Loft draught help

[scu4313]

Loft has been converted prior to me owning it. It's very drafty. Just wanting advice on how to tackle this as keep reading about keeping airflow.

The person before has roughly cut holes through the plasterboard into the eaves for additional storage. Which I was hoping to seal back up. Including in the 2nd picture the underneath of the beam.

Then seal the boarding, skirting boards and any cracks.

Any advice? Thanks

 

[Wayners]

Insulation. Sheet like kingspan.
Plasterboard over.

Maybe look at skill builder or Charlie DIY on YouTube for information