Flat Warm Roof in Ireland — Construction, Cost, and Avoiding Condensation
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Flat warm roof: 0–10° pitch, €120–€180/m². Continuous insulation above the deck. 25–40 year lifespan.
A flat warm roof in Ireland has the insulation on top of the deck (above the structure), not between or below the joists. Continuous insulation, no thermal bridges. €120–€180/m² installed. 25–40 year lifespan. Build-up: deck (concrete or timber), vapour control layer (a 0.2 mm polythene sheet, sealed at all penetrations), insulation (150–200 mm PIR for Part L 2022 backstop; 200–250 mm for A1), single-ply membrane (SBS felt, EPDM, or PVC). Falls of 1:40 to 1:60 must be created to drain water to gutters or outlets. Common failure: condensation from a missing or damaged vapour control layer. The membrane must be continuous and sealed at all penetrations (soil pipes, vents, rooflights).
When this matters most
You're specifying a flat warm roof.
When this doesn't apply
You've already specified a pitched roof.
Sources
Building Regulations 2023, TGD-L. https://www.gov.ie/
Frequently asked questions
How much does a flat warm roof cost in Ireland?
€120–€180/m² installed. For a 150 m² house: €18,000–€28,000. 25–40 year lifespan. Single-ply membrane (EPDM, PVC, or SBS felt) over 150–200 mm PIR insulation.
What is a warm roof?
A roof build-up where the insulation is above the deck (the structural surface), not between or below the joists. Continuous insulation, no thermal bridges. Standard for new builds in Ireland since Part L 2022.
What is the lifespan of a flat roof in Ireland?
25–40 years depending on the membrane. SBS felt: 20–30 years. EPDM rubber: 25–40 years. PVC single-ply: 25–35 years. Plan to re-membrane in 25–35 years.
When this matters most
You're specifying a flat warm roof.
When this doesn't apply
You've already specified a pitched roof.
Where to go next
Next decision
The next step in your build sequence.
Branch into
Adjacent decisions at the same stage.
Watch out for
Common mistakes, hidden costs, gotchas.
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