Flat Roofing Horsham

For most Horsham extensions and garages, GRP fibreglass is the best choice — a seamless, jointless cured system with no laps to fail and a 25-year guarantee, which matters in West Sussex’s damp climate where jointed felt fails at the seams. EPDM rubber suits larger roofs (over about 80m²) or those with multiple penetrations. Traditional felt is now mainly for tight budgets. We match the system to your specific roof at survey. Our GRP vs EPDM comparison weighs up the options in detail.

A new GRP flat roof on a typical extension costs £900–£2,500; an integral garage £900–£1,400; and larger flat roofs £2,000–£6,000. A felt-to-GRP upgrade runs £1,200–£3,000. Prices include labour, materials, trims, outlets and VAT. The main variables are area, the system chosen, and the condition of the timber deck once stripped — which is why an honest quote always includes deck inspection. Our dedicated flat roof cost guide breaks the figures down by roof type.

A correctly installed GRP fibreglass roof lasts 25–30 years; EPDM 25 or more; traditional felt 15–20. Seamless systems consistently outlast jointed felt in West Sussex’s climate because they have no laps or seams to fail — which is where felt roofs almost always go first. The deck matters as much as the covering: a good membrane over a sound, dry deck reaches its full life; the same membrane over a wet or soft deck fails early. Our guide to how long a roof lasts covers all roof types.

Possibly — if the leak is isolated and the felt is otherwise sound, a targeted repair may be viable and cost-effective. But 1970s extension roofs across Horsham are typically on their original or second felt covering and near end of life, so if the felt is blistered or cracked across the surface, water ponds after rain, or the deck feels soft, replacement is the better investment — patching an end-of-life felt roof buys months, not years. We diagnose honestly on site. Our leaking flat roof guide helps you tell which situation you’re in.

Most domestic flat roofs — an extension or garage — are replaced in one to two days, including deck inspection and any board replacement. A small garage roof is often done in a single day; a larger extension with multiple outlets and abutments takes two. Wet weather can extend it, since GRP resin needs dry conditions to cure properly. We confirm the programme in the quote. Our garage roof replacement guide covers what to expect on the most common job.

For most Horsham extensions and garages, GRP fibreglass is the better choice: seamless, hard-wearing, with a 25-year guarantee, and ideal for the small-to-medium roofs that dominate the local housing stock. EPDM rubber comes into its own on larger roofs (over about 80m²) or those with lots of pipes and rooflights, where its single-sheet flexibility is an advantage. Neither is universally ‘best’ — it depends on the roof. We advise on the right one at survey. Our EPDM vs GRP guide compares them fully.

Where the flat roof covers a habitable room, yes — we upgrade it to a warm-deck build-up with rigid insulation above the deck and below the membrane, meeting current Building Regulations and avoiding the interstitial condensation that rots poorly built cold-deck roofs. Over an unheated garage a simpler build-up is fine. On the Southwater and Broadbridge Heath estates, where flat-roofed extensions often cover kitchens and bedrooms, the insulation detail isn’t optional. Our roof insulation guide explains warm versus cold deck and why it matters.