Unless adequate ventilation is provided, measures to reduce heat loss can create problems with condensation, mould and fungal growth, which can create health problems.
Oni ddarperir awyriad digonol, gall mesurau i leihau'r gwres a gollir greu problemau yn gysylltiedig â chyddwysiad, llwydni a thyfiant ffyngaidd, a all greu problemau iechyd.