Flush sash windows are one of the most requested styles in Dublin right now, especially in older homes where a modern window would look out of place. They give you the look of old timber frames without the rot, the repainting or the draughts.
But there’s a question we get asked in the showroom nearly every week: can you claim the SEAI grant on them?
The short answer is yes, flush sash windows can qualify. But it depends far more on the specification you order and the condition of your house than it does on the window style itself. Here’s how it actually works.
What Are Flush Sash Windows?
A flush sash window is a window where the opening sash sits level inside the frame instead of sitting proud of it. From the outside you get one clean, flat face – the same look you’d have seen on period Irish homes a century ago.
Ours are made with a full weld jointed timber-alternative profile, so you get the timber appearance without the upkeep. They’re glazed the same way as a standard casement window, with no bonding needed, which means the fitting day is quicker and less disruptive in your home.
Key features:
- 80mm thick double rebated profile
- Two seals – one against the outside of the window, one on the inside
- Twice the weather protection of a single rebated window
- Double or triple glazing fitted as standard
- Range of external and internal colours
- Period-style internal hardware options
Does the SEAI Grant Cover Window Style or Window Performance?
This is where most homeowners get it wrong.
The SEAI scheme doesn’t have an approved list of window shapes. It doesn’t care whether you pick flush sash, casement or vertical sliders. What it cares about is the thermal performance number on the finished window, plus the overall condition of your home after the work is done.
Under the 2026 SEAI scheme, replacement windows must achieve a U-value of 1.4 W/m²K or better. The grant rules do not specify that north-facing windows must be triple glazed. Full details are on our SEAI windows and doors grant page.
Where Our Flush Sash Windows Stand?
Because the profile is 80mm and double rebated, there’s more material doing the insulating work, and that shows up in the U-values.
| Glazing Option | U-Value | Energy Rating | Meets the 1.4 W/m²K Threshold? |
| Double glazed flush sash | 1.6 W/m²K | C rated (ya B) | No – sits above the limit |
| Triple glazed flush sash | 1.0 W/m²K | A+ / A++ rated | Yes – comfortably inside it |
That table is the whole answer in one line: the triple glazed flush sash meets the requirement, the double glazed version does not.
So if you’re going for the grant, you order the triple glazed spec. You still get the same flat sightlines, the same colours and the same period hardware. Nothing about the look changes.
If you’re not going for the grant, the double glazed option is still an rated window and a big jump from anything single glazed.
Not sure which route suits your house? Call us on 019120600 and we’ll go through it in five minutes.
The Rest of the Eligibility Checklist
Getting the window spec right is one part of it. Your property has to tick a few boxes too.
Your home must:
- Have been built and occupied before 2011
- Have a valid MPRN (your electricity meter number)
- owned by the applicant and meet the SEAI eligibility requirements.
The work must:
- The grant covers replacement of existing single- or double-glazed windows. Windows in extensions built before 1 January 2011 may also be eligible.
- Be carried out by an SEAI registered contractor
- Have been ordered, deposited or started from 27th January 2026 onwards
After the work, your home must:
- Reach a Heat Loss Indicator of 2.3 W/m²K or better
- Have an up to date BER certificate and a post-works BER assessment
That last point trips people up. The HLI target looks at your whole house, not just the glass. Most Dublin homes need attic insulation, and often wall insulation, alongside the windows to get there. Windows on their own rarely move the number far enough.
Flush Sash vs Other Styles Under the Grant
If your house suits a flush sash look, there’s no reason to switch to a different style just to chase the grant. Every window type in our windows range can be specified to hit the threshold.
Where flush sash makes the most sense:
- Period red brick homes in Rathgar, Drumcondra and Ranelagh
- Cottages and older terraces where a chunky modern frame would look wrong
- Houses where planning or conservation guidance pushes you toward a traditional face
- Anyone replacing tired timber windows and wanting the same appearance without the maintenance
For newer estate homes, a uPVC casement often fits better and costs less to spec up to the same performance level.
What If You Don’t Qualify?
Plenty of homes won’t meet the HLI target, and that’s not the end of it. We run a 35% offer on energy efficient windows and doors for homeowners outside the scheme, and we have finance by Humm if you’d rather spread the payments.
You still get the same windows, fitted by the same team.
See Them Before You Decide
Photos only tell you so much with flush sash. The difference is in how the sash sits against the frame, and you need to run your hand across it to see it.
Both showrooms have them on display:
- Swords Showroom – Unit F2, Swords Enterprise Park, Feltrim Road, Drinan, Swords, Co. Dublin, K67 WF72
- Rathgar Showroom – 68 Rathgar Avenue, Rathgar, Dublin 6, D06 KN53
We fit across all of Dublin, from Clontarf out to Blanchardstown and everywhere between.
Conclusion
Flush sash windows qualify for the SEAI grant when they’re specified with triple glazing, which brings them to a 1.0 W/m²K U-value – well inside the 1.4 threshold. The double glazed version, however, typically sits at a 1.6 U-value, which fails to meet the strict 1.4 grant cut-off. Beyond the glass, your home needs to be pre-2011, owner occupied, and reach the HLI target after works, which usually means insulation alongside the windows.
The sensible next step is a survey. We’ll look at your existing windows, tell you straight whether the grant is realistic for your house, and spec the right option either way.
📞 Call 019120600 🌐 Visit thermoglaze.ie 📋 Request your free quote
FAQs
1. Do flush sash windows qualify for the SEAI grant?
Yes, once they’re specified to a U-value of 1.4 W/m²K or better. Our triple glazed flush sash comes in at 1.0 W/m²K, so it qualifies.
2. Does the double glazed flush sash qualify?
No. It’s A rated at 1.6 W/m²K, which is a strong window, but it sits above the grant threshold. Go triple glazed if the grant matters to you.
3. Is the grant based on window style?
No. SEAI looks at thermal performance and your home’s overall heat loss, not whether the window is flush sash, casement or sliding.
4. Do I need triple glazing on every window?
Triple glazing is required on north-facing openings. Elsewhere the minimum is double glazing, though hitting the U-value target usually points toward triple across the board.
5. Will windows alone get me to the HLI target?
Rarely. Most homes need attic insulation, and often wall insulation, to reach a Heat Loss Indicator of 2.3 W/m²K or better.
6. Does my house qualify?
It needs to have been built and occupied before 2011, have a valid MPRN, and be owned by the applicant .
7. Do I need a BER assessment?
Yes. You need an up to date BER certificate and a post-works assessment confirming your home meets the required standard.
8. Can I install the windows before applying for the SEAI grant?
Generally, no. For new applications, you should apply for the grant and receive your SEAI grant offer before starting the work. SEAI also states that grants cannot be backdated. However, specific transitional arrangements apply to upgrades ordered or commenced from 27 January 2026, subject to the scheme requirements.
9. Are flush sash windows suitable for period homes?
That’s exactly what they’re designed for. They copy the look of traditional timber windows found on older Irish properties, with low maintenance and much better thermal performance.
10. What if I don’t qualify for the grant?
You can still upgrade with our 35% offer, or spread the cost with Humm finance. Give us a call and we’ll talk through the options.