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How to Waterproof a Flat Roof


Flat roofs are a very popular choice for homes and businesses, but unlike pitched roofs, they require extra considerations since rainwater doesn’t naturally run off them. To reduce the risk of leaks, structural damage, and mould build-up, it is important to ensure that your flat roof has been properly waterproofed; but how can you achieve this?

Fortunately, there are several different techniques to ensure your flat roof stays waterproof during the good old British weather, from short-term patch repair kits to longer-term solutions. In this article, we’ll explore how to make your flat roof waterproof, maintenance tips, and how a professional can help you protect your investment for years to come!  

Assessing Your Flat Roof

You may be wondering how to waterproof your roof because you've noticed the first signs of a leak. Start by assessing your roof in case there’s an obvious source of the leak, although in many cases, the crux of the matter might not be so obvious. Measure the distance between the internal dripping or ceiling marks and your wall, replicating this distance whilst on your roof to see if there’s anything notable. 

Blocked gutters are often another guilty culprit for flat roof problems since standing water doesn’t have anywhere to escape. If possible, unblock your gutters by clearing any debris that’s built up. If your gutters are damaged or incorrectly installed, these will need to be addressed by a flat roofing specialist, as your issues will continue to persist and potentially worsen over time. 

It’s important to note that you should never climb onto your roof unless it’s safe to do so; if not, then call a professional to inspect it instead. They’ll have the tools and equipment to do the job safely!

How to Identify Surface Damage on Your Flat Roof

surface damage on roof

If you’ve successfully located the location of the leak, it’s worth giving your roof a general inspection for general surface damage: Because this often starts small, but can end up becoming very costly if left untreated. There are three common warning signs of surface damage: Blistering, Alligatoring, and Pooling Water

Blistering appears as raised bubbles or pockets on the roof's surface, caused by moisture trapped between roofing layers due to poor installation, ageing, or temperature fluctuations. If left untreated, blisters can burst, leading to leaks and structural damage.

Alligatoring refers to cracked patterns resembling alligator skin, which are caused by ageing and prolonged UV exposure. Alligatoring signals that the roofing material is deteriorating and nearing the end of its lifespan, increasing the risk of water infiltration into your loft. 

Pooling water, also known as ponding, occurs when water overstays its welcome on your roof - usually for more than 48 hours after rain finishes. It’s often caused by poor drainage or uneven surfaces and can speed up material breakdown, create leaks, and lead to structural problems. 

How To Make Your Flat Roof Waterproof

Debris on Roof

There are several techniques to try when waterproofing your roof, depending on the severity of your needs. In some cases, the most simple of our suggestions will do the trick, but in other scenarios, a full flat roof replacement might be necessary. Let’s take a look at the best waterproofing methods:

Liquid Rubber Membranes

This long-life option involves a flexible and durable coating made from a combination of natural and synthetic polymers, which are mixed with water to make a liquid coating that hardens on the roof surface. You can purchase liquid rubber membranes from high-street DIY shops such as Screwfix, and it is easily applied to the roof surface using a roller or brush. Liquid rubber membranes have highly elastic properties, meaning they can expand and shrink in different weather without becoming damaged or less effective. 

Waterproofing Paint

Another easy yet effective option, waterproofing paint (also known as sealant paint), such as paint-on acrylics, provides a water-resistant layer to your roof’s surface, usually in the form of a resin-based semi-liquid paste. This solution is typically applied with a roller or brush and may require several coatings for stronger protection (although some single-layer options exist). Waterproofing paint is a cost-effective method that is suitable for virtually all types of flat roofs.

Patch Repair Kits

Patch repair kits offer a convenient solution for small-scale repair needs, often containing patches, adhesives, and tools to address minor leaks or surface tears. After cleaning and preparing the surface, patches are adhered to the damaged areas for a quick fix. Although they are not a permanent solution and a long-term plan may still need to be made, patch repair kits are a cost-effective option and ideal for addressing specific spots with ease. 

