Insulation between rafters?

[Ash10010]

I’ve had to remove the lath and plaster from the ceiling and side wall as there was an old roof leak. Can I insulate between the rafters? I’ve read I should leave a 50mm gap behind the insulation for ventilation and to stop any condensation. Should I use an insulation board for this? Thanks I’ve attached some photos.

 

[noseall]

I’ve had to remove the lath and plaster from the ceiling and side wall as there was an old roof leak. Can I insulate between the rafters? I’ve read I should leave a 50mm gap behind the insulation for ventilation and to stop any condensation. Should I use an insulation board for this? Thanks I’ve attached some photos. View attachment 214367View attachment 214368

A vaulted roof insulation system requires more than just an air gap above (cold side)the insulation. I see you have solid wood sarking (Scotland?) which is obscuring whatever membrane or lack of, above. If a breather membrane is absent then there needs to be airflow throughout the airgap.

 

[Ash10010]

Thank you for your reply. There isn’t any breathable membrane behind the timber sarking. Just replace with standard plasterboard then without any insulation in the gap? House is in Kent.

 

[noseall]

Just replace with standard plasterboard then without any insulation in the gap? House is in Kent.

No, go for it regards insulation as long as there is enough air movement on the cold side.

Typical scenario;

Roof tiles

Tile batten

Breather membrane.

25-50mm air gap.

100mm celotex between rafter with foil tape to joints.

50mm celotex across rafters (foil tape to joints).

12.5mm Duplex plasterboard and skim.

If you have a draughty roof then you may be ok regards zero through ventilation.