Final answer:
Green board can be used in bathroom walls that are not subject to constant moisture, but it is not recommended for tub or shower walls. Building codes typically require more water-resistant materials like cement board in these high moisture areas.
Step-by-step explanation:
In tub/shower walls, you can use green board as a type of moisture-resistant drywall. However, it's very important to note that green board is only water-resistant, not waterproof. It was commonly used in the past for bathroom and basement walls because it stands up better to humidity compared to regular drywall.
Nonetheless, the building codes have changed and no longer recommend green board for areas subjected to high levels of moisture like tub surrounds or shower enclosures.
Instead, modern construction standards typically call for cement board or a fiberglass-mat gypsum product which is much more durable in wet conditions.
When using green board, it should never be used in an area where it will come in direct contact with water. It may still be used for bathroom walls outside of the tub and shower area, provided these walls are not expected to endure significant amounts of water.