Providing plumbing design services for a bank

If your work is limited to building plans, plumbing design, or other engineering/construction consultancy services, and you are not directly involved in preparing, recording, managing, or facilitating interest-based transactions, then such technical services are generally permissible.

However, it is preferable to avoid working with conventional (interest-based) banks whenever possible. In the case of an Islamic bank that operates in accordance with Shariah principles, there is greater scope for providing such services.

Therefore, in the situation described where you are working under an architect and only providing plumbing design services, while receiving your payment from the architect there is room for permissibility.