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.
Building an attic.
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.
To meet most building codes your attic should.
An attic sometimes referred to as a loft is a space found directly below the pitched roof of a house or other building.
Then you ll need to build a grid like structure that can hold up the plywood flooring.
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.
When converting an attic to a living space it must meet the same building requirements as the other rooms in your home.
Adding a floor to an attic can increase storage space or create a new room.
In many cases ceiling joists for dead loads are designed to carry 10 pounds per square foot.
You also need to ensure that the joist spacing is adequate.
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.
Joist dimensions are only part of the equation.
Building code often requires stairway access to the attic if the space is to.
Before you start creating a floor for your attic you must make sure that it can handle the additional load.