When Does a Garage Roof Need Replacing?
The majority of garage flat roofs in Horsham were built with traditional felt systems. A felt flat roof has a practical lifespan of 10–20 years in West Sussex's damp climate. Properties built from the 1960s to 1990s — which account for a large proportion of Horsham's housing stock — have garage roofs now well beyond this point.
Signs that replacement is due: water ingress after rain, blistering or cracking of the felt surface, soft or spongy deck boards underneath, established moss retaining moisture, or a roof that has been patched multiple times with bitumen.
GRP Fibreglass vs Felt — The Practical Difference
GRP is applied as a liquid resin and glass mat system that cures to a seamless, jointless surface with no laps or seams to fail. The 25-year manufacturer guarantee covers the complete system. Traditional felt has laps at every overlap and joints at all outlets and perimeters — every one a potential failure point. Over 20 years in West Sussex's damp climate, felt systems consistently require more maintenance than GRP.
The cost premium for GRP over felt is typically £150–£300 on a standard Horsham garage — small for a system that lasts 25 years versus 15–20 for felt.
Integral Garage Flat Roofs
Many Horsham properties on 1990s estates in Southwater and Broadbridge Heath have integral garages with flat roofs built into the main house structure. When these fail, water tracks into the living space above. We include full deck inspection as standard in all integral garage surveys — stripping the covering, checking every board, and replacing failed sections before the new membrane goes down.
Why the Deck Matters More Than the Membrane
The most important decision in any flat roof replacement is what happens before the new membrane goes down. A GRP or EPDM membrane installed over a failed or damp deck will fail prematurely regardless of membrane quality. Water trapped between the deck and membrane causes delamination of GRP and adhesive failure on EPDM. We strip the existing covering fully on every replacement job, inspect every board for softness, and replace failed sections before installation. Our quotes include deck inspection and a per-square-metre rate for deck replacement where condition is unknown at the time of quoting. We do not install new membranes over compromised decks.
EPDM vs GRP — Which Is Right for Your Garage?
Both GRP fibreglass and EPDM rubber are significant improvements over traditional felt. GRP is applied as a liquid and cures to a seamless surface with no joints or seams — the strongest system for small-to-medium flat roofs. EPDM is a pre-formed sheet system with taped seams, typically used for larger areas where the economics of a full GRP installation become significant. For most Horsham garage flat roofs — typically 20–50m² — GRP is the standard specification. EPDM is better suited to roofs over 80m² or roofs with complex penetrations. We advise on the appropriate system during the survey.
Garage Roof Access and Programme
Most Horsham garage flat roof replacements do not require scaffold — they are accessible from a properly secured roof ladder or low-level work platform. We use scaffold on roofs over 3.5 metres to the working level, on roofs adjacent to public areas, and on any roof where the structural condition creates a safety concern before the new system is installed. The scaffold or access equipment decision is made during the survey and included in the quote — we do not arrive expecting to use a ladder and then charge extra for scaffold that should have been quoted from the start.
Getting the Work Done in Horsham
All surveys in Horsham are free with no call-out fee. We attend within 3–5 working days for planned surveys and aim to reach emergency call-outs within 2–4 hours. Every job receives a written, itemised, fixed-price quote before any work starts — no verbal estimates and no bills that exceed the accepted written quote.
We are NFRC registered and carry £5 million public liability insurance. All work carries a written 10-year workmanship guarantee backed by a named, verifiable local contractor. Guarantee and insurance documentation is provided on request before any survey visit.
We cover Horsham and the surrounding West Sussex area including Roffey, Broadbridge Heath, Southwater, Billingshurst, Pulborough, Storrington, Henfield, Crawley, Burgess Hill, Haywards Heath, East Grinstead and Worthing. Call 0140 358 1272 to arrange a free survey.
Last reviewed: July 2026 by Horsham Roofing Experts.