Dormer Window questions answered in plain English

Replacing an existing dormer window in Ireland costs €450 to €950 supplied and fitted in white A-rated uPVC, €650 to €1,250 in colour-foiled triple-glazed (0.8 W/m²K) uPVC or timber-look flush sash, and €850 to €1,750 in thermally broken aluminium or alu-clad. Replacing all 8 to 12 windows on a full dormer bungalow costs €5,200 to €10,500 in uPVC.

Unlike a two-storey masonry house where upstairs windows sit inside a 300mm insulated cavity block wall, a dormer window projects out through the roof on a 100mm timber stud frame. In 1980s to 2005 Irish dormer bungalows, the triangular side walls (dormer cheeks) and window reveals often have thin, slumped fibreglass and no wind-tight breather membrane, letting freezing wind blow straight around the window frame.

Yes — and that is the smartest time to do it. Once the old dormer window frame is removed, the installer or carpenter has direct access to the timber stud cavity and reveals. Fitting rigid PIR insulation board, a breather membrane and maintenance-free uPVC, composite or zinc cheek cladding typically adds €650 to €1,450 per dormer.

For most standard 1.5-storey Irish dormer bungalows where the dormer sits just above the ground-floor eaves, experienced crews replace the window from inside the bedroom combined with a compact mobile access tower outside. Full scaffolding is only needed for high 3-storey dormers or when re-slating and re-leading the entire dormer roof.

Yes. Pre-2011 detached dormer bungalows qualify for the maximum €4,000 SEAI Windows Grant (€3,000 for semi-detached dormers) when all windows are upgraded to Uw ≤ 1.4 W/m²K as part of a qualifying BER Heat Loss Indicator upgrade.

Under Irish Building Regulations Part B, upper dormer bedroom windows must act as emergency escape openings with at least 0.33 m² clear area, a minimum 450mm clear width and 450mm height, and 90-degree Easy-Clean egress friction hinges.

On a standard 3-bed semi-detached house where the existing hipped or pitched roof only gives standing height down the middle 2 metres, a rear box dormer pushes the back wall straight up, typically doubling usable full-height floor space and making room for a double bedroom plus an en-suite.

No — for the first 10 to 14 days all structural steel, floor joists, dormer framing, lead flashing and windows are installed from external scaffolding through the roof before the builders cut the staircase opening through your landing ceiling in the final week.

Yes! Replacing existing dormer window frames with triple-glazed uPVC or aluclad casements and re-insulating the hollow timber side cheeks costs €1,100 to €2,600 per window and requires no planning permission.

Local authority development plans strongly favour rear dormers because they keep the front streetscape unchanged and avoid overlooking neighbours across the road, making planning approval straightforward.

Natural blue-blackfibre-cement or slate cladding with Code 5 lead flashing and standing-seam zinc or anthra-zinc require zero painting and weather severe coastal storms for 40+ years.

A domestic householder planning application takes 8 weeks for a decision from your local authority (plus a 4-week final grant period), so we recommend lodging drawings 3 months before your target build slot.