To achieve this doubling effect in strength and stiffness you will indeed need to gusset the upper and lower joists together.
Doubling up every other floor joise.
I thought i had used way more than enough screws to prevent this i even put them together cup side in if they were slightly cupped and now they.
So instead of having a post run all the way from the roof to the ground it can stop at the double floor joist.
Nail the block in place with 16d.
This allows you to install a supporting post off the double floor joist to hold a second storey or a roof beam.
Cut a piece of 2 by 6 or 2 by 8 lumber according to the width.
If we use strong enough gussets and fasteners we know that the top and bottom joists will deflect by exactly the same amount when loaded.
A day until they re level.
Jacking them up too fast may cause cracks in the walls and floors overhead.
Create space by doubling joists if you need to remove part of a joist double the joists to each side then add doubled joists between them to carry the load of the severed joist.
Place the lumber block between the two joists.
I don t think doubling up a 16 2x8 will all of a sudden span 30.
Tack a beam under the sagging joists.
Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in.
If you double those joists you can span 12 feet 3 inches.
Use joist hangers for all connections.
The main reason for doubling up floor joists is to double the strength of a single floor joist.
Not even a 12 micro will span that far.
For example a joist made from doubled 2 x 6s can span a distance about 25 percent more than a single 2 x 6 but a 2 x 12 can span about 80 percent more than a 2 x 6 even though it has the same amount of wood as a doubled 2 x 6.
Measure the width between the span of two joists.