House plans themselves do not expire. Once you have purchased or obtained a set of house plans, they remain valid and can be used to build the house at any time, as long as they comply with current building codes and regulations.
However, it's important to keep in mind that building codes and regulations can change over time. Depending on when the plans were created, they may not comply with current codes and may need to be updated or modified in order to meet current standards. In some cases, this may require additional design work or modifications to the plans, which could affect the cost and timeline of the building project.
It's a good idea to consult with a licensed architect or builder to determine whether any updates or modifications are needed to the plans in order to comply with current codes and regulations. They can also help you evaluate whether the plans are still suitable for your specific building site, lifestyle, and budget.