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Hi all,
I’ve got a new-build house (just outside the 2-year builder warranty) and one bedroom with an oriel bay window is always 1–2°C colder than the rest. It's also south facing and gets a lot of sun in the day so should be warmer. From investigating in the loft I think I’ve found the cause.
For all the other bedrooms, the loft build-up is: plasterboard ceiling → PIR (Celotex) → mineral wool on top.
Above the oriel bay, the PIR layer stops when it hits a false gable end. Beyond the false gable end there's a “U-shaped” surround with soffits running around it.
That u shaped void above the window head has no insulation at all, so cold outside air circulates freely around it.
I’ve attached 3 photos:
1. The false gable wall inside the loft (OSB face with breather membrane behind).
2. External view of the oriel with soffits highlighted.
3. Inside the false gable end, showing the completely empty void.
Important note: I’m not going back to the builder or NHBC – I’ve already settled compensation, and I’ll be fixing this one myself. I’m only looking for practical advice on the best way to insulate it please.
Plan of action:
Cut an access hatch in the false gable OSB.
Carefully open the breather membrane to reach the void above the oriel head.
Fit PIR (Celotex/Kingspan) boards in the void of the oriel head, then add mineral wool above. leaving a few inch gap at the edge. The Soffits arent too breathable tbh, as the slatted gaps on the underside of soffits have been battened over. However it does catch a draught.
Re-seal the membrane with foil/breather tape and reinstate the OSB hatch.
Leave the soffit vents outside as they are. I will try and leave a gap at the edge.
Questions:
Is this the right approach, or should I be treating this area differently?
Any risk of damp/condensation if I insulate this way?
Would you use only PIR, or PIR plus mineral wool?
Thanks in advance for any advice.
I’ve got a new-build house (just outside the 2-year builder warranty) and one bedroom with an oriel bay window is always 1–2°C colder than the rest. It's also south facing and gets a lot of sun in the day so should be warmer. From investigating in the loft I think I’ve found the cause.
For all the other bedrooms, the loft build-up is: plasterboard ceiling → PIR (Celotex) → mineral wool on top.
Above the oriel bay, the PIR layer stops when it hits a false gable end. Beyond the false gable end there's a “U-shaped” surround with soffits running around it.
That u shaped void above the window head has no insulation at all, so cold outside air circulates freely around it.
I’ve attached 3 photos:
1. The false gable wall inside the loft (OSB face with breather membrane behind).
2. External view of the oriel with soffits highlighted.
3. Inside the false gable end, showing the completely empty void.
Important note: I’m not going back to the builder or NHBC – I’ve already settled compensation, and I’ll be fixing this one myself. I’m only looking for practical advice on the best way to insulate it please.
Plan of action:
Cut an access hatch in the false gable OSB.
Carefully open the breather membrane to reach the void above the oriel head.
Fit PIR (Celotex/Kingspan) boards in the void of the oriel head, then add mineral wool above. leaving a few inch gap at the edge. The Soffits arent too breathable tbh, as the slatted gaps on the underside of soffits have been battened over. However it does catch a draught.
Re-seal the membrane with foil/breather tape and reinstate the OSB hatch.
Leave the soffit vents outside as they are. I will try and leave a gap at the edge.
Questions:
Is this the right approach, or should I be treating this area differently?
Any risk of damp/condensation if I insulate this way?
Would you use only PIR, or PIR plus mineral wool?
Thanks in advance for any advice.
