Purchase the type of lumber that matches the width of the existing joist.
Add joist to existing floor.
Make sure you also buy the same type of joist.
Select or cut sisters that also match as closely as possible the span of the existing.
Building codes specify the minimum joist depth and spacing typically 12 or 16 inches on center for spans up to 20 feet but those requirements are intended to prevent plaster ceilings from cracking not to.
If your floor joist is an i joist for example buy an i joist.
Nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in.
The best way to limit annoying flex in a floor is to make sure that joists are sized correctly before a house or addition is built.
When the sagging joists are level apply a generous bead of construction adhesive to the existing joist.
Measure the width and length of the existing joist.
Even if your joists already have a row of bridging at the center of the span adding a row on each side of the existing bridging will stiffen the floor.
Depending upon the conditions it is possible to strengthen or repair existing framing members such as floor joists or roof rafters by adding reinforcing material.
As a footstep falls on one joist some of the force is transferred to neighboring joists.
Sistering is the process of adding a new joist next to each existing joist.
Of the existing joist.
Find a replacement joist that is the same size as your floor joist.
Cutting the new joists 1 16 longer makes lots of sense as i will be doing lots of the work by myself.
Driving 16d common nails in old hard wood is difficult.
Find a new floor joist with these exact same dimensions.
Looks like i will remove the old decking before adding additional joists.
Then attach the sister joist using three 16d common nails driven every 16 in.
I do have at least one existing joist that is pretty well rotted.
For example if 2 inch by 10 inch material is in place the sister joists must be at least 10 inches wide.
In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side.
If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists.
Sandwiching the member on either side with plywood is sometimes worthwhile but the plywood must be installed correctly for greatest strength.
Most new construction uses 2 by 8 lumber for joists although 2 by 6.
Thanks to all for your helpful replies and suggestions.
Use a sledgehammer or a pry bar to force the bottom of the new joist along the mudsill and center support beam of the floor system or the opposite mudsill on short spans until it s flat against the existing joist.
Bridging or x bracing allows joists to share weight.
