I have a modular home the has 2x3 floor trusses instead of joists. The floors are soft and creaky. What can I do to stiffen them
Is it possible for you to upload some pictures?
You can sister on an actual joist. Something like a 2x10. Depends on the span and the width between the joists. But I would use a nice large piece of lumber. If the span is wide, also place some jack posts between to help support the wider span areas.
Handy Andy In Mt Airy NC