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Sash windows give Irish period homes much of their character, and they are also the windows most likely to be rattling, draughty and single glazed. If you are weighing up sash window replacement, the choices come down to three things: which material, whether to keep a true sliding sash or switch to a sash-look casement, and what the planning rules allow on your house.
This guide walks through each of those decisions, gives realistic 2026 prices for replacing sash windows in Ireland, and explains what happens on installation day. Expert Windows supplies and fits sash windows and sash-style alternatives across Dublin and Ireland.
Key Takeaways
- A replacement uPVC sliding sash window typically costs €900 to €1,600 fitted. Aluminium runs €1,400 to €2,500, and timber €1,500 to €3,000 or more.
- A sash-look casement with astragal bars gives the appearance of a sash window for roughly €600 to €1,000 per window.
- Modern double-glazed sash windows cut heat loss by well over half compared with original single glazing, and remove the rattles and draughts.
- On a protected structure or in an architectural conservation area, replacement windows usually need planning permission and often have to be timber. Check before you order.
What Counts as a Sash Window?
A sliding sash window has two glazed panels, called sashes, that slide vertically past each other in a box frame. Traditionally the sashes were counterbalanced by cast-iron weights on cords hidden in the frame; modern versions use spring balances. Sash windows were the standard in Irish houses from the Georgian period through to the 1930s, which is why they dominate Dublin’s terraces, Victorian red bricks and older town centres nationwide.
Not every window with a grid of small panes is a sash. Many 20th-century houses have casement windows with glazing bars, and many modern “sash-style” windows are actually casements dressed to look like sashes. The distinction matters for both price and planning.
Signs Your Sash Windows Need Replacing
- Single glazing. One pane of glass loses several times the heat of a modern double-glazed unit and condenses on every cold night.
- Rot in the frame or sill. Soft, spongy timber at the bottom rail or sill means water has been getting in for years.
- Rattling and draughts. Worn timber and failed parting beads let the sashes move in the frame and let cold air straight in.
- Sashes that won’t stay open or won’t open at all. Broken cords, seized pulleys or decades of paint.
- Noise. Thin glass and loose sashes do almost nothing to block traffic. See our guide to reducing noise in Dublin homes with acoustic glazing.
Our guide to when to replace windows covers these warning signs in more detail for all window types.
Your Replacement Options
1. uPVC Sliding Sash Windows
Modern uPVC vertical sliders are the most popular sash replacement in Ireland for houses that are not protected. They keep the sliding action and proportions of the original, add double or triple glazing, tilt inwards for cleaning and need no painting. Good uPVC sash windows have run-through sash horns, slim meeting rails and woodgrain or heritage colour foils, so from the street they read as traditional windows. Cheaper ones have chunky frames and clip-on horns that don’t.
Best for: Victorian and Edwardian houses outside conservation areas, 1930s semis, and anyone who wants the sash look with the lowest maintenance.
2. Aluminium Sliding Sash Windows
Aluminium sash windows have the slimmest frames of the three, which gets closest to the fine sightlines of original timber sashes, and they carry large glass panes with ease. Thermally broken aluminium frames insulate well and take any RAL colour. They cost more than uPVC but less than good hardwood, and they last for decades with almost no upkeep.
Best for: Larger period houses, tall Georgian openings, and homeowners who want a crisp, slim frame in a dark or heritage colour.
3. Timber Sliding Sash Windows
New timber sash windows, factory-finished in engineered hardwood or Accoya, are the most authentic replacement and the only option normally accepted on protected structures. Modern timber sashes are double glazed with slim units, draught-sealed and pre-painted, so they perform far better than the originals while looking identical. They do need repainting every eight to ten years.
Best for: Protected structures, architectural conservation areas and anyone who wants a like-for-like match.
4. Sash-Look Casement Windows
If keeping the sliding action isn’t important to you, a flush sash casement with astragal glazing bars and a deep bottom rail gives the look of a sash window at a lower price and with a simpler mechanism. From across the road most people won’t tell the difference. Up close, the window opens outwards rather than sliding, and there is no meeting rail step.
Best for: Estate houses where the original windows were replaced years ago, and budget-conscious projects.
How Much Does Sash Window Replacement Cost in Ireland?
