cracking of the asphalt has occurred.

5. Poorly Detailed Penetrations

Where pipes or services penetrate the roof, it is essential to get the detail right. Here the waterproofing to the roof penetrations has been poorly formed allowing the opportunity for water ingress.

6. Nailed Cables

Cables have been attached to the roof with clips nailed through the waterproofing. Any punctures to the waterproofing system provide an opportunity for water ingress.

7. Ponding

This bituminous cover does not have adequate falls as recommended in BS6229:2002:British Standard Code of Practice for Flat Roofs with Continuously Supported Coverings: Section 7.1.

The absolute minimum fall recommended for a roof is 1:80. When falls are below this figure the roof undulation and any deck deflection increases the risk of ponding.

8. Blocked Rainwater Outlets

It is very common for rainwater outlets to become blocked with general roof debris, we recommend regular good roof husbandry, which includes the cleaning out of all roof outlets, and replacing leaf guards as appropriate.

9. Open Laps

Open laps were observed on this bituminous felt roof in the main field sheet and in the flashings. This is usually caused by shrinkage of the roof membrane or excessive thermal and structural movement of the substrate.

Older roof membranes have less inherent flexibility and they are more susceptible to the effects of movement. A more fundamental cause of open laps is bad workmanship.


If you have a flat or membrane roof that requires some attention or is encountering any of the above problems, please click on the following link to Contact a Technical Services Advisor.