The proposed energy efficiency standards in Part L of the Building Regulations are likely to result in more airtight buildings and it is therefore necessary to amend Part F of the Building Regulations at the same time to ensure that adequate ventilation is provided. The revised Part F will come into force in October 2010.The proposed energy efficiency standards in Part L of the Building Regulations are likely to result in more airtight buildings and it is therefore necessary to amend Part F of the Building Regulations at the same time to ensure that adequate ventilation is provided. The revised Part F will come into force in October 2010.The proposed energy efficiency standards in Part L of the Building Regulations are likely to result in more airtight buildings and it is therefore necessary to amend Part F of the Building Regulations at the same time to ensure that adequate ventilation is provided. The revised Part F will come into force in October 2010.