Dormer Window guides, calculator & reference

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.