You can now use up to 50% of all your land excluding the part the ‘original house’ sits on. All your land includes the front garden, side garden and back garden. The term “original house” means the house as it was first built, so include any extensions you or previous owners have built into the calculation. To sum up, existing additions to your house like extensions, conservatories, sheds and greenhouses, these buildings combined with the garden room should not cover more than 50% of the overall land excluding the original house.