Roof Windows and Dormer Windows in Galway: Replacing and Upgrading on Dormer Bungalows and Attic Rooms

Dormer bungalows and converted attics are common across Galway, from older estates in Knocknacarra and Salthill to one-off houses in Oranmore, Moycullen and Gort. The windows in those top-floor rooms work harder than any others in the house. They take the full force of Atlantic wind and rain, they sit under a hot, poorly ventilated roof space in summer, and they are the hardest to reach when something goes wrong. If the upstairs rooms in your house are draughty, damp around the glass or noticeably colder than the rest of the home, the windows are one of the first places to look.

This guide explains the difference between roof windows and dormer windows, when replacement makes sense, and what a good job involves.

Roof windows and dormer windows: what is the difference?

A roof window (often called a skylight, or by the brand name Velux) sits in the plane of the roof, at the same angle as the slates or tiles. It brings light into a room from above and is common in attic conversions where there is no vertical wall to put a window in.

A dormer window is a small structure that projects out of the roof slope, with its own vertical front wall, side cheeks and usually its own small roof. The window itself is a normal vertical window, but the surrounding build-up of cheeks, flashing and roof is what makes it more complicated than a ground-floor opening.

The two have different problems. Roof windows tend to fail at the seals, flashing and glazing. Dormers tend to fail at the junctions around the window, where timber cheeks, felt and lead meet the frame.

Signs a roof or dormer window needs replacing

• Condensation or fogging between the panes. The sealed unit has failed and cannot be repaired, only replaced. Our guide to window condensation and sealed unit failure explains how to tell this apart from ordinary surface condensation.
• Water staining on the reveal or ceiling after heavy rain. This is often the flashing or the felt, not the glass, so the cause needs tracing before anything is ordered.
• Draughts around the sash, or a window that no longer closes squarely against its gaskets.
• Rot in timber frames or cheeks, particularly on the lower edge, where water sits.
• A room that is hot in summer and cold in winter. Older single-glazed or early double-glazed roof windows have poor U-values compared with what is available now.

Windows from the 1990s and early 2000s often have thin glazing, no low-emissivity coating and gaskets that have long since hardened. Upgrading the glazing alone makes a noticeable difference to comfort.

Glazing: what to specify overhead

Glass in a roof window is exposed to more heat from the sun, more rain impact and more risk of falling debris than a vertical window, so the specification matters.

• Toughened or laminated inner and outer panes. Building regulations require safety glazing in many roof-window situations, and laminated glass keeps the pane together if it cracks.
• Low-E coating and argon fill, as standard. Triple glazing is worth considering on north-facing or exposed Atlantic slopes; our article on whether triple glazing is worth it in Galway covers the trade-offs.
• Solar control glass for south and west slopes, which cuts overheating in summer without making the room dark in winter. Attic rooms can get very hot, and this is often the most useful upgrade.
• Noise-reducing glass if rain on the roof is a complaint. Heavy downpours on a roof window are loud, and a thicker outer pane or laminated glass quietens them.

For dormers, the vertical window can be uPVC, aluminium or aluclad, exactly as for the rest of the house. Matching the downstairs windows gives the best result; see our comparison of uPVC, aluminium and aluclad windows for guidance.

Flashing and weatherproofing: where most leaks start

Most leaks blamed on the window are really flashing failures. A roof window needs a flashing kit matched to its size and to the roof covering, whether natural slate, fibre-cement slate or concrete tile, so that water is channelled around the frame and back onto the roof. Reusing old flashing, or fitting a new window into an opening that has been cut slightly wrong, is a common cause of leaks within a couple of winters.

A good installer will:

1. Strip back and inspect the surrounding battens, felt and insulation before fitting anything new.
2. Replace the underfelt collar and fit a new, correctly sized flashing set.
3. Seal the insulation to the frame so there is no cold gap around it, since this is where condensation often forms on the reveal.
4. Check the roof structure, including rafter trimming, for damage or earlier poor workmanship.

On dormers, the cheeks and roof should be inspected as part of the same job. Replacing the window in a dormer with rotten cheeks or failing lead flashing just moves the problem. It is much cheaper to repair everything at once while the scaffold is up.

Ventilation: do not seal the room up

New windows are far more airtight than the ones they replace. In an attic room with no other ventilation, that can lead to condensation on the glass, damp on the reveals and mould on the ceiling. Choose roof windows with built-in trickle ventilation or a ventilation flap that lets the sash stay closed while still moving air. A top-hung roof window opened slightly for ten minutes a day also helps. If a bathroom or ensuite is in the attic, make sure the extractor fan ducts outside rather than into the roof space.

Safety, access and planning

Roof work needs scaffolding or a safe access system, and it is not a job for a general handyman. Check that your installer works to safe working-at-height standards and is insured for roof work. In most cases, replacing like-for-like windows does not need planning permission, but changing the size or position of roof windows, adding a new dormer, or working on a protected structure or in an architectural conservation area may do. Our attic conversion planning checklist covers what to check.

Plan the work for the right season

Roof window replacement is best done in settled weather, since the roof is open for a short time, typically a few hours per window. In Galway that means late spring through early autumn. If leaks are already showing, though, do not wait. Temporary weatherproofing can be put in place and the proper replacement scheduled for the first dry spell.

Getting started

Because every roof and dormer is different, the sensible first step is a survey. KRB Construction & Windows supplies and fits windows and doors across Galway and surrounding counties, and handles dormer and attic work as part of its construction service. Contact us for a free quote and we will look at the glazing, the flashing and the ventilation together, so you get one clear price for a job that stays dry.