How to fix ponding water on a flat roof

With the British climate being what it is, we know a thing or two about rainfall here in the UK! And standing water on a flat roof is a common problem.

But the good news is YES, you can fix it! You can in fact fix it yourself with a fantastic product originally used in the US but now available in the UK. It’s a DIY product that anyone can apply and it will level out the roof and stop water ponding.

On a performing flat roof, ponding water isn’t a problem as it will just drain away. However, when your flat roof has uneven areas, an insufficient slope, or drainage issues, the water doesn’t dissipate. This can cause issues, including… (Tip: skip straight to solutions or read on to learn more about the common problems caused by ponding water)

Common problems caused by flat roof ponding

Degrading roofing materials, particularly on older modified and built up roofs

Extra stress and damage to the load bearing structure due to the extra weight of the water

In winter freezing standing water will expand causing more damage

Stagnant water is a common breeding ground for insects and mosquitoes

The water focuses any sunlight that travels through it intensifying it and causing more UV degradation.

Ponding water on flat roof solutions

There could be a simple solution to your roof ponding issues and it is definitely worth investigating these before you call in the professionals!

Check your drains
If there is anything obstructing the flow of water to the drain or the drain is blocked, remove any debris or blockage.

Structural issues
If you have improperly installed frames, joists or beams you’ll need to call a professional to come and recommend.

Look for dips
If the roof sags or has small uneven areas these need to be levelled. You can buy a very easy to apply, DIY flat roof levelling compound kit that comes with everything you need to pack in the dip and seal with a waterproof coating. You can even create slopes with it to navigate water towards drainage exits! Super easy and fast to apply, it can save you hundreds on your roof repair. Get your ponding water repair kit here.

6 easy steps!


Outline the area you want to fix with chalk.


Apply primer.


Mix the Greenslope.


Apply the Greenslope with a trowel.


Leave to set.


Apply the top coat with a trowel.

Included in a Greenslope for Ponding Water Kit:

Greenslope mixture (including primer)

Paint brush

Disposable gloves

Greenslope mixture bag


Applying Greenslope

Difficulty Level

Tools we recommend using to assist application

Chalk …to outline your work area

A trowel …to compact the mixture

A solvent or liquid …to stop the mixture sticking to the trowel

A spirit level …to make sure you have the right angle

‘Fibre reinforced top-coat’ …to make your Greenslope mixture water tight

Want some more recommendations on flat roof repair and DIY solutions to ponding water? Give us a call or drop us a line and our team of experts are always happy to help!