Sistering Roof Joists

With roofs this is done to improve the load value of rafters when installing roof mount air conditioning.

Sistering roof joists.

Sistering is the process of adding a new joist next to each existing joist. The best case scenario is to run the sisters the entire length of the existing joists so that you have two additional resting points. 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.

The sloped rafters usually spaced at 16 inch intervals which is sufficient to support standard roof decking and shingles. Doing so strengthens weak joists and can help straighten sagging joists. Our 60 year old floor joists are showing their age. If there was water damage make sure that whatever leaky pipe or condensation issue caused the rot is fixed.

If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. These problems must be addressed firsthand prior to implementing any restoration steps. Framing lumber is the typical choice for sistering. Since this isn t a floor then the allowable deflection tables don t really apply adds jigs n fixtures.

A day until they re level. 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. Essentially sliding a whole member beside it and nail the heck out of it from both sides with a lot of nails.

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. Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall. I forgot to mention the construction adhesive in between them. Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in.

Jacking them up too fast may cause cracks in the walls and floors overhead. Sistering the beams or rafters is one way of adding structural support to the roof. 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.