How To Join Two Floor Joists

Sistering or joining joists the term sistering joists is the practice of overlapping two joists by a certain distance across a beam to create an extended joist.

How to join two floor joists.

The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example. This is unusual in new deck construction and would only be necessary for very long spans that exceed the length of your longest boards. The new sister joist is cut to the same length or slightly shorter as the old joist and is inserted into the joist cavity and snugged up against the old joist. If there was water damage make sure that whatever leaky pipe or condensation issue caused the rot is fixed.

If the floor is sagging the damaged joist and or a few neighboring joists may need to be jacked up slightly to straighten or raise the floor so the sister joist can be put into place. Only raise the jacks about 1 8 inch per. Most often floor joists need to be sistered because of two problems either water damage which leads to rot or termite damage that crumbled the joist. Make sure your joist is straight because once you splice it this way it cannot be repositioned.

But larger is not always better when builders are constructing a home or adding a room addition. Avoid making the joint in the center 1 3 of the span. Common sense tells you that large floor joists can carry more load and spacing joists closer together also increases the load bearing capacity of a floor. These problems must be addressed firsthand prior to implementing any restoration steps.