Reinforced Bitumen Membranes

A more robust answer to your lack of waterproofing is through reinforced bitumen membranes, which are installed by professionals and consist of layers of bitumen reinforced with polyester or fibreglass. These membranes are bonded to the roof using heat (torch-on method) or self-adhesive backing, often installed in multiple layers for added durability. This option is highly resistant to harsh weather conditions, making it a good choice for longer-lasting protection. 

Single-Ply Membranes

Commonly used for larger-scale projects, single-ply membranes are a practical choice when coupled with warm-deck flat roofs (where insulation is installed above the structural deck). These sheets - often approximately 20m long - are lightweight, flexible, and durable, and are installed by professionals using mechanical fastening, adhesives, or ballast (such as gravel). This option is especially suitable for commercial or residential roofs requiring a low-maintenance and long-lasting waterproof barrier.

How to Maintain a Waterproof Roof

Once your flat roof has been patched and waterproofed, you’ll need to make sure it is properly maintained. Here are our top tips to achieve this:

  • Regular Inspections: Check for visible damage like cracks, bubbles, or tears, and inspect seams, edges and flashing for signs of wear or gaps. We recommend you leave this to a specialist for your own safety. 
  • Clean the Surface: Using a soft broom or low-pressure washer, remove debris, dirt, and leaves to prevent clogged gutters and pooling water. 
  • Reapply Coatings: Reapply waterproofing layers and sealants, such as waterproof paint, as and when it’s necessary. 
  • Maintain Surrounding Areas: Trim overhanging branches to prevent debris buildup and physical damage to the roof’s surface.
  • Seasonal Preparations: Inspect the roof before and after severe weather events are due, and take more precautions against snow and ice in the winter. 
  • Replace Materials: at the end of your flat roof material’s lifespan, arrange for a replacement to prevent further issues. 

How Can a Professional Help With My Flat Roof?

Professional services - such as those provided by Empire Roofing - are equipped to handle flat roof issues promptly and efficiently, using their expertise to identify and resolve problems before they escalate. Ignoring minor issues, like leaks, cracks, or pooling water, could lead to significant damage, resulting in much more costly repairs or even the need for a complete roof replacement!

For instance, if your flat roof is heavily leaking, it may indicate that the waterproof layer has deteriorated beyond repair, necessitating the installation of a new roof by professional roofing experts. In such cases, materials like single-ply membranes offer flexible and long-lasting options for creating a watertight barrier, resisting the harsh British weather conditions that we’re accustomed to. 

Contact Us for All Your Flat Roofing Queries

Understanding the causes of your roof leaks can cause a real headache for homeowners, but fortunately, Empire Roofing is here to handle any problems you’re experiencing. Our experts use a proactive approach to handle persistent issues before they become costly, offering the best solutions to protect your flat roof for years to come. 

If you’ve noticed any issues with your flat roof, please don't hesitate to give us a call at 01993 259226, or send us an enquiry online and we’ll be in touch shortly. 

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FAQs

  • How can I find the leak in my flat roof?

    To find a leak in your flat roof, you should:

    1. Inspect your roof surface for obvious signs like cracks, punctures, or pooling water - only if it is safe to do so. Always consult a professional if you cannot safely access the roof.
    2. Pay special attention to seams, flashing, and areas around vents or chimneys, as these are common leak points.
    3. If the leak isn’t visible, check the underside of the roof for water stains or damp areas, which can help trace the leak's location.
    4. If the source of the leak still isn’t visible, contact a roofing specialist such as ourselves, and we’ll handle the task for you.
  • What waterproofing method is most effective?
    The most effective waterproofing method depends on the specific needs of your flat roof. For long-term durability and versatility, liquid rubber membranes and single-ply membranes are highly effective. For a DIY solution, waterproof paints/sealants can be effective.
  • How long do flat roof waterproofing solutions last?
    The lifespan varies by material; liquid rubber membranes can last 20+ years, while single-ply membranes often last 25–30 years with proper maintenance. Sealants and patch repairs are shorter-term solutions.
  • Can I waterproof my flat roof myself?
    Some methods, like applying waterproof paint or using patch repair kits, can be DIY-friendly. However, for more complex methods like liquid rubber or single-ply membranes, it’s best to hire a professional to ensure proper installation.