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Common Flat Roof Problems

Flat roofs are known to cause building owners problems. Leaking is a most common problem with fat roofs. Most of these problems are completely avoidable. The reason for this is because these problems are caused by poor quality workmanship when the flat roof was installed. Or the roof has not been maintained properly by the building owner. A well installed flat roof with the correct roof covering should cause no problems and not leak.

Are Flat Roofs Completely Flat?

No flat roofs are not 100% flat. They have a slight slope. This is to allow rain water to drain off the roof.

The reason these roofs are referred to as flat roofs is that they are flat when compared to traditional pitched roof.

Flat Roofs are Increasingly Popular

The reason for the increase in the popularity of flat roofs is down to them being economical to construct. Due to a flat roof requiring less space than a pitched roof the volume of the building is reduced, which reduces energy costs.

How often does the Waterproofing Membrane on a Flat Roof need to be changed?

The waterproofing membrane used to cover a flat roof usually last between 20 and 30 years. Often this will be how long the roof is guaranteed for by the roofing contractor who installed it. This is not as long lasting as a pitched roof which has been tiled.

For this reason, building owners need to plan to replace the waterproofing membrane on their flat roofs at the appropriate time.

How Often Should You Maintain a Flat Roof to Prevent Problems?

Flat roofs should be regularly maintained to prevent problems occurring. Maintenance is the classic case of prevention is better than cure. One of the most common problems you can encounter with a flat roof is the rainwater outlets becoming blocked. The reason these can become blocked is when leaves and other debris are swept into the rainwater outlets by the wind. Leaf guards can delay the buildup of debris in the rainwater outlets. However, the best thing to do is to contact a local roof contractor to carry pout the maintenance work. This will include roof sweeping which will keep your rainwater outlets clear preventing any unnecessary problems with your flat roof.

Common Flat Roof Problems to Watch Out For

1. A Buildup of Vegetation

Any moss, fungus or weeds growing on the surface of flat roof are tell tales signs there has been a buildup of water on the roofs surface

2. Watermarks on the Roof’s Surface

If you can see patches of lighter or darker shades on your roof. This is a sign there has been large pools of water on the surface of your roof which has since evaporated

3. Large Pools of Water on your Flat Roof’s Surface

Large pools of water on the surface of your flat roof is a very bad sign which you should get inspected immediately. The reason this is such a bad sign is the water will have to escape somewhere either evaporating or as in most cases through your roof. This is how leaks can occur.

4. A Buildup of Debris on the Surface

As mentioned above leafs and general debris swept in to the rainwater outlet is a problem you need to look out for. And a problem which can easily be managed by regular maintenance which will probably include roof sweeping.

5. Not a steep enough angle on your Flat Roof

As we discovered earlier flat roofs shouldn’t be 100% flat. They need a slight gradient for water to roll off the surface. Ideally the gradient of the roof should be between 1 in 40 and 1 in 80. This gradient is very gradual and is not always easy to spot with the naked eye. For this reason, we recommend you check the gradient with a spirit level.

6. Punctures in the Roof’s Surface

You need to make sure anything added to your flat roof which includes the use of nails or screws. If the surface of your roof covering is punctured not only will this compromise your roofs integrity and lead to an increase in the probability of leaks. It can also make any guarantee you have with your roof void.

7. Blistering on the Roof’s Surfaces

Blistering is when you see a bubble-like patch appear on your flat roof. This is a cause for concern and you should call out a roof contractor to survey the condition of your roof. The reason for this is because if the bubble bursts there can be a hole in your roof giving water a way to penetrate through your roofing structure.

8. Rusted and Missing Nails

Nails are not commonly found on modern flat roofs, but on older properties nails were very likely used when the flat roof was installed.  When these nails begin to rust, or fall out of the roof. They become a place where water can potentially penetrate through your roofing system and cause leaks.

9. Poor Quality Roof Repairs

Sometimes roofs are patched up quickly and unprofessionally to save on cost. Look out for parts of the roof that clearly don’t match with the rest of the roof covering material. And look for parts of the roof where excess silicon has been used and untidy finishes are visible.

10. Stretching and Cracking Around the Joints and in the Corners

This is a problem most commonly seen on EPDM Rubber Roofs. As the flat roof ages, the material which make up the waterproofing layers of your roof can crack because of drying out or stretching. In some cases, they can also rip.

11. Subsidence Causing Cracks and Tears

Every property will suffer with movement over time. However, in most cases this movement is only minuscule. But it is possible a moving wall can stretch the roofing material which can lead to cracks and tears in the waterproofing membrane.

How to Minimise the Chances of Problems with your Flat Roof

• Have more than one water outlet to drain each roofing area.

• Use leaf guards for all outlets and regularly inspect them to make sure they do not become blocked.

• Select a reputable roofing contractor with the appropriate qualifications and insurance. Who will also provide guarantees on their workmanship and material used for your flat roof installation.

• Make sure the joint between the flat roof and parapet wall is designed and installed correctly. The reason for this is to make sure there is not any break in the waterproofing membrane.

• Allow for easy inspection and maintenance of the roof once installation is complete. This is vital in making sure the roof has maximum longevity.


If you are in the Woking or Guildford area and having problems with your flat roof. Just call us on  01483 475141 or get in touch via a webform.