You can however strengthen the joists.
Strengthening roof joists.
Sistering is the process of adding a new joist next to each existing joist.
Joists and orient panel ends over joists.
If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists.
How to strengthen beams using plywood.
In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side.
Strengthening existing roof rafters is a difficult process that often requires professional help.
Long spans of joists in newer homes may wobble or bounce from foot traffic.
Laminated and single piece beams are often reinforced with plywood.
Snow increases the overall weight of your roof adding to the forces acting on your rafters.
To prevent sag in 2x6 s and strengthen at same time you could secure lengths of stainless steel or galvanized cable attach at each end of individual ceiling joists have cable go over a one or two spreaders or strut projecting down from the underside of the ceiling joist maybe 12 14 or so as not to lose too much headroom these could.
Add an additional row of fas teners midway between the joists to pull the layers tightly together.
If you have a stick frame roof there are a few basic techniques that you can use to strengthen your rafters.
This is also routine procedure for some ceiling or floor joists that are manufactured in.