Flat roof insulation between rafters or above boards? Information, help and advice on maintaining, installing and repairing a flat roof. Post your questions and view answers here

[NoobNoob999]

Hi :)
I have just bought a house in need of much renovation! One room is flat roof and I am unsure if I need to add any insulation between the rafters or if there is a layer of inuslation above the boards and the space between the rafters is for air flow. I have attached a photo for clarity. Any advice welcome :)
Thanks

[stoneyboy]

Hi noobnoob999,
Suggest you assume the space is for ventilation and fit insulation between the joists leaving a 50mm ventilation gap. Then add a further 50mm + of insulation over the joists before you add plasterboard.
Regards S