"With such thin walls..." is generally how this would be said.
"With walls so thin," is fine, too. No problem with that...(only with the walls!)
Why "aussi" and not normal "si"?
"Avec des murs si minces on entendrait tout" not accepted.
Duo Just refused such again, so many times I put in the correct english response but it doesn't match Duo's fixed translations frustrating!!
Such thin walls in UK English