Level Existing Floor By Sistering Joists

If these problems remain unfixed sistering the damaged floor joists is only a band aid and the damage will only happen again.

Level existing floor by sistering joists.

For example if 2 inch by 10 inch material is in place the sister joists must be at least 10 inches wide. You will have to make sure your joists can handle the addition of considerably more weight from the plywood subfloor and any floor coverings. Select or cut sisters that also match as closely as possible the span of the existing. Now that said when you have a major humpy floor you should bite the bullet and remove the subfloor planks down to the joists.

Although framing lumber is usually chosen as a sistered wood engineered lumber is also a good choice because it can add more stiffness than standard dimensional lumber. When the sagging joists are level apply a generous bead of construction adhesive to the existing joist. On the top side of the floor another fix it idea to lay down new hardwood over the existing floor. A plywood subfloor will bridge any minor waves in the existing floor and leveling compound would help too.

Driving 16d common nails in old hard wood is difficult. You can also lay down new hardwood floor on the top side of the floor. A structural engineer may suggest sistering the joists a process whereby new joists are attached to the existing joists to add strength to the floor. A plywood subfloor acts as a bridge for minor waves in the existing floor as well as a leveling compound.

You will have a level sound surface to lay your new floor on. You just have to make sure that the joists can handle the addition of more weight from the plywood subfloor and any additional floor coverings. Over notching or not jacking enough. Generally newer home floor joists are made from 2x8s or new engineered i beams older homes however may have 2x6s instead.

Then sister the joists will lvl joists at exactly the level you want. Sistering joists is a job for the pros. Then attach the sister joist using three 16d common nails driven every 16 in.