Why Is There Ponding Water On My Flat Roof?


Flat roofs have widely been used on commercial properties, and commonly on garages attached to residential properties. However, they have been gaining in popularity more and more on residential properties over the last 20 years. So what does it mean if your flat roof has started ponding?

What Is Ponding?

Flat roofs are typically fitted with a slight gradient which allows the water to drain off and into your guttering. However, when it doesn’t run off efficiently, ponding can happen. Ponding is when a puddle of water collects and forms on the roof. Typically these are quite shallow and can dry off pretty quickly once the rain stops. If this isn’t the case, it might be worth calling in the professionals to take a look.

What Causes Ponding?

Ponding is considered to be one of the most common issues that flat roofs experience. There can be a number of causes, some of which are quick fixes by a professional roofer, others will require a more in-depth repair. Below are the most common causes.

Structural Issues – This is quite often the cause of ponding when a flat roof has been installed on a new structure or building. Buildings often have a settling period where they may slightly move. When this happens and the building has a flat roof, the slight move can mean that the initial gradient the roof was installed with may no longer be efficient. Thus leaving water on the roof without draining.

Improper Installation – As we mentioned, flat roofs aren’t entirely flat. However, a number of roofs are installed incorrectly without the appropriate gradient. As there is nowhere for the rain to drain, it creates ponding.

Drainage Issues – Larger flat roofs will require more drainage than a simple guttering around the perimeter, such as on commercial properties. These will then need to be installed with internal drainage features. Ponding can arise when these drains are blocked with debris or are not draining efficiently. Alternatively, if these drains are not installed at regular and appropriate intervals ponding will appear elsewhere.

Roof Features – There are a number of features that we can have installed on a flat roof, and each of these can pose an issue if there is a dip surrounding it. For example, skylights and external vents, If you have one of these installed, please ensure that you have a roofing specialist check the area to ensure that it has an appropriate drainage angle and flashing in place.

HVAC Units – HVAC or heating, venting and air conditioning units are commonly installed on commercial properties. While they are great for those inside the building the weight of them can cause the flat roof to dip, which can also worsen over time. Ponding will often form around them, meaning that they will need to be checked regularly to prevent issues further down the line.

Compressed Installation – Flat roofs are typically not designed to have a high level of foot traffic or items stored on them. However, on some commercial roofs and garage roofs, this often happens. This can compress the installation underneath, which will then be exaggerated by the weight of rainwater and snow.

Fixing Ponding On Roofs

When it comes to fixing ponding on your roof, we highly recommend putting down the DIY tools and calling in the professionals. Unfortunately, with flat roofing, small mistakes can lead to bigger problems that will take time to resolve. Here are some common fixes that we may undertake:

Roof Inspection – before any work is carried out, one of our experts will carry out a complete roof inspection to ensure that we are only carrying out the necessary repairs, and that there are no hidden issues that may occur whilst we carry out the work or after we have left the property.

Fix Structural Issues – This is common when the building settling has been a factor in the ponding. However, this may require us to work with a structural engineer or other builders to ensure that the structure of the property is sound before we correct the roof.

Fixing Installation Issues – As mentioned above, the main installation issue is the reduced angle of the slope on the roof. This may require more work than many of the other fixes. To permanently fix the issue and reduce the risk of future ponding, you may require a complete new roof installation. This can be a costly repair, that in many cases is unavoidable.

Drainage Fixes – The majority of drainage issues are on larger, commercial roofs. For the most part, the drainage issue can be repaired by raising the angle of the roof around any installations that are weighing that section down, in order to allow the roof to flow to the drains. You may also find that your drain screen is getting easily blocked, you may want to discuss having an alternative fitted to avoid clogging.

There are a number of other fixes that can be carried out on your roof, each one as individual as the issue itself. For more information on repairing the damage from ponding and installing further preventative measures, please contact a member of our expert team today who will be happy to assist you.