Boarding-out for storage
In most homes, the existing timber joists that form the "floor" of the loft space ( i.e. the ceiling of the rooms below) will not have been designed to support a significant weight (known as "load"). The joists tie the pitched members of the roof together to prevent them spreading and support the ceiling lining of the rooms below.
An excessive additional load, for example from storage, it may mean that the joists are loaded beyond their design capacity. If you decide to lay flooring boards over the existing joists in the loft space, then this may require a Building Regulations Application to Building Control. Your local Building Control body will be able to advise you on this issue.
Creating a liveable space
If you decide to create a liveable space in an existing loft space of a home it is likely to require a range of alterations. Many of these could have an adverse impact on the building and its occupants if they are not properly thought out, planned and undertaken in accordance with the requirements of the legislation.