Flat Roof Replacement in Galway

Replacing a flat roof on a Galway rear extension typically costs €90–€130 per m² for felt, €130–€180 per m² for EPDM rubber, and €160–€220 per m² for GRP fibreglass (indicative 2025 rates, VAT included, for a straightforward 15–25 m² extension). For Salthill and Knocknacarra homes exposed to Galway Bay winds, we recommend fully-adhered EPDM or GRP with mechanically fixed perimeter trims. Call 091 622895 for a fixed-price quote.

Those numbers are the short answer. But on the west coast the material choice is only half the job — the detailing at eaves, upstands and perimeter trims is what stops a flat roof lifting in a south-westerly gale off the Prom. Below we break down the three main systems, what they actually cost on a typical Galway extension, and why wind uplift resistance matters more here than almost anywhere else in Ireland.

The short version

• Felt flat roof replacement runs €90–€130 per m² supplied and fitted, EPDM rubber €130–€180 per m², and GRP fibreglass €160–€220 per m² as indicative 2025 rates including VAT for a straightforward 15–25 m² Galway extension.
• Coastal Galway sits in wind Zone III with a basic wind velocity of 27 m/s, and Met Éireann's Mace Head station regularly logs winter gusts of 90–110 km/h, which is why felt roofs on the Galway Bay coast typically fail at 12–14 years rather than the 15–20 seen inland.
• TGD Part L requires insulation to be upgraded to a U-value of 0.20 W/m²K or better when more than 25% of the roof area is replaced, typically meaning 120–140 mm of PIR insulation and adding roughly €25–€35 per m² to the job.
• BS 6229 requires flat roof upstands of at least 150 mm above finished roof level, and perimeter aluminium trims should be mechanically screwed at 150 mm centres rather than glued, as failures during Storm Éowyn in January 2025 in Salthill and Barna were consistently at the perimeter trim.
• A worked example off Threadneedle Road in Salthill covered an 18 m² extension re-roofed with new OSB3 deck, 130 mm PIR insulation and fully-adhered 1.2 mm EPDM for €2,940 including VAT over two days, working out at €163 per m².
• Like-for-like flat roof replacement is exempted development under Class 50 of the Planning and Development Regulations, but planning permission from Galway City or County Council may be needed if the roof profile changes, height is raised, or rooflights larger than 2 m² are added.

Why Galway flat roofs fail sooner than the national average

Most of the flat-roofed rear extensions we re-roof in Knocknacarra, Renmore, Doughiska and Salthill were built between 1995 and 2010 — the peak of the Celtic Tiger estate expansion. The vast majority were finished in three-layer pour-and-roll felt with a mineral cap sheet. Felt has a realistic service life of 15–20 years inland, but on the Galway Bay coast we routinely see it failing at 12–14 years.

The reasons are specific to this stretch of coast:

• Wind uplift. Galway city sits on the edge of an Atlantic-facing bay. Met Éireann's Mace Head station regularly logs gusts of 90–110 km/h during winter storms, with named storms (Éowyn, Isha, Debi in recent years) pushing well beyond that.
• Salt-laden air. Homes within roughly 2 km of the shoreline — most of Salthill, Grattan Road, Barna Road and the western edge of Knocknacarra — see accelerated UV and chloride degradation of felt bitumen.
• Rainfall persistence. Galway averages around 1,150 mm of rainfall annually, spread across 225+ wet days. Ponding water on a slightly under-falls felt roof stays there for weeks.
• Extension detailing. Many rear extensions were built with minimal upstand height (often only 100–120 mm against the parent wall) which fails BS 6229 recommendations of 150 mm minimum.

If your extension roof is over 12 years old and you're seeing bubbling, splits at the upstands, or damp patches on the ceiling below, it's time to plan a re-roof rather than patch it again.

The three main flat roof systems for Galway extensions

EPDM rubber — our default recommendation for coastal Galway

EPDM (ethylene propylene diene monomer) is a single-ply synthetic rubber membrane, most commonly Firestone RubberCover or Classic Bond. On a typical 20 m² Knocknacarra extension we install it as a single sheet with no seams — a significant advantage against wind-driven rain.

Indicative cost: €130–€180 per m² supplied and fitted, including 18 mm OSB deck, insulation upgrade to current Part L standards, and Kerabond aluminium perimeter trims.

Why it works here: EPDM has a manufacturer-quoted lifespan of 50+ years, remains flexible from -40°C to +120°C, and when fully bonded with contact adhesive it delivers excellent wind uplift resistance — typically rated to Zone 3 exposure under BS EN 1991-1-4, which covers virtually all of Galway city and county.

GRP fibreglass — best for complex shapes and heavy foot traffic

GRP (glass reinforced polyester) is a hand-laminated fibreglass system finished with a pigmented topcoat. It cures to a rigid, seamless finish that handles balcony use and awkward penetrations well.

