Sistering Roof Joists

Sister refers to attaching an additional framing member alongside an existing member.

Sistering roof joists.

These problems must be addressed firsthand prior to implementing any restoration steps. Framing lumber is the typical choice for sistering. Sistering is the process of adding a new joist next to each existing joist. With roofs this is done to improve the load value of rafters when installing roof mount air conditioning.

Set a hydraulic jack and post under the beam and jack up the joists about 1 8 in. If the new sister bears on wood at least 1 5 on each end then you re good to go. I forgot to mention the construction adhesive in between them. Nailing two 2x4s together will work to span about three joists unless the sag is under a weight bearing wall.

Here s how we are correcting the problems. A day until they re level. If there was water damage make sure that whatever leaky pipe or condensation issue caused the rot is fixed. 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.

If the attic joists are not adequate one way to strengthen the floor for live loads is to sister the old joists. Jacking them up too fast may cause cracks in the walls and floors overhead. If you want to upgrade to heavier slate or tile shingles or you decide to add dormers to the roof additional support is necessary. Doing so strengthens weak joists and can help straighten sagging joists.

The sloped rafters usually spaced at 16 inch intervals which is sufficient to support standard roof decking and shingles. Essentially sliding a whole member beside it and nail the heck out of it from both sides with a lot of nails. Sistering joists means beefing them up with additional material. In the case of 2x6 joists you can pair them up with additional 2x6 joists by nailing them together side by side.

The most common way joists are repaired is to sister it up. Our 60 year old floor joists are showing their age. The best case scenario is to run the sisters the entire length of the existing joists so that you have two additional resting points.