Flat Roof Problems: 7 Things To Watch Out For

Flat Roof leaking

From easy access and innovative design to cost, flat roofs offer several advantages over other traditional roof structures. However, there are some common flat roof problems that can crop up. If you spot flat roof issues early and take swift action, you can easily fix them and extend the life of your roof.

This blog will cover five warning signs to take action against as soon as you notice them. Acting fast could save a ton of stress, time and money in the long run.

Flat Roof Problem 1 – Roof Vegetation

Green stuff growing on your flat roof? Beware. This is more than just an aesthetic problem.

A mini eco-system thriving up there is a sign that there has been a build-up of water, leaf debris and dirt. This innocent trio is a flat roof problem waiting to happen, because it makes for a beautifully-composty environment, a hotbed for weed seed germination. 

If moss, lichen, fungi, and weeds begin to grow on your flat roof, arrange for their removal. Leaving plants to grow on your roof will pin moisture against it, weigh it down, prevent runoff and potentially cause damage to the waterproof seams of your roof, not to mention their roots may penetrate the waterproof covering causing you more flat roof problems!

Roof Vegetation
Moss growing on a flat roof with reflective chippings

Flat Roof Problem 2Contracting and Stretching

Roofs made of rubber, specifically EPDM (or Ethylene-Propylene-Diene-Monomer), commonly experience this flat roof problem.

As a flexible roof layer ages, it is stretched and dries out due to consistent weathering. It can begin to wear heavily at corners and joints because of this, and you might spot tears or cracks starting to form, and it pulling away from up-stands or perimeter edges.

Flat Roof Problem 3 – Blistering & Alligatoring

Pockets of air or moisture in a flat roof can cause blisters to form and then expand in the sun, leading to cracks that allow water to enter.

When roofing adhesive is not applied thoroughly, or when condensation builds up from below, it can cause blisters and alligatoring. This problem doesn’t just disappear on its own. A professional repair involves cutting away blistered material and replacing it with a 6-inch overlap to form a new seal and protect your roof. However, this is often a short-term solution and a flat roof replacement would be a better investment. Want to know how much a new flat roof could cost? Read this.

Blisters in roof
Blistering on a flat roof due to moisture under the mineral felt.

Flat Roof Problem 4Pooling or Ponding Water 

Pooling, or ponding water, is effectively a longstanding puddle on your flat roof. And it’s bad news for most traditional coverings. If you find any standing water on your flat roof after two days, you should have it inspected by a professional and fixed quickly to protect the waterproofing’s structural integrity.

The flat roof problem of ponding water can happen for a few reasons.

Poor Fitting

Roofers without sufficient knowledge of complicated roof structures may not employ the level of expertise needed to install a complex flat roof. 

Insufficient Gradient

Flat roofs shouldn’t actually be flat. And a flat roof without enough of a fall means rainwater can’t run off sufficiently.

Clogged Drainage

This is a commonly overlooked flat roof problem, but an easy fix. Drains and gutters stuffed full of leaves and other debris cannot take water away from your flat roof. Therefore, in flash floods or heavy rainfall, water could back up to the roof outlet or drainage point and penetrate in to the building.


As the foundations of a building settle over months, years and even decades, even a well-designed roof can sag, changing the shape of a roof and causing the waterproofing system to buckle.

Spotted a swimming pool on your flat roof? Ponding water requires expert advice and professional action to get sorted. Leave it too late and you could end up with a leaking roof.

Ponding water
Ponding water on a flat roof caused by a damaged and collapsing timber structural deck.

Problem 5 – Building Movement

All properties can be affected by movement over time. Most often, it’s barely noticeable, but in some cases, the land beneath a building can cause serious problems.

Subsidence and land heave can cause significant changes to a building due to soil movement.

Moving walls, whether you notice it happening or not, will stretch a flat roof beyond its capability, often leading to tears in the flexible waterproof membrane. Tears and cracks may not be immediately noticeable, but they leave your home unprotected from water seeping in.

Problem 6 – Dodgy Repairs

Home DIY has a lot to answer for. Questionable decor and minor building work are one thing, but badly repaired flat roofs are a whole other level!

Odd, unmatching patches of waterproofing or excessive sealant on your flat roof could compromise its effectiveness if done by a non-professional. Check for DIY jobs and get them looked at ASAP.

Flat Roof Problem 7 – Punctures & Splits

Punctures are a common but overlooked flat roof problem. Something as simple as a piece of gravel lodged into a workman’s boot is enough to puncture the top layer of some flat roofs, enabling water to leak into the vulnerable area.

Punctures are especially hazardous because they can be tricky to spot. DIY projects can be the cause, however, storms that result in debris landing on your roof can also cause punctures and other damage. Always check your roof after a significant storm and think twice before trying to DIY fix your roof. 

Fast Action Could Prevent Serious Property Damage

For all of their benefits, there are quite a few flat roof problems to look out for. 

Now that you’ve been schooled on the most common culprits, start to keep an eye out! And book regular maintenance checks with a reputable and certified flat roofing company. They’ll have professional insights that you don’t.

Still trying to figure out flat roofing? Every home is different, and it’s great to explore your options. Read more about the difference between felt and single-ply flat roofs in one of our recent blogs “Single-Ply Vs Felt Flat Roofs: An Unbiased Review

Your Next Steps to solving your flat roof problems

  1. Claim your free guide to Flat Roofing here then……..
  2. Book your free flat roof survey or email us your plan [email protected]
  3. Online Quote Generator

After your survey, you’ll receive a free 23-point Roof Condition Report, Action Plan, and comprehensive itemised Quote worth £295+vat.

Before You Go!

Get Our Ultimate Guide to Choosing a Secure, Stylish Flat Roof

Discover the truth about waterproofing, insulation, fitting... and the hidden problem with guarantees. Your pack includes;

Flat Roofing Guide Step 1 Exit Popup