Mind the gap.... At the top of the roller shutter

[TEO]

I do mind, there's a howling gale blowing through the gap at the top of the roller shutter & I'm looking for genius DIY solutions that people have developed.
I'd rather not spend what feels like a small fortune for a brush strip, the gap is approx 6" when the shutter's fully down (door closed, gap at it's most open) and goes to about 3 - 4" when the shutter's fully rolled up.
The doorway opening is approximately 4m.
I've tried stuffing the lad in the gap but he's too short for the full 4m & complained tsk! tsk! the yoof of today, no dedication.
Any ideas folks?

 

[Kram]

Fix a length of 2mm thick rubber sheeting from above.
Off ebay a 2m x 1m roll cost about 10 quid, a few years back, if I remember correctly.

 

[Bullet2012]

I used D.P.C for mine, affixed to the outside but rubbing on the door, no pics sorry as it was at least 3workshops ago
this sort of thing,

https://www.screwfix.com/p/damplas-damp-proof-course-black-30m-x-100mm/172yn

 

[roofman]

 

[Blobber]

Big strip of carpet screwed to the joist and then laid over the roll of the shutter, nice an flexible so it moves as the roller changes size

 

[gaz1]

you want x 3 brush strip

one either side of the shutter and one across the top