Replacing an Old VELUX Window? Find Your Size Code First (Lucan and Naas Guide)

Many attic conversions and dormer bedrooms in Lucan, Naas and across Dublin got their roof windows in the late 1990s and 2000s. Twenty-plus years of Irish wind and rain later, those windows often stick, whistle, fog up between the panes or let in a damp patch around the frame.

The good news is that replacing a roof window is usually a much smaller job than people expect. The key is getting the right size, and that starts with one small metal plate on the window itself.

This guide explains where to find it, what to note down, and what to expect from a like-for-like replacement.

Signs your roof window is due for replacement

Not every tired roof window needs replacing. A worn seal or a stiff hinge can sometimes be repaired. Replacement is usually worth considering when you see:

• Misting between the panes that you cannot wipe away, which means the sealed glazing unit has failed
• Rotten or blackened timber on the sash or frame, especially at the bottom rail where condensation collects
• A handle or hinge that no longer closes the sash tightly, leaving draughts or rattles in the wind
• Damp staining on the lining around the window, which may be the flashing rather than the window itself
• A noticeably cold room under the window compared with the rest of the house

If the problem is a leak, it helps to rule out the flashing first. Our guide to roof window flashing checks covers the difference, and our repair or replace guide for old roof windows goes into the decision in more detail.

Where to find the VELUX type sign

VELUX puts a metal type sign on every window it has made since 1968. According to VELUX Ireland, it sits in the right corner of the top sash, behind the ventilation flap. Their replacement page gives the same advice: open the window and look in the corner of the top sash behind the ventilation flap.

You can do this safely from inside the room:

1. Open the window as you normally would, using the handle or control bar.
2. Look along the top of the sash, behind the ventilation flap, for a small metal plate.
3. Take a clear, close-up photo of the plate. Use your phone torch if the attic room is dim.
4. Photograph the whole window from inside as well, so the installer can see the lining and the condition of the frame.

Never go out onto the roof to look at a window from outside. Everything you need for sizing is on the inside.

What the type sign tells you

VELUX lists four pieces of information on the type sign:

Current VELUX pitched roof windows use a letter and number size code, such as MK04 or PK08. On older windows you may see a different style of code. Do not try to guess the modern equivalent yourself. Send the photo of the plate to your installer or to VELUX, and they can match it to a current size.

Common VELUX roof window sizes

Here is a selection of current pitched roof window sizes from the VELUX Ireland size guide, shown as width x height:

VELUX notes that this is only a selection and more sizes are available. Measuring the glass or the inside lining with a tape is not a reliable way to choose a size, so the type sign is always the better starting point.

What a like-for-like replacement involves

When the new window fits the existing opening, the job is usually quick and tidy. VELUX Ireland says on its replacement page that most replacements can be completed from inside the home in about 4 hours, and that their roof windows fit into existing roof openings with no structural work needed.

A typical replacement visit looks like this:

• Protect the room: dust sheets go down and furniture under the window is moved or covered.
• Remove the old sash and frame: usually from inside, which avoids scaffolding in most cases.
• Check the opening: the timber trimmers, underlay and any insulation around the frame are inspected. Rot or wet insulation is dealt with before the new window goes in.
• Fit the new frame and flashing: the flashing kit must suit your roof covering, whether that is concrete tiles, clay tiles or slate.
• Make good inside: the lining is checked and finished so there are no gaps for draughts or condensation.

VELUX also notes that its designs need installer validation to make sure they comply with building regulations, so a site check before ordering is normal.

When it becomes a bigger job

Sometimes a replacement is not quite like-for-like. Expect more work if:

• you want a larger window or an extra window, which means cutting the roof and new trimmers
• the timber around the old window is rotten, often from years of condensation
• the roof covering is in poor condition and tiles or slates break as the old flashing comes out
• the window is on the front roof slope and you want to change its size. Our guide to the front roof window planning exemption explains the current size limits

Cost and guarantee: what VELUX says

VELUX Ireland's replacement page gives a guide of between €1,400 and €1,800 for the supply and installation of one roof window. Treat this as a starting point. The final price depends on the model, glazing, access, the roof covering and anything found once the old window is out.

On guarantees, the VELUX Ireland guarantee page states that roof windows are covered by a 10-year guarantee, with a 5-year guarantee on the electrical components of solar and electric roof windows. VELUX also says this cover can be extended by an additional 5 years by registering your window. Read the full guarantee document for the exact terms and keep your installation paperwork safe.

If you are torn between manual, electric and solar models, see our guide to manual, electric and solar roof windows.

Why winter is a sensible time to plan

You do not have to wait for summer. Because most replacements are done from inside and the roof is only open for a short time, a careful installer can plan around a dry spell even in November. Winter is also when you notice draughts, condensation and cold rooms the most, so it is a good time to decide which windows need attention.

What matters is that the job is booked on a dry day with a settled forecast, and that the opening is never left exposed overnight.

Quick checklist before you ask for a quote

• Photo of the type sign, taken from inside with the window open
• Photo of the whole window and lining from inside
• Note of any problems: misting, draughts, leaks, stiff handle, rot
• Whether you want the same type of window or an upgrade, such as electric or solar
• Rough idea of the roof covering: tiles or slate
• Any blinds you want to keep or replace, since blind sizes follow the window size code

Replacing roof windows in Lucan, Naas and Dublin

We replace and repair VELUX and other roof windows across Dublin City, North Dublin, South Dublin, Lucan, Bray, Wicklow, Naas and nearby areas. Send us a photo of the type sign and a picture of the window from inside, and we can tell you what is likely needed before we visit.

Contact us by WhatsApp, call 083 066 3462, or email hi@perfectroofing.ie.