Section 42 of the Planning & Development Act allows a Planning Authority to extend the appropriate period if the authority is satisfied in relation to the permission that-
1. Development commenced before the expiration of the appropriate period to be extended,
2. Substantial works were carried out during that period (in most cases a Planning Authority use the 'up to roof level' rule of thumb,
3. The development will be completed within a reasonable time,
4. The application is made prior to the end of the appropriate period.
If you buy a house now, will you be in a financial position to carry out substantial works prior to expiration of the planning permission?
You def don't want to be a situation whereby your permision expires, the development Plan changes and you find you no longer meet development plan criteria to build.