Joist dimensions are only part of the equation.
Building an attic.
Before you start creating a floor for your attic you must make sure that it can handle the additional load.
To meet most building codes your attic should.
Other structural issues are also factors including whether there is adequate space to install a stairway to the attic.
Building code often requires stairway access to the attic if the space is to.
You also need to ensure that the joist spacing is adequate.
Have at least 7 feet of vertical clearance in the majority of the room be a minimum of 7 feet wide and have at least 70 square feet of space available.
Building code also requires that the prospective attic living space be accessible by a full size staircase with at least 6 foot 8 inch clearance above it.
Adding a floor to an attic can increase storage space or create a new room.
Attics only accessible by trapdoor style staircases or ladders aren t technically finishable.
Attic joists that are made from 2x8s may be acceptable for building your attic floor but because every room is variable there are no absolutes.
When converting an attic to a living space it must meet the same building requirements as the other rooms in your home.
Make sure the attic has a full size staircase.
An attic may also be called a sky parlor or a garret because attics fill the space between the ceiling of the top floor of a building and the slanted roof they are known for being awkwardly shaped spaces with exposed rafters and difficult to reach corners.