If a new room is being created as a result of the addition of an internal wall then care must also be taken to ensure that the existing room is ventilated adequately.
Os bydd ystafell newydd yn cael ei chreu wrth ychwanegu wal fewnol, dylid cymryd camau hefyd i sicrhau bod yr ystafell sy'n bodoli eisoes yn cael ei hawyru'n ddigonol.