Indicative cost: €160–€220 per m² supplied and fitted, including 18 mm WBP ply deck, pre-formed GRP trims and a 25-year installer warranty.

Where we specify it: Renmore and Mervue extensions where the flat roof is walked on (roof terraces above garages), or where there are multiple rooflights and soil vent pipe penetrations. GRP handles complex detailing better than EPDM, and the rigid finish resists dropped tools and ladder feet.

The downside on the west coast: GRP is less forgiving of thermal movement, and if the deck flexes, hairline cracks can develop at internal corners. Deck rigidity matters more than the topcoat.

Torch-on felt — budget option, but with caveats

Modern SBS-modified torch-on felt is a significant step up from the pour-and-roll systems of the 1990s. A properly installed three-layer system will give 20–25 years inland.

Indicative cost: €90–€130 per m² supplied and fitted.

Honest assessment for Galway: Felt is the cheapest upfront and it's what most Doughiska and Ballybane estate extensions were originally covered in. But on coastal exposures the seams are the weak point, and we won't specify a single-layer felt system within 1 km of the shore. If budget is the driver, we'll quote three-layer SBS with a mineral cap and mechanically fixed perimeter — but we'll usually recommend EPDM for €30–€50 per m² more given the lifespan difference.

Prices above are indicative 2025 market rates — ring us on 091 622895 to confirm exact figures for your specific extension.

Wind uplift resistance: what actually matters on the Prom side

The Irish wind map places Galway city in Zone III (basic wind velocity 27 m/s), and coastal Salthill effectively sits in the highest exposure category once you factor in Category 0 terrain roughness over Galway Bay. In practice this means:

1. Perimeter fixings must be mechanical, not adhesive alone. We use aluminium drip and gutter trims screwed at 150 mm centres into the deck, not the cheaper glue-only trims some installers still use.
2. Fully-adhered membranes outperform ballasted or loose-laid systems. Ballast (gravel or paving) is a non-starter on most Galway extensions anyway due to load limits.
3. Upstands must be 150 mm minimum above the finished roof level, dressed into a chase cut and sealed with a compatible termination bar.
4. Insulation boards should be adhered, not loose-laid, to prevent the whole build-up shifting under negative pressure.

We've re-roofed a number of extensions in Salthill and Barna where the original felt lifted clean off during Storm Éowyn in January 2025 — in every case, the failure was at the perimeter trim, not the field of the roof.

Insulation upgrades and Part L compliance

If you're replacing more than 25% of the roof area, TGD Part L requires you to upgrade insulation to a U-value of 0.20 W/m²K or better. On a warm-deck build-up that typically means 120–140 mm of PIR insulation (Xtratherm, Kingspan Thermaroof or Recticel).

This adds roughly €25–€35 per m² to the job but it's non-negotiable on any full re-roof, and it makes a noticeable difference to the room below — most Knocknacarra extensions we upgrade were originally insulated to about 0.35 W/m²K, so you're roughly halving heat loss through the roof.

There's no direct SEAI grant for flat roof insulation as a standalone measure, but it can form part of a broader One Stop Shop retrofit if you're combining it with wall or attic work.

A typical Salthill extension re-roof: worked example

A recent job on a 1998-built semi off Threadneedle Road, Salthill:

• Roof area: 18 m² (3.0 m × 6.0 m rear kitchen extension)
• Existing: Three-layer pour-and-roll felt, 22 years old, ponding at the outlet corner, two blown seams
• Specified: Strip back to joists, new 18 mm OSB3 deck, 130 mm PIR insulation, fully-adhered 1.2 mm EPDM in a single sheet, new aluminium trims mechanically fixed at 150 mm centres, replacement 110 mm rainwater outlet
• Total: €2,940 including VAT, two-day job, 20-year workmanship guarantee on top of the 50-year Firestone material warranty

That works out to €163 per m² — mid-range for EPDM but with the full insulation upgrade included.

Which system should you choose?

For most homeowners in Knocknacarra, Renmore, Doughiska and coastal Salthill, EPDM is the sensible default: seamless, wind-rated, 50-year membrane life, and mid-range on cost. Choose GRP if you have a walked-on roof, a roof terrace or multiple penetrations. Consider felt only if you're inland (Oranmore, Athenry) and the budget genuinely won't stretch.

For a full breakdown of systems, warranties and case studies, see our dedicated Galway flat roofing service page. You can also get a ballpark figure using our roofing cost calculator before we visit, or browse recent flat roof projects in our gallery to see the finish quality.

If you'd like us to look at your extension in person, book a free site visit through our Galway roofers page or get in touch here — we cover all of Galway city and county, and quotes are fixed-price with no upsells on site.