Realistic 2026 supply-and-fit prices for a standard sash window of roughly 900 mm by 1,500 mm, replacing an existing window in the same opening:
| Option | Typical fitted price per window | Maintenance |
|---|---|---|
| uPVC sliding sash, double glazed | €900 to €1,600 | None beyond cleaning |
| Aluminium sliding sash, double glazed | €1,400 to €2,500 | None beyond cleaning |
| Timber sliding sash, double glazed | €1,500 to €3,000+ | Repaint every 8 to 10 years |
| Sash-look flush casement, uPVC | €600 to €1,000 | None beyond cleaning |
A typical Dublin terraced house with six to eight sash windows therefore comes in somewhere between €6,000 and €14,000 in uPVC or aluminium, and more in hardwood. Tall Georgian windows, curved heads, coloured foils, triple glazing and acoustic glass all push prices up. Our window replacement cost guide for Ireland covers whole-house budgets and what drives them.
Planning Rules for Sash Windows in Ireland
This is the part that catches people out. Replacing windows on an ordinary house is exempt from planning permission, but there are two important exceptions:
- Protected structures. If your house is on the Record of Protected Structures, replacing the windows almost always needs planning permission and the local authority’s conservation officer will usually require timber sashes matching the originals. Repair is preferred to replacement, and uPVC is very rarely accepted.
- Architectural Conservation Areas (ACAs). In an ACA, works that affect the character of the exterior need permission. Many councils will accept slim-profile timber or aluminium sashes that match the original pattern, but check with the planning office before ordering.
You can check whether your house is protected or in an ACA on your local authority’s online planning map or by calling the planning office. Our guide to energy-efficient windows for Dublin period homes goes into the options for older houses in more depth.
What to Expect on Installation Day
Replacing a sash window is a bigger job than swapping a casement, because the original box frame is deep and often built into the brickwork. A good installer will:
- Survey each opening individually. Period openings are rarely square or identical, so every window is measured and made to size.
- Remove the old sashes and box frame carefully to avoid damaging the internal reveals, architraves and window boards, which are usually kept.
- Fit the new frame plumb and square, packed and fixed to the masonry, then insulated around the perimeter.
- Seal inside and out, make good the plaster and reinstate or replace the window board and architraves.
- Adjust and demonstrate the sliding action, tilt function and locks.
Expect one to two windows per fitter per day on sash replacements, so a whole terraced house is typically a two to three day job. Our installation timeline explains the full process from survey to finish.
Choosing Colours and Details
Getting a replacement sash window to look right is mostly about the details: run-through horns rather than clip-ons, a slim meeting rail, astragal bars that match the original pane layout, and the right colour. White is still the most common choice, but heritage colours such as cream, sage green and slate grey suit period brick well. Our RAL colour chart shows the most popular window colours in Ireland, and our guide to the most popular window styles in Dublin shows how sash windows fit alongside the other options.
Frequently Asked Questions
How much does it cost to replace sash windows in Ireland?
Budget €900 to €1,600 per window for uPVC sliding sash, €1,400 to €2,500 for aluminium and €1,500 to €3,000 or more for timber, all supplied and fitted. Sash-look casements cost €600 to €1,000.
Are uPVC sash windows any good?
Good-quality uPVC sliding sashes with run-through horns and slim profiles are a big improvement on worn timber originals and look convincing from the street. Budget versions with thick frames look obviously modern. Ask to see a sample before you commit.
Can I replace sash windows on a protected structure?
Only with planning permission, and the council will normally insist on timber sashes matching the originals. Talk to the conservation officer first.
Do new sash windows open for cleaning?
Modern uPVC and aluminium sliding sashes tilt inwards so both faces of the glass can be cleaned from inside. Most new timber sashes do too.
Are double-glazed sash windows draughty?
No. New sash windows run in sealed channels with brush and compression seals, so the rattles and draughts of the originals disappear.
How long do replacement sash windows last?
Expect 25 to 35 years from uPVC, 40 or more from aluminium and 60 or more from well-maintained hardwood. Our guide to how long uPVC windows last has more detail.
Final Verdict
For most Irish homes, uPVC sliding sash windows are the practical choice: they keep the look, cut heating bills and never need painting. Choose aluminium where slim frames and dark colours matter, timber where the house is protected or authenticity comes first, and a sash-look casement where budget is the priority and the sliding action isn’t.
Expert Windows can survey your home, confirm any planning constraints and price sash windows in each material side by side. Request a free quote for sash window replacement in Dublin and across Ireland.
