Foundations outside main base but still within TC is decaying

[missvanjie]

I have a base with high external wooden walls, I have built numerous foundations within my toolcupboard outside my base, I have enough materials in the TC to stop it from decaying but all the foundations I build outside my main base foundations are decaying.

But all the new foundations are covered by main TC.

[potato.exe]

if its connected to the building it doesn't decay pretty sure.

[Ben_Dover]

It needs to be connected to the main building!!