Thanks for your reply John - I'm not sure i'd get 50mm board insulation down there due it being solid and the gap being as it is. Might be worth a go though.
I've posted this somewhere else and someone suggested using multifoil down the gaps as it will go down easier - but I have never used it...
I have a 1930s semi with condensation issues. I plan to install a PIV unit to help airflow in the house and properly insualte the loft - it hasn't been done in around 40 years and needs insualting and boarding out.
However we have 'Dropped Eaves' (the eaves cut into the ceiling space in the...