--- title: "5 Signs Your Flat Roof Needs Replacing (Not Just Repairing)" description: "Five concrete signs your flat roof is past repair. Written by a Hertfordshire roofer who installs EPDM and GRP every week. Free quotes in 48 hours." lang: en-GB json-ld: | [ { "@context": "https://schema.org", "@type": "BlogPosting", "headline": "5 Signs Your Flat Roof Needs Replacing — Not Just Patching", "description": "Five concrete signs your flat roof is past repair. Written by a Hertfordshire roofer who installs EPDM and GRP every week. Free quotes in 48 hours.", "mainEntityOfPage": "https://jandco-contractorsltd.co.uk/blog/how-to-tell-if-your-flat-roof-needs-replacing/", "datePublished": "2026-05-07", "dateModified": "2026-05-07", "author": { "@type": "Person", "name": "Jamie Pocock", "jobTitle": "Owner & Lead Contractor", "worksFor": { "@id": "https://jandco-contractorsltd.co.uk/#business" } }, "publisher": { "@type": "Organization", "name": "J&Co Contractors", "url": "https://jandco-contractorsltd.co.uk", "logo": { "@type": "ImageObject", "url": "https://jandco-contractorsltd.co.uk/logo.png" } }, "image": [ "https://jandco-contractorsltd.co.uk/assets/wa-435-47-C__F_29U.jpeg" ], "articleSection": "Roofing", "keywords": "Flat Roofing, Decision Guide" }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ { "@type": "ListItem", "position": 1, "name": "Home", "item": "https://jandco-contractorsltd.co.uk/" }, { "@type": "ListItem", "position": 2, "name": "Blog", "item": "https://jandco-contractorsltd.co.uk/blog/" }, { "@type": "ListItem", "position": 3, "name": "5 Signs Your Flat Roof Needs Replacing — Not Just Patching", "item": "https://jandco-contractorsltd.co.uk/blog/how-to-tell-if-your-flat-roof-needs-replacing/" } ] }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "Can you replace just one section of a flat roof?", "acceptedAnswer": { "@type": "Answer", "text": "Sometimes — if the old and new sections are different builds (e.g. extension vs garage with separate decks). On a single continuous roof, partial replacement creates a seam that becomes the next leak point, so we'd usually advise a full strip." } }, { "@type": "Question", "name": "How long does flat roof replacement take?", "acceptedAnswer": { "@type": "Answer", "text": "EPDM: 1 day for a typical garage or single-storey extension roof. GRP: 2–3 days because each resin layer has to cure. Both are weather-dependent for the install day." } } ] } ] --- We use essential cookies to run this site, and optional cookies only with your consent. [Cookie policy](/cookie-policy/) AcceptReject Open 7 days · Hours vary by day · 25 years' experience [Office: 01279 216 215](tel:01279216215) | [Mobile: 07379 964569](tel:07379964569) [![J&Co Contractors logo](/assets/jandco-logo-DkXiFtbE.png)](/) Services Areas [About](/about/) [Our Work](/our-work/) [Blog](/blog/) [Reviews](/reviews/) [Contact](/contact/) [01279 216 215](tel:01279216215) [Free Quote](/contact/) 1. [Home](/) 2. [Blog](/blog/) 3. 5 Signs Your Flat Roof Needs Replacing — Not Just Patching Roofing # 5 Signs Your Flat Roof Needs Replacing — Not Just Patching Updated May 2026 6 min read By Jamie Pocock ![EPDM flat roof replacement on a domestic extension in Bishop's Stortford](/assets/wa-435-47-C__F_29U.jpeg) Patching buys time. But there's a point where every additional repair is money thrown at a roof that needs replacing — and we'd rather be straight about that than keep returning every six months. Here are the five signs we use on every flat roof inspection to call replacement vs repair. ## 1\. The roof is over 20 years old and it's felt Three-layer felt past 20 years has typically lost its bitumen elasticity, oxidised, and is now brittle. Patches bond poorly because the substrate flexes around them. If your roof is felt and over 20, plan for replacement, not repair. ## 2\. Visible ponding more than 24 hours after rain Water sitting on the roof 24+ hours after a downpour means falls have failed — usually from rotted decking or compressed insulation. No surface repair fixes a structural fall problem; the deck has to come up. ## 3\. Multiple bubbles, splits or blisters One blister we'll patch. Five blisters across a 20m² roof tells us the membrane has lost adhesion to the deck across the whole surface. New patches bond to the loose layer and peel off in months. ## 4\. Internal damp on the ceiling below Once water is showing internally, the felt + insulation + decking are already wet. Even if we stop further water entry today, the existing trapped moisture continues to damage timbers. Strip and replace is the only honest fix. ## 5\. You've had three or more repairs in two years Each successive leak appears in a different spot because the membrane is failing across the whole roof. At that point continued patching costs more over 5 years than a full [EPDM or GRP replacement](/flat-roofing/) with a 20-year guarantee. ## What replacement actually involves For a typical 25–30m² extension or garage roof: strip the old covering, check & replace any rotten decking, fit new firrings to correct falls if needed, install new insulation, then EPDM rubber (1-day install) or GRP fibreglass (2–3 days). Total cost £2,500–£4,500 with a 20-year manufacturer guarantee. Read our full [EPDM vs GRP comparison](/guides/epdm-vs-grp-flat-roofs/) to see which system suits your roof. Flat Roofing Decision Guide FAQs ## Frequently asked questions ### Can you replace just one section of a flat roof? ### How long does flat roof replacement take? ## Need a straight answer on repair vs replace? We'll inspect the roof, send you photos of every defect, and tell you honestly which option is the right spend. No upsell, no pressure. [Get a flat roof quote](/flat-roofing/) [01279 216 215](tel:01279216215) More from the blog ## Keep reading [ ![Pitched tile roof inspection on a Hertfordshire home before winter](/assets/wa-435-169-BMBPQKLs.jpeg) Roofing ### Winter Roof Checklist: 12 Things Every Hertfordshire Homeowner Should Check Before December The 12 things that cause 90% of winter roof leaks in Hertfordshire — and how to spot them in 20 minutes from the ground. Read article ](/blog/winter-roof-checklist-hertfordshire/)[ ![Gutter cleaning on a Hertfordshire semi-detached home](/assets/upload-009-DFap0EVo.jpeg) Maintenance ### What Blocked Gutters Actually Cost You — and Why a £120 Clean Saves £6,000 Later The maths on what blocked gutters cause downstream — and the simple annual habit that prevents all of it. Read article ](/blog/blocked-gutters-real-cost/)[ ![Repointed chimney stack with new lead flashing on a Hertfordshire property](/assets/upload-019-BqExN-Zc.jpeg) Roofing ### Chimney Leak After a Storm — What to Check Before You Call Storm-driven chimney leaks have four common causes. Here's how to identify which one you're looking at. Read article ](/blog/chimney-leak-after-storm-what-to-do/) ![J&Co Contractors](/assets/jandco-logo-DkXiFtbE.png) Owner-led roofing and building contractors covering Bishop's Stortford, Hertfordshire and Essex. 25 years of hands-on trade experience. Open seven days. 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