Sistering Roof Joists

Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall.

Sistering roof joists.

In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side. The sag could be reduced or eliminated by installing king posts or leom could sister 2x8s to the 2 6 joists to roughly triple the load bearing capacity of the ceiling. With roofs this is done to improve the load value of rafters when installing roof mount air conditioning. Sistering the beams or rafters is one way of adding structural support to the roof.

If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. 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. If there was water damage make sure that whatever leaky pipe or condensation issue caused the rot is fixed. Sistering is the process of adding a new joist next to each existing joist.

I forgot to mention the construction adhesive in between them. If the new sister bears on wood at least 1 5 on each end then you re good to go. Sister refers to attaching an additional framing member alongside an existing member. A day until they re level.

Framing lumber is the typical choice for sistering. Here s how we are correcting the problems. Since this isn t a floor then the allowable deflection tables don t really apply adds jigs n fixtures. These problems must be addressed firsthand prior to implementing any restoration steps.

The most common way joists are repaired is to sister it up. If you want to upgrade to heavier slate or tile shingles or you decide to add dormers to the roof additional support is necessary. Jacking them up too fast may cause cracks in the walls and floors overhead. Essentially sliding a whole member beside it and nail the heck out of it from both sides with a lot of nails.

Doing so strengthens weak joists and can help straighten sagging joists. The best case scenario is to run the sisters the entire length of the existing joists so that you have two additional resting points. Our 60 year old floor joists are showing their age.